WO2020053214A1 - Fluidic qcm-pnc sensor - Google Patents

Fluidic qcm-pnc sensor Download PDF

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Publication number
WO2020053214A1
WO2020053214A1 PCT/EP2019/074117 EP2019074117W WO2020053214A1 WO 2020053214 A1 WO2020053214 A1 WO 2020053214A1 EP 2019074117 W EP2019074117 W EP 2019074117W WO 2020053214 A1 WO2020053214 A1 WO 2020053214A1
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Prior art keywords
sensor device
fluid
acoustic
present
piezoelectric transducer
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PCT/EP2019/074117
Other languages
French (fr)
Inventor
Ralf LUCKLUM
Nikolay MUKHIN
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Otto-Von-Guericke-Universität Magdeburg Patentwesen
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Publication of WO2020053214A1 publication Critical patent/WO2020053214A1/en

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    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/22—Details, e.g. general constructional or apparatus details
    • G01N29/28—Details, e.g. general constructional or apparatus details providing acoustic coupling, e.g. water
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N11/00—Investigating flow properties of materials, e.g. viscosity, plasticity; Analysing materials by determining flow properties
    • G01N11/10—Investigating flow properties of materials, e.g. viscosity, plasticity; Analysing materials by determining flow properties by moving a body within the material
    • G01N11/16—Investigating flow properties of materials, e.g. viscosity, plasticity; Analysing materials by determining flow properties by moving a body within the material by measuring damping effect upon oscillatory body
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/02—Analysing fluids
    • G01N29/022—Fluid sensors based on microsensors, e.g. quartz crystal-microbalance [QCM], surface acoustic wave [SAW] devices, tuning forks, cantilevers, flexural plate wave [FPW] devices
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/02—Analysing fluids
    • G01N29/036—Analysing fluids by measuring frequency or resonance of acoustic waves
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
    • G01N29/22—Details, e.g. general constructional or apparatus details
    • G01N29/222—Constructional or flow details for analysing fluids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N9/00—Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity
    • G01N9/002—Investigating density or specific gravity of materials; Analysing materials by determining density or specific gravity using variation of the resonant frequency of an element vibrating in contact with the material submitted to analysis
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N11/00—Investigating flow properties of materials, e.g. viscosity, plasticity; Analysing materials by determining flow properties
    • G01N2011/006—Determining flow properties indirectly by measuring other parameters of the system
    • G01N2011/0073—Determining flow properties indirectly by measuring other parameters of the system acoustic properties
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
    • G01N2291/00—Indexing codes associated with group G01N29/00
    • G01N2291/02—Indexing codes associated with the analysed material
    • G01N2291/028—Material parameters
    • G01N2291/02818—Density, viscosity

Definitions

  • the present invention relates to a sensor device for detecting volumetric proper- ties of fluids and a method for detecting volumetric properties of fluids using the sensor device.
  • Phononic Crystal (PnC) sensors are a new class of ultrasonic sensors that still require fundamental research.
  • Quartz Crystal Microbalance (QCM) sensors are in the meanwhile commercial sensors with a broad application range, including liquid sensors.
  • Af - K-f 2 -Am, (1 ) wherein the resonance frequency is denoted by f, a difference in the resonance frequency due to the mass attached is denoted by Af and a change in mass is de- noted by Am and wherein K is a constant depending on the area of an electrode, density, and an elastic constant of a material of the quartz crystal.
  • US7036375B2 discloses that a plurality of quartz crystal resonators having different resonance frequencies are connected in parallel wherein a combined admittance of the resonators is measured for mass detecting.
  • the problem to be solved is to provide a sensor for characterizing fluids to obtain qualitative and quantitative information of the composition of fluid and thermody- namic properties including molecular interactions within the (free) fluid that firstly is based on measurements of velocity of sound in fluids and secondly save the ad- vantages of QCM approach.
  • a sensor device for detecting volumetric properties of fluids comprising:
  • a sensor device Preferred is a sensor device according to the present invention, wherein the sen- sor device is further supplemented with measuring means for measuring at least two electrical responses. Further preferred is a sensor device according to the present invention, wherein the at least two electrical responses are selected from the group consisting of res- onant frequencies, crystal damping, admittance, impedance, and reflection.
  • the piezoelectric transducer provides a set of electrodes that are arranged in two- dimensions and connected in the form of a matrix.
  • the intermediate acoustic artificial mate- rial layer is a phononic crystal, an acoustic metamaterial or is made of an irregular system of elements.
  • a sensor device wherein the finite structure of the phononic crystal, the finite structure of the acoustic met- amaterial or the structure of the irregular system of elements provides a reflection coefficient of acoustic waves in the range from 60 to 100 % within the operating frequencies of the sensor device.
  • a sensor device according to the present invention, wherein the sensor device is further supplemented with means for measuring and control- ling a temperature of the fluid in the at least one fluid-filled cavity.
  • a sensor device according to the present invention, wherein the sensor device comprises a set of fluid-filled cavities.
  • Another object of the present invention is a method for detecting volumetric prop- erties of fluids, comprising the steps of:
  • step (b) involves a comparison with calibrating media.
  • the sensor device of the present invention measures volumetric properties of fluid analytes in a cavity instead of interfacial properties to some artificial sensor sur- face as the majority of classical chemical and biochemical sensors of the prior art. Furthermore, it is advantageous that influence of interfaces towards monitoring of (biochemical) reactions in free space are at least reduced. Furthermore, the sen- sor device of the present invention relates generally to measurement of volumetric properties of fluids on the basis of acoustic sensor principles.
