DE102021100692A1 - SAW-based flow sensor - Google Patents

Abstract

The present invention relates to a method for determining a flow property of a fluid. The method comprises: transmitting a first wave from a first transmitter to a first receiver, the first wave traversing the fluid on its way from the first transmitter to the first receiver, and receiving a signal of the first wave at the first receiver, having a first characteristic based on the first wave signal, transmitting a second wave from a second transmitter to a second receiver, the second wave traversing the fluid on its way from the second transmitter to the second receiver, and receiving a second wave signal at the second receiver , and determining a second feature based on the second wave signal. The method further comprises: subtracting one of the features from the other feature and thus generating a difference measure. The method additionally comprises: determining a dwell time, which indicates a propagation time that is required for the first wave to pass through the fluid on its way from the first transmitter to the first receiver, and / or a propagation time for the second wave to pass through the fluid is required on its way from the second transmitter to the second receiver, and using the difference measure and the dwell time to determine the flow property. Furthermore, the present invention also relates to a respective sensor for determining a flow property of a fluid.

Description

The present invention relates generally to measuring the flow properties of a fluid. In particular, the present invention relates to a method and an apparatus for measuring a flow property of a fluid, e.g. B. a fluid flow in a pipe or a flow velocity and / or a flow rate of a fluid flow.

The present invention will be described with a particular focus on the measurement of fluid flow in liquid chromatography (LC) - and in particular high performance liquid chromatography (HPLC). HPLC, and more generally liquid chromatography, is a method of separating samples into their components, which can be detected and quantified and / or whose parts can be saved for later use. It should be understood, however, that the present technology can also be used in connection with other applications in which flow properties are measured, e.g. B. when measuring a flow rate.

The principle of chromatography is based on the injection of a sample (e.g. with a sampling unit) into a fluid path, whereby a mobile phase, e.g. B. comprises liquid solvents provided by a pump that transports them to and through a chromatography column which has a stationary phase, e.g. B. a solid porous material comprises. The separation of the individual components of the sample depends on the interactions between the components, the stationary phase and the mobile phase. In general, the more strongly a constituent interacts with the stationary phase, the longer it can take for the mobile phase to elute it from the column. These interactions are characteristic of the constituents and thus lead to corresponding characteristic residence times for the constituents, which can depend on the specific conditions (e.g. composition of the mobile and stationary phases).

The separation of compounds can be influenced by adjusting the composition of the mobile phase over time, which can be referred to as solvent gradients, as the composition can typically be changed continuously. That is, typically two (or more) different solvents can be combined, such as using sophisticated fluidic devices such as mixers and proportional valves, and the ratio of the two solvents can be changed over time. Thus, a given compound can elute once the solvent composition exceeds a threshold (e.g., a certain volumetric concentration of solvent A in a mixture of solvents A and B). This threshold value can be characteristic of this given connection.

The eluting compound can then be detected by a suitable detector which is arranged downstream of the separation column. As the detector passes through the connection, a spike can be obtained in the respective signal. Such a signal is called a chromatogram. Depending on the complexity of the sample, it can consist of several tips in quick succession. Individual peaks can be characteristic of certain compounds, which can thus be identified based on the time allocated to the detection of the peak, taking into account further parameters such as the solvent or solvent mixture used, the composition of the solid phase and the flow rate can.

In general, the exact knowledge of the flow rates can be advantageous for a good analytical result of an HPLC measurement, since the flow rate can directly influence the analysis speed and the reproducibility. According to the prevailing working principles of HPLC pumps, it is currently not possible to build a pump that (simultaneously) corresponds to the gradient and the flow rate without an additional sensor. If, however, a flow sensor is installed, a gradient-compliant pump can also operate in accordance with the flow, e.g. B. by means of a feedback loop. This means that the signal from a flow sensor can be used to ensure that a pump that is built in accordance with the gradient is also in accordance with the flow.

Known sensors for flow measurements are generally based on four different working principles: thermal sensors, Coriolis sensors, ultrasonic sensors and sensors based on particle tracking.

In thermal sensors, also referred to as thermal mass flow sensors, a heater in contact with the fluid flow heats the fluid flowing past and at least one temperature sensor, which is placed somewhat away from the heater, measures the temperature of the liquid flowing past. The temperature change at the sensor location caused by the movement of the fluid is a measure of the flow velocity.

In contrast, with a Coriolis sensor, a flow of a fluid is forced not to move in a straight line through a curved pipe geometry, whereby the fluid flow can orbit a point. The tube is made to vibrate and, due to its rotational flow, the liquid causes a torsion on the tube by means of the Coriolis force. The resulting change in vibration related to frequency or direction is taken as a measure of the flow velocity.

Ultrasonic sensors can be based either on the Doppler effect or on a measurement of the time of flight. In a flow sensor based on the Doppler effect, a frequency shift is measured in an ultrasonic signal, which is reflected by particles or air bubbles moving in the fluid flow, which is proportional to the flow velocity. Alternatively, the speed of propagation of an ultrasonic signal in the moving fluid is measured, usually by measuring a travel time. The transit time also depends on the flow velocity of the fluid stream.

In the case of sensors based on particle tracking, first particles can be added to the fluid flow. These particles serve as test pieces in the fluid and are captured by the flow in such a way that they move with the flow. The trajectories of the particles are measured and the movement of the particles is used as a measure of the flow velocity.

However, known flow sensors can have certain disadvantages: Flow measurements with thermal sensors and ultrasonic sensors are material-dependent. This is due to the material constants of the fluids, which have an effect on the fluid properties and thus on the flow measurements. Therefore, such sensors require careful calibration. However, such calibration can be a difficult process, especially when using solvent gradients, as the material properties of the fluid can change over time. While Coriolis sensors enable the independent measurement of the mass flow rate and the density of a fluid, which in principle can enable a material-independent measurement of the volume flow rate, these sensors are typically temperature-dependent and therefore require calibration with regard to the temperature of the fluid and thus also its measurement. In addition, thermal sensors and Coriolis sensors in particular can be quite complex.

While thermal sensors, Coriolis sensors and ultrasonic sensors can generally be used in the high pressure range, particle tracking may be less suitable for high pressure applications: the particles have to be added to the fluid flow, which in a pressure system is at best possible with great effort. In addition, the particles must be detectable from the outside, optical methods normally requiring a transparent pipe wall, which is typically not sufficiently pressure-resistant. Furthermore, particles must also be removed from the fluid again, e.g. B. at the outlet of the pump, otherwise they cause a number of problems, e.g. B. can clog a column or other fluidic components downstream of the pump. Therefore, particle tracking based sensors may not be readily usable for high pressure applications such as HPLC. Furthermore, the particles comprise a mass, and therefore inertial forces influence the particle trajectories and falsify the measurement.

In general, the use of sound waves in microfluidics is also known. For example, relates US 10,570,361 B2 on sound waves in microfluidics, including surface acoustic waves, and on the control and manipulation of fluid species. In particular, method for sorting cells and / or droplets in a microfluidic device using surface acoustic waves

Recently, flow sensors using ultrasonic waves generated by surface acoustic waves (SAW) have also been developed. For example disclosed DE 10 2019 110 514 A1 a fluid measuring device for determining at least one property of a fluid, wherein the measuring method is based on the use of the influence of a fluid flow on the propagation speed of an ultrasonic wave that is generated by means of a surface acoustic wave. However, even for such a SAW-induced ultrasonic flow sensor, calibration with respect to the fluid used is required, which makes the use of such sensors for HPLC difficult or even unusable for this purpose, in particular when solvent gradients are used. Reveals the same as well US 9,581,572 B2 a device for determining the properties of a medium based on SAW-induced ultrasonic waves. However, the measurements again depend on the material properties of the fluids, such as that the flow velocity or flow rate cannot be determined independently of other properties of the fluid without an initial fluid-specific calibration.

Also disclosed DE 10 2018 104 669 A1 that influences of a fluid flow on the propagation speed of a surface acoustic wave provide a measure of the flow speed, in particular the change in the propagation speed due to changes in the propagation time or changes in the phase position of a transmitted surface acoustic wave. Here too, however, a reference measurement is required in order to determine the flow rate independently of other properties of the fluid.

Therefore, the known sensors which are suitable for use in high pressure applications such as HPLC are disadvantageously dependent on other properties of the fluids used and therefore require a fluid-specific calibration or reference measurements, which can be particularly disadvantageous when using solvent gradients.

Against this background, one aim is to overcome or at least alleviate the shortcomings and disadvantages of the prior art. In particular, it is an object of the present invention to provide a flow sensor that does not require fluid dependent calibration.

These objects are achieved by the present invention.

In a first embodiment, the present invention relates to a method for determining a flow property of a fluid. The method comprises: transmitting a first wave from a first transmitter to a first receiver, the first wave traversing the fluid on its way from the first transmitter to the first receiver, and receiving a signal of the first wave at the first receiver, having a first characteristic based on the first wave signal, transmitting a second wave from a second transmitter to a second receiver, the second wave traversing the fluid on its way from the second transmitter to the second receiver, and receiving a second wave signal at the second receiver , and determining a second feature based on the second wave signal. The method further comprises: subtracting one of the features from the other feature and thus generating a difference measure. The method additionally comprises: determining a dwell time, which indicates a propagation time that is required for the first wave to pass through the fluid on its way from the first transmitter to the first receiver, and / or a propagation time for the second wave to pass through the fluid is required on its way from the second transmitter to the second receiver, and using the difference measure and the dwell time to determine the flow property. Thus, the method can include determining the flow property based at least on the difference measure and the dwell time.

In other words, the present invention may include sending two waves from a respective transmitter to a respective receiver such that each of the two waves traverses the fluid on its way. A difference measure can then be determined which relates to the signals received by the two respective receivers, in particular a difference measure of features which are determined based on the received signals of the waves. Such features can be, for example, a phase difference between the emitted and the received signal. Furthermore, a dwell time can be determined, which indicates the propagation time of at least one of the two waves, and the dwell time and the difference measure can then be used to determine a flow property, which can be, for example, a flow velocity or a flow rate of the fluid.

A first transducer can form the first transmitter and the second receiver, and a second transducer can form the second transmitter and the first receiver. That is, in some embodiments of the method, the first transmitter and the second receiver can consist of the same transducer (i.e. the first transducer), and likewise the second transmitter and the first receiver can also consist of a single transducer (i.e. the second transducer). This can advantageously enable a compact sensor design and / or reduce the number of transducers required and thus the complexity of the sensor used for the method.

Alternatively, a first converter can form the first transmitter and the second transmitter, a second converter can form the first receiver and a third converter forms the second receiver. In other words, in some embodiments of the present method, three transducers can form the first and second transmitter and the first and second receiver.

Again as an alternative to this, a first converter can form the first transmitter, a second converter can form the first receiver, a third converter can form the second transmitter and a fourth converter forms the second receiver. In other words, each of the first and second transmitters and the first and second receivers can be provided by a single transducer.

The second transducer can have the same properties as the first transducer. The same properties can relate, for example, to the wavelength, the size and / or the electrode design of the transducer. In particular, two transducers that have the same properties can have an identical design. In other words, two transducers that have the same properties can be considered identical.

In embodiments, the third transducer can have the same properties as the first transducer.

In some embodiments, the third transducer can have the same properties as the second transducer.

In some embodiments, the fourth transducer can have the same properties as the first transducer.

In some embodiments, the fourth transducer can have the same properties as the second transducer.

In some embodiments, the fourth transducer can have the same properties as the third transducer.

In some embodiments, the method may further include directing the fluid through a channel.

The step of transmitting the first wave from the first transmitter to the first receiver can include reflecting and / or breaking the first wave at least once. Likewise, the step of transmitting the second wave from the second transmitter to the second receiver can include reflecting and / or breaking the second wave at least once.

The fluid can include a direction of flow. The second wave can traverse the fluid in a direction which is opposite to the first wave with respect to the direction of flow. This can advantageously make it possible to cancel out flow-independent contributions by generating the difference measure, which in combination with the dwell time can advantageously make it possible to determine the flow property independently of fluid properties and / or local fluid and / or ambient temperature. In other words, this can advantageously enable a fluid-independent measurement of the flow property.

The signal of the first and / or the second wave may not be received by the respective receiver directly after the fluid has passed through. This means that the first and / or the second wave can propagate for a time Δt _SAW > 0 before it is received by the respective receiver. For example, after passing through the fluid, the wave can be coupled into a chip and propagate as a SAW before it is received by the designated receiver. In other words, it may be that the first and / or the second wave does not hit the transducer directly, which forms the respective receiver that receives the wave.

The first and second waves can propagate as sound waves when passing through the fluid.

In some embodiments, determining the feature based on the signal of the respective wave may include determining a phase shift between the wave transmitted by the respective transmitter and the signal of the wave received by the respective receiver.

Using the difference measure and the residence time to determine the flow characteristic may include dividing the difference measure by the residence time to derive a flow rate term that is proportional to the flow rate of the fluid

Determining the dwell time may include sending a dwell wave from a dwell transmitter to a dwell receiver, the dwell wave traversing the fluid on its way from the dwell transmitter to the dwell receiver, and receiving a signal of the dwell wave at the dwell receiver. Furthermore, the dwell time wave can propagate as a sound wave when passing through the fluid.

In some embodiments, one of the first and second waves can form the dwell wave.

The dwell time wave signal can be received by the dwell time receiver immediately after the fluid has passed through. That is, the dwell wave essentially cannot propagate as a SAW before it is received by the dwell receiver. Here, the term essentially serves to include the time it takes for the receiver to receive the sound wave, i.e. H. the dwell time wave after passing through the fluid. Specifically, this may include the time (and propagation) it takes to convert the sound wave back to a SAW and for the receiver to receive the SAW, during which time the propagation may be significantly less than the expansion of the dwell receiver.

Determining the dwell time may _{include determining the total propagation time dt IDT} between the dwell transmitter transmitting the wave and the dwell receiver receiving the wave's signal. Furthermore, determining the dwell time can include _{correcting the total propagation time Δt IDT} for a fluid- and flow-independent offset time Δt _offset. The fluid-independent offset time Δt _offset corresponds to the time in which the dwell time wave is generated and induced in the fluid, and the time in which the sound wave is converted back into a SAW and received by the dwell time receiver, since the wave is not flow-dependent during these times Subject to postponement.

The method can further include determining the fluid- and flow-independent offset time Δt _offset by means of a sensor-specific calibration measurement. This means that a one-time calibration measurement can be carried out, which can preferably only be required once for a specific sensor design or for each individual sensor. The calibration measurement could, for example, already be carried out during manufacture and made available to a user together with the sensor.

In some embodiments, a wave that the fluid traverses may include the wave that crosses the channel at least once. That is, the wave can cross the channel at least once in a direction perpendicular to the direction of flow. Furthermore, the first and / or the second wave, which the fluid traverses, can include reflecting and / or breaking the respective wave at least once on an inner surface of the channel. Additionally or alternatively to this, the dwell time wave which the fluid traverses can comprise reflecting and / or breaking the dwell time wave at least once on an inner surface of the channel.

Determining the dwell time may include taking into account the number of times the dwell time wave crossed the channel in traversing the fluid.

In some embodiments, the first, second, third, or fourth transducer may further form the dwell transmitter. In addition or as an alternative to this, the converter which forms the first transmitter or the converter which forms the second transmitter can furthermore form the dwell time transmitter.

In some embodiments, a time transmitter transducer can form the dwell transmitter.

The first, the second, the third or the fourth transducer can furthermore form the dwell time receiver. In addition or as an alternative to this, the converter which forms the first receiver or the converter which forms the second receiver can furthermore form the dwell time receiver.

In some embodiments, a timing transducer may form the dwell time transmitter.

The flow property can be a flow rate of the fluid, alternatively the flow property can be a flow rate of the fluid.

In some embodiments, the transducers may be interdigital transducers (IDT) configured to transmit and receive surface acoustic waves (SAW).

In some embodiments, the dwell receiver may be located downstream of the dwell transmitter.

In some embodiments, the first wave and the second wave can each be pulse-shaped waves in the time domain. Additionally or alternatively, the dwell time wave can be a pulse-shaped wave in the time domain.

Sending the first wave, the second wave and / or the dwell time wave can include providing an AC voltage signal to the converter, which forms the respective transmitter for the wave. Furthermore, the AC voltage signal can alternate at one voltage frequency and the voltage frequency can be in the range from 10 MHz to 1000 MHz, preferably in the range from 20 MHz to 200 MHz, more preferably in the range from 30 MHz to 100 MHz. Additionally or alternatively, the AC voltage signal can comprise an effective voltage (RMS voltage) and the effective voltage can be in the range from -90 dBm to 30 dBm, preferably in the range from -60 dBm to 10 dBm, more preferably in the range from -40 dBm to 0 dBm , lie. In some embodiments, the effective voltage can be in the range from 1 μV to 10 V, preferably in the range from 10 μV to 1 V, more preferably in the range from 100 μV to 100 mV.

The AC voltage signal can be a pulsed AC voltage signal. Furthermore, the pulsed AC voltage signal can comprise a pulse length and the pulse length can be in the range from 0.1 ns to 100 microseconds, preferably in the range from 1 ns to 10 microseconds, more preferably in the range from 10 ns to 3 microseconds.

In some embodiments, the fluid can have a fluid pressure and the fluid pressure can exceed 100 bar, preferably 500 bar, more preferably 1000 bar, approximately 2000 bar.

The flow property can be determined for a fluid which comprises a flow rate which is at least in the range from 1 μl / min to 3 ml / min, preferably 500 nl / min to 5 ml / min, more preferably 1 nl / min to 10 ml / min , can lie.

The method may not require fluid dependent calibration.

The method can further comprise determining at least one additional fluid property. Furthermore, the at least one additional fluid property can be density, speed of sound, viscosity and / or conductivity. The determination of at least one additional fluid property can include the determination of a flow-independent phase shift of a wave that the fluid traverses. Additionally or alternatively, determining at least one additional fluid property can include determining a SAW phase shift of a SAW that propagates from the first transmitter to the first receiver and / or from the second transmitter to the second receiver without passing through the fluid.

Furthermore, the method can include deriving at least one potential fluid candidate for the fluid based on the at least one additional fluid property. In some embodiments, inferring the at least one potential fluid candidate may include using statistical methods.

In another embodiment, the present invention relates to a sensor for determining a flow property of a fluid. The sensor comprises a channel for guiding the fluid, a transmitter and receiver arrangement, which forms at least a first transmitter, a first receiver, a second transmitter and a second receiver, and a data processing unit, wherein the flow sensor is configured to use the method according to a to carry out the preceding procedural embodiments.

The transmitter and receiver arrangement can comprise a first transducer, which forms the first transmitter and the second receiver, and a second converter, which forms the second transmitter and the first receiver.

Alternatively, the transmitter and receiver arrangement can comprise a first transducer, which forms the first transmitter and the second transmitter, a second transducer, which forms the first receiver, and a third converter, which forms the second receiver.

Again, alternatively, the transmitter and receiver arrangement can comprise a first transducer, which forms the first transmitter, a second transducer, which forms the first receiver, a third transducer, which forms the second transmitter, and a fourth transducer, which forms the second receiver .

The second transducer can be of the same design as the first transducer. That is, the second transducer comprises the same properties as the first transducer, it being possible for the properties to include, for example, geometric dimensions, periodicity, wavelength, and so on.

In embodiments, the third transducer can have the same design as the first transducer.

In embodiments, the third transducer can have the same design as the second transducer.

In embodiments, the fourth transducer can have the same design as the first transducer.

In embodiments, the fourth transducer can have the same design as the second transducer.

In embodiments, the fourth transducer can have the same design as the third transducer.

The transmitter and receiver arrangement can also form a dwell time transmitter and a dwell time receiver. In some embodiments, the first, second, third, or fourth transducer can further form the dwell time receiver. In addition or as an alternative to this, the converter which forms the first receiver or the converter which forms the second receiver also forms the dwell time receiver.

The transmitter and receiver arrangement can comprise a time measuring transducer which forms the dwell time receiver.

In some embodiments, the first, second, third, or fourth transducer also form the dwell transmitter. In addition or as an alternative to this, the converter which forms the first transmitter or the converter which forms the second transmitter can furthermore form the dwell time transmitter.

The transmitter and receiver arrangement can comprise a time transmitter transducer which forms the dwell time transmitter.

In some embodiments, the first transmitter can be arranged downstream of the first receiver and the second transmitter can be arranged upstream of the second receiver. Alternatively, the first transmitter can be arranged upstream of the first receiver and the second transmitter can be arranged downstream of the second receiver.

The first transmitter and the first receiver can be arranged directly one after the other in the direction of flow. That is, the first transmitter can be arranged either directly upstream or downstream of the first receiver, the term “directly one after the other” means that no other transmitter or receiver may be arranged in between.

The second transmitter and the second receiver can be arranged directly one after the other in the direction of flow.

In some embodiments, the first transmitter and the first receiver can be located on the same side of the channel. In other words, the first transmitter and receiver can be arranged such that a wave emitted by the first transmitter and received by the first receiver passes through the fluids an even number of times. For example, in a channel with a rectangular cross-section, the channel comprises four sides and the first transmitter and the first receiver can both be arranged on a single side thereof.

Alternatively, the first transmitter and the first receiver are arranged on opposite sides of the channel. In other words, the first transmitter and receiver can be arranged such that a wave emitted by the first transmitter and received by the first receiver passes through the fluids an odd number of times. For example, in a channel with a rectangular cross section, the channel comprises four sides and the first transmitter and the first receiver can each be arranged on two opposite sides.

The dwell time receiver and the dwell time transmitter can be arranged directly one after the other in the direction of flow.

