DE102019126795A1 - Acoustic transducer and method for generating / receiving an acoustic wave - Google Patents

Abstract

An acoustic transducer for generating or receiving an acoustic wave (50) comprises: a first diaphragm (110) having a first piezoelectric transducer (210); and a second diaphragm (120) with a second piezoelectric transducer (220). The first diaphragm (110) and the second diaphragm (120) are oscillatable and separated from one another by a cavity (115) in order to generate the acoustic wave (50) through excitations of the first piezoelectric transducer (210) and / or the second piezoelectric transducer (220 ) to generate or receive.

Description

The present invention relates to an acoustic transducer and a method for generating or receiving an acoustic wave, and in particular to a combined piezoelectric-capacitive acoustic transducer.

BACKGROUND

Acoustic transducers convert electrical energy into acoustic energy and vice versa. Examples are loudspeakers (electrical to acoustic) or microphones (acoustic to electrical). Different conversion principles are used depending on the frequency range. In loudspeakers for the listening area, electrodynamic converters dominate, microphones usually work according to the capacitive principle. The air-ultrasonic area is covered by capacitive and piezoelectric transducers. Both principles can also be micromachined. The corresponding transducers are called "piezo electric micromachined ultrasound transducers" (PMUT) or "capacitive micromachined ultrasound transducers" (CMUT).

4a shows a structure of a CMUT as it is for example in the DE 10 2010 042 875 A1 is revealed. The acoustic transducer shown comprises a diaphragm 410 that act as a deformable / bendable plate on a frame 420 is held and a plate electrode 431 having. The frame (housing) 420 forms a cavity 415 that passes through the membrane 410 is limited on one side. On a floor (opposite the membrane 410 ) is a back electrode 432 educated. The transducer can, for example, be circular so that it is rotationally symmetrical about the axis of rotation R. can be formed.

In the CMUT shown, it creates an electric field between the plate electrode 431 and the back electrode 432 a deformation of the bending plate (membrane 410 ) in broadcast mode. The membrane is mechanically pretensioned by a vacuum cavity and an applied bias voltage (DC). The plate is deformed in reception mode 410 by sound waves for a measurable change in capacitance.

4B shows a structure of a conventional PMUT with a piezoelectric element 440, which the bending plate (diaphragm 410 ) can stimulate vibrations. The diaphragm is also in this converter 410 on a frame 420 formed, which has a cavity 415 forms, which in turn through the membrane 410 is limited on one side. This cavity 415 can also be open on one side. The piezoelectric transducer 440 comprises, for example, a piezoelectric material 441 and an insulation layer 442 that are on the membrane 410 are trained. The piezoelectric material 441 is exposed to an electric field (by applying a voltage AC), which, depending on the orientation of the dipoles present in the piezoelectric material, leads to a deformation (expansion or contraction) of the piezoelectric material 441 leads. Corresponding electrode layers are again provided for applying the electrical field, with the membrane 410 can itself act as an electrode if it comprises electrically conductive material.

With PMUT, the piezoelectric effect is the cause of expansion of the piezo material in the radial direction. This creates a solid bond between the piezoelectric material 441 with the bending plate 410 deformation of the flexure plate 410 perpendicular to the expansion of the piezoelectric transducer due to the monomorphic effect. In reception mode, after the plate has been deformed, an electrical voltage can be picked up due to the direct piezoelectric effect.

Ideally, these converters would convert over a large frequency range with high efficiency; in fact, the conversion is only efficient with mechanical resonance. This means that the conversion is only efficient in a certain frequency range determined by the design. In addition, the optimal frequencies of the two directions of conversion differ: the conversion from electrical to acoustic energy is most efficient with resonance, in the opposite case from acoustic to electrical energy with anti-resonance

5a , 5b show the magnitude of an electrical impedance of an ultrasonic transducer as a function of the frequency, where in 5a the resonance and anti-resonance are shown and in the 5b the receive bandwidth. As already mentioned, the most efficient conversion of electrical energy into sound takes place at the resonance in the minimum of the impedance. Conversely, the conversion of sound into an electrical signal is most sensitive with anti-resonance at the maximum of the impedance (see 5a) . The reception bandwidth is defined as the frequency range Δf in which the impedance is at least 2 ^-1/2 = 0.707 of the maximum. The 5b shows an example of a narrow-band converter (solid line) with the reception bandwidth Δf ₁ and a broadband converter (dashed line) with the reception bandwidth Δf ₂ . The same definition can also be used for the transmission bandwidth around the minimum of the electrical impedance (not shown). In the following, we no longer differentiate between receive and transmit bandwidth, but rather use the general term bandwidth.

The more pronounced the two resonances, the more efficient the conversion in the respective direction. In return, the frequency band of the optimal conversion is narrow. In the case of a narrow-band converter, the resonance points are very pronounced. With a broadband converter, the resonances are less pronounced, but efficient conversion is possible in a broader frequency range. The design of a converter is therefore always a compromise between bandwidth and converter efficiency.

If the same transducer is used in pulse-echo mode, i.e. for sending and receiving, it can also be operated neither at the optimal transmission frequency nor the optimal reception frequency.