  • the sensor device of the present invention takes advantage of the extremely high frequency resolution in the ppm-range of acoustic resonators.
  • the achievable res- olution of the sensor device according to the present invention is comparable with scientific instruments only.
  • the piezoelectric transducer of the sensor device of the present invention excites acoustic waves propagating towards the intermediate acoustic artificial layer and detects the acoustic load generated by the intermediate acoustic artificial layer, especially in case of the phononic crystal, and the fluid-filled cavity.
  • the origin of the sensor signal is a small frequency change caused by small variations of acoustic properties of the analyte within the fluid-filled cavity.
  • the new capability of the sensor device of the present invention is the direct link to thermodynamic properties including molecular interactions within the (free) fluid.
  • the resonant frequency of the quartz crystal on which the piezoelectric transducer of the sensor device of the present invention is based is a fundamental frequency or harmonic frequency.
  • the quartz crystal of the piezoelectric transducer either operates in a thickness shear mode or in an extensional mode.
  • the sensor device of the present invention comprises at least one fluid-filled cavi- ty. Further it is also possible that the sensor device comprises a set of fluid-filled cavities which is advantage in order to increase the quality factor (Q) of the fluid resonances and the sensitivity to the change in the speed of sound in the analyte.
  • Q quality factor
  • the third key element of the sensor device of the present invention is an acoustic artificial material layer that controls propagation of acoustic waves between the piezoelectric transducer and the at least one fluid-filled cavity due to its specific acoustic properties.
  • the main purpose of inputting of this layer is the creation of conditions for weak mechanical coupling of two resonators, wherein the first reso- nator is a piezoelectric transducer and the second is at least one fluid-filled cavity.
  • the intermediate acoustic artificial layer should have a high reflection coeffi- cient of acoustic waves in the range of 60 to 100 % in the operating range of the sensor frequencies.
  • the intermediate acoustic artificial material layer can be made from various artifi cial materials like a phononic crystal or an acoustic metamaterial or an irregular acoustic system, a composite or a porous material.
  • the phononic structure can be constructed as one-, two- or three-dimensional structure. Despite the various pos- sible designs and materials, the most significant and common for the invention is its functional purpose of weak mechanical coupling.
  • Phononic crystals are synthet- ic materials that are formed by periodic variation of the acoustic properties of the material and their most important properties is the possibility of having a phononic bandgap.
  • acoustic metamaterials exhibit spectral gaps two orders of magnitude smaller than the wavelength of sound. Acoustic properties of this artificial materials are defined not only by the material properties of the structure constituents, but by the design (geometry, symmetry, periodicity). A propagation through such structures of elastic waves is featured by the wave- length regions, within which sound cannot propagate through the structure
  • the acoustic properties of the composite arrange- ment depend on material properties of structure constituents, their variation caus- es a change in a structure transmission behaviour. That feature allows to apply solid-liquid periodic composite arrangements for liquid sensor purposes. A control of the frequency position of isolated narrow transmission bands is more beneficial rather than deviation of bandgap edges. For that reason, the phononic crystal based sensor device of the present invention is focused on the obtainment of the structure isolated transmission peaks (dips) that correspond to material properties of the fluid constituent. In contrast to well-developed microacoustic liquid sensors, the sensor device of the present invention enables the detection of the velocity of sound of fluid analyte.
  • the sensor device of the present invention allows to evaluate thermodynamic quanti- ties of the fluid analyte analysing the speed of sound at a certain range of pres- sures.
  • the reaction on molecule interactions is reflected as a change in a fluid compressibility that can be detected by probing the analyte with ultrasonic veloci- metry methods.
  • the sensor device of the present invention allows to keep the ad- vantages of velocimetry based methods and at the same time to apply the meas- urement principle based on a control of structure resonances similar to microa- coustic sensor devices.
  • the sensor device of the present invention might also be supplemented by meas- uring means for thermostating or for preventing contamination build up on said resonator surface.
  • the measurement of the resonance frequency shift of the method according to the present invention is associated with the resonance in at least one fluid-filled cavity, in the response of weakly coupled resonators of piezoelectric transducer loaded by intermediate acoustic artificial material layer and fluidic structure.
  • the determination of the volumetric properties of the fluid in the method according to the present invention is performed on the basis of a certain relationship between the speed of sound in fluid, the resonant frequency of at least one fluid-filled cavi- ty, and the geometry design of the at least one fluid-filled cavity.
  • the fluid used in the present invention can be a liquid as well as a gas.
  • Fig. 1 shows a schematic illustration of the principle structure of the sensor device according to the present invention
  • Fig. 2 shows a schematic illustration of one possible example of the sensor device according to Fig. 1 ,
  • FIG. 3 shows a schematic illustration of a second possible example of the sensor device according to Fig. 1 ,
  • Fig. 4a shows possible variations of the shape of at least one single liquid-filled cavity of the sensor device according to the present invention
  • Fig. 4b shows a principle graph of the dependence of the pressure resonance in the fluid-filled cavity of the sensor device according to the present invention on the sound velocity of the fluid
  • Fig. 5 shows possible variations of structure of the intermediate acoustic artificial layer of the sensor device according to the present invention
  • Fig. 6a shows a graphic describing a typical magnitude frequency dependence of admittance of the sensor device according to the present invention
  • Fig. 6b shows a graphic describing a phase frequency dependence of admittance of the sensor device according to the present invention
  • Fig. 7 shows a graphic describing a frequency dependence of mechanical re- sponse on the surface of the piezoelectric transducer of the sensor device accord- ing to the present invention
  • Fig. 8 shows a graph describing a dependence of characteristic frequencies of the sensor device according to the present invention
  • Fig. 9a shows a graph describing frequency dependencies of admittance on the surface of the piezoelectric transducer when a sinusoidal electric field is applied to the electrodes of the sensor device according to the present invention
  • Fig. 9b shows a graph describing the mechanical response on the surface of the piezoelectric transducer when a sinusoidal electric field is applied to the electrodes of the sensor device according to the present invention.
