DE102019104093B3 - Ultrasonic transducer with improved sensitivity and sound radiation - Google Patents

Abstract

The invention relates to an ultrasound transducer for emitting and receiving sound waves in a fluid (HO) with a piezoelectric sound transducer element (PZT) and with a first sound wave optical functional element (PEI, 92). The piezoelectric sound transducer element (PZT) is designed and intended to be operated at a first resonance frequency (f) of its resonance frequencies. The sound wave optical functional element (200) is placed between the sound transducer element (PZT) and fluid (HO). The sound wave optical functional element (200) is made from the material (31) of the housing.

Description

Generic term

The invention is directed to an ultrasonic transducer for emitting and receiving sound waves in a fluid.

General introduction

The ultrasound measurement is based on the speed of sound. Sound can be used as a measuring device because there is a measurable time interval between sound generation and sound reception. This period of time and the time-dependent damping that occurs can be converted into usable information. Ultrasonic transmitters generate a sound signal with a sound frequency above 20 KHz and ultrasonic receivers receive the returning echo signal and convert it into a respective received signal. Signal processors then interpret the time course of the returning echo in the form of the time course of these received signals. It is preferable to use a combined sound transducer, which is spatially separated in space multiplex and an ultrasound receiver, and which works in different time periods as an ultrasound transmitter and another time as an ultrasound receiver in time multiplex. When speaking of a sound transducer in this text, the combination of ultrasonic transmitter and ultrasonic receiver is therefore always included. The sound transducer now generates such a sound signal and detects the returning echo. This is received by the sound transducer and converted into an information-bearing electrical signal, the received signal, which enables intelligent processing of the echo profiles, for example by an analysis circuit and / or a signal processor.

The typical transducer system for ultrasound level measurement requires some components. One is the sound transducer, which generates the ultrasound signal and receives the echo, another component is a reception circuit or the signal processor, which determines the data from the electrical reception signal and derives a measurement result. Although ultrasound devices combine the components in one unit, the individual functionality remains different. The measurement outputs generally communicate with a programmable logic controller for process control.

The typical operating principle is that a piezoelectric crystal is used as the piezoelectric transducer element ( PZT ) inside the sound transducer converts an electrical feature of an electrical signal, typically the signal voltage, into sound energy when a mechanical wave is transmitted into the measuring medium, the sound wave propagates in the measuring medium and is then reflected back to the sound transducer. The sound transducer then acts as a receiving device and converts the sound energy returning as an echo back into a received signal. An electronic signal processor or other suitable receiving circuitry analyzes the return echo contained in the received signal of the transducer and calculates the distance between the transducer and the target that caused the echo. The time period between the triggering of the sound impulse and the reception of the return echo is directly proportional to the distance between the sound transducer and the echo-causing inhomogeneities of the sound wave resistance in the measuring room, for example in a container whose level is to be determined. This basic principle is at the heart of ultrasonic measurement technology and is illustrated in the equation: $$\text{distance}=\left[\left(\text{Speed of sound}\right)\times \left(\text{Flight time}\right)\right]/\mathrm{2nd}$$

The aim here is to disclose an ultrasonic transducer that can measure the fluid level, flow rate and oil quality in the automotive environment. The goal is a cost-effective converter for the flow measurement and level sensor market.

A transducer is disclosed which, for a low price and with low quality demands on the piezo oscillator, is used as a piezoelectric sound transducer element ( PZT ) can be sold to enable the duration of the direct pulse detection. The result is a high-performance ultrasound transducer. The disclosed high performance ultrasonic transducer enables time-of-flight measurement techniques to be used to measure liquid levels, flow rate and identify the oil mixture or quality. Suitable available evaluation circuits are, for example, the integrated Elmos switching circuits E703.15 and E703.25. They have picosecond time-of-flight resolution and great potential in automotive, industrial and medical applications. However, the ultrasound transducers on the market are either of poor quality or too expensive for these applications. Therefore, a new ultrasonic transducer design will be proposed here, which enables the cost-effective mass production of ultrasonic transducers at a frequency of 2 MHz.

From the DE 20 2004 002 107 U1 is known an ultrasonic transducer for emitting and receiving sound waves in a fluid, with a piezoelectric sound transducer element and a first acoustic matching layer. The piezoelectric sound transducer element is designed and provided to operate at a first resonance frequency ( fr ) its resonance frequencies to be operated. The first matching layer is placed between the transducer element and the fluid. The layer thickness ( d ₂ ) of the first matching layer deviates from the quarter wavelength of the wavelength of the sound at the first resonance frequency ( for _r ) of the piezoelectric sound transducer element in the first matching layer preferably only insignificantly. This principle can be applied to liquids.

A device with similar features is known from the DE 25 41 492 B2 known.

A method for the electrical contacting of an acoustic transducer is known from US 2002/0 114 217 A1.

From the EP 1 769 854 A1 is the shape of an acoustic lens (reference number 3 of the EP 1 769 854 A1 ) known that modifies sound propagation and sound radiation. The in the figures of the EP 1 769 854 A1 disclosed assembly technology is relatively complicated. However, there is a need for a better encapsulated housing that ensures that no moisture or possibly corrosive liquid can enter the housing. This is the case with a housing according to the technical teaching of EP 1 769 854 A1 not ensured.