In some embodiments, the dwell receiver may be located downstream of the dwell transmitter. Alternatively, the dwell time receiver can be arranged upstream of the dwell time transmitter. In some embodiments, the dwell receiver and the dwell transmitter can be located on the same side of the channel. Alternatively, the dwell time receiver and the dwell time transmitter can be arranged on opposite sides of the channel.

The channel may include an interior surface configured to be in contact with the fluid directed through the channel. The channel can comprise a channel cross section, wherein the channel cross section can be at least rectangular or round or elliptical or any combination thereof. In some embodiments, the channel cross-section can be rectangular.

The channel can comprise a channel geometry, wherein the channel geometry is straight, curved and / or curved, wherein curved can for example denote a geometry in which the channel has a corner, e.g. B. comprises a 90 ° corner.

Furthermore, the channel can comprise a direction of flow, wherein the fluid can be conducted through the channel in the direction of flow. Additionally or alternatively, the channel can comprise a channel length which corresponds to the extension of the channel along which the fluid is conducted. The channel length can be up to 30 mm, preferably up to 10 mm, more preferably up to 5 mm.

The transmitter and receiver arrangement can comprise at least one chip. Furthermore, the at least one chip can comprise a substrate. In some embodiments, the substrate can be piezoelectric. Additionally or alternatively, the substrate can be coated with a piezoelectric layer. The substrate and / or the piezoelectric layer can consist of a crystal made of lithium niobate (LiNbO ₃ ), quartz (SiO ₂ ), lithium tantalate (LiTaO ₃ ) and / or lanthanum gallium silicate (La ₃ Ga ₅ SiO ₁₄ ). In some embodiments, the substrate and / or the piezoelectric layer can consist of a LiNbO ₃ crystal with a 128 ° XY cut.

The at least one chip can include at least one transducer configured to transmit and / or receive a wave. Furthermore, the converter can be at least the first converter, the second converter, the third converter, the fourth converter, the time measuring converter and / or the time transmitter converter.

The transducer can be arranged on top of the piezoelectric substrate or the piezoelectric layer. The transducer can be configured to transmit and / or receive a wave with a transducer wavelength, wherein the transducer wavelength can be in the range from 4 μm to 400 μm, preferably 20 μm to 200 μm, more preferably 40 μm to 133 μm.

The at least one transducer can be an interdigital transducer (IDT) configured to transmit and / or receive a surface acoustic wave. Furthermore, each interdigital transducer can comprise at least two interdigitated electrodes. Additionally, each of the at least two interdigitated electrodes can include multiple finger electrodes, wherein the finger electrodes of the interdigitated electrodes can be interdigitated. That is, for example, the IDT may include two interdigitated electrodes that resemble an interdigitated comb structure.

In some embodiments, each of the at least two interdigitated electrodes can include an identical number of finger electrodes. In addition or as an alternative to this, the interdigital transducer comprises 2 interlocking electrodes. Furthermore, the 2 interdigitated electrodes can be arranged such that the two interdigitated electrodes alternately encompass the interdigitated electrode fingers. In other words, a period of the IDT can include a pair of fingers, ie, two finger electrodes, each finger electrode of the pair of fingers being part of a different interdigitated electrode. Such an IDT may be referred to as a single-electrode type IDT or a fixed-electrode type IDT, for example.

Alternatively, the interdigitated electrodes can be arranged such that the two interdigitated electrodes can alternately comprise the electrode groups each comprising an equal number of multiple adjacent finger electrodes. For example, one period of the IDT can include 4 or 8 finger electrodes. Such an IDT can, for example, as an IDT of the double or Multi-electrode type or more generally referred to as IDT of the split-electrode type. Such split-electrode type IDTs can advantageously provide access to harmonic bands, which in turn can increase the versatility of such IDTs.

In some embodiments, the finger electrodes can be periodically spaced.

In some embodiments, the finger electrodes can be beveled and / or tapered. For example, the finger electrodes may be beveled and tapered toward one of the interdigitated electrodes such that the thickness of the finger electrodes 21 and change the distance therebetween in a direction perpendicular to the direction of propagation of the SAW. Such an IDT can be referred to as an oblique finger IDT or a tapered IDT, for example. Tapered and / or oblique finger electrodes can advantageously provide an IDT that has a wide bandwidth.

The transducer can be configured to transmit and / or receive a chirped surface acoustic wave. Furthermore, the finger electrodes can comprise a finger electrode width, wherein a distance between successive finger electrodes and the finger electrode width can decrease in a direction perpendicular to a greatest extent of the finger electrodes.

In some embodiments, each of the at least two interdigitated electrodes can comprise between 3 and 1000 finger electrodes, preferably between 3 and 700 finger electrodes.

The interdigital transducer can have an electrical impedance of 1 Ω to 500 Ω, preferably 10 Ω to 200 Ω, more preferably 30 Ω to 100 Ω, approximately 50 Ω. include.

The interdigital transducer can comprise an acoustic screen which designates an overlapping length of the at least two electrodes. Furthermore, the acoustic screen can be in the range from 100 μm to 3000 μm, preferably in the range from 200 μm to 100 μm, more preferably in the range from 300 μm to 800 μm.

The at least one transducer can be configured to emit surface acoustic waves with an excitation power below 1 W, preferably below 10 mW, more preferably below 1 mW.

The first converter, the second converter, the third converter, the fourth converter, the time measuring converter and / or the time transmitter converter can be a unidirectional converter.

The first converter, the second converter, the third converter, the fourth converter, the time measuring converter and / or the time transmitter converter can be a bidirectional converter.

The chip can comprise a sealing layer that covers the at least a portion of the chip surface, and preferably comprises components that the chip comprises. Furthermore, the sealing layer can cover the at least one transducer. The sealing layer can consist of a material of the polyaryletherketone (PAEK) family, preferably polyetheretherketone (PEEK), an oxide-ceramic material, fused SiO ₂ (silica glass) or Si ₃ N ₄ . That is, the preferred material from the PAEK family can be PEEK. The sealing layer can comprise a sealing layer thickness, the sealing layer thickness being less than 10 times the converter wavelength, preferably less than 5 times the converter wavelength, more preferably less than the converter wavelength and even more preferably less than 0.25 times the converter wavelength .

The chip may include a top, where at least a portion of the top may be part of the inner surface of the channel. In some embodiments, at least a portion of the interior surface of the channel can be provided by an acoustic reflector. The acoustic reflector can be reflective and / or refractive.

In some embodiments, the acoustic reflector can be made from sapphire. Alternatively, the acoustic reflector can be a refractive reflector, which is preferably made from a synthetic material such as plastic. It can preferably be made from a material of the polyaryletherketone (PAEK) and in particular PEEK.

At least a portion of the chip can be configured as a waveguide for SAW.

The channel can comprise a channel height which corresponds to the expansion of the channel in a direction perpendicular to the chip and to the direction of flow. Furthermore, the channel height can be at most 20 mm, preferably at most 5 mm, more preferably at most 1 mm.

The channel can comprise a channel width which corresponds to the expansion of the channel in a direction parallel to the chip and perpendicular to the direction of flow. Furthermore, the channel width can be at most 10 mm, preferably at most 3 mm, more preferably at most 1 mm.

The sensor can be configured for flow rates in the range from 1 μl / min to 3 ml / min, preferably 500 nl / min to 5 ml / min, more preferably 1 nl / min to 10 ml / min. Furthermore, the sensor can be configured to measure the flow rates with a relative error of up to 0.1%, preferably up to 0.01%, even more preferably up to 0.001%.

The sensor can be configured for pressures exceeding 100 bar, preferably exceeding 500 bar, more preferably exceeding 1000 bar, exceeding approximately 2000 bar.

In some embodiments, fluid-conveying components of the sensor can be chemically stable, preferably chemically inert.

The flow property can be a flow rate of the fluid; additionally or alternatively, the flow property can be a flow rate of the fluid.

The first transmitter and the first receiver can be arranged on the same chip. Alternatively, the first transmitter and the first receiver can be arranged on different chips.

The second transmitter and the second receiver can be arranged on the same chip. Alternatively, the second transmitter and the second receiver can be arranged on different chips.

In some embodiments, the second transmitter and the second receiver can be arranged on a different chip than the second transmitter and the second receiver.

The dwell time transmitter and the dwell time receiver can be arranged on the same chip. Alternatively, the dwell time transmitter and the dwell time receiver can be arranged on different chips.

The piezoelectric substrate or the piezoelectric layer can _{comprise a SAW speed of sound c S} , which corresponds to the propagation speed of a SAW within the piezoelectric substrate or the piezoelectric layer. Additionally or alternatively, the fluid passed through the sensor can _{include a fluid sound velocity c F} , which corresponds to the propagation velocity of a sound wave within the fluid.

The dwell receiver can comprise a dwell receiver length in the direction of flow, and the dwell transmitter can comprise a dwell transmitter length in the direction of flow, the dwell receiver length being greater than the dwell transmitter length.

The residence time receiver can comprise a residence time receiver length in the direction of flow, wherein the residence time receiver length can be in the range from 0.1 mm to 100 mm, preferably 0.2 mm to 50 mm, more preferably 0.2 mm to 20 mm.

The dwell time transmitter can comprise a dwell time transmitter length in the direction of flow, the dwell time transmitter length being in the range from 12 μm to 40 mm, preferably 60 μm to 20 mm, more preferably 120 μm to 14 mm.

The dwell time transmitter and the dwell time receiver can be separated in the direction of flow by a delay line length, wherein the delay line length can be at least 10 μm, preferably at least 50 μm, more preferably at least 100 μm.

The processing unit can be configured to receive signals from the transmitter and receiver arrangement. Furthermore, the processing unit can be configured to send signals to the transmitter and receiver arrangement. The transmitter and receiver arrangement can be configured to send signals to be received by a signal generator. Furthermore, the processing unit can be configured to send signals to the signal generator.

The processing unit can be configured to determine the dwell time. Furthermore, the processing unit can be configured to determine a dwell time based on a signal received from the dwell time receiver.

The processing unit can be configured to carry out steps of the method according to one of the preceding method embodiments. The processing unit can be configured to determine a difference measure based on signals received from the first and second receivers.

The processing unit can be configured to use the dwell time and the difference measure to determine the flow property.

The processing unit can be configured to carry out digital post-processing of signals that are received from the transmitter and receiver arrangement.

The processing unit can be configured to carry out digital post-processing of the difference measure.

In some embodiments, at least a portion of the channel can be configured to provide an acoustic waveguide for waves traversing the fluid.

The channel can be formed from a channel material, wherein the channel material _{can comprise a material sound velocity c m} , which is less than the SAW sound velocity. Furthermore, the chip can comprise a top side, the top side possibly not being part of the inner surface of the channel.

The chip can be coupled to the channel material via a coupling material, wherein the coupling material can be configured to allow a SAW to propagate from the chip to the channel material and vice versa. Furthermore, the coupling material can comprise a coupling material thickness, wherein the coupling material thickness can be less than 50%, preferably less than 25% and more preferably less than 10% of the transducer wavelength.

The method described above can include the use of a sensor as described above.

In general, the present invention encompasses a new technology for measuring a flow characteristic of a fluid, e.g. B. the flow of a liquid, by means of a shaft, e.g. B. a surface acoustic wave (SAW), which can be coupled at least partially as a volume wave, in particular a sound wave, into the fluid. The measurement can be based on a flow-induced local displacement (also referred to as a local "displacement") of a sound wave that is generated by a transducer, e.g. B. an interdigital transducer (IDT) received by another transducer located upstream or downstream of the generating (e.g., emitting) transducer. Due to the flow-induced local displacement, the sound wave can be received with a time delay (or a lead time). In the ideal case, the local displacement can be exclusively linear to the average flow velocity of the fluid channel. However, the signal can also be influenced by other variables such as changes in pressure, temperature, density, conductivity and viscosity of the fluid. That is, the fluid properties and / or environmental parameters can affect the time delay of the sound wave - a problem that means that sensors therefore require careful calibration and control of the environmental parameters.

In general, the undesired variables can be compensated for by a mutual measurement that differs over time. Before the present invention, however, the local displacement of the sound wave could not be separated from the pure propagation time of the sound wave in the fluid, which can also be referred to as the dwell time. This can lead to a fluid dependency, which in general can be unsuitable for HPLC and leads to the need for a fluid-dependent calibration. The present invention can enable the measurement of the above-described signal, which comprises (combined) information about both the flow-independent propagation time and the local displacement of the sound wave, as well as a further signal that enables the propagation time of the sound wave to be extracted. Therefore The overall information that can be obtained from these signals can make it possible (e.g. continuously) to determine a flow signal that is independent of the flow. A corresponding flow property, for example a flow rate, can be determined based on the flow signal. Thus, advantageously, the present invention may not require fluid dependent calibration.

Reference is made below to method embodiments. These embodiments are abbreviated by the letter “M” followed by the number. Whenever "method embodiments" are referred to in this document, these embodiments are meant.

• M1. A method for determining a flow property of a fluid, the method comprising:
  • Sending a first wave from a first transmitter to a first receiver, the first wave traversing the fluid on its way from the first transmitter to the first receiver, and receiving a signal of the first wave at the first receiver,
  • Determining a first feature based on the signal of the first wave,
  • Sending a second wave from a second transmitter to a second receiver, the second wave traversing the fluid on its way from the second transmitter to the second receiver, and receiving a signal of the second wave at the second receiver,
  • Determining a second feature based on the signal of the second wave,
  • Subtract one of the features from the other feature and thus generate a difference measure,
  • Determining a dwell time which specifies a propagation time required by the first wave to pass through the fluid on its way from the first transmitter to the first receiver and / or a propagation time required by the second wave to pass through the fluid on its way from the second transmitter to the second receiver,
  • Using the difference measure and the dwell time to determine the flow property.
• M2. Method according to the preceding method embodiment, wherein a first converter forms the first transmitter and the second receiver and a second converter forms the second transmitter and the first receiver.
• M3. Method according to the penultimate embodiment, wherein a first transducer forms the first transmitter and the second transmitter, a second transducer forms the first receiver and a third transducer forms the second receiver.
• M4. Method according to method embodiment M1, wherein a first converter forms the first transmitter, a second transducer forms the first receiver, a third converter forms the second transmitter and a fourth transducer forms the second receiver.
• M5. Method according to one of the 3 preceding method embodiments, wherein the second converter has the same properties as the first converter.
• M6. Method according to one of the 3 preceding method embodiments, wherein the third converter has the same properties as the first converter.
• M7. Method according to one of the 4 preceding method embodiments, wherein the third converter has the same properties as the second converter.
• M8. Method according to one of the 4 preceding method embodiments, wherein the fourth converter has the same properties as the first converter.
• M9. Method according to one of the 5 preceding method embodiments, wherein the fourth converter has the same properties as the second converter.
• M10. Method according to one of the 6 preceding method embodiments, wherein the fourth converter has the same properties as the third converter.
• M11. Method according to one of the preceding method embodiments, the method further comprising directing the fluid through a channel.
• M12. Method according to one of the preceding method embodiments, wherein the step of transmitting the first wave from the first transmitter to the first receiver comprises reflecting and / or breaking the first wave at least once.
• M13. Method according to one of the preceding method embodiments, wherein the step of transmitting the second wave from the second transmitter to the second receiver comprises reflecting and / or breaking the second wave at least once.
• M14. Method according to one of the preceding method embodiments, wherein the fluid comprises a direction of flow.
• M15. Method according to the preceding method embodiment, wherein the second wave traverses the fluid in a direction which is opposite to the first wave with respect to the direction of flow.
• M16. Method according to one of the preceding method embodiments, wherein the signal from the first and / or the second wave is not received by the respective receiver directly after the fluid has passed through.
• M17. Method according to one of the preceding method embodiments, wherein the first and second waves propagate as sound waves when passing through the fluid.
• M18. Method according to one of the preceding method embodiments, wherein the determination of the feature based on the signal of the respective wave comprises the determination of a phase shift between the wave transmitted by the respective transmitter and the signal of the wave received by the respective receiver.
• M19. A method according to any of the preceding method embodiments, wherein using the difference measure and the dwell time to determine the flow property comprises dividing the difference measure by the dwell time to derive a flow rate term proportional to the flow rate of the fluid.
• M20. Method according to one of the preceding method embodiments, wherein determining the dwell time comprises sending a dwell time wave from a dwell time transmitter to a dwell time receiver, the dwell time wave passing through the fluid on its way from the dwell time transmitter to the dwell time receiver, and receiving a signal of the dwell time wave at the dwell time receiver.
• M21. Method according to the preceding method embodiment, wherein the dwell time wave propagates as a sound wave when passing through the fluid.
• M22. Method according to one of the 2 preceding method embodiments, wherein the first and / or the second wave forms the dwell time wave.
• M23. Method according to one of the 3 preceding method embodiments, wherein the signal of the dwell time wave is received by the dwell time receiver directly after the fluid has passed through.
• M24. Method according to one of the 4 preceding method embodiments, wherein determining the dwell time _{comprises determining the total propagation time Δt IDT} between the dwell time transmitter which transmits the wave and the dwell time receiver which receives the signal of the wave.
• M25. Method according to the preceding method embodiment, wherein determining the dwell time further comprises _{correcting the total propagation time Δt IDT} for a fluid- and flow-independent offset time Δt _offset.
• M26. Method according to the preceding method embodiment, the method further comprising determining the fluid- and flow-independent offset time Δt _offset by means of a sensor-specific calibration measurement.
• M27. Method according to one of the preceding method embodiments and having the features of M11, wherein a wave which the fluid passes through comprises the wave which crosses the channel at least once.
• M28. Method according to the preceding method embodiment, wherein the first and / or the second wave which the fluid traverses comprises reflecting and / or breaking the respective wave at least once on an inner surface of the channel.
• M29. Method according to one of the 2 preceding method embodiments and having the features of M20, wherein the dwell time wave through which the fluid passes comprises the reflection and / or breaking of the dwell time wave at an inner surface of the channel at least once.
• M30. Method according to one of the preceding method embodiments and having the features of M20 and M26, wherein the determination of the dwell time comprises taking into account the frequency with which the dwell time wave crossed the channel when the fluid passed through.
• M31. Method according to one of the preceding method embodiments and having the features of method embodiments M20 and one of M2, M3, M4, the first, second, third or fourth converter also forming the dwell time transmitter.
• M32. Method according to one of the preceding method embodiments and having the features of method embodiments M20 and one of M2, M3, M4, wherein the converter which forms the first transmitter or the converter which forms the second transmitter also forms the dwell time transmitter.
• M33. Method according to one of the preceding method embodiments and having the features of M20, wherein a time transmitter converter forms the dwell time transmitter.
• M34. Method according to one of the preceding method embodiments and having the features of method embodiments M20 and one of M2, M3, M4, the first, second, third or fourth converter also forming the dwell time receiver.
• M35. Method according to one of the preceding method embodiments and having the features of method embodiments M20 and one of M2, M3, M4, wherein the converter which forms the first receiver or the converter which forms the second receiver also forms the dwell receiver.
• M36. Method according to one of the preceding method embodiments and having the features of M20, wherein the time measuring transducer forms the dwell time transmitter.
• M37. Method according to one of the preceding method embodiments, wherein the flow property is a flow velocity of the fluid.
• M38. Method according to one of the preceding method embodiments with the exception of method embodiment M37, wherein the flow property is a flow rate of the fluid.
• M39. Method according to one of the preceding method embodiments and having the features of at least one of M2, M3, M4, M33 and M36, wherein the transducers are interdigital transducers (IDT) which are configured to transmit and receive surface acoustic waves (SAW).
• M40. Method according to one of the preceding method embodiments with the features of M20, wherein the time measuring transducer is arranged downstream of the dwell time transmitter.
• M41. Method according to one of the preceding method embodiments, wherein the first wave and the second wave are each pulse-shaped waves in the time domain.
• M42. Method according to one of the preceding method embodiments and having the feature of M20, wherein the dwell time wave is a pulse-shaped wave in the time domain.
• M43 . Method according to one of the preceding method embodiments and with the features of at least one of the embodiments M2, M3, M4, M33 and M36, wherein the transmission of the first wave, the second wave and / or the dwell time wave is the provision of an AC voltage signal to the converter, the each transmitter for the wave forms includes.
• M44. Method according to the preceding method embodiment, wherein the AC voltage signal changes at a voltage frequency and wherein the voltage frequency is in the range from 10 MHz to 1000 MHz, preferably in the range from 20 MHz to 200 MHz, more preferably in the range from 30 MHz to 100 MHz.
• M45. Method according to one of the 2 preceding method embodiments, wherein the AC voltage signal comprises an effective voltage (RMS voltage) and wherein the effective voltage is in the range from -90 dBm to 30 dBm, preferably in the range from -60 dBm to 10 dBm, more preferably in the range from -40 dBm to 0 dBm.
• M45b. Method according to one of the 3 preceding method embodiments, wherein the AC voltage signal comprises an effective voltage (RMS voltage) and wherein the effective voltage is in the range from 1 μV to 10 V, preferably in the range from 10 μV to 1 V, more preferably in the range from 100 μV to 100 mV.
• M46. Method according to one of the 4 preceding method embodiments, wherein the AC voltage signal is a pulsed AC voltage signal.
• M47. Method according to the preceding method embodiment, wherein the pulsed AC voltage signal comprises a pulse length, the pulse length being in the range from 0.1 ns to 100 microseconds, preferably in the range from 1 ns to 10 microseconds, more preferably in the range from 10 ns to 3 microseconds.
• M48. Method according to one of the preceding method embodiments, wherein the fluid has a fluid pressure and the fluid pressure 100 bar, preferably 500 bar, more preferably 1000 bar, about 2000 bar.
• M49. Method according to one of the preceding method embodiments, wherein the flow property is determined for a fluid that has a flow rate at least in the range from 1 μl / min to 3 ml / min, preferably 500 nl / min to 5 ml / min, more preferably 1 nl / min to 10 ml / min.
• M50. Method according to one of the preceding method embodiments, the method not requiring any fluid-dependent calibration.
• M51. Method according to one of the preceding method embodiments, wherein the method further comprises determining at least one additional fluid property.
• M52. Method according to the preceding method embodiment, wherein the at least one additional fluid property is density, speed of sound, viscosity and / or conductivity.
• M53. Method according to one of the two preceding method embodiments, wherein the determination of at least one additional fluid property comprises the determination of a flow-independent phase shift of a wave through which the fluid passes.
• M54. Method according to one of the 3 preceding method embodiments, wherein determining at least one additional fluid property comprises determining a SAW phase shift of a SAW that propagates from the first transmitter to the first receiver and / or from the second transmitter to the second receiver without passing through the fluid.
• M55. Method according to one of the 4 preceding method embodiments, the method comprising deriving at least one potential fluid candidate for the fluid based on the at least one additional fluid property.
• M56. Method according to the preceding method embodiment, wherein deriving the at least one potential fluid candidate comprises using statistical methods.