  • Figure 1 depicts a general scheme of the sensor device 1 according to the inven- tion. These are the principle structures of the sensor device 1 , which are connect- ed to a measuring circuit consisting of measuring means 2.
  • the measuring means comprise an electrical circuit 20, a signal generator 21 , thermocontrolling 22, sig nal processing 23 and data processing 24.
  • the key elements of the sensor device 1 of the present invention are a piezoelectric transducer 10 which is based on a quartz crystal, an intermediate acoustic artificial material layer 12 and at least one fluid-filled cavity 11.
  • the piezoelectric transducer 10 is designed as a plate that comprises electrodes 100.
  • the intermediate acoustic artificial material layer 12 controls propagation of acoustic waves between the piezoelectric trans- ducer 10 and the at least one fluid-filled cavity 11.
  • the geometry of at least one fluid-filled cavity 11 , intermediate acoustic artificial material layer 12, electrodes 100 can be different.
  • the possible geometries that can be used for at least one fluid-filled cavity are shown in figure 4a and for the intermediate acoustic artificial material layer are shown in figure 5.
  • the crystallographic orientation and thick- ness of the quartz crystal plate are selected to obtain the necessary resonance mode and frequency.
  • a single fluid-filled cavity 11 of the sensor device 1 of the present invention can be changed to a set of fluid-filled cavities 11.
  • the design is determined by wide possibilities for optimizing characteristics, in particular for the fluids under study.
  • the sensor device 1 is supplemented with measuring means 2 for measuring at least two electrical responses selected from the group consisting of resonant frequencies, crystal damping, admittance, impedance, and reflection. Those measuring means 2 can be extended by means for thermostating and for measuring a temperature of a fluid.
  • the quartz crystal acts as electromechanical transducer. It excites acoustic waves propagating towards the intermediate acoustic artificial material layer 12 and de- tects the acoustic load generated by the intermediate acoustic artificial material layer 12 crystal and the at least one fluid-filled cavity 11.
  • the piezoelectric transducer preferably designed as a plate, can have two large electrodes 100 on both sides of the plate or a set of electrodes 100 that are arranged in the form of a two-dimensional matrix. On the common electrode 100 is ground and on the second electrode 100 (or a set of electrodes 100) the periodic potential is applied.
  • Figures 2 and 3 show two possible examples of the functional part of the sensor device 1 according to the present invention. Those examples do not restrict the sensor device 1 of the present invention to any design.
  • FIG 2 shows the example wherein the piezoelectric transducer 10 based on a quartz crystal operates in a thickness shear mode. Further in this figure it is shown that fluidic channels 110 are arranged as a set of fluid-filled cavities 11. Those flu- idic channels 110 are directed perpendicularly to the plane of propagating of shear waves (Fig. 2B, 2C). Figures 2B and 2C represent displacement (in solid) and pressure (in liquid) distribution. Standing waves of pressure in liquid in the channel, are excited by the act of the quartz crystal transducer 10. In Figures 2B and 2C, standing waves in the liquid-filled cavity are excited due to the reflection ofwaves from the walls of the channels.
  • Using a set of fluid (liquid)-filled cavities 11 increases the quality factor of the liquid resonances and increases the sensitivity to the change in the speed of sound in analyte.
  • the fluid-filled cavities 11 can be directed parallel to the plane of propagating of shear waves. In this case standing waves are excited due to the periodic system of elements applied along the channel and forming a tubular phonon ic crystal.
  • Figure 3 shows the example of the sensor device 1 , wherein the piezoelectric transducer based on a quartz crystal operates in an extensional mode.
  • the fluid is in fluid-filled cavity 11 formed as a slit.
  • Standing pressure waves in the fluid-filled cavity 11 form in the direction perpen- dicular to the plane of the piezoelectric transducer 10, which is designed as a plate in this example.
  • Figure 4A shows schematically the possible variations of the shape of a single flu- id-filled cavity 11 or its arrangement for example for the structure type of the sen- sor device 1 according to the present invention as shown in figure 2A.
  • the shape can be either rectangular (top row), round (second row from the top) or triangular (second row from the bottom).
  • the fluid in the fluid-filled cavity 11 can be isolated from all sides of a solid body of either of the described shapes. Further the fluid- filled cavity 11 can also have a free surface at the top (bottom row).
  • the most significant aspect of the fluid-filled cavities 11 for the present invention is their frequency response as shown in figure 4b.
  • a res- onant peak shifts (depicted as V1 and V2) with a change in the speed of sound (V) in the fluid.
  • Figure 5 shows possible variations of structure of the intermediate acoustic artifi- cial material layer 12.
  • Those variations can be selected from an arrangement of rods or voids of rectangular (top row), cylindrical (second row from the top) or tri angular (third row from the top row) shape; a composite or a porous material (third row from the bottom); a multilayer structure (second row from the bottom) or a set of mechanical supports (bottom row). It can be made from various materials like a phononic crystal or an acoustic metamaterial or an irregular acoustic system, a composite or a porous material.
  • the phononic structure of the intermediate acous- tic artificial material layer 12 can be constructed as one-, two- or three-dimensional structure.
  • the most significant aspect of the intermediate acoustic artificial material layer 12 for the sensor device (not shown) according to the present invention is its functional purpose of weak mechanical coupling.