Also from the DE 198 33 213 A1 the formation of a lens is known as an acousto-optical functional element. The same disadvantages apply here as with the technical teaching of EP 1 769 854 A1 .

For example, the encapsulation of electronic components with mold compound is known from US 2017/0 018 700 A1.

More information about ultrasonic transducers can be found at www.wikipedia.de

task

A design for an inexpensive sound transducer for a flow meter and / or a level sensor is to be specified.

This object is achieved by a device according to claim 1 and a method according to claim 6.

Solution of the task

The basic idea is to manufacture the ultrasonic sensor using a manufacturing process based on PEI plastic injection molding. Here is the abbreviation PEI for polyetherimides (abbreviation PEI ). They are polyimides and are polymers with imide and ether groups in the main chains. They are resistant to high temperatures, transparent and typically have a golden yellow color. Dyes and additives can modify the properties.

The polyetherimide is processed here by injection molding. Depending on the type, the processing temperature is between 320 and 400 ° C, the tool temperature between 120 and 180 ° C. The granulate must be dried to a maximum moisture content of 0.05% before processing. The components according to the invention PEI can be welded, for example, by induction, vibration or ultrasound, or glued, for example, with epoxy, polyurethane or silicone adhesive.

Another basic idea of the invention is a λ / 4 Adaptation layer for adapting the acoustic wave resistance of the piezoelectric sound transducer element ( PZT ) to the liquid medium to be measured and to do this using the PEI plastic material used for the housing. The consequently improved sound coupling and decoupling maximizes the radiated sound power and the sensitivity of the ultrasound transducer. Ultimately, the basic idea of the invention is to modify the acoustic reception and transmission properties through the use of wave-optical functional elements, which are made from the PEI housing material of an electromechanical device as part of the housing process of the electromechanical device.

Digital optics, such as, for example, lenses, Fresnel lenses, phononic crystals, etc., are suitable as acoustic wave-optical functional elements.

The invention is explained below with reference to the figures.

The invention based on the Elmos E703.15 / E703.25 integrates flow and temperature measurement units with a fully equipped 16-bit microcontroller. All analog input circuits are also integrated in the Elmos E703.15 / E703.25. The flow measurement is based on the time of flight principle already described above. A time-to-digital converter, English time-to-digital converter ( TDC ), measures the runtime in upward and downward direction with picosecond accuracy. An integrated in the Elmos E703.15 / E703.25 Receive amplifier uses pulse shaping to minimize jitter. The integrated 16-bit microcontroller processes the raw flow and temperature measurement data for the respective measurement result. A software library in a read-only memory (ROM) integrated in the Elmos E703.15 / E703.25 enables the 16-bit microcontroller to determine and transfer immediately usable measurement results.

Figure 1

For the following explanations, we assume that the piezoelectric sound transducer element ( PZT ) a rectangular shape with a height a in the z direction, a width b in the x direction and a depth c in the y direction. The height a be less than the width b and the depth c . With a suitable crystal alignment, two oscillation modes are possible if an AC voltage is applied to the crystal along the z-axis. Exemplary piezoelectric sound transducer elements (also called piezoelectric vibrating elements) have a height a of, for example, 1mm, an exemplary width b of 7mm and an exemplary depth c of 5mm.

Figure 1a

1a shows a first vibration mode referred to here as transverse mode.

Figure 1b

1b shows a second mode of vibration referred to here as the longitudinal mode.

In the course of the elaboration of the invention it was recognized that the transverse mode has some advantages if the piezoelectric sound transducer element ( PZT ) should interact directly with the fluid to be measured even without a detour via a vibrated membrane or the like.

The first thing to mention here is the enlarged surface, which makes the use of a membrane superfluous.

Secondly, the strength and the width of the transverse resonance in transverse mode are to be mentioned, which in 2nd is outlined in dashed lines and marked with an arrow. The large width enables on the one hand the emission of more complex transmission signals for better analysis of the reflecting objects and on the other hand the reception of shorter ultrasound bursts and thus an improved resolution.

MANUFACTURING PROCESS

The construction of the proposed ultrasonic transducer according to the invention will become clearer from a description of the manufacturing process.