Reference is made below to sensor embodiments. These embodiments are abbreviated by the letter “F” followed by the number. Whenever "sensor embodiments" are referred to in this document, these embodiments are meant.

• F1. A sensor for determining a flow property of a fluid, the sensor comprising:
  • a channel for guiding the fluid,
  • a transmitter and receiver arrangement which forms at least a first transmitter, a first receiver, a second transmitter and a second receiver, and
  • a data processing unit,
  • wherein the flow sensor is configured to carry out the method according to one of the preceding method embodiments.
• F2. Sensor according to the preceding sensor embodiment, wherein the transmitter and receiver arrangement comprises:
  • a first transducer forming the first transmitter and the second receiver, and
  • a second transducer that forms the second transmitter and the first receiver.
• F3. Sensor according to sensor embodiment F1, wherein the transmitter and receiver arrangement comprises:
  • a first transducer that forms the first transmitter and the second transmitter,
  • a second transducer forming the first receiver, and
  • a third transducer forming the second receiver.
• F4. Sensor according to sensor embodiment F1, wherein the transmitter and receiver arrangement comprises:
  • a first transducer, which forms the first transmitter,
  • a second transducer, which forms the first receiver,
  • a third transducer forming the second transmitter, and
  • a fourth transducer forming the second receiver.
• F5. Sensor according to one of the 3 preceding sensor embodiments, wherein the second transducer comprises the same design as the first transducer. That is, the second transducer comprises the same properties as the first transducer, it being possible for the properties to include, for example, geometric dimensions, periodicity, wavelength, and so on.
• F6. Sensor according to one of the 3 preceding sensor embodiments, wherein the third transducer comprises the same design as the first transducer.
• F7. Sensor according to one of the 4 preceding sensor embodiments, wherein the third transducer comprises the same design as the second transducer.
• F8. Sensor according to one of the 4 preceding sensor embodiments, wherein the fourth transducer comprises the same design as the first transducer.
• F9. Sensor according to one of the 5 preceding sensor embodiments, wherein the fourth transducer comprises the same design as the second transducer.
• F10. Sensor according to one of the 6 preceding sensor embodiments, wherein the fourth transducer comprises the same design as the third transducer.
• F11. Sensor according to one of the preceding sensor embodiments, wherein the transmitter and receiver arrangement further forms a dwell time transmitter and a dwell time receiver.
• F12. Sensor according to the preceding sensor embodiments and with the features of the sensor embodiments F2 , F3 or F4 wherein the first, the second, the third or the fourth transducer further forms the dwell time receiver.
• F13. Converter according to one of the 2 preceding sensor embodiments and with the features of the sensor embodiments F2 , F3 or F4 wherein the transducer which forms the first receiver or the transducer which forms the second receiver further forms the dwell receiver.
• F14. Sensor according to sensor design F11 wherein the transmitter and receiver arrangement comprises a time transducer which forms the dwell time receiver.
• F15. Sensor according to one of the 4 preceding sensor embodiments and with the features of the sensor embodiments F2 , F3 or F4 wherein the first, the second, the third or the fourth transducer further forms the dwell time transmitter.
• F16. Sensor according to one of the 2 preceding sensor embodiments and with the features of the sensor embodiments F2 , F3 or F4 wherein the transducer which forms the first transmitter or the transducer which forms the second transmitter further forms the dwell transmitter.
• F17. Sensor according to one of the sensor embodiments F11 , F12 , F13 or F14 wherein the transmitter and receiver arrangement comprises a time transmitter transducer forming the dwell time transmitter.
• F18. Sensor according to one of the preceding sensor embodiments, wherein the first transmitter is arranged downstream of the first receiver and the second transmitter is arranged upstream of the second receiver.
• F19. Sensor according to one of the preceding sensor embodiments and with the exception of the features of the preceding embodiment, wherein the first transmitter is arranged upstream of the first receiver and the second transmitter is arranged downstream of the second receiver.
• F20. Sensor according to one of the preceding sensor embodiments, wherein the first transmitter and the first receiver are arranged directly one after the other in the direction of flow.
• F21. Sensor according to one of the preceding sensor embodiments, wherein the second transmitter and the second receiver are arranged directly one after the other in the direction of flow.
• F22. Sensor according to one of the preceding sensor embodiments, wherein the first transmitter and the first receiver are arranged on the same side of the channel. The first transmitter and the first receiver are both arranged on one side thereof.
• F23. Sensor according to one of the preceding sensor embodiments with the exception of the preceding sensor embodiment, wherein the first transmitter and the first receiver are arranged on opposite sides of the channel.
• F24. Sensor according to one of the preceding sensor embodiments and having the features of F11, wherein the dwell time receiver and the dwell time transmitter are arranged directly one after the other in the direction of flow.
• F25. Sensor according to one of the preceding sensor embodiments and having the features of F11, wherein the dwell time receiver is arranged downstream of the dwell time transmitter.
• F25b. Sensor according to one of the preceding sensor embodiments and having the features of F11, but with the exception of the features of the preceding sensor, wherein the dwell time receiver is arranged upstream of the dwell time transmitter.
• F26. Sensor according to one of the preceding sensor embodiments and having the features of F11, wherein the dwell time receiver and the dwell time transmitter are arranged on the same side of the channel.
• F27. Sensor according to one of the preceding sensor embodiments with the exception of the preceding embodiment and having the features of F11, wherein the dwell time receiver and the dwell time transmitter are arranged on opposite sides of the channel.
• F28. A sensor according to any of the preceding sensor embodiments, wherein the channel includes an interior surface configured to be in contact with the fluid directed through the channel.
• F29. Sensor according to one of the preceding sensor embodiments, wherein the channel comprises a channel cross section and wherein the channel cross section is rectangular, round, elliptical and / or any combination thereof.
• F30. Sensor according to the preceding sensor embodiment, wherein the channel cross-section is rectangular.
• F31. Sensor according to one of the preceding sensor embodiments, wherein the channel comprises a channel geometry and wherein the channel geometry is straight, curved and / or bent.
• F32. Sensor according to one of the preceding sensor embodiments, wherein the channel comprises a flow direction and wherein the fluid is conducted in the flow direction through the channel.
• F33. Sensor according to one of the preceding sensor embodiments, wherein the channel comprises a channel length which corresponds to the extension of the channel along which fluid is conducted.
• F34. Sensor according to the preceding sensor embodiment, the channel length being up to 30 mm, preferably up to 10 mm, more preferably up to 5 mm.
• F35. Sensor according to one of the preceding sensor embodiments, wherein the transmitter and receiver arrangement comprises at least one chip.
• F36. Sensor according to the preceding sensor embodiment, wherein the at least one chip comprises a substrate.
• F37. Sensor according to the preceding sensor embodiment, wherein the substrate is piezoelectric.
• F38. Sensor according to one of the 2 preceding sensor embodiments, wherein the substrate is coated with a piezoelectric layer.
• F39. Sensor according to one of the 2 preceding sensor embodiments, wherein the substrate and / or the piezoelectric layer consists of a crystal of lithium niobate (LiNbCb), quartz (SiO ₂ ), lithium tantalate (LiTaO ₃ ) and / or lanthanum gallium silicate (La ₃ Ga ₅ SiO ₁₄ ) .
• F40. Sensor according to one of the 3 preceding sensor embodiments, wherein the substrate and / or the piezoelectric layer consists of a 128 ° XY-cut LiNbO ₃ crystal.
• F41. Sensor according to one of the 6 preceding sensor embodiments, wherein the at least one chip comprises at least one transducer which is configured to transmit and / or receive a wave.
• F42. Sensor according to the preceding sensor embodiment and with the features of at least one of the sensor embodiments F2, F3, F4, F14 and F17, wherein the at least one converter of the is the first converter, the second converter, the third converter, the fourth converter, the time measuring converter and / or the time transmitter converter. F43. Sensor according to one of the two preceding sensor embodiments and having the features of F37 or F38, the transducer being arranged on the piezoelectric substrate or the piezoelectric layer.
• F44. Sensor according to one of the 3 preceding sensor embodiments, wherein the transducer is configured to transmit and / or receive a wave with a transducer wavelength, the transducer wavelength in the range from 4 μm to 400 μm, preferably 20 μm to 200 μm, more preferably 40 μm to 133 µm.
• F45. Sensor according to one of the 4 preceding sensor embodiments, wherein the at least one transducer is an interdigital transducer (IDT) which is configured to transmit and / or receive a surface acoustic wave.
• F46. Sensor according to the preceding sensor embodiment, wherein each interdigital transducer comprises at least two interdigitated electrodes.
• F47. A sensor according to any of the preceding sensor embodiments, wherein each of the at least two interdigitated electrodes comprises a plurality of finger electrodes, the finger electrodes of the interdigitated electrodes interdigitated.
• F48. The sensor of the preceding sensor embodiment, wherein each of the at least two interdigitated electrodes comprises an identical number of finger electrodes.
• F49. Sensor according to one of the 2 preceding sensor embodiments, wherein the interdigital transducer 2 includes interdigitated electrodes.
• F50. Sensor according to the preceding sensor embodiment, wherein the 2 interdigitated electrodes are arranged such that the two interdigitated electrodes alternately encompass the interdigitated electrode fingers.
• F51. Sensor according to the penultimate sensor embodiment, wherein the 2 interlocking electrodes are arranged in such a way that the two interlocking electrodes alternately comprise electrode groups which each comprise an equal number of several adjacent finger electrodes.
• F52. Sensor according to one of the 5 preceding sensor embodiments, wherein the finger electrodes are periodically spaced.
• F53. Sensor according to one of the 6 preceding sensor embodiments, wherein the finger electrodes are beveled and / or tapered.
• F54. Sensor according to one of the preceding sensor embodiments and having the features of F41, wherein the transducer is configured to transmit and / or receive a chirped surface acoustic wave.
• F55. Sensor according to the preceding sensor embodiments and having the features of F47, wherein the finger electrodes comprise a finger electrode width and wherein a distance between successive finger electrodes and the finger electrode width decreases in a direction perpendicular to a largest extension of the finger electrodes.
• F56. Sensor according to one of the preceding sensor embodiments and having the features of F47, wherein each of the at least two interdigitated electrodes comprises between 3 and 1000 finger electrodes, preferably between 3 and 700 finger electrodes.
• F57. Sensor according to one of the preceding sensor embodiments and with the features of F45, wherein the interdigital transducer has an electrical impedance of 1 Ω to 500 Ω, preferably 10 Ω to 200 Ω, more preferably 30 Ω to 100 Ω, approximately 50 Ω.
• F58. Sensor according to one of the preceding sensor embodiments and having the features of F45, wherein the interdigital transducer comprises an acoustic screen which denotes an overlapping length of the at least two electrodes.
• F59. Sensor according to the preceding sensor embodiment, the acoustic screen being in the range from 100 μm to 3000 μm, preferably in the range from 200 μm to 1000 μm, more preferably in the range from 300 μm to 800 μm.
• F60. Sensor according to one of the preceding sensor embodiments and having the features of F41, wherein the at least one transducer is configured to emit surface acoustic waves with an excitation power below 1 W, preferably below 10 mW, more preferably below 1 mW.
• F61. Sensor according to one of the preceding sensor embodiments and with the features of at least one of the sensor embodiments F2, F3, F4, F14 and F17, wherein the first converter, the second converter, the third converter, the fourth converter, the time measuring converter and / or the time transmitter converter are unidirectional Converter is.
• F62. Sensor according to one of the preceding sensor embodiments and with the features of at least one of the sensor embodiments F2, F3, F4, F14 and F17, wherein the first converter, the second converter, the third converter, the fourth converter, the time measuring converter and / or the time transmitter converter are bidirectional Converter is.
• F63. Sensor according to one of the preceding sensor embodiments and having the features of F35, wherein the chip comprises a sealing layer which covers the at least a portion of the chip surface and preferably components which the chip comprises.
• F64. Sensor according to the preceding sensor embodiment and with the features of F41, wherein the sealing layer covers the at least one transducer.
• F65. Sensor according to one of the 2 preceding sensor embodiments, wherein the sealing layer consists of a material of the polyaryletherketone (PAEK) family, preferably polyetheretherketone (PEEK), an oxide ceramic material, fused SiO ₂ (silica glass) or Si ₃ N ₄ .
• F66. Sensor according to one of the 3 preceding sensor embodiments and with the features of F44, wherein the sealing layer comprises a sealing layer thickness and wherein the sealing layer thickness is less than 10 times the transducer wavelength, preferably less than 5 times the transducer wavelength, more preferably less than the transducer wavelength and still more preferably less than 0.25 times the transducer wavelength.
• F67. Sensor according to one of the preceding sensor embodiments and having the features of embodiments F28 and F35, wherein the chip comprises a top side and wherein at least a portion of the top side is part of the inner surface of the channel.
• F68. Sensor according to one of the preceding sensor embodiments and having the features of F28, wherein at least a portion of the inner surface of the channel is provided by an acoustic reflector.
• F69. Sensor according to the preceding sensor embodiment, wherein the acoustic reflector is made of sapphire.
• F70. Sensor according to the penultimate sensor embodiment, wherein the acoustic reflector is a refractive reflector, which is preferably made of a synthetic material, such as plastic.
• F71. Sensor according to one of the preceding sensor embodiments and having the features of sensor embodiment F35, wherein at least a portion of the chip is configured as a waveguide for SAW.
• F72. Sensor according to one of the preceding sensor embodiments and having the features of sensor embodiments F32 and F35, wherein the channel comprises a channel height which corresponds to the expansion of the channel in a direction perpendicular to the chip and the direction of flow.
• F73. Sensor according to the preceding sensor embodiment, the channel height being at most 20 mm, preferably at most 5 mm, more preferably at most 1 mm.
• F74. Sensor according to one of the preceding sensor embodiments and having the features of sensor embodiments F32 and F35, the channel having a channel width which corresponds to the expansion of the channel in a direction parallel to the chip and perpendicular to the direction of flow.
• F75. Sensor according to the preceding sensor embodiment, the channel width being at most 10 mm, preferably at most 3 mm, more preferably at most 1 mm.
• F76. Sensor according to one of the preceding sensor embodiments, the sensor being configured for flow rates in the range from 1 μl / min to 3 ml / min, preferably 500 nl / min to 5 ml / min, more preferably 1 nl / min to 10 ml / min.
• F77. Sensor according to the preceding sensor embodiment, wherein the sensor is configured to measure the flow rates with a relative error of up to 0.1%, preferably up to 0.01%, more preferably up to 0.001%.
• F78. Sensor according to one of the preceding sensor embodiments, wherein the sensor is configured for pressures that exceed 100 bar, preferably exceed 500 bar, more preferably exceed 1000 bar, exceed approximately 2000 bar.
• F79. Sensor according to one of the preceding sensor embodiments, wherein fluid conveying sections of the sensor are chemically resistant, preferably chemically inert.
• F80. A sensor according to any of the preceding sensor embodiments, wherein the flow characteristic is a flow rate of the fluid.
• F81. Sensor according to one of the preceding sensor embodiments, wherein the flow property is a flow velocity of the fluid.
• F82. Sensor according to one of the preceding sensor embodiments and having the features of F35, wherein the first transmitter and the first receiver are arranged on the same chip.
• F83. Sensor according to one of the preceding sensor embodiments with the exception of the preceding embodiment and having the features of F35, wherein the first transmitter and the first receiver are arranged on different chips.
• F84. Sensor according to one of the preceding sensor embodiments and having the features of F35, wherein the second transmitter and the second receiver are arranged on the same chip.
• F85. Sensor according to one of the preceding sensor embodiments with the exception of the preceding embodiment and having the features of F35, wherein the second transmitter and the second receiver are arranged on different chips.
• F86. Sensor according to one of the preceding sensor embodiments and having the features of F35, wherein the second transmitter and the second receiver are arranged on a different chip than the second transmitter and the second receiver.
• F87. Sensor according to one of the preceding sensor embodiments and having the features of F11 and F35, wherein the dwell time transmitter and the dwell time receiver are arranged on the same chip.
• F88. Sensor according to one of the preceding sensor embodiments with the exception of the preceding embodiment and having the features of F11 and F35, the dwell time transmitter and the dwell time receiver being arranged on different chips.
• F89. Sensor according to one of the preceding sensor embodiments and having the features of F37 or F38, wherein the piezoelectric substrate or the piezoelectric layer _{comprises a SAW speed of sound, c S} , which corresponds to the propagation speed of a SAW within the piezoelectric substrate or the piezoelectric layer.
• F90. Sensor according to one of the preceding sensor embodiments and having the features of F37 or F38, wherein the fluid conducted through the sensor _{comprises a fluid sound velocity, c F} , which corresponds to the propagation speed of a sound wave within the fluid.
• F91. Sensor according to one of the preceding sensor embodiments and having the features of sensor embodiment F11, wherein the dwell time receiver comprises a dwell time receiver length in the flow direction and wherein the dwell time transmitter comprises a dwell time transmitter length in the flow direction, the dwell time receiver length being greater than the dwell time transmitter length.
• F92. Sensor according to one of the preceding sensor embodiments and with the features of sensor embodiment F11, wherein the dwell time receiver comprises a dwell time receiver length in the direction of flow and the dwell time receiver length in the range from 0.1 mm to 100 mm, preferably 0.2 mm to 50 mm, more preferably 0.2 mm to 20 mm.
• F93. Sensor according to one of the preceding sensor embodiments and with the features of sensor embodiment F11, the dwell time transmitter comprising a dwell time transmitter length in the direction of flow and the dwell time transmitter length in the range from 12 μm to 40 mm, preferably 60 μm to 20 mm, more preferably 120 μm to 14 mm .
• F94. Sensor according to one of the preceding sensor embodiments and with the features of sensor embodiment F11, the dwell time transmitter and the dwell time receiver being separated by a delay line length in the direction of flow and the delay line length being at least 10 µm, preferably at least 50 µm, more preferably at least 100 µm.
• F95. Sensor according to one of the preceding sensor embodiments, wherein the processing unit is configured to receive signals from the transmitter and receiver arrangement.
• F96. Sensor according to one of the preceding sensor embodiments, wherein the processing unit is configured to send signals to the transmitter and receiver arrangement.
• F97. Sensor according to one of the preceding sensor embodiments, wherein the transmitter and receiver arrangement is configured to receive signals from a signal generator.
• F98. Sensor according to one of the preceding sensor embodiments, wherein the processing unit is configured to send signals to the signal generator.
• F99. Sensor according to one of the preceding sensor embodiments, wherein the processing unit is configured to determine the dwell time.
• F100. Sensor according to the preceding sensor embodiment and with the features of F11 and F95, wherein the processing unit is configured to determine a dwell time based on a signal received from the dwell time receiver.
• F101. Sensor according to one of the preceding sensor embodiments, wherein the processing unit is configured to carry out steps of the method according to one of the preceding method embodiments.
• F102. Sensor according to any of the preceding sensor embodiments and having the features of F95, wherein the processing unit is configured to determine a difference measure based on signals received from the first and second receivers.
• F103. Sensor according to the preceding sensor embodiment and with the features of F99, wherein the processing unit is configured to use the dwell time and the difference measure to determine the flow property.
• F104. Sensor according to one of the preceding sensor embodiments and having the features of F95, wherein the processing unit is configured to carry out digital post-processing of signals received from the transmitter and receiver arrangement.
• F105. Sensor according to one of the 3 preceding sensor embodiments and with the features of F95, the processing unit being configured to carry out digital post-processing of the difference measure.
• F106. The sensor of any preceding sensor embodiment, wherein at least a portion of the channel is configured to provide an acoustic waveguide for waves traversing the fluid.
• F107. Sensor according to one of the preceding sensor embodiments and having the features of F89, wherein the channel is formed from a channel material and wherein the channel material _{comprises a material sound velocity, c m} ,, which is less than the SAW sound velocity.
• F108. Sensor according to the preceding sensor embodiment and including the features of F28, but with the exception of the features of F67, wherein the chip comprises a top side and wherein the top side is not part of the inner surface of the channel.
• F109. Sensor according to one of the 2 preceding sensor embodiments and with the exception of the features of F67, wherein the chip is coupled to the channel material via a coupling material, the coupling material being configured to allow a SAW to propagate from the chip to the channel material and vice versa.
• F110. Sensor according to the preceding sensor embodiment and with the features of F44, wherein the coupling material comprises a coupling material thickness and wherein the coupling material thickness is less than 50%, preferably less than 25% and more preferably less than 10% of the transducer wavelength.