  • Figure 6 shows two graphics describing frequency dependence of admittance of the sensor device (not shown) of the present invention: its magnitude (Figure 6A) and phase (Figure 6B) frequency dependencies in the case of 5 MFIz fitted quartz resonator of the piezoelectric transducer (not shown).
  • Figure 6A magnitude
  • Figure 6B phase
  • the dotted curve shows how the frequency dependence of admittance of unloaded QCM (without intermediate acoustic artificial material layer and a fluid- filled cavity) should be.
  • the first peak is a resonance of the sensor device according to the invention (loaded quartz) and its vibrational mode is shown in figures 2B and 3B. But it should be noted that the frequency shift of the sensor device of the present inven- tion does not satisfy equation (1 ). This is due to the fact that the sensor device of the present invention comprises an intermediate acoustic artificial material layer. The piezoelectric transducer of the sensor device of the present invention behaves as if it is loaded with a smaller mass than it actually is. This fact demonstrates the first fundamental difference between the sensor device according to the present invention and known sensors based on QCM.
  • the second peak in figure 6A is liq uid resonance in the structure of the sensor device of the present invention, whose frequency depends on the speed of sound in liquid. Its vibrational mode is shown in figure 2C and figure 3C.
  • the piezoelectric transducer and at least one fluid-filled cavity of the sensor device according to the present invention can also be fitted to other frequencies.
  • the position of peaks on the graph on figure 6 will be in other frequency range.
  • the behaviour of the curves will be the same.
  • Figure 7 shows two graphics describing the frequency dependence of mechanical response on the surface of the piezoelectric transducer (designed as quartz plate with electrodes) of the sensor device according to the invention, when a sinusoidal electric field is applied to the electrodes.
  • Figure 8 shows a graphic describing a typical dependence of characteristic fre- quencies of the sensor device according of the present invention consisting of weakly coupled resonators, such as a piezoelectric transducer loaded by solid- fluid structure (intermediate acoustic artificial material layer and at least one fluid- filled cavity) on the speed of sound in liquid.
  • the graphs show the positions of the two maxima and minima corresponding to the graphic in figure 7.
  • the graph shows a linear dependence of the frequency on the speed of sound.
  • D ⁇ ki k2Av (4)
  • ki is a constant depending on the material properties and thegeometry of the at least one fluid-filled cavity
  • k2 is a constant depending on the properties of intermediate acoustic artificial ma- terial layer.
  • Figure 9 shows two graphics describing the example of characteristics of the sen- sor device of the present invention, calculated for the case wherein resonant fre- quency of quartz crystal of the piezoelectric transducer is 5th harmonic frequency and the resonant frequency of at least one fluid-filled cavity is 1 st harmonic fre- quency.
  • the operating frequency range of the sensor device according of the present invention can be near the fundamental frequency of quartz oscillator or near har- monic frequencies.
  • the choice of operating frequency range is determined primari- ly by the desired size of fluid-filled cavity. The smaller the size, the higher the fre- quency.
  • resonator based QCM platform enables the efficient readout of fluid- solid structures sensing modes at the resonance conditions of the quartz resonator that leads to significant improve of the sensor response.
  • the present invention is associated with challenges related to the appearance of couple resonances and as a result broadening of spectral properties and loss of sensitivity.
  • inter- mediate acoustic artificial material layer with artificial elastic properties that allows to tune the coupling between the resonating part of sensor device according to the present invention in a predefined manner, was introduced.
  • the result of the struc- ture coupling is the achievement of structure readout in a form of narrow-band resonance that is sensitive to the variation of material properties of fluids.

Abstract

The present invention relates to a sensor device for detecting volumetric properties of fluids and a method for detecting volumetric properties of fluids using the sensor device. The sensor device comprises a quartz-crystal transducer, a fluid-filled cavity and an acoustic artificial material layer between the transducer and the cavity.

Description

Fluidic QCM-PnC sensor
The present invention relates to a sensor device for detecting volumetric proper- ties of fluids and a method for detecting volumetric properties of fluids using the sensor device.
Phononic Crystal (PnC) sensors are a new class of ultrasonic sensors that still require fundamental research. By contrast, Quartz Crystal Microbalance (QCM) sensors are in the meanwhile commercial sensors with a broad application range, including liquid sensors.
The principle of measurement by a QCM sensor device based on the change in the resonance frequency is denoted by equation (1 ) [Bunseki Kagaku; Develop- ment of piezoelectric bio-sensor and latex piezoelectric element immunoassay for clinical examination; Analytical Chemistry, Vol. 46, No. 12, 917 - 930 (1997)]:
Af = - K-f2-Am, (1 ) wherein the resonance frequency is denoted by f, a difference in the resonance frequency due to the mass attached is denoted by Af and a change in mass is de- noted by Am and wherein K is a constant depending on the area of an electrode, density, and an elastic constant of a material of the quartz crystal.
It is clear from equation (1 ) that, if the difference in the resonance frequencies of the quartz resonator can be measured before and after the attachment of the mass, it is possible to calculate the change in mass. Moreover, if a piezoelectric transducer having high resonance frequency is used, it is possible to increase the sensitivity of the mass detection.
US7036375B2 discloses that a plurality of quartz crystal resonators having different resonance frequencies are connected in parallel wherein a combined admittance of the resonators is measured for mass detecting.