Figure 3

In a first step ( 100 ) a so-called lead frame is made from a copper sheet or another suitable material by means of a stamping or etching process or another suitable process ( 1 ) manufactured. 3rd shows a first exemplary leadframe ( 1 ) for an exemplary ultrasonic sensor according to the invention. The leadframe ( 1 ) has a first connection leg ( 2nd ) and a second connection leg ( 3rd ), which enable later push-through installation when using the exemplary ultrasonic sensor in a printed circuit (PCB). Other assembly techniques, such as SMD techniques are of course also possible and are covered by the stress. The push-through installation is only an example. Both the first leg ( 2nd ) as well as the second connection leg ( 3rd ) each have a thickening point ( 15 ), which prevents the exemplary ultrasonic sensor according to the invention from sinking deeper into the holes in the printed circuit after assembly and before soldering in later manufacture when using the ultrasonic sensor according to the invention. At this point, the first leg ( 2nd ) and the second connection leg ( 3rd ) by a footbridge ( 5 ) mechanically connected to each other, which in a later process step is cut ( 30th ) is again electrically and mechanically separated. The second connection leg ( 3rd ) ends in a connection plate ( 4th ). The first leg ( 2nd ) goes into a rectangular mechanical holding frame, the outer frame ( 6 ), above which the actual vibrating element holder ( 7 , 8th , 9 ) framed. The vibrating element holder ( 7 , 8th , 9 ) comprises a first web as the first spring element ( 7 ) and a first web as a second spring element ( 8th ) and an inner frame ( 9 ) opposite the outer frame ( 6 ) by the first spring element ( 7 ) and the second spring element ( 8th ) is suspended within certain limits. One only through the first spring element ( 7 ) and the second spring element ( 8th ) interrupted circumferential gap ( 13 ) separates the inner frame ( 9 ) from the outer frame ( 6 ). The inner frame ( 9 ) has a key breakthrough ( 14 ) on. The exemplary lead frame ( 1 ) the 3rd also has a mounting plate ( 10th ) as an assembly aid, which is connected to the outer frame ( 6 ) connected is. The mounting plate ( 10th ) is in the example of a lead frame ( 1 ) with a mounting hole ( 11 ) for a screw. Notches ( 12 ) stop the mass added later in subsequent process steps.

Figure 4

4th shows the exemplary lead frame of 3rd as an exemplary dimensioned construction drawing.

Figure 5

Another process step relates to a first injection molding step. The copper substructure in the form of the lead frame ( 1 ) with its substructures with PEI plastic mass ( 31 ) molded and at least partially covered. In the example of the 5 become the first spring element ( 7 ) with a first plastic block ( 32 ) made of PEI plastic mass (31) and the second spring element ( 8th ) with a second plastic block ( 33 ) made of PEI plastic (31). In the example of the 5 the outer frame ( 6 ) initially only in the lower part through the first plastic block ( 32 ) dresses. The inner frame ( 9 ) is not with plastic mass ( 31 ) covered and remains for the assembly of the piezoelectric transducer element ( PZT ) free. The opening ( 14 ) inside the inner frame ( 6 ) is, however, with PEI plastic mass ( 31 ) filled during this injection molding process. The surface of this plastic mass ( 35 ) forms with the surface of the inner frame ( 6 ) preferably a plane that the mounting surface for the piezoelectric sound transducer element to be assembled later ( PZT ) represents. In this exemplary extrusion coating with PEI plastic compound ( 31 ) an additional frame ( 34 ) made of the outer frame ( 6 ) further mechanically stabilized. The mounting hole ( 11 ) remains free to enable the later use of a screw. The construction of the PEI plastic mass ( 31 ) preferably has a first thickness ( d ₁ ). Note the assembly channel ( 36 ) through which the electrical wire connection from the connection plate ( 4th ) to the top of the piezoelectric transducer element ( PZT ) is pulled.

In addition to the process step of overmolding with PEI plastic, the so-called "Trim &Form" process is carried out in a further process step, which can be combined with the process step of overmolding in a tool, where 5 ) the 3rd through a cut ( 30th ) is separated electrically and mechanically.

Figure 6

6 shows the semi-finished product 5 with exemplary dimensions.

Figure 7

7 shows the semi-finished product 5 the piezoelectric sound transducer element ( PZT ) by means of a vibration element assembly step on the assembly surface consisting of the surface of the inner frame ( 6 ) and the surface of the PEI filling ( 35 ) is mounted. This assembly can take place, for example, by means of adhesive, preferably using an electrically conductive adhesive. In this exemplary form of assembly of the electrically conductive adhesive, this provides the electrical rear contact between the underside of the piezoelectric sound transducer element ( PZT ) and the inner frame ( 6 ), which in turn with the first connection leg ( 2nd ) via the corresponding segment of the lead frame ( 1 ) is electrically and mechanically connected.

Figure 8

8th equals to 7 after a bond joining step. In this the top of the piezoelectric transducer element ( PZT ) by means of a wire ( 80 ), which is preferably a bond wire typically made of gold, through the wiring channel ( 36 ) with the connection surface ( 4th ) electrically connected. This in turn is connected to the second connection leg ( 3rd ) via the corresponding segment of the lead frame ( 1 ) electrically and mechanically connected. The piezoelectric sound transducer element ( PZT ) first over the first connection leg ( 2nd ) electrically contacted on the back and via the second connection leg ( 3rd ) electrically contacted on its front and mechanically on the inner frame by means of said exemplary adhesive ( 6 ) and the PEI filling ( 35 ), which completes its installation and connection.

Figure 9

In the next process step, the semi-finished product is made in a second injection molding process step 8th with a second amount of PEI plastic material ( 90 ) envelops. The PEI plastic material ( 90 ) this second injection molding step does not necessarily have to be the same as the material of the first injection molding step. For example, it may differ in its fillers and its composition and chemical structure. In the example of the 9 cover the top with a second layer thickness ( d ₂ ) on PEI plastic material ( 92 ) covered as the first matching layer and the back with a third layer thickness ( d ₃ ) at PEI - plastic material as a second matching layer ( 93 ) covered. We assume that the surface of the piezoelectric transducer element ( PZT ) with the surface of the plastic frame ( 34 ) is in alignment, which is not necessarily the case. For the purposes of this disclosure, the second layer thickness ( d ₂ ) the layer thickness of the PEI material ( 92 ) on the surface of the piezoelectric transducer element ( PZT ) is applied. For the purposes of this disclosure, the third layer thickness ( d ₃ ) the layer thickness of the PEI material ( 93 ) that on the bottom of the leadframe ( 1 ) is applied. The mounting hole ( 11 ) remains free for fastening with a screw.