M57. Method according to one of the preceding method embodiments, the method comprising using a sensor according to one of the preceding sensor embodiments.

• 1A stellt ein Ausführungsbeispiel eines Durchflusssensors gemäß der vorliegenden Erfindung in einer ersten Konfiguration dar,
• 1B stellt das Ausführungsbeispiel von 1A in einer zweiten Konfiguration dar,
• 2 stellt schematisch beispielhafte Designs von IDT dar,
• 3 veranschaulicht eine Abbildung der strömungsabhängigen Verlagerung auf eine Zeitverzögerung,
• 4 veranschaulicht die Fluidabhängigkeit der Verweilzeit,
• 5A veranschaulicht Parameter, die relevant sind, um eine gewünschte Platzierung des Verweilzeitempfängers abzuschätzen,
• 5b veranschaulicht Parameter, die relevant sind, um eine gewünschte Länge des Verweilzeitempfängers zu schätzen,
• 6 stellt ein weiteres Ausführungsbeispiel eines Durchflusssensors nach der vorliegenden Erfindung dar,
• 7A stellt eine beispielhafte Sender- und Empfängeranordnung dar, die 4 Phasenverschiebungswandler umfasst,
• 7B stellt eine beispielhafte Sender- und Empfängeranordnung dar, die 3 Phasenverschiebungswandler umfasst,
• 7C stellt eine beispielhafte Sender- und Empfängeranordnung dar, die 2 Phasenverschiebungswandler umfasst,
• 8A stellt ein weiteres Ausführungsbeispiel eines Durchflusssensors gemäß der vorliegenden Erfindung in einer ersten Konfiguration dar,
• 8B stellt das Ausführungsbeispiel von 1B in einer zweiten Konfiguration dar,
• 9A veranschaulicht ein Beispiel eines Signals einer Welle, die von einem Wandler empfangen wird,
• 9B veranschaulicht Änderungen eines beispielhaften Signals, das von einem Wandler aufgrund von Änderungen der Kanalhöhe empfangen wird,
• 10 veranschaulicht eine beispielhafte Messung von Stufenströmungsrampen für zwei verschiedene Fluide, und
• 11 veranschaulicht noch eine weitere Ausführungsform der vorliegenden Erfindung.

Embodiments of the present invention will now be described with reference to the accompanying drawings. These embodiments are only intended to give examples of the present invention, but not to limit them.

• 1A shows an embodiment of a flow sensor according to the present invention in a first configuration,
• 1B represents the embodiment of 1A in a second configuration,
• 2 shows schematically exemplary designs from IDT,
• 3 illustrates a mapping of the flow-dependent shift to a time delay,
• 4th illustrates the fluid dependence of the residence time,
• 5A illustrates parameters that are relevant to estimate a desired placement of the dwell time receiver,
• 5b illustrates parameters that are relevant to estimate a desired length of the dwell time receiver,
• 6th represents a further embodiment of a flow sensor according to the present invention,
• 7A represents an exemplary transmitter and receiver arrangement comprising 4 phase shift converters,
• 7B illustrates an exemplary transmitter and receiver arrangement comprising 3 phase shift converters,
• 7C represents an exemplary transmitter and receiver arrangement comprising 2 phase shift converters,
• 8A shows a further embodiment of a flow sensor according to the present invention in a first configuration,
• 8B represents the embodiment of 1B in a second configuration,
• 9A illustrates an example of a signal of a wave received by a transducer,
• 9B illustrates changes in an exemplary signal received by a transducer due to changes in channel height,
• 10 illustrates an exemplary measurement of step flow ramps for two different fluids, and
• 11 illustrates yet another embodiment of the present invention.

It is noted that not all drawings bear all reference numbers. Instead, some of the reference numbers have been omitted in some drawings for reasons of space and simplicity of illustration. Embodiments of the present invention will now be described with reference to the accompanying drawings.

With reference to 1A becomes an exemplary embodiment for a flow sensor 1 discussed in accordance with the present invention. The flow sensor 1 can generally have a channel 11 for directing a fluid flow, the flow characteristic of which, e.g. B. flow rate and / or flow velocity is to be measured. The fluid can flow through the channel in a direction of flow indicated by the solid arrow 11 flow, e.g. B. the fluid can be directed in a flow direction through the channel. That is, whenever the words “upstream” or “downstream” are used here, these words are to be understood in relation to the direction of flow. So when something is said to be downstream of something else, it is lower down the flow, and the reverse is true for anything that is said to be upstream. For example, in 1A the dotted arrows generally upstream (ie the projection onto the x-direction points upstream), while the solid arrow, which indicates the flow direction, points downstream.

The channel 11 can be an inner surface 111 include that of the surface of the channel 11 which can be in contact with a fluid when it is passed through, ie through the channel 11 and with it the flow sensor 1 flows through. In general, the channel can 11 comprise different channel geometries and / or channel cross-sections. For example, the cross section of the channel 11 rectangular, round, elliptical, or any combination thereof. It goes without saying that the cross section refers to a section through the channel 11 relates in a plane perpendicular to the direction of flow. Furthermore, the geometry of the channel 11 for example straight, curved or bent, e.g. B. a corner, about a 90 ° corner, include. That is, the channel 11 may assume a geometry in which the fluid can be directed, for example, straight or along a curved or curved path, e.g. B. along a continuous, smooth bend or around a sharp corner. In some embodiments, two different channel geometries can be connected in series, for example in order to detect the occurrence of turbulent flow rates. In other words, two (sub) sensors can be connected in series, with the channel geometries of the two sensors being able to differ, for example the occurrence of turbulent flows can be detected. For example, for applications with a broad spectrum of flow rates, it can be advantageous if two sensors are connected in series, it being possible for the channel and / or sensor geometry to differ between the two sensors. In particular, one sensor can be optimized for a region with a lower flow rate than the other sensor in such a way that a larger area can be covered overall. In such an embodiment, for example, one can initially measure a flow rate with the sensor that is optimized for lower flow rates, and then, e.g. When detecting turbulence, return to the sensor which is optimized for higher flow rates, which for example may comprise a generally larger geometry. That is to say, by connecting two sensors in series, an overall “combined” sensor can be provided which, for example, can enable an overall higher accuracy for a larger range of fluid flows.

Preferably the channel 11 and all fluid conveying sections of the sensor, ie all parts of the sensor that come into contact with the fluid passed through the flow sensor, be chemically resistant. That is, it can be resistant to fluids such as organic solvents, acids, alkalis and salts, in particular to fluids that are typically used in liquid chromatography, e.g. B. HPLC, can be used. The fluid conveying sections of the flow sensor can preferably be chemically inert.

In addition, the flow sensor 1 a transmitter and receiver assembly generally configured to excite and / or detect surface acoustic waves (“SAW”). The transmitter and receiver arrangement can have at least one chip 12th comprise, wherein the at least one chip 12th a substrate 121 may include e.g. B. a monolithic substrate, which may preferably be piezoelectric. For example, the substrate can be a crystal made of lithium niobate (LiNbO ₃ ), quartz (SiO ₂ ), lithium tantalate (LiTaO ₃ ) or lanthanum gallium _{silicate (La 3} Ga ₅ SiO ₁₄ ). In particular, the substrate can be a 128 ° XY-cut LiNbO ₃ crystal. It goes without saying, however, that the substrate can also be formed from a different material and that only one piezoelectric layer, e.g. B. formed by one of the aforementioned materials can be formed on the substrate, e.g. B. by vapor deposition. In other words, the chip can 12th in some embodiments, a substrate 121 , e.g. B. a silicon crystal, which may be coated with a piezoelectric layer (not shown), rather than just a substrate 121 to use, which is itself piezoelectric. In the following embodiments, it is assumed that the flow sensor 1 a piezoelectric substrate 121 but it should be understood that the same is true with a special piezoelectric layer on a substrate 121 can be realized, which may not be piezoelectric.

On the piezoelectric substrate 121 (or the piezoelectric layer) can have at least one transducer 122 be arranged. The at least one converter 122 may generally be configured to, for example, emit and / or receive a wave, e.g. B. detected a wave or a signal corresponding to a wave. That is, the at least one converter 122 can generally be configured to convert an electrical signal into a wave and / or vice versa. The at least one converter can preferably 122 an interdigital transducer (IDT) configured to generate surface acoustic waves (SAW), e.g. B. to emit and receive, e.g. B. to detect. In other words, an IDT 122 generally be configured to send and / or receive SAW. IDT and the general principle of generating a SAW with an IDT on a piezoelectric substrate is described, for example, in Direct piezoelectric coupling to surface elastic waves, RM White and FW Voltmer, Appl. Phys. Lett 7, 314 (1965) , discussed. In principle, an IDT can be designed in such a way that it converts electrical signals into elastic surface waves, ie surface acoustic waves (SAW), or vice versa, in order to convert surface waves into electrical signals. In order to generate a surface acoustic wave, an alternating voltage can typically be applied to two interdigitated electrodes that comprise the IDT, which due to the inverse piezoelectric effect causes the piezoelectric material to be subjected to periodic deformations. These periodic deformations can lead to the excitation of a SAW. The exact properties can depend heavily on the design of the IDT, especially its electrodes. For example, an IDT can comprise two electrodes, each comprising a comb-like structure, which can be arranged opposite one another in such a way that the fingers of the comb interlock. Such a structure can make it possible to periodically deform the piezoelectric substrate (or the piezoelectric layer) under the IDT and thus to excite a SAW. The exact The design of the electrodes of an IDT can, for example, influence the frequency and / or the maximum power of a generated SAW. In addition, the design can, for example, allow the IDT SAW to emit / receive symmetrically or in a preferred direction.

The electrodes of an IDT can generally be interdigitated and are therefore also referred to as interdigitated electrodes. In particular, the interdigitated electrodes of the IDT can each comprise a plurality of finger electrodes, the finger electrodes of the various interdigitated electrodes interdigitated. In general, a variety of designs for such IDTs are known and can be used with the present invention. Some exemplary IDT configurations are in 2 shown schematically.

2 a) shows an IDT 122 , of two interlocking electrodes 2 comprises, each of the interdigitated electrodes 2 multiple finger electrodes 21 includes those with the finger electrodes 21 the respective other interdigitated electrode 2 interlock. In this design, the finger electrodes 21 as well as the respective gaps between the finger electrodes 21 each have an identical width of preferably .1 / 4, where λ is the designated wavelength of the IDT 122 emitted / transmitted SAW. Therefore, a period P of the IDT, that is, a portion corresponding to a length of λ, comprises two finger electrodes 21 each with a different electrode 2 includes. That is to say, in this case, a period comprises exactly one pair of fingers, that is to say one pair of electrode fingers 21 , the two electrode fingers 21 each comprising a different interdigitated electrode 2 the two electrode fingers 21 includes. In other words, the in 2 a) IDT 122 shown 4 pairs of fingers and / or the like a number of periods n of 4, ie 4 periods P. A SAW is in the underlying substrate 121 within the overlapping region of the finger electrodes 21 also known as the acoustic shutter w, and generally spreads in a direction in which the finger electrodes are 21 overlap (typically perpendicular to the largest extent of the finger electrodes 21 ) as indicated by the solid arrows. In general, such a design may also be referred to as a single electrode type IDT or a fixed electrode type IDT.

With reference to 2 B) a similar design is shown, but this time a single period P includes 4 electrode fingers 21 , ie 2 pairs of fingers, with the finger electrodes 21 of the two interlocking electrodes 2 interlock in pairs, ie two finger electrodes 21 same interdigitated electrode 2 always lie next to each other. The width of the electrode fingers can therefore be adjusted here 21 and the gaps between the electrode fingers are preferably λ / 8. This design can also be referred to as a dual electrode type IDT or a split electrode type IDT. It goes without saying that a higher number of fingers per period can of course also be used for an IDT of the split electrode type, e.g. B. can be a period 8th Grasp your fingers. In other words, not only double-electrode type IDTs can be used, but multi-electrode type IDTs in general.

Furthermore, with reference to 2 c) the finger electrodes 21 be beveled and tapered. Especially for two interlocking electrodes 2 can connect the finger electrodes to one of the interdigitated electrodes 2 be beveled and tapered so that the thickness of the finger electrodes 21 and change the distance between them in a direction perpendicular to the direction of propagation of the SAW. This can advantageously make it possible for the IDT to encompass a large bandwidth, since the period on one side of the acoustic screen is different than on the other side of the acoustic screen and thus different proportions of the acoustic screen w can be suitable for different wavelengths. Such a design can also be referred to as a tapered IDT or angled finger IDT and can be combined with an IDT of the fixed electrode type or an IDT of the split electrode type.

With reference to 2d ) the IDT can also be configured to have a changing width and separation of the finger electrodes 21 to include in the direction of propagation. In other words, the period of the IDT can change in the direction of propagation of an emitted SAW. This in turn can increase the bandwidth of the IDT and, in particular, enable the emission and reception of chirped SAW pulses. Such a design can therefore also be referred to as a chirped IDT.

Referring again to FIG 1A may, in some embodiments, have an optional sealing layer 123 to protect the converter 122 serve. For example, the converters 122 be covered with a thin layer of quartz glass (Fused SiO ₂ (silica glass)). The thickness (also referred to as the height) of the sealing layer can preferably be 123 be much smaller than a wavelength of the respective transducer 122 generated wave, e.g. B. one from a respective IDT 122 generated SAW. For example, the sealing layer 123 a thickness less than half a wavelength that of the transducer 122 generated wave, preferably less than a quarter of a wavelength, more preferably less than 10% of the wavelength of the wave excited by the transducer.

In the following the flow sensor 1 general, as IDT 122 that are configured to incorporate SAW in a piezoelectric substrate 121 or to generate a piezoelectric layer. It should be understood, however, that other types of transducers are more generally 122 can be used to generate corresponding waves (e.g. to emit and / or transmit).

In general, the chip can 12th a top 124 which may be at least partially in contact with a fluid passing through the channel 11 flows. The top 124 of the chip 12th can for example be the outer surface of the sealing layer 123 correspond. At least part of the top 124 can thus be part of the inner surface 111 of the canal 11 be. That is, at least a portion of the top 124 of the chip 12th can be in contact with the through the channel 11 flowing fluid. In other words, at least a portion of a fluid that is passed through the flow sensor 1 and in particular through the canal 11 is directed with the top 124 of the chip 12th be brought into contact on or next to the SAW using an IDT 122 can be stimulated.

Therefore, the piezoelectric substrate 121 (or the piezoelectric layer) using at least one IDT 122 be excited, for example, a first transmitter 122A-1 or a second transmitter 122A-2 forms. That is, by applying an AC voltage signal to the IDT 122 and especially on electrodes that the IDT 122 includes, the piezoelectric material can be periodically deformed and thus a SAW generated (z. B. started or emitted). The SAW can move generally perpendicular to the chip normal and along the chip surface, wherein the SAW can include a surface displacement in the direction perpendicular to the direction of movement, ie along the chip normal. In other words, when the piezoelectric substrate is excited 121 (or the piezoelectric layer) using at least one of the IDT 122 at least partially SAW are generated along the normal to the surface of the chip (ie in the direction of the upper side 124 ) can swing (e.g. deflect). When the SAW with the fluid in the channel 11 comes into contact, the displacement can excite a bulk wave within the fluid. This means that the wave can at least partially transfer itself into the fluid at the so-called Rayleigh angle θ _R , where it can propagate as an ultrasonic wave (sound wave), i.e. as a (longitudinal) pressure wave, as indicated generally by the arrows leading from IDT 122 going out emitting a wave. This can be a first sender 122A-1 or a second transmitter 122A-2 form (cf. 1A and 1B) . In other words, an ultrasonic wave, ie a sound wave, can be generated (and also received / detected) by means of surface acoustic waves. This process is generally explained by A. Wixforth and T. Franke in their treatise Microfluidics for Miniaturized Laboratories on a Chip (ChemPhysChem 2008, 9, 2140-2156) and is also used, for example, in the above-mentioned document US 10,570,361 B1 used. In principle, the longitudinal sound wave generated by the SAW propagates due to the phase adjustment at an angle θ _R , which is typically referred to as the Rayleigh angle θ _R , and due to the speed of sound of the SAW (c _S ) in the chip 12th , e.g. B. the substrate 121 or a piezoelectric layer on the substrate, and the sound wave in the fluid (c _F ) is defined by the following relationship: $$sin{\theta }_{\mathrm{R.}}=\frac{c_{\mathrm{F.}}}{c_{\mathrm{S.}}}.$$

That is, if the SAW comes into contact with a fluid and if the speed of sound of the SAW (c _S ) is greater than the speed of the sound wave in the fluid (c _F ), it can (at least partially) at the Rayleigh angle θ _R in Relation to the surface normal of the chip 12th be deflected into the fluid.

More generally, a SAW that resides in a substrate (e.g., a piezoelectric substrate 121 or more generally in a chip 12th ) and spreads close to it or on its surface (e.g. on a substrate) into a medium (e.g. fluid) that covers the substrate, "licking", provided that the sound velocity of the medium is less than the Is the speed of sound of the substrate, and further provided that the medium has a thickness that is significantly greater than the wavelength of the SAW. In such a case, a fraction of the wave is continuously transmitted into the medium while the SAW propagates on the substrate surface. In other words, the wave is transmitted into the medium with a certain fixed part. Thus, the temporal and spatial transition of the SAW amplitude follows a falling exponential function, provided there is no additional SAW source, e.g. B. electrically at an IDT or by an ultrasonic wave entering the medium. Such SAW are therefore also referred to as "leaking SAW" because licking them into the adjacent medium. This process can also be understood as an acoustic equivalent to the refraction of light.

The wave, ie the sound wave (also referred to as a volume wave), can then pass through the fluid. In other words, the wave can travel through the channel 11 and in particular move through the fluid flowing in the channel, the direction of movement running at least partially in the y-direction. That is, the wave can move in the y-direction through the channel, while at the same time it also moves with or against the flow direction (ie x-direction). In other words, the wave can cross the channel in the y-direction when it passes through the fluid, with the γ-direction generally perpendicular to the flow direction and to the chip 12th can be, ie along the surface normal of the chip 12th . Thus, the expansion of the channel 11 in y-direction also as height H1 of the canal 11 or duct height H1 are designated.

As indicated by the dotted arrows in 1A specified, a wave generated by a first IDT 122-1 is emitted by the first transmitter 122A-1 forms, on the other side of the canal 11 be reflected as soon as the wave hits the channel 11 crosses in y-direction, the other side generally being the emitting IDT 122 , e.g. B. the first IDT 122-1 , can be opposite. In particular, a portion of the channel 11 and in particular a portion of the interior surface of the channel 111 , from an acoustic reflector 16 , for example from sapphire, be formed or provided by this. After reflecting, the (sound) wave can cross the fluid flow again and move back in the direction of the chip 12th spread. When hitting the chip 12th can send the sound wave (at least partially) as a SAW into the chip 12th be fed back. That is to say, the reflected sound wave can, for example, as a SAW partially into the surface of the substrate 121 of the chip 12th are coupled. The SAW can then be accessed by a second IDT 122-2 will be received, who is the first recipient 122B-1 that can convert the SAW back into an electrical signal. That is, the SAW can be detected using the second IDT 122-2 the first recipient 122B-1 forms. In general, a sound wave can also be reflected multiple times, each time the sound wave hits the chip 12th comes into contact, at least a portion of the sound wave as a SAW in the chip 12th can be coupled. In other words, the wave can cross the channel multiple times as it traverses the fluid. For example, in some embodiments of the present invention, at least a portion of the channel can be configured as an acoustic waveguide for the sound waves traversing the fluid, wherein each wave can be reflected multiple times. While increasing the number of reflections can increase the total phase shift accumulated by the wave as it traverses the fluid, the signal strength can decrease due to losses, e.g. B. because the wave is partially in the chip 12th is fed back and / or not reflected perfectly, decrease. Thus, the number of reflections can be limited by the attenuation of the sound wave passing through the fluid so that any remaining signal is strong enough to be transmitted by a receiving transducer 122B to be received. In general, it may also be possible for the wave to pass through the channel 11 crosses only once and is detected on the other side of the channel, ie measurements in which the wave passes through the fluid without reflection can also be carried out in different embodiments of the flow sensor 1 be realized.

The process by which a sound wave in the fluid hits the chip 12th meets and at least partially in the chip 12th is fed back can be understood as the reverse process of partially coupling a SAW into the fluid. In particular, the SAW induced by an impinging sound wave is again a leaking SAW, which can therefore be partially deflected again as a sound wave into the fluid. This process can also be referred to as (partial) reflection of the sound wave. In other words, the conversion between SAW and sound wave can generally be the same process that goes in both directions, i.e. an incident longitudinal sound wave creates a SAW within the crystal, and once this is significantly built up it starts to leak again, i.e. it directs partially as a sound wave in the fluid. This can lead to a (partial) “reflection” of the incident longitudinal sound wave. That is, when referencing a sound wave that is on the chip 12th is reflected, this can refer to the fact that the sound wave induces a leaking SAW, which in turn is at least partially deflected back into the fluid and thus induces a sound wave which can be referred to as a reflected sound wave. Thus, the SAW moving in the chip may be subject to losses due to partial leakage into the fluid, but these losses can, provided that the distance between re-launching into the chip and receiving the re-launching SAW by the receiving IDT 122B is not too big, can be neglected, e.g. B. they may not affect the reception of the SAW or at least not significantly.