When QCM is used in a liquid, the resonance frequency changes depending on the viscosity (h) and the density (p) of the liquid so that the viscosity and the densi- ty of the liquid can be determined from the resonance frequency. US 5798452 A discloses that combining smooth and textured QCM resonators in a monolithic sensor allows simultaneous measurement of liquid density and viscosi- ty. The frequency shifts that occur upon immersion of a smooth- (DT) and tex- tured-surface (Af2) device can be written as [J. Martin, K. 0. et al, Measuring liquid properties with smooth- and textured-surface resonators. Proceedings of the An- nual Frequency Control Symposium, 603-608 (1993)]:
D7i = - ci(pq)1/2; (2) f2 = - ci(pq)1/2 - C2hp (3) where ci and C2 are constants.
But this methods and devices do not allow to detect the velocity of sound in a fluid, which is the direct link to thermodynamic properties including molecular interac- tions within the (free) fluid.
The problem to be solved is to provide a sensor for characterizing fluids to obtain qualitative and quantitative information of the composition of fluid and thermody- namic properties including molecular interactions within the (free) fluid that firstly is based on measurements of velocity of sound in fluids and secondly save the ad- vantages of QCM approach.
The problem is solved, according to the present invention by providing a sensor device for detecting volumetric properties of fluids, comprising:
(a) a piezoelectric transducer based on a quartz crystal,
(b) at least one fluid-filled cavity, in which fluid resonances can be excited, and
(c) an intermediate acoustic artificial material layer that controls propagation of acoustic waves between the piezoelectric transducer and the at least one fluid- filled cavity.
Preferred is a sensor device according to the present invention, wherein the sen- sor device is further supplemented with measuring means for measuring at least two electrical responses. Further preferred is a sensor device according to the present invention, wherein the at least two electrical responses are selected from the group consisting of res- onant frequencies, crystal damping, admittance, impedance, and reflection.
Preferred is also a sensor device according to the present invention, wherein the piezoelectric transducer is a quartz crystal plate with at least two electrodes.
Further preferred is a sensor device according to the present invention, wherein the piezoelectric transducer provides a set of electrodes that are arranged in two- dimensions and connected in the form of a matrix.
Preferred is also a sensor device, wherein the intermediate acoustic artificial mate- rial layer is a phononic crystal, an acoustic metamaterial or is made of an irregular system of elements.
Especially preferred is a sensor device according to the present invention, wherein the finite structure of the phononic crystal, the finite structure of the acoustic met- amaterial or the structure of the irregular system of elements provides a reflection coefficient of acoustic waves in the range from 60 to 100 % within the operating frequencies of the sensor device.
Further preferred is a sensor device according to the present invention, wherein the sensor device is further supplemented with means for measuring and control- ling a temperature of the fluid in the at least one fluid-filled cavity.
Also preferred is a sensor device according to the present invention, wherein the sensor device comprises a set of fluid-filled cavities.
Another object of the present invention is a method for detecting volumetric prop- erties of fluids, comprising the steps of:
(a) providing a sensor device, according to the present invention,
(b) measuring a resonance frequency shift,
(c) determining the volumetric properties of the fluid.
Preferred is a method according to the present invention, wherein step (b) involves a comparison with calibrating media. The sensor device of the present invention measures volumetric properties of fluid analytes in a cavity instead of interfacial properties to some artificial sensor sur- face as the majority of classical chemical and biochemical sensors of the prior art. Furthermore, it is advantageous that influence of interfaces towards monitoring of (biochemical) reactions in free space are at least reduced. Furthermore, the sen- sor device of the present invention relates generally to measurement of volumetric properties of fluids on the basis of acoustic sensor principles.
The sensor device of the present invention takes advantage of the extremely high frequency resolution in the ppm-range of acoustic resonators. The achievable res- olution of the sensor device according to the present invention is comparable with scientific instruments only.
The piezoelectric transducer of the sensor device of the present invention excites acoustic waves propagating towards the intermediate acoustic artificial layer and detects the acoustic load generated by the intermediate acoustic artificial layer, especially in case of the phononic crystal, and the fluid-filled cavity. The origin of the sensor signal is a small frequency change caused by small variations of acoustic properties of the analyte within the fluid-filled cavity. The new capability of the sensor device of the present invention is the direct link to thermodynamic properties including molecular interactions within the (free) fluid.
Further, the resonant frequency of the quartz crystal on which the piezoelectric transducer of the sensor device of the present invention is based, is a fundamental frequency or harmonic frequency.
The quartz crystal of the piezoelectric transducer either operates in a thickness shear mode or in an extensional mode.
The sensor device of the present invention comprises at least one fluid-filled cavi- ty. Further it is also possible that the sensor device comprises a set of fluid-filled cavities which is advantage in order to increase the quality factor (Q) of the fluid resonances and the sensitivity to the change in the speed of sound in the analyte.
The third key element of the sensor device of the present invention is an acoustic artificial material layer that controls propagation of acoustic waves between the piezoelectric transducer and the at least one fluid-filled cavity due to its specific acoustic properties. The main purpose of inputting of this layer is the creation of conditions for weak mechanical coupling of two resonators, wherein the first reso- nator is a piezoelectric transducer and the second is at least one fluid-filled cavity. Thus, the intermediate acoustic artificial layer should have a high reflection coeffi- cient of acoustic waves in the range of 60 to 100 % in the operating range of the sensor frequencies. By changing the reflection coefficient of the intermediate acoustic artificial material layer, it is possible to control the degree of mechanical coupling between the resonators and adjust the sensitivity and resolution of the sensor device of the present invention.
The intermediate acoustic artificial material layer can be made from various artifi cial materials like a phononic crystal or an acoustic metamaterial or an irregular acoustic system, a composite or a porous material. The phononic structure can be constructed as one-, two- or three-dimensional structure. Despite the various pos- sible designs and materials, the most significant and common for the invention is its functional purpose of weak mechanical coupling.