It is now important that it has been recognized that the second layer thickness ( d ₂ ) for the acoustic coupling between the medium to be measured (e.g. water) and the piezoelectric transducer element ( PZT ) is critical and preferred λ _PEI / 4 should be, where λ _PEI the wavelength of the sound in the first matching layer ( 92 ) at the resonance frequency for _r the piezoelectric transducer element ( PZT ) is in landscape mode in the construction described above. In order to be able to set this thickness well and, on the other hand, good mechanical stability of the attachment of the first connection leg ( 2nd ) and the second connection leg ( 3rd ) the areas of mechanical attachment of the first connection leg ( 2nd ) and the second connection leg ( 3rd ) made thicker than the areas that should emit the ultrasound. Therefore, the exemplary ultrasonic transducer has 9 a step ( 91 ) on its top, which is the second layer thickness ( d ₂ ) in the area of sound radiation, that is the area above the surface of the piezoelectric sound transducer element ( PZT ), to the particularly preferred value of λ _PEP / 4 reduced.

Figure 10

10th shows an isometric, not to scale, simplified drawing of the device 9 .

Figure 11

11 summarizes the manufacturing process again in a simplified manner in the essential steps. The process begins with the deployment ( 100 ) of the leadframe ( 1 ) and its structuring, for example by punching and / or etching. Another coating is preferably carried out ( 101 ) surfaces of the leadframe to be wetted with epoxy resin, whereby electrical contact surfaces must be left out. Possibly. the surface is further refined, for example by gold plating etc. The first injection molding step is then preferably carried out ( 102 ) that is related to the semi - finished product of 5 leads. The assembly takes place ( 103 ) and the electrical connection of the piezoelectric sound transducer element ( PZT ) in the semi-finished product of 5 , for example by gluing and bonding, resulting in the semi-finished product 8th leads. With the second injection molding step ( 104 ) the housing of the sound transducer according to the invention is completed. The second layer thickness is ( d ₂ ) above the surface of the piezoelectric transducer element ( PZT ) within the ultrasonic transducer preferably only a quarter of the sound wavelength ( λ _PEI / 4 ) in the PEI material ( 92 ).

Figure 12

12 shows a further exemplary device according to the invention. The third layer thickness ( d ₃ ) chosen so that the adjustment is particularly bad in contrast to the other side. This leads to a directivity in the radiation of the ultrasound waves and in the reception of the ultrasound waves, the side with the second layer thickness ( d ₂ ) is preferred due to the better acoustic impedance matching. Since the side of the device with the third layer thickness ( d ₃ ) also the leadframe ( 1 ) and thus a disturbance of the homogeneity of this layer, the second matching layer ( 93 ), the optimal third layer thickness must be obtained by simulation and / or a DOE (DOE = Design of Experiment = experimental series of experiments) ( d ₃ ) depending on the type, etc.

Figure 13

13 illustrates the basic principle again. The applied AC voltage in the piezoelectric sound transducer element ( PZT ) generates an acoustic wave. This is reflected at the interfaces. In order to achieve maximum energy in the medium to be measured, here, for example, water ( H ₂ O ) the layer material acts ( PEI ) in the layer, the first adaptation layer ( 92 ), between the piezoelectric transducer element ( PZT ) and the medium to be measured ( H ₂ O ) as a shaft adapter that minimizes the joints and reflections.

The reduction in the degree of reflection on the surface of the piezoelectric oscillating element coated by the PEI material is achieved by destructive interference of the reflected acoustic waves.

Of course, it is conceivable to use more than one layer. To simplify matters, only one layer ( 92 ) a second layer thickness ( d ₂ ) went out.

For this exemplary simplest case of a single, homogeneous compensation layer ( 92 ), preferably made of PEI material, we consider an acoustic wave of any wavelength λ ₀ perpendicular to the surface of the piezoelectric transducer element ( PZT ) comes from the right. It is partially reflected at the interface between the surface of the coating layer in the form of the PEI layer and the water surface. In part, however, it passes through this first interface (PEI / H ₂ O) and is then at the next interface between the PIE material ( PEI , 92 ) and the material of the piezoelectric transducer element ( PZT ) partially reflected. So that interfere completely destructively with both reflected partial waves and thus a complete transport of the acoustic wave energy from the liquid medium ( H ₂ O ) in the piezoelectric transducer element ( PZT ), the amplitudes of the reflected waves must be the same size (amplitude condition) and opposite in phase (phase difference π) to each other (phase condition).