In contrast, a particular acoustic reflector does not rely, or at least not significantly, on leaking SAW. That is, a good acoustic reflector can, for example, at least provide approximately a complete internal reflection of the pressure wave within the channel when the speed of sound on its surface covered with fluid is higher than that of the transducer material used, ie the chip material. A preferred (for example ideal) acoustic reflector has a significantly higher sound velocity on its surface (for which the mass sound velocity can serve as a good indicator) than the transducer material used. Thus, there may be only one negligible wave mode that spreads preferentially on the surface, which in turn implies a negligible leaky SAW mode.

It is understood that a receiving IDT 122B or more generally a receiving transducer 122B denotes an IDT / converter that includes a receiver, e.g. B. a first recipient 122B-1 , a second recipient 122B-2 and / or a dwell receiver 122C , forms. That is, a receiving IDT 122B forms a receiver 122B . Likewise denotes an emitting IDT 122A or more generally an emissive transducer 122A an IDT / converter forming a transmitter, e.g. B. a first transmitter 122A-1 , a second transmitter 122A-2 and / or a dwell transmitter 122C . That is, an emitting IDT 122A forms a receiver 122A .

As in 1A indicated, the transmitting and receiving arrangement can be used in a first configuration I, the first transducer 122-1 as the first broadcaster 122A-1 can act, which a first shaft to the second transducer 122-2 who can send as the first recipient 122B-1 , for example in the upward direction, acts. In other words, a first sender can 122A-1 a first wave to a first receiver 122B-1 send. For example, the first converter 122-1 receive a voltage pulse that is used to excite a SAW in the piezoelectric substrate 121 is configured, in turn, at least partially at the angle θ _R in that through the channel 11 can deflect flowing fluid. The wave can then channel 11 cross and then on a portion of the inner surface of the channel 111 be reflected, advantageously by an acoustic reflector 16 can be provided. Thus, the wave can channel 11 cross again and get to the chip 12th move back where they are as SAW at least partially into the substrate 121 can be fed back. Then a signal of the wave from the second transducer 122-2 received, e.g. B. be detected. That is, the displacement of the piezoelectric substrate 121 can through the second converter 122-2 and in particular by electrodes that the second transducer 122-2 includes, can be converted back into a voltage signal. Therefore, a signal can be measured that corresponds to a first wave that the fluid traverses in a generally upstream direction when the transmit and receive arrangement in the illustrated first configuration I is used.

In general, the exact path of the shaft can depend on the Rayleigh angle and the fluid velocity. In particular, the Rayleigh angle θ _R , ie the angle at which a SAW is deflected into the fluid, changes with the speed of sound of the fluid. Thus, the path of the wave includes information about the flow velocity of the fluid. In particular, the sound wave can experience a flow-related local displacement as it passes through the fluid, which is dependent on the flow velocity of the fluid. A measurement of the flow-dependent displacement, also referred to as displacement, can therefore enable information about a flow property of the fluid to be extracted. An IDT 122 however, it generally cannot be configured to locate where the sound wave enters the chip 12th was fed back. Especially when the sound wave hits the area of the chip directly 12th that meets the receiving IDT 122B includes, the receiving IDT converts 122B possibly only the respective displacement of the piezoelectric substrate 121 (or the layer) into an electrical signal without information regarding the exact location of the displacement within the range of the receiving IDT 122B are present.

With reference to 3 For example, a solution according to an embodiment of the present invention can consist in _{mapping the shift to a time delay Δt SAW} with which the SAW passes the receiving IDT 122B reached. 3 shows the flow-dependent displacement for two waves that are _{emitted at different flow velocities νx 1,2} , where: ν _x1 <ν _x2 . For example, for a first wave, which is indicated by the dotted arrows, ν _{x1 can be} zero, while for a second wave, which is indicated by the dashed arrows, ν _{x2 can be} greater than zero. While the Rayleigh angle may not change if the same fluid is used, the sound wave that traverses the fluid with the higher flow velocity ν _x2 experiences a greater displacement (dashed arrows) than the sound wave that the fluid with the lower flow velocity ν passes through _x1 passes. Therefore, the two respective sound waves hit at different points and thus at different distances from the receiving IDT 122B on the chip 12th . The time covered as the SAW that was coupled in again, Δt _SAW1,2 , is therefore dependent on the displacement caused by the flow. That is, for ν _x1 < _{νx2 it} follows that Δt _SAW1 > Δt _SAW2 , since the distance traveled by the first wave is longer than that traveled by the second wave (ie Distance as re-coupled SAW). Consequently, information about the flow rate can vary from the time and / or phase of the receiving IDT 122B received signal can be derived.

In other words, information about the flow velocity can also be based on the envelope curve amplitude of a from the receiving IDT 122B received signal, ie without taking the phase into account. However, in general, deriving information about the flow rate from the phase of the signal can be much more accurate (orders of magnitude) than attempting to track slight shifts in the amplitude envelope of the signal. It can therefore be advantageous to take into account at least the phase signal for deriving information about the flow rate, which can in particular enable a fluid-independent measurement of the flow rate if it is combined with corresponding further measurements, as explained below.

In this connection it is noted that the dwell time Δt _us , ie the propagation time of the wave within the fluid, is independent of the flow velocity. Thus, the flow-induced displacement can affect the time delay between launching into the chip 12th and reaching the receiving IDT 122B can be mapped. This mapping of the flow dependent displacement can be achieved by the receiving IDT 122B is generally arranged such that the sound wave does not hit the area of the chip directly 12th that meets the receiving IDT 122B instead, it is inside the chip first 12th before being received by the receiving IDT 122B as SAW spreads. In this way, the received signal includes a time delay that is directly related to the point at which the wave enters the chip 12th is fed back, and thus the flow rate of the fluid. This time delay can generally also be represented by a phase shift of the received signal in relation to the transmitted signal.

Thus, a flow sensor 1 in accordance with the present invention generally enable a signal to be measured which includes information about the flow induced displacement of the shaft through which the fluid passes. In general, the delay time and / or the phase shift of the wave can thus be used to derive the flow velocity.

The wave, ie SAW and / or sound wave, can, however, experience an additional phase shift due to temperature fluctuations and other variable fluid, flow or environmental parameters, which can naturally be present in a non-ideal environment, for example. The actual measurable phase shift Δϕ can therefore be a function of many variables: Δϕ = f (t, v _x , Δt _us , s ₁ , ..., s _n )., Where t is the time, v _x the mean flow velocity (in Direction of flow x), Δt _{us is} the residence time and s _{i are} phase-sensitive variables that are symmetrical with respect to the direction of flow and are constant as a function of the speed of sound in the fluid. For example, s _i can denote the fluid density (p) or the permittivity of the fluid (ε) or the temperature and / or conductivity of the fluid.

It can therefore be advantageous to compensate for these unwanted signals. In other words, while it contains information about the local displacement as a function of the flow rate of the fluid, the phase shift can also make undesirable contributions due to environmental fluctuations and / or changes in fluid parameters, e.g. B. due to a solvent gradient include.

The flow sensor 1 can generally have at least two converters 122 include, e.g. B. a first and a second IDT 122-1 , 122-2 , one being the emitting IDT 122A , e.g. B. as the first sender 122A-1 , and the other as the receiving IDT 122B , e.g. B. as the first recipient 122B-1 , can act. That is, as in 1A shown, the first sender 122A-1 generate a SAW which in turn can induce a sound wave in the fluid that travels through the channel 11 can move and potentially at least partially on the inner wall 111 of the canal 11 can be reflected. At some point, e.g. B. after a reflection, the sound wave can at least partially in a piezoelectric material, e.g. B. the substrate of the chip 12th , are coupled. A sound wave-induced SAW can thus penetrate the chip 12th and to the first recipient 122B-1 move, which in turn converts the SAW at least partially into an electrical signal, e.g. B. a voltage, which can be detected and processed. In particular, a feature can be determined based on the received signal, wherein the feature can preferably be the phase shift between the wave transmitted by the respective transmitter and the wave signal received by the second receiver. The phase difference between the emitted and the received signal, ie the measured phase shift Δϕ, can provide information about the local shift due to the flow of the fluid in the channel 11 , the flow-independent Dwell time of the sound wave in the fluid and undesired additional phase shifts due to environmental changes and / or changes in the fluid properties include.

In order to compensate for undesired phase shifts, the signals of two waves can be measured, in particular of two waves which move in opposite directions with respect to the direction of flow, these two waves otherwise preferably being identical. This can advantageously enable the correction of flow-independent phase shifts. For example, in some embodiments, two IDTs may alternately serve as emitting 122A and receiving 122B transducers. That is, the transmitter and receiver arrangement can be used in alternating configurations, with two transducers 122 can alternately form an emitting 122A and a receiving 122B transducer. In other words, the SAW (and therefore the sound wave) can alternate between two IDTs 122 are emitted in such a way that the direction of movement for the sound wave between the two IDT 122 can switch between upstream and downstream. That is, a second wave can be sent from the transducer that is the first wave 122B-1 receives, and received by the transducer which is the first wave 122A-1 emitted. In other words, a second wave can be sent in a direction opposite to the first wave by switching the role of the two transducers. Thus, a first converter 122-1 the first transmitter 122A-1 and a second recipient 122B-2 form while a second converter 122-2 a second transmitter 122A-2 and the first recipient 122B-1 can form. That is, each of the two converters 122 , e.g. B. IDT 122 , for example, can alternate between emitting 122A and receiving 122B transducers. Thus, the two IDTs can be configured to transmit and emit waves of the same frequency.

With reference to 1B the transmitter and receiver arrangement in the embodiment shown can therefore be used in a second configuration II in which the respective functions of the first transducer 122-1 and the second converter 122-2 , which are also referred to as phase shift converters, are interchanged. That is, the first converter 122-1 who is the first transmitter 122A-1 in the first configuration I can also use the second receiver 122B-2 form II in the second configuration. The second converter can do the same 122-2 who is the first recipient 122B-1 in the first configuration I, also forms the second transmitter 122A-2 form II in the second configuration.

It is noted that the term phase shift converter can generally designate converters that contribute to the measurement of the phase shift of the first and / or the second wave. That is, converters that are the first transmitter 122A-1 , the first recipient 122B-1 , the second transmitter 122A-2 and / or the second recipient 122B-2 form. Likewise, the term phase shift IDT denotes IDT which is the first transmitter 122A-1 , the first recipient 122B-1 , the second transmitter 122A-2 and / or the second recipient 122B-2 form.

As in the 1A and 1B specified, either of the two converters involved can 122-1 , 122-2 generally both for sending, e.g. B. emit, as well as be configured to receive a wave. In other words, the configuration of the emitting 122A and receiving 122B transducers may vary between the two in FIG 1A and 1B Alternate configurations I, II shown. Thus, the flow sensor can 1 comprise at least two phase shift converters, for example both on the chip 12th and in particular on the piezoelectric substrate 121 or the piezoelectric layer may be arranged, e.g. B. on a non-piezoelectric substrate, the two transducers 122-1 , 122-2 serve alternately as sending / emitting and receiving transducers. In the embodiment shown, the two phase shift converters can preferably be constructed identically. That is, they may have identical properties, including, for example, overall dimensions and transducer wavelengths, e.g. B. a SAW frequency.

More generally, the present invention includes emitting a first wave with a first transmitter 122A-1 and receiving the first wave with a first receiver 122B-1 and further emitting a second wave with a second transmitter 122A-2 and receiving the second wave with a second receiver 122B-2 , wherein the direction of movement through the fluid for the first wave compared to the second wave can be different. That is, one of the first and second waves can generally travel upstream and the other can travel generally downstream. In some embodiments, a single transducer can form more than just the first transmitter, the second transmitter, the first receiver, and the second receiver. For example, with reference to FIG 1A and 1B the two identical transducers 122-1 , 122-2 one of the transmitters and one of the receivers. In particular, the first converter forms 122-1 in 1A and 1B the first transmitter 122A-1 and the second recipient 122B-2 while the second converter 122-2 the second transmitter 122A-2 and the first receiver 122B-1 forms. Thus, the two transducers 122 , e.g. B. IDT 122 , for example, switch roles, that is, switch between the emitting 122A and receiving 122B transducers.

Then the difference between the respective phase shifts between the emitted and the received signal of each of two successive measurements, ie a measurement in which the sound wave is upstream of the emitting transducer 122A received, e.g. B. is detected, and a measurement in which the wave is downstream of the emitting transducer 122A will be received. In other words, a difference measure can be generated by subtracting the respective phase shifts from two successive measurements, wherein the phase shift Δϕ (t) can correspond to a measurement of the phase shift between the emitted and the received signal. Assuming that the time between two successive measurements is sufficiently short that the flow velocity does not change significantly (e.g. only within the measurement error), all phase signals independent of the flow direction are deleted and only signals from the flow signal are dependent, remain in the difference of the phase shifts. It goes without saying that this assumes the distance between the first transmitter 122A-1 and the first recipient 122B-1 equal to the distance between the second transmitter 122A-2 and the second recipient 122B-2 is such that flow-independent phase signals picked up during the propagation of the wave can be approximately the same. In other words, it is assumed that the distance between the emitting IDT 122A and the receiving IDT 122B is the same for both waves that contribute to the difference measure. This can advantageously apply for system-related reasons for a flow sensor embodiment, as shown in FIG 1A and 1B is shown, with two transducers 122-1 , 122-2 alternately send and receive the respective waves.

$$\Delta \varphi \left(t_2\right)=f_2\left(t_{\mathrm{2,}}\Delta t_{us},v_x,s_1\mathrm{,...,}{s}_n\right)\simeq \Delta {\varphi }_2\left(t_2,\Delta t_{us},s_1\mathrm{,...,}{s}_n\right)-k_{SAW}{v}_x\Delta t_{us},$$

wobei v_x die mittlere Strömungsgeschwindigkeit in x-Richtung bezeichnet, d. h. in der stromabwärtigen Richtung des Kanals 11, Δt_us, die Flugzeit (Verweilzeit) oder mit anderen Worten die Ausbreitungszeit der Schallwelle im Fluid bezeichnet, s_i phasensensitive Variablen sind, die bezüglich der Strömungsrichtung symmetrisch und in Abhängigkeit von der Schallgeschwindigkeit in dem Fluid konstant sind, und k_SAW der Wellenvektor der SAW ist, der in hinreichend genauer Annäherung als konstant angenommen werden kann. Diese Berechnung basiert auf der linearen Abhängigkeit der Strömungsgeschwindigkeit von der Phasenänderung. Vorausgesetzt also, dass die Entfernung zwischen dem emittierenden und dem empfangenden IDT für beide Messungen gleich ist, kann das Differenzmaß von zwei aufeinanderfolgenden Phasendifferenzmessungen mit entgegengesetzter Ausbreitungsrichtung näherungsweise angegeben werden als $$\begin{array}{l}\Delta \Phi =\Delta \varphi \left(t_1\right)-\Delta \varphi \left(t_2\right)\simeq \Delta {\varphi }_1\left(t_1,\Delta t_{us},s_1\mathrm{,...,}{s}_n\right)-\Delta {\varphi }_2\left(t_2,\Delta t_{us},s_1\mathrm{,...,}{s}_n\right)+2k_{SAW}{v}_x\Delta t_{us}\\ \simeq 2k_{SAW}{v}_x\Delta t_{us}.\end{array}$$

In particular, assuming that a first measurement in which the sound wave is downstream of the receiving IDT 122B ( 1A) is emitted, is _{carried out at time t 1} , and a subsequent measurement in which the receiving IDT 122B downstream of the emitting IDT 122A ( 1B) is carried out at a point in time t ₂ = t ₁ + Δt, the two phase shifts are approximately given as $$\Delta \varphi \left(t_1\right)=f_1\left(t_{\mathrm{1,}}\Delta t_{us},v_x,s_1\mathrm{,\; ...,}{s}_n\right)\simeq \Delta {\varphi }_1\left(t_1,\Delta t_{us},s_1\mathrm{,\; ...,}{s}_n\right)+k_{\mathrm{S.}\mathrm{A.}\mathrm{W.}}{v}_x\Delta t_{us},$$

$$\Delta \varphi \left(t_2\right)=f_2\left(t_{\mathrm{2,}}\Delta t_{us},v_x,s_1\mathrm{,\; ...,}{s}_n\right)\simeq \Delta {\varphi }_2\left(t_2,\Delta t_{us},s_1\mathrm{,\; ...,}{s}_n\right)-k_{\mathrm{S.}\mathrm{A.}\mathrm{W.}}{v}_x\Delta t_{us},$$

where v _x denotes the mean flow velocity in the x direction, ie in the downstream direction of the channel 11 , Δt _us denotes the flight time (dwell time) or in other words the propagation time of the sound wave in the fluid, s _{i are} phase-sensitive variables that are symmetrical with respect to the direction of flow and are constant as a function of the speed of sound in the fluid, and k _{SAW is} the wave vector of the Is SAW, which can be assumed to be constant in a sufficiently precise approximation. This calculation is based on the linear dependence of the flow velocity on the phase change. Provided that the distance between the emitting and the receiving IDT is the same for both measurements, the difference measure of two successive phase difference measurements with opposite propagation directions can be specified approximately as $$\begin{array}{l}\Delta \Phi =\Delta \varphi \left(t_1\right)-\Delta \varphi \left(t_2\right)\simeq \Delta {\varphi }_1\left({\mathrm{<figure-callout\; id="1"\; label="t"\; filenames="DE102021100692A1\_0026.png,DE102021100692A1\_0028.png"\; state="\{\{state\}\}">t</figure-callout>}}_1,\Delta t_{us},{\mathrm{<figure-callout\; id="1"\; label="s"\; filenames="DE102021100692A1\_0026.png,DE102021100692A1\_0028.png"\; state="\{\{state\}\}">s</figure-callout>}}_1\mathrm{,\; ...,}{s}_n\right)-\Delta {\varphi }_2\left({\mathrm{<figure-callout\; id="2"\; label="t"\; filenames="DE102021100692A1\_0027.png,DE102021100692A1\_0028.png"\; state="\{\{state\}\}">t</figure-callout>}}_2,\Delta t_{us},{\mathrm{<figure-callout\; id="1"\; label="s"\; filenames="DE102021100692A1\_0026.png,DE102021100692A1\_0028.png"\; state="\{\{state\}\}">s</figure-callout>}}_1\mathrm{,\; ...,}{s}_n\right)+2k_{\mathrm{S.}\mathrm{A.}\mathrm{W.}}{v}_x\Delta t_{us}\\ \simeq 2k_{\mathrm{S.}\mathrm{A.}\mathrm{W.}}{v}_x\Delta t_{us}.\end{array}$$

This applies under the assumption that Δt = t ₂ - t _{1 is} sufficiently small that it can be assumed that the flow velocity only changes within the measurement error and that in particular the phase shifts independent of the flow direction can be specified as approximately constant, such that they cancel each other out when subtracting the two phase shifts. In general, the time difference Δt = t ₂ −t ₁ , also referred to as the switching time, can preferably be kept as small as possible. This can advantageously also make it possible for the change in the symmetrical (flow direction-independent) phase shift contributions to be small (e.g. negligible) during this switching time, in such a way that these undesired phase shift contributions / signals are compensated for by subtracting successive phase difference measurements, at least in a sufficiently precise approximation can. The switching time .DELTA.t is preferably less than 100 microseconds. In particular, the flow-induced phase shift can only be based on the mapping of the flow-induced (or flow-dependent) shift of the wave to the time covered as SAW before it was received by the receiving IDT 122B received, measured.

It is noted that the above calculation can be adapted accordingly if the distance between the emitting and the receiving IDT is not the same for the two subtracted measurements. That is, based on a respective calibration, the phase difference measurements can be scaled accordingly to account for a difference in distance traveled between the IDTs that are each used for the two (e.g., consecutive) phase difference measurements. Advantageously, however, the emitting and receiving IDTs used for the phase shift measurements are equidistant from one another, in such a way that the distance between the emitting and the receiving IDT is the same for both measurements.

In other words, after each measurement of the relative phase shift Δϕ between the emitted and the received signal, the phase shift of the current signal can be continuously subtracted back by one time step from the phase shift of the signal (in practical use in HPLC, the phase change due to the flow velocities occurring can be such small that ambiguities generally do not have to be taken into account - the phase changes can typically be in the range of a few degrees). Assuming that changes in the flow velocity in this time window are only in the range of the measurement error, all phase components that are symmetrical with respect to the flow direction can be negated. On the other hand, for an embodiment like that in FIGS 1A and 1B the double antisymmetric flow signal shown remain.

As can be seen above, the flow-related phase shift and thus the difference ΔΦ (at least in a sufficiently precise approximation) can be linearly dependent on the dwell time of the (sound) wave in the fluid Δt _us (also referred to as the propagation time in the fluid or the time of flight in the fluid ) and depend on the flow velocity. The following applies: ΔΦ ∝ k _SAW v _x Δt _us , where again Δt _us denotes the dwell time of the wave packet in the fluid, v _x the flow velocity (along the channel 11 ) and k _SAW includes the SAW speed and frequency of the SAW. The latter are constant in a sufficiently precise approximation, which is why k _SAW can be assumed to be constant. For a fixed flow velocity v _x , the ratio of the difference and the residence time can therefore be constant: $$\frac{\Delta \Phi }{\Delta t_{us}}=kOnst.$$

This leads to a simple expression that only depends on the average flow velocity. In other words, if the dwell time Δt _{us is} known, the difference ΔΦ of the phase shifts Δϕ can make it possible to at least approximately determine the flow velocity of the fluid.