Artificial materials designed to control, direct, and manipulate sound waves are called phononic crystals or acoustic metamaterials. Phononic crystals are synthet- ic materials that are formed by periodic variation of the acoustic properties of the material and their most important properties is the possibility of having a phononic bandgap. In contrast to phononic crystals, acoustic metamaterials exhibit spectral gaps two orders of magnitude smaller than the wavelength of sound. Acoustic properties of this artificial materials are defined not only by the material properties of the structure constituents, but by the design (geometry, symmetry, periodicity). A propagation through such structures of elastic waves is featured by the wave- length regions, within which sound cannot propagate through the structure
(bandgap). Therefore, almost complete reflection or scattering of incident acoustic waves occurs. For the frequencies corresponding to a bandgap region, the period- ic structure can be described in terms of high acoustic impedance for an incident acoustic wave. Thus, one of the most advantageous features of phononic struc- tures is the ability to be applied in those cases, where rather high acoustic imped- ance boundaries are required and application of standard materials (such as tung- sten) is limited. In fact, some irregular synthetic structures (porous systems, for example) may have frequency bands in which the propagation of acoustic waves is greatly weakened, so such artificial materials are also of interest for the present invention. Since among other parameters the acoustic properties of the composite arrange- ment depend on material properties of structure constituents, their variation caus- es a change in a structure transmission behaviour. That feature allows to apply solid-liquid periodic composite arrangements for liquid sensor purposes. A control of the frequency position of isolated narrow transmission bands is more beneficial rather than deviation of bandgap edges. For that reason, the phononic crystal based sensor device of the present invention is focused on the obtainment of the structure isolated transmission peaks (dips) that correspond to material properties of the fluid constituent. In contrast to well-developed microacoustic liquid sensors, the sensor device of the present invention enables the detection of the velocity of sound of fluid analyte. Similarly, to ultrasonic velocimetry sensor approach, the sensor device of the present invention allows to evaluate thermodynamic quanti- ties of the fluid analyte analysing the speed of sound at a certain range of pres- sures. The reaction on molecule interactions is reflected as a change in a fluid compressibility that can be detected by probing the analyte with ultrasonic veloci- metry methods. The sensor device of the present invention allows to keep the ad- vantages of velocimetry based methods and at the same time to apply the meas- urement principle based on a control of structure resonances similar to microa- coustic sensor devices.
The sensor device of the present invention might also be supplemented by meas- uring means for thermostating or for preventing contamination build up on said resonator surface.
The measurement of the resonance frequency shift of the method according to the present invention is associated with the resonance in at least one fluid-filled cavity, in the response of weakly coupled resonators of piezoelectric transducer loaded by intermediate acoustic artificial material layer and fluidic structure.
The determination of the volumetric properties of the fluid in the method according to the present invention is performed on the basis of a certain relationship between the speed of sound in fluid, the resonant frequency of at least one fluid-filled cavi- ty, and the geometry design of the at least one fluid-filled cavity.
The fluid used in the present invention can be a liquid as well as a gas.
The present invention is further described with the following figures, where Fig. 1 shows a schematic illustration of the principle structure of the sensor device according to the present invention,
Fig. 2 shows a schematic illustration of one possible example of the sensor device according to Fig. 1 ,
Fig. 3 shows a schematic illustration of a second possible example of the sensor device according to Fig. 1 ,
Fig. 4a shows possible variations of the shape of at least one single liquid-filled cavity of the sensor device according to the present invention,
Fig. 4b shows a principle graph of the dependence of the pressure resonance in the fluid-filled cavity of the sensor device according to the present invention on the sound velocity of the fluid,
Fig. 5 shows possible variations of structure of the intermediate acoustic artificial layer of the sensor device according to the present invention,
Fig. 6a shows a graphic describing a typical magnitude frequency dependence of admittance of the sensor device according to the present invention,
Fig. 6b shows a graphic describing a phase frequency dependence of admittance of the sensor device according to the present invention,
Fig. 7 shows a graphic describing a frequency dependence of mechanical re- sponse on the surface of the piezoelectric transducer of the sensor device accord- ing to the present invention,
Fig. 8 shows a graph describing a dependence of characteristic frequencies of the sensor device according to the present invention,
Fig. 9a shows a graph describing frequency dependencies of admittance on the surface of the piezoelectric transducer when a sinusoidal electric field is applied to the electrodes of the sensor device according to the present invention, and Fig. 9b shows a graph describing the mechanical response on the surface of the piezoelectric transducer when a sinusoidal electric field is applied to the electrodes of the sensor device according to the present invention.
Figure 1 depicts a general scheme of the sensor device 1 according to the inven- tion. These are the principle structures of the sensor device 1 , which are connect- ed to a measuring circuit consisting of measuring means 2. The measuring means comprise an electrical circuit 20, a signal generator 21 , thermocontrolling 22, sig nal processing 23 and data processing 24. The key elements of the sensor device 1 of the present invention are a piezoelectric transducer 10 which is based on a quartz crystal, an intermediate acoustic artificial material layer 12 and at least one fluid-filled cavity 11. Preferably the piezoelectric transducer 10 is designed as a plate that comprises electrodes 100. The intermediate acoustic artificial material layer 12 controls propagation of acoustic waves between the piezoelectric trans- ducer 10 and the at least one fluid-filled cavity 11. The geometry of at least one fluid-filled cavity 11 , intermediate acoustic artificial material layer 12, electrodes 100 can be different. The possible geometries that can be used for at least one fluid-filled cavity are shown in figure 4a and for the intermediate acoustic artificial material layer are shown in figure 5. The crystallographic orientation and thick- ness of the quartz crystal plate are selected to obtain the necessary resonance mode and frequency.