Durch diese Bedingung wird die Amplitudengleichheit der beiden reflektierten Wellen sichergestellt. Hierbei steht n_PZT für den akustischen Brechungsindex des piezoelektrischen Schwingelements und n_H2O für den akustischen Brechungsindex des Fluids oder flüssigen Mediums, das zu vermessen ist.From the Fresnel formulas it follows that the acoustic refractive index n _{PEI of} the coating layer at the resonance frequency for _r , i.e. the PEI layer ( PEI , 92 ) can be calculated for: $$n_{PE\mathrm{I.}}=\sqrt{n_{PZT}\ast n_{H\mathrm{20th}}}$$

This condition ensures the amplitude equality of the two reflected waves. Here n _PZT stands for the acoustic refractive index of the piezoelectric vibrating element and n _H2O for the acoustic refractive index of the fluid or liquid medium that is to be measured.

$${\text{n}}_{\text{PEI}}={\text{c}}_0/{\text{c}}_{\text{PEI}};$$

$${\text{n}}_{\text{PZT}}={\text{c}}_0/{\text{c}}_{\text{PZT}};$$

Mehrfachreflektionen werden hier vernachlässigt.Incidentally, within the scope of this disclosure, we define the acoustic refractive index n of a substance as the ratio of the speed of sound c ₀ in a reference medium (e.g. synthetic air at 1 bar and 20 ° C) to the speed of sound in the medium in question ( C _H2O in H ₂ O ; c _PZT in the material of the piezoelectric acoustic transducer element ( PZT ); c _PEI in PEI plastic material). We find: $${\text{n}}_{\text{H2O}}={\text{c}}_0/{\text{c}}_{\text{H2O}};$$

$${\text{n}}_{\text{PEI}}={\text{c}}_0/{\text{c}}_{\text{PEI}};$$

$${\text{n}}_{\text{PZT}}={\text{c}}_0/{\text{c}}_{\text{PZT}};$$

Multiple reflections are neglected here.

The typically assumed speed of sound in air at 20 ° C is approx. 343.2 m / s (1236 km / h). The transverse formwork speed in quartz 3750 m / s. (We assume here that the piezoelectric vibrating element is made of quartz.) For the PEI material, we can assume about 2390m / s as the speed of sound.

Thus we find the relationship n _PZT <n _PEI <n _H2O . Because of this relationship, a phase shift of -π takes place at both boundary layers ([PZT / PEI], [PEI / H ₂ O]), which strictly corresponds to a reflection with a change of sign. However, this has no influence on the interference.

For the necessary phase difference of π, the acoustic path length Δ of the wave in the coating layer, i.e. the PEI layer ( 92 ) of the formula Δ = kλ / 2 with k = 1, 3, 5, ... are sufficient.

If one uses the thinnest possible layer (k = 1), the result is Δ = 2 * d ₂ * n _PEI for the optimal second layer thickness d ₂ the PEI layer ( PEI , 92 ) over the piezoelectric transducer element ( PZT ): $${\text{d}}_{\mathrm{2nd}}={\mathrm{\lambda }}_0/\left(\mathrm{4th}*{\text{n}}_{\text{PEI}}\right)$$

It is λ ₀ the wavelength in the reference medium at reference conditions.

For the wavelength in the PEI material λ _PEI we can specify: λ _PEI = c _PEI / f _r

If we assume an exemplary resonance frequency for _r for the piezoelectric transducer element ( PZT ) at f _r = 2.2MHz, we get with c _PEI = 2390m / s as wavelength λ _PEI in PEI material ( PEI , 92 ) λ _PEI = 1.086mm. This gives us the optimal second layer thickness ( d ₂ ) of the PEI layer ( 92 ) over the piezoelectric transducer element ( PZT ) d ₂ = λ _PEI / 4 = 271.5 µm.

Note that this optimization is only optimal for waves that are perpendicular to the surface of the piezoelectric transducer element ( PZT ) hit. The thickness must be adjusted accordingly for other angles.

If the beam does not hit the surface perpendicularly, but at an angle α, the acoustic path length in the PEI coating changes according to Snellius' law of refraction and outside with the same layer thickness due to the laterally offset exit, so that a higher optimal second Layer thickness d ₂ results or at a given second layer thickness d ₂ a shortening of the appropriate wavelength. This can be used to manipulate the spatial orientation of the ultrasound system by changing the frequency.

Deviating wavelengths are increasingly reflected or do not interfere completely destructively.

Figure 14

14 shows the principle of an acousto-optical function element using an adaptation layer with a modified acoustic refractive index ( n _{PEI '} ). The matching layer ( 200 ) is now exemplary on the side of the medium to be measured ( H ₂ O ) structured. They are grooves ( 201 ) intended. In the example of the 14 is the Width of the grooves constant and smaller than the wavelength λ _PEI in the material of the modified matching layer ( 200 ) and smaller than the wavelength λ _H2O in the material of the medium to be measured ( H ₂ O ). The width of the grooves is preferably constant and less than 10% of the wavelength λ _PEI in the material of the modified matching layer ( 200 ) and less than 10% of the wavelength λ _H2O in the material of the medium to be measured ( H ₂ O ) was chosen to keep the scattering effects small.