That is, for two successive measurements of the phase shift Δϕ (t _1,2 ) = Δϕ _1,2 , where the switching time Δt = t ₂ - t _{1 is} short enough for the assumption that flow-independent phase shift contributions (at least in a sufficiently precise approximation) are constant are, and the two measurements are carried out at an average flow velocity v _x in opposite directions, ie v ₁ = -v ₂ = v _x , the local displacement Δx _1,2 (also referred to as spatial displacement) of a SAW-induced ( Ultrasonic) wave specified as follows: $$\Delta x_{1.2}=v_x\Delta t_{us}.$$

Here, Δt _us again denotes the flow-independent residence time.

After spreading through the canal 11 the wave can be at least partially in the chip as a SAW 12th (e.g. the surface of the chip 12th ) can be fed back. The exact point at which the SAW is at least partially re-inserted into the chip 12th coupled is dependent on the local displacement of the wave through which the fluid passes. Thus, the local displacement Δx can also be expressed by the time delay Δt _{SAW, 1,2} , which specifies the total time that has been passed as the newly coupled SAW, and Δt _{SAW, 0} , which specifies the time passed as the newly coupled SAW at v _{x = 0} can. Specifically, Δx _1,2 can be expressed as: $$\Delta x_{1.2}=\left(\Delta t_{\mathrm{S.}\mathrm{A.}\mathrm{W.}\mathrm{,\; 0}}-\Delta t_{\mathrm{S.}\mathrm{A.}\mathrm{W.}\mathrm{,\; 1.2}}\right)c_{\mathrm{S.}\mathrm{A.}\mathrm{W.}}.$$

Therefore, the time delay Δt _{SAW, 1,2} can be expressed as follows: $$\Delta t_{\mathrm{S.}\mathrm{A.}\mathrm{W.}\mathrm{,\; 1.2}}=\Delta t_{\mathrm{S.}\mathrm{A.}\mathrm{W.}\mathrm{,\; 0}}-\frac{\Delta x_{1.2}}{c_{\mathrm{S.}\mathrm{A.}\mathrm{W.}}}.$$

The corresponding phase difference between the emitted and received signal in radians is given by Δϕ _1,2 = 2πf (Δt _us + Δt _{SAW, 1,2} ). Combining this expression with (I) and (II) gives: $$\Delta {\varphi }_{1.2}=2\pi f\left(\Delta t_{us}+\Delta t_{\mathrm{S.}\mathrm{A.}\mathrm{W.}\mathrm{,\; 0}}\right)-\frac{2\pi f{v}_{1.2}\Delta t_{us}}{c_{\mathrm{S.}\mathrm{A.}\mathrm{W.}}}.$$

wobei gilt: v₁ = -v₂ = v_x. Wenn also c_SAW/f = λ_SAW ≅ konst. angenommen wird, wird das Differenzmaß durch Folgendes angegeben: $$\Delta \mathrm{\Phi }=-4\pi \frac{v_x\Delta t_{us}}{{\lambda }_{SAW}}.$$

Auflösen nach v_x ergibt: $$v_x=-\frac{\Delta \mathrm{\Phi }}{\Delta t_{us}}\frac{{\lambda }_{SAW}}{4\pi }=-\frac{\Delta \varphi }{\Delta t_{us}}\frac{1}{2k_{SAW}},$$

wobei k_SAW = 2π/λ_SAW der SAW-Wellenvektor ist. Diese Lösung basiert auf der Annahme, dass die mittlere Strömungsgeschwindigkeit innerhalb des Strömungskanals und der Schaltzeit konstant ist und daher streng genommen nur eine Annäherung an die tatsächliche mittlere Strömungsgeschwindigkeit bereitstellt. Diese Annäherung kann jedoch im Allgemeinen für kleine Schaltzeiten in Bezug auf die Änderungsrate der Strömungsgeschwindigkeit und unter der Annahme eines Kanaldesigns ausreichend sein, wobei die mittlere Strömungsgeschwindigkeit innerhalb des Sensorbereichs ungefähr gleich bleibt.The difference ΔΦ) can then be calculated as described above, which results in the following: $$\Delta \Phi =\Delta {\varphi }_1-\mathrm{<figure-callout\; id="2"\; label="\Delta \; \phi "\; filenames="DE102021100692A1\_0027.png,DE102021100692A1\_0028.png"\; state="\{\{state\}\}">\Delta </figure-callout>}{\varphi }_{}{}_2=-\frac{2\mathrm{<figure-callout\; id="1"\; label="\pi \; f\; v"\; filenames="DE102021100692A1\_0026.png,DE102021100692A1\_0028.png"\; state="\{\{state\}\}">\pi </figure-callout>}f{v}_{}{}_1\Delta t_{us}}{c_{\mathrm{S.}\mathrm{A.}\mathrm{W.}}}+\frac{2\mathrm{<figure-callout\; id="2"\; label="\pi \; f\; v"\; filenames="DE102021100692A1\_0027.png,DE102021100692A1\_0028.png"\; state="\{\{state\}\}">\pi </figure-callout>}f{v}_{}{}_2\Delta t_{us}}{c_{\mathrm{S.}\mathrm{A.}\mathrm{W.}}},$$

where: v ₁ = -v ₂ = v _x . So if c _SAW / f = λ _SAW ≅ const. Is assumed, the difference measure is given by the following: $$\Delta \mathrm{\Phi }=-\mathrm{4th}\pi \frac{v_x\Delta t_{us}}{{\lambda }_{\mathrm{S.}\mathrm{A.}\mathrm{W.}}}.$$

Solving for v _x gives: $$v_x=-\frac{\Delta \mathrm{\Phi }}{\Delta t_{us}}\frac{{\lambda }_{\mathrm{S.}\mathrm{A.}\mathrm{W.}}}{\mathrm{4th}\pi }=-\frac{\Delta \varphi }{\Delta t_{us}}\frac{1}{2k_{\mathrm{S.}\mathrm{A.}\mathrm{W.}}},$$

where k _SAW = 2π / λ _{SAW is} the SAW wave vector. This solution is based on the assumption that the mean flow velocity within the flow channel and the switching time is constant and therefore, strictly speaking, only provides an approximation of the actual mean flow velocity. However, this approximation can generally be sufficient for short switching times in relation to the rate of change of the flow velocity and assuming a channel design, the mean flow velocity remaining approximately the same within the sensor range.

However, while k _{SAW can} generally be assumed to be constant, at least in a sufficiently precise approximation, Δt _us depends on the speed of sound of the fluid, c _F , and thus on the density and compressibility of the fluid: $$\Delta t_{us}=f\left(c_{\mathrm{F.}}\right)=f\left(\sqrt{\frac{K}{\rho }}\right).$$

In other words, Δt _{us is} fluid-dependent, as in 4th further shown, two measurements with the same flow velocity v _x , but for two different fluids are shown. Due to the change in the density and compressibility of the fluid and thus the respective speed of sound c _F , the Rayleigh angle θ _{R changes} and consequently the dwell time Δt _us . That is, for the fluid 2 in 4th , which has a higher speed of sound, c _F2 , compared to fluid 1 includes, both the Rayleigh angle θ ₂ and consequently also the dwell time Δt _{us2 are} greater than the respective parameters for fluid 1 . Consequently, it can be important to also determine Δt _us for deriving the flow velocity from the phase measurements in order to enable a fluid-independent measurement of the flow velocity. This can advantageously enable the flow sensor 1 can be used without calibration to a specific fluid and therefore the fluid can change during a continuous measurement without influencing the flow measurement. In HPLC, the fluid independence can be advantageous, since the analysis sample together with the mobile phase can often be undefined fluids, which under certain circumstances are only temporarily present at the flow sensor. Furthermore, the solvent composition can also change, e.g. B. when a gradient is used.

The change in dwell time, Δt _us , also changes the propagation time of the wave as a SAW after passing through the fluid, Δt _SAW , as in FIG 4th specified. In other words, different fluids lead to variable dwell times of the (sound) wave in the fluid channel 11 and at a correspondingly variable propagation time of the wave as a SAW, ie as a SAW that emanates from the wave that is at least partially fed back into the substrate. That is to say, the SAW can arise from the renewed coupling of the wave after it has propagated once or several times in the fluid vertically through the channel, ie after it has passed through the fluid. The propagation time of the wave as SAW, Δt _SAW , is also dependent on the flow-dependent displacement of the wave, as described above. Based on a measurement of the total propagation time (or the phase) of the wave as a pressure wave in the fluid (ie sound wave) and as a SAW, negligible (or no) information about the pure residence time in the fluid, Δt _us , can be obtained. That is, as opposed to taking measurements to obtain a signal that includes fluid dependent displacement information, it would be desirable to cancel the contribution of the SAW's propagation time, Δt _SAW , to the dwell time measurement, Δt _us .

Based on the above, the dwell time, Δt _us , can be measured, for example, by the receiving IDT 122B is arranged so that the sound wave directly hits the area of the chip 12th that meets the receiving IDT 122B includes, ie contrary to the desired arrangement for measuring the flow-dependent displacement. However, the typical size of the phase shifting IDTs that make up the emitting 122A and receiving 122B IDTs may be compared to the overall dimensions of the channel 11 be so small that the receiving IDT 122B may not be arranged such that the shaft for all relevant Rayleigh angles θ _{R is} directly on the receiving IDT 122B would meet. While there may of course be the possibility of expanding the size of the phase shifting IDTs acting as receiving IDT122B, the problem remains that the flow dependent displacement of the wave cannot be measured when the entire wave packet directly reaches the receiving IDT 122B meets. For example, if in an embodiment like the one in 1A and 1B both phase shift IDT (ie the IDT 122-1 , 122-2 ) are arranged in such a way that the wave hits them directly when they act as the receiving IDT 122B function, no fluid-dependent shift would be measurable. That is, the flow measurement is based on the displacement of the wave along the flow direction, which may not be detected if the sound wave enters the receiving IDT directly 122B is coupled (albeit still via an induced SAW). In other words, the displacement of the sound wave can be differentiated in time by using smaller receiving IDTs 122B can be selected and therefore the displacement of the wave is mapped to the time covered as SAW, which contradicts the requirements for measuring the dwell time Δt _us .

In other words, while one solution to the problem at hand may be to have the receiving IDT 122B is placed exactly in such a way that the sound wave is coupled directly to it, a small extension of the reciprocal transmit and receive IDT 122 , ie the phase shift IDT, compared to the size of the fluid channel 11 at most enable the precise measurement of the propagation time, Δt _us , for a small variation in the fluid sound velocity, since the Rayleigh angle varies accordingly. In addition, the use of much wider send or receive IDTs can be used 122 generally disadvantageously lead to a significantly high proportion of undesired sound in the cell. Furthermore, and in particular, no time offset of the wave related to the fluid velocity could be measured if the entire wave packet is sent to the receive IDT 122B meets because, as already mentioned, the pure propagation time of the entire wave packet through the fluid is independent of the fluid velocity for a specific fluid.

Thus, the flow sensor can 1 and in particular the transmitter and receiver arrangement generally a dwell time receiver 122C and a dwell transmitter 122D include, each generally consisting of a transducer 122 can exist. For example, a dedicated timing transducer 125 the dwell receiver 122C by possibly being configured to receive a signal indicating the dwell time. In other words, in some embodiments, the dwell receiver 122C from a separate converter 125 exist, which is only intended for measuring the dwell time. Alternatively, in other embodiments, an emitting 122A and / or receiving 122B converter, ie, one of the phase shift converters, may also be the dwell receiver 122C form. That is, in some embodiments, a single transducer 122 as a dwell receiver 122C and emitting 122A and / or receiving transducer 122B act. Likewise, a dedicated time transmitter converter can act as the dwell transmitter 122D form. Preferably, the dwell transmitter 122D but from a converter 122 which also acts as an emitting 122A and / or receiving 122B converter.

It is now back on 1B Referenced. To enable a measurement of the propagation time, Δt _us , embodiments of the present invention may include an additional timing IDT 125 include the dwell receiver 122C which can be significantly wider (in the x direction) than the phase shift IDT, ie the first and second transducers 122-1 , 122-2 , and therefore also as Wide IDT 125 referred to as. The timing IDT 125 can be designed to be sensitive to the SAW frequency generated by the transmit and receive IDTs 122A , 122B , also referred to as phase shift IDT, as they are configured to determine the phase shift based on flow velocity.

mit 800 m/s < c_F < c_s, die für den gewünschten Messbereich des Sensors relevant sind, direkt auf den Zeitmess-IDT 125 treffen und nicht auf das Substrat davor oder danach, d. h. stromaufwärts oder stromabwärts des Zeitmess-IDT 125. Das heißt, während c_s im Allgemeinen durch das Sensordesign und insbesondere die für das piezoelektrische Substrat 121 verwendeten Materialien bestimmt werden kann, hängt c_F von dem zu messenden Fluid ab, das erheblich variieren kann. Daher kann die Größe und Position des Zeitmess-IDT 125 derart gewählt werden, dass ein gewünschter Bereich von Schallgeschwindigkeiten durch den Sensor abgedeckt werden kann. Ganz allgemein kann die Schallgeschwindigkeit des durch den Kanal fließenden Fluids für Fluide, die typischerweise in der HPLC verwendet werden, im Bereich von 800 m/s < c_F < 2300 m/s liegen. Die Schallgeschwindigkeit für die SAW im Chip c_s kann im Allgemeinen im Bereich von 2540 m/s < c_F < 6000 m/s liegen.In general, the timing IDT 125 upstream or downstream of the phase shift IDT. In some embodiments, the timing IDT 125 on the same chip 12th be arranged like the phase shift IDT. In addition, the timing IDT 125 be expanded and positioned in such a way that the sound maxima of one of the two phase shift IDTs at least for all angles $sin{\theta }_{\mathrm{R.}}=\frac{c_{\mathrm{F.}}}{c_{\mathrm{S.}}},$

with 800 m / s <c _F <c _s , which are relevant for the desired measuring range of the sensor, directly to the timing IDT 125 and not on the substrate before or after, ie upstream or downstream of the timing IDT 125 . That is, during c _s in general due to the sensor design and in particular that for the piezoelectric substrate 121 materials used can be determined, c _F depends on the fluid to be measured, which can vary considerably. Therefore, the size and position of the timing IDT 125 can be selected such that a desired range of sound velocities can be covered by the sensor. In general, the speed of sound of the fluid flowing through the channel for fluids that are typically used in HPLC can be in the range of 800 m / s <c _F <2300 m / s. The speed of sound for the SAW in the chip c _s can generally be in the range of 2540 m / s <c _F <6000 m / s.

Therefore, based on that for the piezoelectric substrate 121 material used and the duct height H1 some general design considerations should be made. The distance between the dwell transmitter 122D and the dwell receiver 122C , ie the distance between the timing IDT 125 and the respective phase shift IDT that emits the signal used for the dwell time measurement can be referred to as the delay line length.

In relation to 5A Therefore, a maximum delay line _{length (L Verz max} ) can be dependent on the minimum Rayleigh angle θ _{R, min} , which in turn depends on c _s and the minimum speed of sound for a fluid to be measured c _f . In addition to this, the maximum delay line _{length L Verz max is} also dependent on the height H1 of the channel. In addition, the flow-induced local displacement may also have to be taken into account, ie Δx = v _x Δt _us . As a rule, however, Δ can be so small compared to the wavelength that it can be omitted for the sake of simplicity. In particular, the maximum delay line _{length L Verz max} can be given as follows: $${\mathrm{L.}}_{Verzmax}=tan\left({\theta }_{\mathrm{R.},min}\right)2H1-\Delta x.$$

und ferner der Sollschallgeschwindigkeit für die SAW im Substrat 121 von c_s = 4700 m/s der minimale Rayleigh-Winkel (θ_R,min ≈ 9,8°, und gälte folglich: L_{Verz max} ≈ 0,34H1 - Δx.For example, taking into account a minimum target sound velocity for a fluid, would be $c_f=800\frac{m}{s}$

and also the target sound velocity for the SAW in the substrate 121 from c _s = 4700 m / s the minimum Rayleigh angle (θ _{R, min} ≈ 9.8 °, and would therefore apply: L _{Verz max} ≈ 0.34H1 - Δx.

Similarly, when looking at 5B a length of the timing IDT 125 be dependent on a maximum Rayleigh angle θ _{R, mαx} , which in turn depends on the speed of sound in the substrate 121 and the maximum speed of sound of the fluids flowing through the sensor is dependent. This can provide the necessary length such that a reflected sound wave generated by the wave of the dwell time transmitter 122D is still emitted on the timing IDT 125 (i.e. the dwell receiver 122C ) meets. In addition, the timing IDT 125 however by a length nλ _SAW corresponding to the length of the Dwell transmitter 122D to be extended further. Here n denotes the number of periods of the dwell time transmitter 122D which can be the same as the number of pairs of fingers for a design, like 2a) shows, and λ _SAW denotes the wavelength of the emitted and received SAW. This expansion can be advantageous, since the maximum of the received SAW in the time measurement IDT 125 may not occur directly at the time and place at which the maximum of the sound wave (e.g. ultrasonic pulse) in the fluid hits the IDT 125 meets. Instead, the ultrasonic pulse in the fluid can increase the power in the IDT 125 cumulate (ie integrate), that is, a SAW can be built up in the substrate of the chip in order to (at least in part) be dependent on the timing IDT 125 to be received, while the resulting SAW at the same time transmits the sound power in the Rayleigh angle back to the fluid. Therefore, the timing IDT 125 at least as described above to take this fact into account and thus that of the sound measurement IDT 125 to increase the total received sound power.

Again, the flow-induced local displacement Δx _x can also be taken into account, in such a way that the length of the time measurement IDT as a whole can be indicated by $${\mathrm{L.}}_{T\mathrm{M.}\mathrm{I.}\mathrm{D.}T}=tan\left({\theta }_{\mathrm{R.},max}\right)2\mathrm{<figure-callout\; id="1"\; label="H"\; filenames="DE102021100692A1\_0026.png,DE102021100692A1\_0028.png"\; state="\{\{state\}\}">H</figure-callout>}1+n\lambda +\Delta x-{\mathrm{L.}}_{Verzmax}.$$

unter Umständen entsprechend einer minimalen Länge L_{TM IDT,min} des Zeitmess-IDT 125 von $$L_{TM\text{ IDT}\text{,min}}=\text{tan}\left(\text{arcsin}\left(\frac{2200}{3390}\right)\right)sH{1}_{min}+n_{min}{\lambda }_{min}+\Delta x-L_{Verzmax},$$

Therefore, some exemplary considerations can be made regarding the overall limits on the length of the timing IDT. To estimate a lower bound for the length of the timing IDT 125 For example, a minimum upper limit for the Rayleigh angle can be, for example, approximately 40 ° $\left(c_f=2200\frac{m}{s},c_s=3390m/s\right),$

possibly corresponding to a minimum length L _{TM IDT, min of} the timing IDT 125 of $${\mathrm{L.}}_{T\mathrm{M.}\text{IDT}\text{, min}}=\text{tan}\left(\text{arcsin}\left(\frac{2200}{3390}\right)\right)sH{1}_{min}+n_{min}{\lambda }_{min}+\Delta x-{\mathrm{L.}}_{Verzmax},$$

wobei n die Anzahl der Perioden des Verweilzeitsenders 122D und A die SAW-Wellenlänge ist. Unter Berücksichtigung einer oberen Frequenzgrenze von 100 MHz, einer unteren Kanalhöhengrenze von H1_min= 0,2 mm und mit einem Minimum von n_min= 5 kann eine untere Grenze für die Länge des Zeitmess-IDT 125 L_{TM IDT,min} ≈ 0,4 mm sein, was ungefähr 2,4 nmin entsprechen kann λ_min.In view of the above result for L _{Verz max} , which can be expressed as $${\mathrm{L.}}_{T\mathrm{M.}\mathrm{I.}\mathrm{D.}T,min}\approx 1.36H{1}_{min}+n_{min}{\lambda }_{min},$$

where n is the number of periods of the dwell time transmitter 122D and A is the SAW wavelength. Taking into account an upper frequency limit of 100 MHz, a lower channel height limit of H1 _min = 0.2 mm and with a minimum of n _min = 5, a lower limit for the length of the timing IDT 125 L _{TM IDT, min} ≈ 0.4 mm, which can correspond to approximately 2.4 nmin λ _min .

Bei einer Obergrenze der Kanalhöhe von H1_max = 20 mm, einer unteren Frequenzgrenze von 40 MHz und einer oberen Periodenzahl n von 50 (Verweilzeitsender) kann eine Obergrenze für die Länge betragen: $$L_{TMIDT,max}\approx \text{tan}\left(arcsin\left(\frac{2300}{2540}\right)\right)2H{1}_{max}+\left(n_{max}-3\right){\lambda }_{max}\approx 85\text{ mm},$$

was ungefähr 27 n_max λ_max entsprechen kann. Im Gegensatz dazu gilt unter Berücksichtigung von H1_max = 3 mm: L_{TM IDT,max} ≈ 13 mm, was ungefähr 4,1 n_max λ_max entsprechen kann.To estimate an upper bound for the length of the timing IDT 125 L _{TM IDT, max} , the largest possible Rayleigh angle and the lower limit of the delay line length can be taken into account. A lower limit of the delay line length between the dwell time transmitter and the dwell time receiver could be a few (~ 3) λ. A reasonable upper limit on the Rayleigh angle can be 65 ° $\left(c_f=2230\frac{m}{s},c_s=2540m/s\right).$

With an upper limit of the channel height of H1 _max = 20 mm, a lower frequency limit of 40 MHz and an upper number of periods n of 50 (dwell time transmitter), an upper limit for the length can be: $${\mathrm{L.}}_{T\mathrm{M.}\mathrm{I.}\mathrm{D.}T,max}\approx \text{tan}\left(arcsin\left(\frac{2300}{2540}\right)\right)2H{1}_{max}+\left(n_{max}-3\right){\lambda }_{max}\approx 85\text{mm},$$

which can correspond to approximately 27 n _max λ _max . In contrast, taking into account H1 _max = 3 mm _{, the following applies: L TM IDT, max} ≈ 13 mm, which can correspond to approximately 4.1 n _max λ _max .