Further it is preferred that a single fluid-filled cavity 11 of the sensor device 1 of the present invention can be changed to a set of fluid-filled cavities 11. The design is determined by wide possibilities for optimizing characteristics, in particular for the fluids under study. The sensor device 1 is supplemented with measuring means 2 for measuring at least two electrical responses selected from the group consisting of resonant frequencies, crystal damping, admittance, impedance, and reflection. Those measuring means 2 can be extended by means for thermostating and for measuring a temperature of a fluid.
The quartz crystal acts as electromechanical transducer. It excites acoustic waves propagating towards the intermediate acoustic artificial material layer 12 and de- tects the acoustic load generated by the intermediate acoustic artificial material layer 12 crystal and the at least one fluid-filled cavity 11.
Further the piezoelectric transducer, preferably designed as a plate, can have two large electrodes 100 on both sides of the plate or a set of electrodes 100 that are arranged in the form of a two-dimensional matrix. On the common electrode 100 is ground and on the second electrode 100 (or a set of electrodes 100) the periodic potential is applied.
Figures 2 and 3 show two possible examples of the functional part of the sensor device 1 according to the present invention. Those examples do not restrict the sensor device 1 of the present invention to any design.
Figure 2 shows the example wherein the piezoelectric transducer 10 based on a quartz crystal operates in a thickness shear mode. Further in this figure it is shown that fluidic channels 110 are arranged as a set of fluid-filled cavities 11. Those flu- idic channels 110 are directed perpendicularly to the plane of propagating of shear waves (Fig. 2B, 2C). Figures 2B and 2C represent displacement (in solid) and pressure (in liquid) distribution. Standing waves of pressure in liquid in the channel, are excited by the act of the quartz crystal transducer 10. In Figures 2B and 2C, standing waves in the liquid-filled cavity are excited due to the reflection ofwaves from the walls of the channels. Using a set of fluid (liquid)-filled cavities 11 increases the quality factor of the liquid resonances and increases the sensitivity to the change in the speed of sound in analyte. In other possible designs the fluid-filled cavities 11 can be directed parallel to the plane of propagating of shear waves. In this case standing waves are excited due to the periodic system of elements applied along the channel and forming a tubular phonon ic crystal.
Figure 3 shows the example of the sensor device 1 , wherein the piezoelectric transducer based on a quartz crystal operates in an extensional mode.
The fluid is in fluid-filled cavity 11 formed as a slit. Standing pressure waves in the fluid-filled cavity 11 , as shown in figure 3B and 3C, form in the direction perpen- dicular to the plane of the piezoelectric transducer 10, which is designed as a plate in this example.
Figure 4A shows schematically the possible variations of the shape of a single flu- id-filled cavity 11 or its arrangement for example for the structure type of the sen- sor device 1 according to the present invention as shown in figure 2A. The shape can be either rectangular (top row), round (second row from the top) or triangular (second row from the bottom). The fluid in the fluid-filled cavity 11 can be isolated from all sides of a solid body of either of the described shapes. Further the fluid- filled cavity 11 can also have a free surface at the top (bottom row). Despite the various possible designs, the most significant aspect of the fluid-filled cavities 11 for the present invention is their frequency response as shown in figure 4b. A res- onant peak shifts (depicted as V1 and V2) with a change in the speed of sound (V) in the fluid.
Figure 5 shows possible variations of structure of the intermediate acoustic artifi- cial material layer 12. Those variations can be selected from an arrangement of rods or voids of rectangular (top row), cylindrical (second row from the top) or tri angular (third row from the top row) shape; a composite or a porous material (third row from the bottom); a multilayer structure (second row from the bottom) or a set of mechanical supports (bottom row). It can be made from various materials like a phononic crystal or an acoustic metamaterial or an irregular acoustic system, a composite or a porous material. The phononic structure of the intermediate acous- tic artificial material layer 12 can be constructed as one-, two- or three-dimensional structure. Despite the various possible designs and materials, the most significant aspect of the intermediate acoustic artificial material layer 12 for the sensor device (not shown) according to the present invention is its functional purpose of weak mechanical coupling.
Figure 6 shows two graphics describing frequency dependence of admittance of the sensor device (not shown) of the present invention: its magnitude (Figure 6A) and phase (Figure 6B) frequency dependencies in the case of 5 MFIz fitted quartz resonator of the piezoelectric transducer (not shown). In both figures, three curves are shown. The dotted curve shows how the frequency dependence of admittance of unloaded QCM (without intermediate acoustic artificial material layer and a fluid- filled cavity) should be. The other two curves show the response of the sensor de- vice according to the present invention for different values (Vs=1485 m/s and Vs=1490 m/s) of speed of sound in liquid.
This graphic represents typical characteristics in particular for the designs of the sensor device according to the present invention as shown in figures 2 and 3 but also for other design, which are not exemplary shown. Those graphs clearly demonstrate the joint work of two weakly coupled resonators. The first resonator is the piezoelectric transducer. The second resonator is at least one fluid-filled cavity. Their joint work results in two peaks on the frequency dependence (Figure 6A).