The depth of the undisturbed modified matching layer ( d2a ) and the total thickness of the modified matching layer ( d2b ) can then be chosen so that for the resonance frequency for _r the piezoelectric vibrating element ( PZT ) in the construction modified in this way, the phases and the amplitude condition can be fulfilled simultaneously. This results in an effective thickness ( d2 _eff ) the modified matching layer with an effective speed of sound ( c _PEIeff ) within this modified adaptation layer ( 200 ). Possibly. fillers in the PIE material of the modified matching layer ( 200 ) can be provided to further adjust the average speed of sound. In this way, not only the phase condition can be met, but both conditions can be met.

Figure 15

15 equals to 14 with the difference that the width of the grooves ( 201 ) is now spatially modulated and is typically chosen to be larger than the wavelength and / or larger than 10% of the wavelength. 15 is an example of digital acoustic wave optics.

Profiling modulates sound propagation through constructive and destructive interference. Instead of the parallel to the surface of the piezoelectric vibrating element ( PZT ) Drawn surfaces can also be tilted or curved. In this way, lenses and / or Fresnel lenses etc. can be produced.

Summary

The invention thus relates to an ultrasonic transducer for transmitting and receiving sound waves in a fluid ( H ₂ O ) with a piezoelectric transducer element ( PZT ) and a first acoustic matching layer ( PEI , 92 ). The piezoelectric transducer element ( PZT ) is designed and provided for at a first resonance frequency ( for _r ) its resonance frequencies to be operated. The first adjustment layer ( PEI , 92 ) is between the transducer element ( PZT ) and fluid ( H ₂ O ) placed. The layer thickness ( d ₂ ) the first matching layer ( PEI , 92 ) does not deviate more than +/- 25%, better not more than +/- 10%, better no more than +/- 5%, better no more than +/- 2%, better no more than +/- 1 % of the quarter wavelength ( λ _PEI / 4 ) the wavelength ( λ _PEI / 4 ) of the sound at the first resonance frequency ( for _r ) of the piezoelectric transducer element ( PZT ) in the first adjustment layer ( 92 ).

The ultrasonic transducer according to the invention preferably has a second matching layer ( 93 ) related to the piezoelectric transducer element ( PZT ) on the first matching layer ( PEI , 92 ) opposite side of the piezoelectric sound transducer element ( PZT ) lies. The layer thickness ( d ₃ ) the second matching layer ( 93 ) is then preferably designed such that the reception sensitivity of the ultrasound transducer in the direction of this second matching layer ( 93 ) from the piezoelectric transducer element ( PZT seen less than 50%, better less than 20%, better less than 10% of the reception sensitivity of the ultrasonic transducer in the direction of the first matching layer ( PEI , 93 ) from the piezoelectric transducer element ( PZT seen from.

In the ultrasonic transducer, the first matching layer ( 92 ) and / or the second matching layer ( 93 ) made of PIE plastic material.

The ultrasonic transducer also includes a lead frame ( 1 ) with an outer frame ( 6 ) and with an inner frame ( 9 ) and with a first spring element ( 7 ) and with a second spring element ( 8th ). The inner frame is preferred ( 9 ) via the first spring element ( 7 ) and the second spring element ( 8th ) with the outer frame ( 6 ) connected. The piezoelectric sound transducer element ( PZT ) attached.

The opening ( 14 ) of the inner frame ( 9 ) with the material ( PEI ) the first matching layer ( 92 ) filled.

The ultrasound transducer described above can be in the transverse mode at a first frequency due to the broadband f _r1 and a second frequency f _r2 operate. Therefore, a method is possible that operates the ultrasound transducer at a first frequency f _r1 and detecting a first reflection signal S ₁ and operating the ultrasound transducer at a second frequency f _r2 that from the first frequency f _r1 is different, and detecting a second reflection signal S ₂ enables. The first distance is then calculated on the basis of these results a ₁ for a first angle θ ₁ depending on the first reflection signal S ₁ us from the second reflection signal S ₂ and the calculation of a second distance a ₂ for a second angle θ ₂ from the first angle θ ₁ is different, depending on the first reflection signal S ₁ us from the second reflection signal S ₂ .

In addition to this method for operating the ultrasonic sensor, the invention also includes a method for producing an ultrasonic sensor according to the invention. This process includes providing ( 100 ) of a lead frame ( 1 ), the selective surface treatment ( 101 ) of the leadframe ( 1 ), performing a first injection molding step ( 102 ), the assembly ( 103 ) and electrical connection of the piezoelectric transducer element ( PZT ) with the resonance frequency ( for _r ) and the implementation ( 104 ) a second injection molding step. In the second injection molding step ( 104 ) the first matching layer ( 92 ) manufactured with respect to the first resonance frequency ( for _r ) the layer thickness ( d ₂ ) which has no more than +/- 25% and / or no more than +/- 10% and / or no more than +/- 5% and / or no more than +/- 2% and / or no more as +/- 1% of the quarter wavelength ( λ _PEI / 4 ) the wavelength ( λ _PEI / 4 ) of the sound at the first resonance frequency ( for _r ) of the piezoelectric transducer element ( PZT ) in the first adjustment layer ( 92 ) deviates.