Thus, the position and extent of the timing IDT 125 relative to one of the phase shift IDT can be calculated based on the above considerations.

It is noted that the above considerations apply equally to any transducer that uses the dwell time receiver 122C forms, and not just for the timing converter 125 apply to the dwell receiver 122C forms as a separate converter.

It will be understood that the positioning of the timing IDT 125 relative to one of the phase shift IDTs as discussed above and in FIG 1B shown advantageously the measurement of the dwell time Δt _us and the phase shift of a wave that is received simultaneously from the receiving IDT 122B is received, can enable. That is, if the emitting transducer 122A between the timing transducer 125 and the receiving transducer 122B is arranged, the emitting transducer 122A send out a wave in both directions at the same time and therefore also the dwell time transmitter 122D form. Thus, the dwell time can be measured simultaneously with the phase shift of the wave received by the receiving IDT 122B Will be received. This is also in 1B shown, the second transmitter 122A-2 between the timing transducer 125 and the second recipient 122B-2 is arranged. So if the second transmitter 122A-2 If a wave is emitted in both directions, as indicated by the arrows, the respective waves can be measured by the timing transducer 125 , ie the dwell receiver 122C or the second recipient 122B-2 which therefore makes it possible to determine both the dwell time and the phase shift of the second wave. It goes without saying, however, that a time transmitter converter which is specifically only provided for emitting a signal for the dwell time measurement, ie the dwell time transmitter 122D forms, can be used. In other words, the measurement of the dwell time can be implemented separately from the measurement of the phase shift of the first and second waves. However, it may be preferable to combine these measurements.

derart, dass der Ausdruck $\frac{\Delta \Phi }{\Delta t_{IDT}-\Delta t_{Offset}}$

konstant wird. Die Kalibrierung kann unter Verwendung verschiedener Fluide durchgeführt werden, die sich zumindest durch die Schallgeschwindigkeit unterscheiden können. Es wird angemerkt, dass die Kalibrierung vorteilhafterweise nur von der IDT-Geometrie, der Übertragungsimpulslänge und gegebenenfalls der Gesamtgeometrie der das Fluid umfassenden Teile, z. B. der Fluidzelle, abhängig ist. Daher kann eine Kalibrierung für einen einzigen Durchflusssensor 1 einer ganzen Serie möglicherweise nur einmal erforderlich sein, bevor ein Durchflusssensor 1 in Betrieb genommen wird.The time in which the sound wave is generated and the time in which the sound wave is converted back into a SAW are periods of time in which the wave is not displaced by the flow. These times, which can also be referred to as the offset time Δt _offset , can be constant for a fixed pulse length of the transmission pulse of the emitting phase shift IDT and for all possible sound velocities of different fluids if the approximation is sufficiently accurate. Thus, on the converter 122 , who is the dwell receiver 122C forms, a sound wave maximum can be received after a total propagation time Δt _IDT = Δt _us + Δt _offset . It should be noted that the wave is not essentially a SAW within the chip 12th spreads out before it from the transducer 122 is received by the dwell receiver 122C forms as the converter 122 is arranged such that the wave through which the fluid passes hits it directly. In other words, Δt _SAW can be assumed to be zero in a sufficiently precise approximation. The constant offset time Δt _offset can be obtained through a global calibration of the difference measure ΔΦ (also referred to as phase offset) at a constant flow rate, normalized by the propagation time Δt _us in the fluid, which is obtained from the time measurement IDT 125 or more generally, the converter 122 , who is the dwell receiver 122C forms, what is measured is: $$\frac{\Delta \Phi }{\Delta t_{us}}=\frac{\Delta \Phi }{\Delta t_{\mathrm{I.}\mathrm{D.}T}-\Delta t_{Offset}},$$

such that the expression $\frac{\Delta \Phi }{\Delta t_{\mathrm{I.}\mathrm{D.}T}-\Delta t_{Offset}}$

becomes constant. The calibration can be carried out using different fluids, which can differ at least in terms of the speed of sound. It is noted that the calibration advantageously depends only on the IDT geometry, the transmission pulse length and possibly the overall geometry of the parts comprising the fluid, e.g. B. the fluid cell, is dependent. A calibration can therefore be carried out for a single flow sensor 1 an entire series may only be required once before a flow sensor 1 is put into operation.

Thus, the in 1A and 1B enable the measurement of the phase difference Δϕ (t) between transmission and reception of a first and second wave, the second wave generally propagating in the opposite direction compared to the first wave with respect to the direction of flow. In particular, the flow sensor 1 comprise two phase shift IDTs which can alternately transmit and receive waves such that two successive waves propagate in opposite directions while traveling the same distance in total in the flow direction (x-direction). The phase shift IDT can be arranged such that each wave propagates partly as a sound wave that _{traverses the fluid for a time Δt us} and partly as a SAW that results from the feedback of the sound wave into the chip 12th after passing through the fluid for a time Δt _SAW emerges. During the passage of the fluid, the two waves can each experience a flow-dependent shift, which in turn is due to a time or phase shift of the signal can be mapped based on the difference in Δt _SAW. By calculating a measure of the difference between the two phase differences ΔΦ = Δϕ (t ₁ ) - Δϕ (t ₂ ), a signal can be determined which is proportional to the flow velocity v _x and the dwell time Δt _{us of} the wave when passing through the fluids, i.e. Δ∝ ∝ kv _x Δt _us . While k can be assumed to be constant in a sufficiently precise approximation, the dwell time Δt _{us can be} fluid-dependent. In order to implement a fluid-independent flow measurement, the dwell time Δt _us can thus be determined.

Since the dwell time Δt _us is independent of the flow, it can be measured using a dwell time receiver 122C be measured, e.g. B. a timing converter 125 which is configured to send the sound wave directly to the transducer after passing through the fluid 122 who meets the dwell receiver 122C forms. That is, the sound wave gets into the chip 12th fed back within the range that the transducer 122 includes the dwell receiver 122C forms, e.g. B. the time transducer 125 . This measurement can enable the determination of Δt _IDT = Δt _us + Δt _offset , where Δt _SAW can be assumed to be zero in a sufficiently precise approximation for this measurement, since the sound wave hits the transducer directly 122 who meets the dwell receiver 122C forms. By determining the phase difference ΔΦ and Δt _IDT , measured on the converter 122 , who is the dwell receiver 122C forms for different fluids, the constant offset Δt _offset can be determined in such a way that the pure dwell time Δt _us can be determined. Since the calibration measurement is fluid and flow independent and mainly depends on the overall geometry of the transducers involved and the flow sensor as well as the pulse length used to generate the wave, it may only be required once for a certain sensor geometry and pulse property. Therefore, the flow sensor 1 enable a fluid-independent measurement of a flow property, e.g. B. the flow velocity or the flow rate of a fluid that is passed through the fluid sensor 1 is directed. The sensor can preferably be configured to measure flow rates at least in the range from 1 μl / min to 3 ml / min, preferably 500 nl / min to 5 ml / min, more preferably 1 nl / min to 10 ml / min. In particular, the sensor can be configured to measure these flow rates with a relative error of up to 0.1%, preferably up to 0.01%, even more preferably up to 0.001%. Furthermore, the flow sensor can be configured for pressures of at least up to 100 bar, preferably at least up to 500 bar, more preferably at least up to 1000 bar, for example at least up to 2000 bar. That is, the flow sensor can advantageously be configured for high fluid pressures and operate over a wide range of pressures, ranging from essentially 0 bar to pressures typically found in HPLC applications.

In general, the flow sensor can be a data processing unit for processing the transducers from the receiving transducers 122B received signals as well as triggering the generation of waves by the emitting transducers 122A include. That is, the processing unit can generally be configured to perform a method in accordance with the present invention and, in particular, to perform the respective calculations required to determine the flow characteristic based on that from the receiving transducers 122B to determine received signals and the generation of waves at the emitting transducers 122A to initiate. In some embodiments, the flow sensor can share the respective processing unit with other devices. For example, a central computer comprising a processing unit can be connected to the flow sensor and other components of an HPLC system, e.g. B. further sensors, detectors, pumps and / or valves can be connected.

It goes without saying that those in the 1A and 1B The illustrated embodiment is only one embodiment of the present invention, and other embodiments are also contemplated, for example, as discussed below. However, the general principle for determining a flow characteristic can be the same. That is to say that the method for determining the flow property can generally comprise the generation of the difference measure and the determination of the dwell time, in order then to use these parameters for determining the flow property. In particular, the measurement of the residence time advantageously enables a fluid-independent measurement of the flow property.

In general, a flow sensor according to embodiments of the present invention can be less complex than known flow sensors, e.g. B. it may not include any moving parts or complex position measurements and also enables a fluid-independent measurement of a flow property based on a single one-time calibration, which can already be carried out, for example, by a manufacturer of the sensor. In addition, the manufacture of SAW chips used in the flow sensor can be based on established chip processing techniques that are readily available. Advantageously, a sensor according to the present invention may not require materials that will dissolve and thereby contaminate a pump, e.g. B. an HPLC Pump, provided solvent. In addition, the fluid-conveying parts can advantageously be made of materials that cannot be attacked by conventional eluents, e.g. B. chemically inert materials. Such a sensor can therefore offer an inexpensive alternative, in particular as a flow sensor for HPLC pumps, which have to correspond to the gradient and the flow at the same time.

As already mentioned, the present invention can be used in flow sensors 1 which differ from the in the 1A and 1B different illustrated exemplary embodiment. For example, the timing IDT 125 on a separate chip 12th be arranged, e.g. B. on an opposite side of the channel 11 , as in 6th shown. In other words, at least a portion of the acoustic reflector can 16 through a chip 12th be replaced. It is noted that for timing, IDT 125 also other positions within the channel 11 can be possible. Normally, however, it is ensured that the maximum of the wave packet that propagates in the fluid of one of the at least two (bidirectional) phase shift IDTs directly on the timing IDT 125 meets. It is also noted that in this regard, the term “direct” refers to the wave packet that hits the timing IDT 125 and not on any other portion of the chip 12th meets. This means that the wave packet can still be exposed to reflections before it hits the timing IDT “directly” 125 meets. Again, the discussed extent of the timing IDT 125 by nλ _SAW on both sides for the total dimension of the timing IDT 125 must be taken into account. The same placement and / or dimension considerations apply to any transducer 122 , who is the dwell receiver 122C forms, e.g. B. also in the event that the flow sensor does not have a dedicated time transducer 125 includes.

It goes without saying that the measured dwell time depends on the relative position of the timing IDT 125 may require appropriate scaling with respect to the phase shift IDT. For example, in the in 6th The illustrated embodiment waves the fluid only once before it is received by the timing IDT 125 is received while it is reflected at least once before it is received by the second receiver 122B-2 is received and thus the fluid crosses at least twice. The dwell time contained in the difference measure can therefore correspond to twice the measured dwell time, for example.

In addition, the transmitter and receiver arrangement can generally have different numbers of IDTs 122 include. During at least two IDT 122 configured to function as emitting 122A and / or receiving 122B IDT, they can be provided with a number of different configurations of transducers 122 be realized.

In general, the transmitter and receiver arrangement can have at least one first transmitter 122A-1 , a first recipient 122B-1 , a second transmitter 122A-2 and a second recipient 122B-2 form. During the operation of the flow sensor 1 can send a first wave from the first transmitter 122A-1 to the first recipient 122B-1 The first wave carries the fluid on its way from the first transmitter 122A-1 to the first recipient 122B-1 runs through at least once. A first wave signal can then be sent from the first receiver 122B-1 received and recorded, for example, as voltage, current or another analog or digital signal. A second wave can come from the second transmitter 122A-2 to the second recipient 122B-2 (e.g. after sending the first wave), the second wave carrying the fluid on its way from the second transmitter 122A-2 to the second recipient 122B-2 runs through at least once. A second wave signal can then be sent from the second receiver 122B-2 received and recorded, for example, as voltage, current or another analog or digital signal.

Thus, the transmitter and receiver arrangement can have multiple transducers 122 include, e.g. B. Interdigital converter 122 who have a transmitter 122A and / or a recipient 122B can form. That is, a single converter 122 can be a single transmitter 122A and / or recipient 122B or multiple channels 122A and / or recipient 1222B form. For example, the transmitter and receiver arrangement can comprise an array of transducers which are arranged in such a way that at least one signal that contains information about the flow-dependent displacement of a wave passing through the fluid, as well as the dwell time, and at least one further signal that contains the Determining the flow-independent dwell time enables it to be sent and received.

With reference to 5A to 5C possible exemplary arrangements are discussed, the different numbers and functionalities of transducers 122 illustrate which form the required first and second transmitters and receivers. It is noted that these figures are only different arrangements of the emitting and receiving transducers 122A , 122B concern and that any reference to the dwell receiver 122C and the dwell transmitter 122D and especially to additional converters 122 , e.g. B. the time transducer 125 , have been omitted for the sake of simplicity. That is, the 5A to 5C may only represent part of a flow sensor 1 and can, for example, also include a time measurement converter 125 include, or alternatively, at least one of the illustrated transducers 122 furthermore a dwell time receiver 122C and / or a dwell transmitter 122D form.

In some embodiments, the transmitter and receiver assembly can include at least 4 transducers 122-1 , 122-2 , 122-3 , 122-4 include, as in 7A shown, with each transducer being the first transmitter 122A-1 , the second transmitter 122A-2 , the first recipient 122B-1 or the second recipient 122B-2 can provide. That is, every converter 122 can either form a receiver or a transmitter. Furthermore, the converter 122 be arranged such that the first wave extending from the first transmitter 122A-1 to the first recipient 122B-1 (indicated by the dotted arrows) moves, with respect to the direction of flow, can move in a different direction than the second wave coming from the second transmitter 122A-2 issued and by the second recipient 122B-2 is received (indicated by the dashed arrows). Furthermore, the transducer can preferably be arranged in such a way that the separation of the first transmitter 122A-1 and the first recipient 122B-1 is the same as the separation of the second transmitter 122A-2 and the second recipient 122B-2 . Furthermore, the emitting transducers 122A-1 , 122A-2 be unidirectional converters. That is, they can be configured to emit waves in only one direction, which can, for example, advantageously reduce any crosstalk between transducers and / or limit the power emitted by the transducers. While such an arrangement may advantageously allow signals to be sent and received unambiguously, it may be preferable to reduce the number of transducers while maintaining functionality.

For example, the transmitter and receiver arrangement may only include three transducers 122-1 , 122-2 , 122-3 constituting the first and second transmitters and the first and second receivers, as in FIG 7B shown, with a single emitting transducer 122A , 122-1 the first transmitter 122A-1 and the second transmitter 122A-2 can form and the two remaining transducers the first and second receivers, respectively 122B-1 or. 122B-2 form. The receiving transducers 122B can each be on a different side of the emitting transducer 122A be arranged with respect to the flow direction such that the first and the second wave run in opposite directions (dashed and dotted arrows). That is, the first 122A-1 and the second 122A-2 transmitter can consist of a single transducer 122-1 which can for example be configured to send a wave in two directions, ie upstream and downstream, in such a way that the first and second waves can for example advantageously be sent simultaneously. Again, the first and second recipients can 122B-1 , 122B-2 preferably at the same distance from the emitting transducer 122A be arranged such that the first and second waves are each the same distance from the emitting transducer 122A return to the respective recipient.

Furthermore, in some embodiments, the transmitter and receiver arrangement can only have two transducers 122-1 , 122-2 which form the first and second transmitters and receivers, as in FIG 7C (and 1A and 1B) shown. In such an embodiment, either of the two transducers 122-1 , 122-2 a transmitter 122A and a receiver 122B form. For example, the first converter 122-1 the first transmitter 122A-1 and the second recipient 122B-2 and can form the second converter 122-2 the second transmitter 122A-2 and the first recipient 122B-1 form. It goes without saying that each transducer alternately sends and receives a signal in such a way that there is always a transducer as the transmitter 122A works and the other as recipient 122B acts. The waves can thus move alternately upstream and downstream (indicated by the dashed and dotted arrows) and can therefore advantageously cancel out signals that are independent of the flow.

Those skilled in the art will recognize that the transducers 122 in general, they may not all be on a single chip 12th are arranged, as already in 6th specified. That is, the converter 122 can be on separate chips 12th be arranged on the same and / or different sides of the channel 11 can be arranged. This can, for example, advantageously crosstalk between the transducers 122 reduce. For example, in one embodiment as in 7A shown the two converters 122-1 , 122-2 who have favourited the first channel 122A-1 and the recipient 122B-1 form, on a chip 12th lie that of another chip 12th is separated from the second transmitter 122A-2 and recipient 122B-2 includes. Such a configuration can advantageously prevent a SAW from emitting from the first one Converter 122A-1 to the second emitting transducer 122A-2 and / or to the second receiving transducer 122B-2 spreads.

In general, you need a chip 12th not necessarily over a full length of the channel 11 (in the direction of flow) extend. The illustrated embodiments in this regard are for an illustrative purpose only, and the at least one chip 12th can for example be embedded in a larger channel structure that extends over the upstream and / or downstream end of the chip 12th extends beyond. In other words, the chip can 12th for example, be placed on an ideally flat base plate or, for example, in a corresponding recess within the base plate, which in turn includes a portion of the channel, e.g. B. one side of the channel. Furthermore, for example, a rectangular channel arrangement on the chip 12th , especially the chip surface 124 and thus the chip side that the IDT 122 and optionally the protective layer 123 includes, be placed such that the chip 12th the sound power in the duct 11 can emit. As an alternative to this, the channel arrangement can for example be placed on the base in such a way that the chip is located within the channel formed thereby. Thus, at least a part of the SAW or the ultrasonic wave (ie the sound wave) can travel in or against the through the channel 11 the defined flow direction. Furthermore, at least the side opposite the functional chip surface, ie the chip surface comprising the IDT, can be configured in such a way that at least part of the wave propagating in the channel can be reflected.

While in the embodiments so far with respect to 1A , 1B and 4th discussed, the flow sensor has at least two phase shift IDTs and an additional timing IDT 125 includes the number of IDTs and thus the complexity of the flow sensor 1 can be further reduced. That is, in some embodiments, the flow sensor can 1 only two IDT 122-1 , 122-2 to measure the phase shifts and the dwell time Δt _us . In other words, in some embodiments, the present invention may not include a separate timing IDT 125 but instead one of the phase shift IDTs may further be configured to provide the time measurement. That is, one of the phase shift IDT may also be the dwell receiver 122C while the other is the dwell transmitter 122D can form. In general, this can be achieved by using two different sized IDTs as phase shifting IDTs. That is to say, the two IDTs can have different dimensions, in particular lengths in the direction of flow.

The two IDT 122 can be configured to emit and receive signals at identical frequencies. That is, each IDT can be configured to operate at substantially the same SAW frequencies. Here, the term “essentially the same” is used to denote differences due to limitations in the manufacturing process and / or inevitable deviations in the material properties, e.g. B. material purity to include. Both IDT 122 comprise essentially the same frequency. It is understood that a transducer can generally emit and receive signals with a certain bandwidth around a center frequency. This means that the frequency response of a transducer may generally not be a delta-like function, but instead comprises a certain bandwidth. That is, when the frequency of a converter, e.g. B. an IDT, is referred to, the center frequency is meant. In general, the bandwidth of the two IDT 122 also due to the difference in size, in particular the difference in length in the direction of flow and thus the difference in the number of finger electrodes. However, such a difference cannot affect the relative phase of the measured signal, at least if it is measured at a fixed frequency which is at or near the center frequency of the transducer, preferably within a frequency range of the center frequency, the sound power level not being more than 3 dB below the maximum sound power level (at the center frequency).

mit 1000 m/s < c_F < c_s direkt auf den Verweilzeitempfänger 122C treffen, und nicht auf den Chip 12, z. B. das Substrat 121, vor oder nach dem, d. h. stromaufwärts oder stromabwärts des, zweiten IDT 122-2, der den Verweilzeitempfänger 122C bildet. Mit anderen Worten ist in der in 8A dargestellten Konfiguration Δt_SAW ungefähr 0, derart, dass die am zweiten IDT 122-2 gemessene Zeitverzögerung Δt_IDT dem Signal entspricht, das von einem bestimmten Zeitmess-IDT 125 gemessen wird, wie vorstehend erörtert, d. h. er stellt eine Messung für die Verweilzeit, speziell Δt_IDT = Δt_us + Δt_Offset, bereit.With reference to 8A the transmitter and receiver arrangement can be used in a first configuration I for measuring a first wave, the first IDT 122-1 the first transmitter 122A-1 and the dwell transmitter 122D can form, while the second IDT 122-2 the first recipient 122B-1 and the dwell receiver 122C can form. The second IDT 122-2 further configured to include the dwell receiver 122C to provide a measurement of the dwell time .DELTA.t _us can have a greater expansion in the direction of flow compared to the first IDT 122-1 include. It can thus be ensured that a sound wave emitted by the first IDT 122-1 goes directly to the area that the second IDT 122-2 includes who is the first recipient 122B-1 and the dwell receiver 122C forms. That is, the second IDT 122-2 can be configured such that one of the first IDT 122-1 The transmitted sound wave may not first be sent into a leaking SAW in a region of the chip 12th without IDT 122 is converted, but instead directly to the larger, second IDT 122-2 meets. In particular, the residence time receiver 122C be configured in such a way that the maxima are one of the dwell time transmitter 122D emitted sound wave for all angles $sin{\theta }_{\mathrm{R.}}=\frac{c_{\mathrm{F.}}}{c_{\mathrm{S.}}}$

with 1000 m / s <c _F <c _s directly to the dwell time receiver 122C hit, and not on the chip 12th , e.g. B. the substrate 121 , before or after, ie upstream or downstream of, the second IDT 122-2 , who is the dwell receiver 122C forms. In other words, the in 8A configuration Δt _{SAW shown} approximately 0, such that the one on the second IDT 122-2 measured time delay Δt _IDT corresponds to the signal from a specific time measurement IDT 125 is measured as discussed above, ie it provides a measurement for the dwell time, specifically Δt _IDT = Δt _us + Δt _offset .