The first peak is a resonance of the sensor device according to the invention (loaded quartz) and its vibrational mode is shown in figures 2B and 3B. But it should be noted that the frequency shift of the sensor device of the present inven- tion does not satisfy equation (1 ). This is due to the fact that the sensor device of the present invention comprises an intermediate acoustic artificial material layer. The piezoelectric transducer of the sensor device of the present invention behaves as if it is loaded with a smaller mass than it actually is. This fact demonstrates the first fundamental difference between the sensor device according to the present invention and known sensors based on QCM. The second peak in figure 6A is liq uid resonance in the structure of the sensor device of the present invention, whose frequency depends on the speed of sound in liquid. Its vibrational mode is shown in figure 2C and figure 3C.
The piezoelectric transducer and at least one fluid-filled cavity of the sensor device according to the present invention can also be fitted to other frequencies. In this case the position of peaks on the graph on figure 6 will be in other frequency range. However, the behaviour of the curves will be the same.
Figure 7 shows two graphics describing the frequency dependence of mechanical response on the surface of the piezoelectric transducer (designed as quartz plate with electrodes) of the sensor device according to the invention, when a sinusoidal electric field is applied to the electrodes.
Figure 8 shows a graphic describing a typical dependence of characteristic fre- quencies of the sensor device according of the present invention consisting of weakly coupled resonators, such as a piezoelectric transducer loaded by solid- fluid structure (intermediate acoustic artificial material layer and at least one fluid- filled cavity) on the speed of sound in liquid. The graphs show the positions of the two maxima and minima corresponding to the graphic in figure 7. The graph shows a linear dependence of the frequency on the speed of sound.
The corresponding equation for the shift of the resonance frequency (Af) from the change in the speed of sound in liquid (Dn) is:
Dί = ki k2Av (4) where ki is a constant depending on the material properties and thegeometry of the at least one fluid-filled cavity; k2 is a constant depending on the properties of intermediate acoustic artificial ma- terial layer.
Thus, applying phononic crystal concepts in the construction of an intermediate layer and a fluid-filled cavity into the sensor device of the present invention in- creases the values of ki and k2, which increases the sensitivity and resolution of the sensor device of the present invention.
Figure 9 shows two graphics describing the example of characteristics of the sen- sor device of the present invention, calculated for the case wherein resonant fre- quency of quartz crystal of the piezoelectric transducer is 5th harmonic frequency and the resonant frequency of at least one fluid-filled cavity is 1 st harmonic fre- quency.
Thus, the operating frequency range of the sensor device according of the present invention can be near the fundamental frequency of quartz oscillator or near har- monic frequencies. The choice of operating frequency range is determined primari- ly by the desired size of fluid-filled cavity. The smaller the size, the higher the fre- quency.
Application of resonator based QCM platform enables the efficient readout of fluid- solid structures sensing modes at the resonance conditions of the quartz resonator that leads to significant improve of the sensor response. The present invention is associated with challenges related to the appearance of couple resonances and as a result broadening of spectral properties and loss of sensitivity. In order to de- couple the resonances of the QCM structure and fluid-filled cavity modes, inter- mediate acoustic artificial material layer with artificial elastic properties that allows to tune the coupling between the resonating part of sensor device according to the present invention in a predefined manner, was introduced. The result of the struc- ture coupling is the achievement of structure readout in a form of narrow-band resonance that is sensitive to the variation of material properties of fluids.

Claims

Claims
1. A sensor device (1 ) for detecting volumetric properties of fluids, comprising:
(a) a piezoelectric transducer (10) based on a quartz crystal,
(b) at least one fluid-filled cavity (11 ), in which fluid resonances can be excited, and
(c) an intermediate acoustic artificial material layer (12) that controls propaga- tion of acoustic waves between the piezoelectric transducer (10) and the at least one fluid-filled cavity (11 ).
2. The sensor device (1 ) according to claim 1 , wherein the sensor device (1 ) is further supplemented with measuring means (2) for measuring at least two electrical responses.
3. The sensor device (1 ) according to claim 2, wherein the at least two electrical responses are selected from the group consisting of resonant frequencies, crystal damping, admittance, impedance, and reflection.
4. The sensor device (1 ) according to at least one of the claims 1 to 3, wherein the piezoelectric transducer (10) is a quartz crystal plate with at least two elec- trodes (100).
5. The sensor device (1 ) according to at least one of the claims 1 to 4, wherein the piezoelectric transducer (10) provides a set of electrodes (100) that are ar- ranged in two-dimensions and connected in the form of a matrix.
6. The sensor device (1 ) according to at least one of the claims 1 to 5, wherein the intermediate acoustic artificial material layer (12) is a phononic crystal, an acoustic metamaterial or is made of an irregular system of elements.
7. The sensor device (1 ) according to claim 6, wherein the finite structure of the phononic crystal, the finite structure of the acoustic metamaterial or the struc- ture of the irregular system of elements provides a reflection coefficient of acoustic waves in the range from 60 to 100 % within the operating frequencies of the sensor device (1 ).
8. The sensor device (1 ) according to claim 6 or 7, wherein the intermediate acoustic artificial material layer (12) is a phononic crystal.
9. The sensor device (1 ) according to at least one of the claims 1 to 8, wherein the sensor device (1 ) is further supplemented with means for measuring and controlling a temperature of the fluid in the at least one fluid-filled cavity (11 ).
10. The sensor device (1 ) according to at least one of the claims 1 to 9, wherein the sensor device comprises a set of fluid-filled cavities (11 ).
11. The sensor device (1 ) according to at least one of the claims 1 to 10, wherein the fluid is a liquid.
12. A method for detecting volumetric properties of fluids, comprising the steps of:
(a) providing a sensor device, according to at least one of the claims 1 to 11 ,
(b) measuring a resonance frequency shift,
(c) determining the volumetric properties of the fluid.
13. The method according to claim 12, wherein step (b) involves a comparison with calibrating media.
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