In general, ultrasonic transducers for transmitting and receiving sound waves in a fluid ( H ₂ O ) with a piezoelectric transducer element ( PZT ) a first sound wave optical functional element ( PEI , 92 ) disclosed. The piezoelectric transducer element ( PZT ) is generally designed and provided for at a first resonance frequency ( for _r ) its resonance frequencies to be operated. A sound wave optical functional element ( 200 ) is between a surface of the piezoelectric transducer element ( PZT ) and the measuring medium, typically a fluid ( H ₂ O ) placed. According to the invention, the sound wave optical functional element ( 200 ) from the material ( 31 ) of the housing of the ultrasonic transducer according to the invention is manufactured. This has the advantage that the sound-optical functional element can be manufactured in an injection molding process together with the housing of the ultrasonic transducer. Therefore, the material of the housing of the ultrasonic transducer according to the invention is preferably made of PEI plastic. The said surface of the sound wave optical functional element ( 201 ) can be from a surface parallel to the surface of the piezoelectric transducer element ( PZT ) deviate to form, for example, sound wave optical Fresnel lenses, sound wave optical lenses etc. Will the thickness d2a the design of sound wave optical grids for sound wave optical spectrometers is also very large. Such a sound wave optical functional element ( 200 ) than is, for example, a sound wave optical lens and / or is a sound wave optical λ / 4 plate and / or is a sound wave optical phase adjustment element and / or act as a sound wave optical Fresnel lens. For example, the sound wave optical functional element ( 201 ) Grooves ( 201 ) or have functionally similar depressions. In the broadest sense, these are spatial or areal modulations of the speed of sound propagation within the modified adaptation layer ( 200 ), which should be included here by the term creasing.

advantage

Such an ultrasonic transducer enables increased sensitivity and improved sound radiation, at least in some implementations. The advantages are not limited to this.

In one implementation, this enables an operating frequency-dependent directional dependence of the radiation.

Figure list

• 1 1 shows the vibration modes of a piezoelectric vibrating element chip known from the prior art.
• 2nd 2nd shows in principle the amplitude response and the phase response of a typical piezoelectric vibrating element.
• 3rd 3rd shows a first exemplary leadframe ( 1 ) for an exemplary ultrasonic sensor according to the invention.
• 4th 4th shows the exemplary lead frame of 3rd as an exemplary dimensioned construction drawing.
• 5 5 shows the semi-finished product after the first injection molding step.
• 6 6 shows the semi-finished product 5 with exemplary dimensions.
• 7 7 shows the semi-finished product 5 the piezoelectric sound transducer element ( PZT ) by means of a vibration element assembly step on the assembly surface consisting of the surface of the inner frame ( 6 ) and the surface of the PEI filling ( 35 ) is mounted.
• 8th 8th equals to 7 after a bond joining step.
• 9 9 shows the semi-finished product after the second injection molding step.
• 10th 10th shows an isometric, not to scale, simplified drawing of the device 9 .
• 11 11 represent the manufacturing process simplified in the essential steps.
• 12 12 shows a further exemplary device according to the invention.
• 13 13 illustrates once again the basic principle of the adaptation layer ( PEI , 92 ).
• 14 14 shows the principle of an acousto-optical function element using an adaptation layer with a modified acoustic refractive index ( n _{PEI '} ).
• 15 15 equals to 14 with the difference that the width of the grooves ( 201 ) is modulated

Reference symbol list

1

Leadframe;

2nd

first connection leg;

3rd

second leg;

4th

Connection plate;

5

Connection bridge for mechanical connection of the first connection leg ( 2nd ) and the third connecting leg ( 3rd ) in the first manufacturing process steps;

6

outer frame;

7

first spring element;

8th

second spring element;

9

inner frame;

10th

Mounting plate;

11

Mounting hole;

12

Notches;

13

Gap;

14

central breakthrough;

15

Thickening in the first leg ( 2nd ) and the second connection leg ( 3rd );

30th

Cut in the jetty ( 5 );

31

PEI plastic mass;

32

first plastic block;

33

second plastic block;

34

additional frame;

35

Plastic mass inside ( 14 ) of the inner frame ( 9 );

36

Assembly channel;

90

second amount of PEI plastic material;

91

Level to adjust the second layer thickness ( d ₂ );

92

first matching layer;

93

second matching layer;

100

Provision of the lead frame ( 1 );

101

Remuneration for the surface of the lead frame ( 1 );

102

first injection molding step;

103

Assembly step for the piezoelectric transducer element ( PZT );

104

second injection molding step;

a

Height of the piezoelectric transducer element ( PZT );

b

Width of the piezoelectric transducer element ( PZT );

c

Depth of piezoelectric transducer element ( PZT );

d ₁

first layer thickness;

d ₂

second layer thickness;

d ₃

third layer thickness;

H ₂ O

Water;

PEI

Polyetherimide or function-like element;

PZT

Sound transducer element;

TDC

Time-to-digital converter;

Claims (12)