Thus, in this embodiment, the flow sensor comprises only two IDTs 122-1 , 122-2 , wherein an IDT has the functionality of a phase shift IDT and the timing IDT 125 combined.

So when the first IDT 122-1 before the second IDT 122-2 can be placed, induces a sound wave in the fluid flow by excitation of a SAW, the sound wave can move at the Rayleigh angle θ _R through the fluid flow and on the inner wall 111 of the canal 11 be reflected. The sound wave can then be sent directly to the second IDT 122-2 meet, as indicated by the dashed arrows in 8A indicated, which can therefore provide a measurement of the flow-independent residence time Δt _us . That is, the one from the second IDT 122-2 received signal may not include a flow-dependent phase shift. However, it can still include a flow-independent phase shift due to fluid properties and / or environmental parameters.

To measure a second wave and with reference to 8B the transmitter and receiver arrangement can be used in a second configuration II, the first IDT 122-1 who is the first transmitter 122A-1 in the first configuration I now forms the second receiver 122B-2 forms, ie as the receiving IDT 122B acts while the second IDT 122-2 , who is the dwell receiver 122C forms, and the first recipient 122B-1 now the second transmitter 122A-2 form, that is, as an emitting IDT 122A can act.

So if the second IDT 122-2 induces a sound wave, as in 8B indicated by the dotted arrow, the maximum of the respective reflected sound wave does not hit the first IDT directly 122-1 but instead induces a SAW first. That is, as indicated by the dotted arrows, the sound wave can pass the channel 11 pass through, on the inner surface 111 be reflected and the channel 11 (and the fluid contained) run through again. The first IDT 122-1 may be arranged such that the sound wave is downstream of the first IDT 122-1 on an area of the chip 12th hits in such a way that it is first at least partially back into the chip 12th couples and propagates as a SAW before passing from the first IDT 122-1 is received by the second recipient B2 forms. Thus, in this configuration, the flow-dependent shift of the sound wave that passes through the fluid is mapped back to the time and / or phase of the signal that is sent by the first IDT 122-1 Will be received. The signal received in this configuration thus includes a flow-dependent contribution which can make it possible to determine a flow property of the fluid.

In other words, that includes from the second IDT 122-1 (which is the dwell receiver 122C and the first recipient 122B-1 forms) received signal in the first configuration I, which is shown in 8A is shown, information about the dwell time Δt _us , which is determined by the envelope curve of the oscillating signal and additionally by phase changes due to flow-independent contributions, such as fluid-specific properties and / or environmental parameters, e.g. B. the temperature of the fluid is determined. However, it does not contain a flow-dependent contribution. In contrast, the second signal from the first IDT 122-1 is received by the second recipient 122B-2 in the second configuration II shown in FIG. 8B forms isolated information about the dwell time, but it provides information about the phase shift due to the flow-dependent shift as well as flow-independent contributions to the phase shift, such as fluid-specific properties and / or environmental parameters. Therefore, a differential measure of these two signals can cancel out the flow independent contributions to the phase signal while maintaining the flow dependent contribution made by the signal received by the smaller transducer in this embodiment. This means that under certain circumstances only one of the two signals that contribute to the difference measure includes a flow-dependent contribution. The difference measure can, however, still be proportional to the flow velocity and to the dwell time ΔΦ ∝ kv _x Δt _us . Since that from the second converter 122-2 , who is the dwell receiver 122C in the in the 6A and 6B forms illustrated embodiment, the measured signal also provides a measure of the residence time, the fluid velocity and more generally a fluid property can be derived, as explained above.

Preferably, in an embodiment which comprises only 2 converters, the larger converter, ie the converter, which has the dwell time receiver 122C be arranged downstream of the other (smaller) transducer, ie the transducer which forms the dwell time transmitter D. Such an arrangement may be preferred because the wave experiences a positive flow-dependent displacement as it propagates with the flow, i.e. the distance the wave travels in passing through the fluid increases, while it experiences a negative flow-dependent displacement as it moves propagates against the flow, that is, the distance that the wave travels when passing through the fluid decreases.

As previously discussed, an AC voltage signal can be sent to an emissive IDT 122A can be applied to generate a SAW, e.g. B. to emit and / or send. In particular, a voltage that alternates at a high frequency can be applied to the transducer and in particular to electrodes that the transducer, e.g. B. an IDT, to be included in the material below the transducer, e.g. B. due to the inverse piezoelectric effect to cause periodic deformations. The high frequency voltage excites SAW and can be applied to the IDT, which is an emitting IDT 122A form in alternating pulsed mode. The AC voltage signal that is applied to an emitting transducer to generate a wave can also be referred to as a transmission pulse. A possible length of the transmission pulse Δt _tp can be based on the number of IDT periods n of the emitting IDT 122A can be derived in such a way that the sound pulses are as short as possible while still reaching full sound power if possible, which can lead to Δt _tp = n / f, where / denotes the frequency of the generated and / or received SAW. Again, n is the number of periods of the emitting IDT 122A for measuring the phase difference and thus the minimum number of periods of the transmission signal for a "full" SAW power. The resulting SAW pulse can thus be selected in such a way that it covers a temporal extent of 2 n / f, where the factor 2 is due to the electrical excitation time, which can correspond to the length of the transmission pulse. This can advantageously make it possible to provide a signal with (almost) maximum power and bandwidth, which in turn leads to a pulse that can be as sharp as possible in the time domain. The periodicity of the transmission pulse can be selected such that the response signal of the transmission pulse is only very small or preferably zero. That is, the periodicity can be chosen such that the received signal is very small, preferably zero, due to the last signal transmitted, before the next SAW is transmitted, e.g. B. by the previously receiving IDT.

The AC voltage signal can, for example, from a high frequency voltage source, e.g. B. an HF generator, a generator for arbitrary waveforms (AWG) or another signal generator can be provided. For example, the processing unit can trigger the high-frequency source in order to send a corresponding AC voltage signal, preferably a pulse, to an emitting transducer in order to generate a wave, e.g. B. a SAW to trigger. In some embodiments, the processing unit can provide a desired waveform for the AC voltage signal to the high frequency voltage source.

In general, it is understood that the sound wave can be a pulse-shaped sound wave with respect to time. For example, the sound wave can have a temporal form which corresponds to a square pulse, a Gaussian pulse, a Sinc pulse, a Dirac pulse, a Lorentz pulse or the like. In other words, the present technology is preferably based on sending SAW pulses and therefore generating sound waves in the form of a pulse, e.g. B. sound pulses, preferably ultrasonic pulses.

9A FIG. 10 depicts an exemplary signal sequence generated by a receiving IDT 122B received, e.g. B. can be detected. In particular shows 9A different signals of a receiving IDT 122B in response to a harmonic signal pulse that is 360 ns in length. Here, the initial signal may be due to crosstalk between the transmitting 122A and the receiving 122B IDT, which is a nearly instantaneous direct electromagnetic coupling of the phase shift IDT (electrically coupled input signal). The second signal (labeled SAW) may correspond to the SAW that is going through the chip 12th and in particular through the surface of the chip 12th emotional. That is, only a fraction of that from the emitting IDT 122A generated (ie transmitted) SAW can be deflected into the fluid, while part of the SAW is in the chip 12th remain and register as a SAW to the receiving IDT 122B can move, which in turn receives a signal from the SAW and delivers a corresponding electrical signal. This signal can be suppressed, for example, by placing the two phase shift IDTs on separate chips 12th to be placed. However, it can also be viewed as a reference signal that can be used in the analysis of the received signal sequence.

The next signal (with the designation SAW-US-SAW) corresponds to a SAW-induced sound wave, which again on the SAW chip 12th hits (after it has passed through the fluid and has been reflected) and is at least partially coupled into the chip again as a SAW, which in turn is from the receiving IDT 122B received, e.g. B. is detected. That is, the initial SAW generated by the emitting IDT 122A is generated can be at least partially diverted into the fluid passing through the channel 11 flows where it can propagate as a sound wave, more precisely as an ultrasonic sound wave - the "US" used in the designation of the pulse is the designation of an ultrasonic pulse or, more generally, an ultrasonic sound wave. As previously described, the sound wave that can be induced at the Rayleigh angle can be on the opposite side of the channel 11 , especially on its inner surface 111 , be reflected. For example, the inner surface can be used in particular as an acoustic reflector 16 configured. For example, in some embodiments it can be a sapphire plate. As soon as the sound wave is reflected, it can be sent back onto the chip 12th hit, with at least a portion of the sound wave as SAW in the chip 12th can be fed back. The SAW can in turn also from the receiving IDT 122B be received. Because of the longer running distance compared to the proportion of SAW that is in the chip 12th remained, and the difference in the speed of sound of the chip 12th and the fluid, however, the signal is related to the signal of the SAW, which only passes through the chip 12th moving, delayed. The third signal (with the designation SAW-US-SAW-US-SAW) corresponds to a SAW that emanates from an ultrasonic pulse induced by the first SAW. That is, when the first ultrasonic pulse goes back into the chip 12th is fed back, a SAW is generated, which in turn can be at least partially deflected and thus generates a subsequent second sound wave, which after the reflection again as a SAW in the chip 12th can be coupled and therefore to one of the receiving IDT 122B detected signal leads. In other words, ultrasonic waves can be generated after one or more reflections on the inner surface 111 of the canal 11 , e.g. B. on a (reflective) cover plate of the channel 11 , again on the SAW chip 12th hit, again spread as SAW. Such a SAW can then generate a new sound pulse. Subsequent signals that 9A shows, thus correspond to further reflections of the ultrasonic wave in the channel 1 .

Since the time delay between the separated signals is due to the difference in distance traveled by the wave, that is, as a sound wave and as a SAW, it can be changed by changing the distance between the chip 12th and the opposite inner surface 111 of the canal 11 can be varied. That is, the channel can have a height H1 in the y-direction, which is perpendicular to the surface of the chip 12th is (cf. 1A) that can be varied. For example, the chip 12th opposite inner surface 111 through an acoustic reflector 16 provided, e.g. B. by a sapphire plate, which can be moved in y-direction to the height H1 of the canal 11 to vary.

9B shows changes in the received signal of the wave due to a change in the channel height H1 . The height H1 of the canal 11 increases from left to right. That is, in the field on the far left, the height is smallest for the three measurements shown, and in the field on the far right is the height H1 largest for the three measurements shown. The changing received signal shows that the altitude is increasing H1 of the canal 11 the separation between those at the receiving IDT 122B due to the different pulses (or pulse components) detected signals. In other words, the signals emanating from the singly and doubly reflected sound pulses “wander” due to the vertical variation of the inner surface 111 , e.g. B. the sapphire plate 16 or more generally the acoustic reflector 16 in the time domain.

Furthermore shows 9B that changing the channel height H1 can also change the relative strengths of the signals received. This can be understood on the basis of the consideration that a reflection of the SAW is not an infinitely short process, but instead requires a limited amount of time. In particular, every SAW that goes through the chip is 12th spreads, a leaky SAW that also constantly loses a fraction of its power due to the deflection in the fluid. Therefore, the position of the IDT with respect to the point at which the SAW is at least partially fed back into the chip can change the strength of the received signal. For example, if the position of the receiving IDT spatially corresponds to a maximum of an integral of the entry and exit ultrasound power over time, the received signal pulse can be a maximum. Thus, changing the altitude can also change the strength of the received signal.

A flow sensor according to the present invention can advantageously enable high repetition rates of the measurement compared to standard flow sensors currently used in HPLC. That is, once the SAW and all remaining stray waves have disappeared, i.e. the chip 12th and / or the channel 11 a new measurement can be carried out. This can take less than 20 microseconds, for example, so that the measurement can be repeated every 20 microseconds, that is to say at a repetition rate of 50 kHz. The present invention can therefore make it possible to obtain a flow characteristic with a significantly higher repetition rate than the current state of the To measure flow sensors, which can advantageously allow an improvement in the signal-to-noise ratio through repeated measurements. For example, the cycle time for flow sensor measurements in a feedback loop for controlling an HPLC pump can be 50 or even 100 times less such that multiple measurements can be averaged to provide a signal with an improved signal-to-noise ratio.

With reference to 10 exemplary measurements of flow velocity-dependent phase differences are discussed. The results shown include phase difference measurements of two different fluids: water and isopropanol, where for water the phase difference of the second peak, i.e. the peak corresponding to two reflections of the sound waves, was measured and for isopropanol the phase difference of the first peak, i.e. the peak that corresponds to a single reflection of a sound wave. The flow rate was varied between 0 and 2 ml / min in flow steps of 0.1 ml / min and a horizontal step length of 30 s. In addition, for each fluid 5 Measurements superimposed. This shows the reproducibility of the measurement, since the curves (and thus the measurements) show almost identical behavior for a fluid. The dwell time of the sound wave was not taken into account in these measurements, which explains that the flow measurement is not fluid-independent. Overall, the measurements show that the flow velocity can be clearly measured by measuring the phase difference according to the present invention. The remaining fluid dependency can be eliminated taking into account the dwell time Δt _us and a corresponding one-time calibration with regard to the fluid-independent offset time t _offset , as described above.

In some embodiments of the present invention, the present invention may also enable other fluid properties to be measured, e.g. B. density, speed of sound, viscosity or conductivity. These properties can be derived, for example, on the basis of the flow-independent phase shift of the wave passing through the fluid, which can be dependent on these properties. In addition, a SAW can be drawn directly from the emitting transducer 122A to the receiving transducer 122B can propagate, ie a portion of a transmitted SAW that is not deflected into the fluid, due to the decaying field of the SAW that comes into contact with the fluid flowing through the channel, include information about the fluid properties and thereby record a corresponding phase shift. In particular, a “mixed substrate” can be used, ie a substrate that can support the generation of Rayleigh and Shear and / or Love waves, wherein the Shear / Love waves can continue to move along the chip surface when they come into contact with a fluid flowing above the chip surface. An example of a substrate that can generate Love and Rayleigh waves at the same time is a LiTaO ₃ -YX-36 ° crystal. This can advantageously enable a parallel measurement of a wave that traverses the fluid (based on a Rayleigh wave) and an increased proportion of a SAW that travels directly through the chip to the receiving transducer 122B moves without deflecting into the fluid. The latter signal can advantageously be used to measure further fluid properties. Fluid detection with shear waves is for example in Guided acoustic wave sensors for liquid environments, C. Caliendo and M. Hamidullah 2019 , J. Phys. D: 52 153001. Additionally, in some embodiments, the fluid properties can be used to infer potential fluid candidates, e.g. B. with the help of statistical methods such as machine learning and / or neural networks. That is, the fluid can be identified, or at least a limited number of candidates for the fluid can be identified based on the fluid properties.

It should be understood that when accessing an IDT 122 When referring to receiving or detecting the signal of a sound wave, it is meant that the IDT receives the signal of a SAW, e.g. B. detected that originates from the sound wave that is at least partially in the piezoelectric substrate 121 or the piezoelectric layer is coupled in and thereby induces a SAW. That is, the receiving IDT 122B , which can receive a signal based on the emitted sound wave, for example, does not receive the signal of the sound wave directly, but instead via a sound wave-induced SAW. This SAW can be generated after the (sound) wave propagating one or more times through a channel vertically, ie vertically to the top 124 of the chip 12th , in the chip 12th , e.g. B. the piezoelectric substrate 121 , is fed back.

With reference to 11 For example, the present invention can also be implemented in embodiments in which at least some of the transducers, which form transmitters and / or receivers of the transmitter and receiver arrangement, are external to the channel 11 are arranged. That is, the converter 122 may not be in direct contact with the fluid or are only through a sealing layer 123 Cut. That is, at least one chip 12th the transmitter and receiver arrangement can be outside of the channel 11 be arranged.

In such an embodiment, the channel 11 from a duct material 18th be formed, which comprises a speed of sound c _m for s- and / or p-waves, which is less than the speed of sound of the substrate c _s . The chip 12th can then by means of a coupling material 19th having a thickness (ie height) smaller than the SAW wavelength λ with the channel material 18th be coupled. For example, the coupling material 19th comprise a coupling material thickness that is less than 50%, preferably less than 25% and more preferably less than 10% of the transducer wavelength. Thus one can from the converter 122 in the chip 12th generated SAW via the coupling material 19th with the duct material 18th can be coupled and the SAW due to the different speed of sound c _m <c _s in the direction of the channel 11 to get broken. In addition, c _m can be greater than the speed of sound in the fluid c _f , such that the SAW is deflected into the fluid at a boundary between the media, similar to the refraction of light. Such an embodiment can therefore reduce the placement of the chip 12th and the converter 122 without them coming into contact with the fluid, which can allow different channel designs, the use of different (e.g. more aggressive) fluids and / or easier replacement / easier replacement of chips.

Whenever a relative term such as “approximately,” “substantially,” or “approximately” is used in this specification, that term should also be construed to include the exact term. That is, e.g. B. “essentially straight” should also be interpreted to include “(exactly) straight”.

If steps are given in the foregoing or also in the appended claims, it should be noted that the order in which the steps are given in the text may be random. That is, unless otherwise specified or if it is not clear to a person skilled in the art, the order in which the steps are listed can be any. That is, when this document indicates that e.g. B. a method comprises steps (A) and (B), this does not necessarily mean that step (A) precedes step (B), but it is also possible that step (A) (at least partially) simultaneously with step ( B) is carried out or that step (B) precedes step (A). Moreover, if a step (X) is to precede another step (Z), this does not mean that there is no step between steps (X) and (Z). That is, step (X) preceding step (Z) includes the situation that step (X) is performed immediately before step (Z), but also the situation that (X) is performed before one or more steps ( Y1 ), ... followed by step (Z). Similar considerations apply when expressions such as “after” or “before” are used. While in the foregoing a preferred embodiment has been described with reference to the accompanying drawings, those skilled in the art will understand that this embodiment has been provided for purposes of illustration only and is in no way to be construed as a restriction on the scope of this invention, which is defined by the claims should.

QUOTES INCLUDED IN THE DESCRIPTION

This list of the documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• US 10570361 B2 [0014]
• DE 102019110514 A1 [0015]
• US 9581572 B2 [0015]
• DE 102018104669 A1 [0016]
• US 10570361 B1 [0148]

Non-patent literature cited

• R.M. White and F.W. Voltmer, Appl. Phys. Lett 7, 314 (1965) [0139]

Claims (11)

A method for determining a flow property of a fluid, the method comprising: Sending a first wave from a first transmitter to a first receiver, the first wave traversing the fluid on its way from the first transmitter to the first receiver, and receiving a signal of the first wave at the first receiver, Determining a first feature based on the signal of the first wave, Sending a second wave from a second transmitter to a second receiver, the second wave traversing the fluid on its way from the second transmitter to the second receiver, and receiving a signal of the second wave at the second receiver, Determining a second feature based on the signal of the second wave, Subtract one of the features from the other feature and thus generate a difference measure, Determining a dwell time which indicates a propagation time required by the first wave to pass the fluid on its way from the first transmitter to the first receiver and / or a propagation time required by the second wave to pass the fluid on its way from the second transmitter to the second receiver, Using the difference measure and the dwell time to determine the flow property. Procedure according to Claim 1 wherein the fluid comprises a direction of flow, the second wave traversing the fluid in a direction that is opposite to the first wave with respect to the direction of flow. Procedure according to Claim 1 or 2 , wherein the signal of the first and / or the second wave is not received by the respective receiver directly after the fluid has passed through. A method according to any one of the preceding claims, wherein determining the dwell time comprises sending a dwell time wave from a dwell time transmitter to a dwell time receiver, the dwell time wave passing through the fluid on its way from the dwell time transmitter to the dwell time receiver, and receiving a signal of the dwell time wave at the dwell time receiver. Procedure according to Claim 4 wherein one of the first and second waves forms the dwell wave. Procedure according to Claim 4 or 5 , wherein the signal of the dwell time wave is received by the dwell time receiver immediately after the fluid has passed through. A sensor for determining a flow property of a fluid, the sensor comprising: a channel for guiding the fluid, a transmitter and receiver arrangement which forms at least a first transmitter, a first receiver, a second transmitter and a second receiver, and a data processing unit, wherein the flow sensor is configured to the method according to one of Claims 1 to 6th perform. The sensor according to the preceding claim, wherein the transmitter and receiver arrangement comprises at least one chip, wherein the at least one chip comprises at least one transducer which is configured to transmit and / or receive a wave. Sensor according to the preceding claim, wherein the at least one chip comprises a substrate, wherein the substrate is piezoelectric or the substrate is coated with a piezoelectric layer. Sensor after one of the Claims 8 to 9 wherein the at least one transducer is an interdigital transducer (IDT) configured to transmit and / or receive a surface acoustic wave. Sensor after one of the Claims 7 to 10 , wherein the processing unit is configured to carry out steps of the method according to one of Claims 1 to 6th to execute.

Images