Ultrasonic transducer for emitting and receiving sound waves in a fluid (H ₂ O) with a piezoelectric sound transducer element (PZT) and with a first acoustic matching layer (PEI, 92) and wherein the piezoelectric sound transducer element (PZT) is designed and provided for this purpose in one first resonance frequency (f _r ) of its resonance frequencies to be operated and wherein the first matching layer (PEI, 92) is placed between sound transducer element (PZT) and fluid (H ₂ O) and the layer thickness (d ₂ ) of the first matching layer (PEI, 92) not more than +/- 25% and / or not more than +/- 10% and / or not more than +/- 5% and / or no more as +/- 2% and / or not more than +/- 1% of the quarter wavelength (λ _PEI / 4) of the wavelength (λ _PEI ) of the sound at the first resonance frequency (f _r ) of the piezoelectric sound transducer element (PZT) in the deviates first matching layer (92). characterized in that - it has a second matching layer (93) which, with respect to the piezoelectric sound transducer element (PZT), lies on the side of the piezoelectric sound transducer element (PZT) opposite the first matching layer (PEI, 92) and - that the layer thickness (d ₃ ) of the second matching layer (93) is designed such that the reception sensitivity of the ultrasonic transducer in the direction of this second matching layer (93) from the piezoelectric sound transducer element (PZT) is less than 50% and / or less than 20% and / or less than 10% the reception sensitivity of the ultrasonic transducer in the direction of the first matching layer (PEI, 93) from the piezoelectric sound transducer element (PZT). Ultrasonic transducer after Claim 1 characterized in that the first matching layer (92) and / or the second matching layer (93) is made of PEI plastic material. Ultrasonic transducer according to one or more of the Claims 1 to 2nd characterized in that - it has a lead frame (1) - with an outer frame (6) and - with an inner frame (9) and - with a first spring element (7) and - with a second spring element (8) and - that the inner frame (9) is connected to the outer frame (6) via the first spring element (7) and the second spring element (8) and - that the piezoelectric sound transducer element (PZT) is fastened to the inner frame. Ultrasonic transducer after Claim 3 characterized in that - the opening (14) of the inner frame (9) is filled with the material (PEI) of the first matching layer (92). Method for operating an ultrasonic transducer according to one or more of the Claims 1 to 4th comprising the steps of: operating the ultrasound transducer at a first frequency f _r1 and detecting a first reflection signal S ₁ ; Operating the ultrasonic transducer at a second frequency f _r2 , which is different from the first frequency f _r1 , and detecting a second reflection signal S ₂ ; Calculating a first distance a ₁ for a first angle θ ₁ as a function of the first reflection signal S ₁ and the second reflection signal S ₂ and - calculating a second distance a ₂ for a second angle θ ₂ , which is different from the first angle θ ₁ , as a function of the first reflection signal S ₁ and the second reflection signal S ₂ . Method of manufacturing an ultrasonic sensor according to one or more of the Claims 1 to 4th comprising the steps: - providing (100) a lead frame (1); - Selective surface coating (101) of the lead frame (1); - performing a first injection molding step (102); - Assembly (103) and electrical connection of the piezoelectric transducer element (PZT) with the resonance frequency (f _r ); - performing (104) a second injection molding step; characterized in that - in the second injection molding step (104) the first matching layer (92) is produced, which has a second layer thickness (d ₂ ) with respect to the first resonance frequency (f _r ), which does not exceed +/- 25% and / or not more than +/- 10% and / or no more than +/- 5% and / or no more than +/- 2% and / or no more than +/- 1% of the quarter wavelength (λ _PEI / 4) of Wavelength (λ _PEI ) of the sound at the first resonance frequency (f _r ) of the piezoelectric sound transducer element (PZT) in the first matching layer (92) and - that in the second injection molding step (104) the second matching layer (93) is produced and - that the second matching layer (93) with respect to the piezoelectric sound transducer element (PZT) lies on the side of the piezoelectric sound transducer element (PZT) opposite the first matching layer (PEI, 92) and - that the layer thickness (d ₃ ) of the second matching layer (93) is designed in such a way that the reception sensitivity of the Ultra sound transducer in the direction of this second matching layer (93) from the piezoelectric sound transducer element (PZT) seen less than 50% and / or less than 20% and / or less than 10% of the reception sensitivity of the ultrasonic transducer in the direction of the first matching layer (PEI, 93) from Piezoelectric transducer element (PZT) seen from. Ultrasonic transducer for emitting and receiving sound waves in a fluid (H ₂ O) with a piezoelectric sound transducer element (PZT) and with a first sound wave optical functional element (PEI, 92) and wherein the piezoelectric sound transducer element (PZT) is designed and provided for this purpose a first resonance frequency (f _r ) of its resonance frequencies to be operated and wherein the sound wave optical functional element (200) is placed between sound transducer element (PZT) and fluid (H ₂ O), characterized in that the sound wave optical functional element (200) is made of the material (31) of the housing is manufactured and the material (31) of the housing comprises the sound transducer element (PTZ) at least in a ring shape and the sound wave optical functional element (200) is part of the housing and forms a unit with it. Ultrasonic transducer after Claim 7 the material (31) of the housing made of PEI plastic. Ultrasonic transducer after Claim 7 or 8th wherein a surface of the sound wave optical functional element (201) is shaped differently from a parallel surface to the surface of the piezoelectric sound transducer element (PZT). Ultrasonic transducer according to one or more of the Claims 7 to 9 wherein the sound wave optical functional element is a phase adapter. Ultrasonic transducer according to one or more of the Claims 7 to 10th wherein the sound wave optical functional element is a Fresnel lens. Ultrasonic transducer according to one or more of the Claims 7 to 11 wherein the sound wave optical functional element (201) has grooves (201) or functionally similar depressions.

Images