It would therefore be desirable to generate ultrasound at the optimal transmission frequency and then to receive the transmitted ultrasound signal with the optimal reception frequency.

BRIEF DESCRIPTION OF THE INVENTION

At least part of the above problems is solved by an acoustic transducer according to claim 1 and a method according to claim 11. The dependent claims define further advantageous embodiments for the subjects of the independent claims.

The present invention relates to an acoustic transducer for generating or receiving an acoustic wave. The transducer comprises a first diaphragm with a first piezoelectric transducer and a second diaphragm with a second piezoelectric transducer. The first membrane and the second membrane are oscillatable. In addition, the first membrane and the second membrane can be separated from one another by a cavity in order to generate or receive the acoustic wave by excitations of the first piezoelectric transducer and / or the second piezoelectric transducer.

It goes without saying that the acoustic transducer generally generates a plurality of acoustic waves through the plurality of transducers, which waves then overlap and can be emitted. The transducers can emit the resulting acoustic wave in one direction of propagation or in different directions (e.g. in opposite directions). When receiving acoustic waves - like in a microphone - the acoustic energy is converted into electrical energy, while when transmitting, electrical energy is converted into acoustic energy.

In addition, the term “converter” is to be interpreted broadly within the scope of the present invention and is not necessarily limited to converters operating independently of one another. Regardless of whether the same or different membranes are used to transmit / receive acoustic waves, every possibility of converting an electrical signal into an acoustic signal (and vice versa) should fall under a transducer. Thus, each piezoelectric transmission / reception and electrostatic transmission / reception can be referred to as a transducer.

Optionally, the first membrane and / or the second membrane are exposed on both sides. The cavity can contain air or another gas or be evacuated, so that the acoustic transducer is able to transmit or receive acoustic waves in two opposite directions. The propagation of sound is largely suppressed by an air-free cavity, so that all of the converted electrical energy is bundled and emitted in both directions away from the cavity. If air or another gas is present in the cavity, a small opening can be provided for pressure equalization of the cavity to the outside (a so-called venting channel, as is also used, for example, with every electrostatic microphone).

Optionally, the first diaphragm and the second diaphragm are arranged at a predetermined distance in order to amplify an acoustic pressure due to a structural interference between the generated acoustic waves. This option is particularly advantageous when there is air in the cavity or complete ventilation is not possible. In this case, the two converters should advantageously not interfere with one another. As I said, this can be achieved by choosing the distance. However, the targeted setting of the distance can also be useful in the event that a vacuum should actually prevail in the cavity, but the ingress of air cannot reliably be avoided over time. With this approach, the air that has entered would not degrade the efficiency of the transducers over time.

Optionally, the acoustic transducer can have at least one acoustic reflector in order to reflect acoustic waves emitted in different directions in a preferred direction. The at least one reflector can be formed on both sides of the membranes (there can also be two separate reflectors) in order to redirect the acoustic waves emitted by the membranes (for example in a desired direction). A parabolic reflector can also be present underneath the second membrane to deflect the acoustic wave from the second To direct the membrane in the same direction as the acoustic wave emitted by the first membrane. The same applies in turn to the reception of acoustic waves, which can also be directed separately onto the two membranes.

Optionally, the transducer further comprises a resonator cavity, the second membrane being formed between the first membrane and the resonator cavity in order to at least partially transmit acoustic waves into the resonator cavity or to receive them from there. The resonator cavity can be designed to reflect the generated acoustic waves and thus to increase a sound pressure of radiated acoustic waves. For this purpose, the resonator cavity can have a predetermined depth in the direction of propagation of the acoustic wave (e.g. half a wavelength) in order to generate standing waves there. For this embodiment it is also advantageous if air is present in the cavity between the membranes, so that the acoustic wave reflected in the resonator cavity can easily propagate through the cavity. In order not to cause any undesired destructive interference on the first membrane, the distance between the first and second membrane can be selected again accordingly (e.g. a multiple of the wavelength of the acoustic wave).

• - ein erstes Wechselspannungssignal an/von dem ersten piezoelektrischen Wandler,
• - ein zweites Wechselspannungssignal zwischen der ersten Membrane und der zweiten Membrane, um einen zusätzlichen kapazitiven Wandler zu bilden,
• - ein drittes Wechselspannungssignal an/von dem zweiten piezoelektrischen Wandler.

Optionally, the acoustic transducer further comprises a control unit which is designed to apply and / or tap at least one of the following AC voltage signals:

• - a first AC voltage signal to / from the first piezoelectric transducer,
• - a second AC voltage signal between the first membrane and the second membrane to form an additional capacitive transducer,
• - A third AC voltage signal to / from the second piezoelectric transducer.

It goes without saying that corresponding electrodes are present for applying / tapping off an electrical voltage. For example, an electrode can be formed directly on the first or second membrane (possibly as part of the corresponding piezoelectric transducer). It is also possible that the first and / or the second membrane can itself act as an electrode (e.g. if they have an electrically conductive material).

Optionally, the control unit is further designed to apply an (additional) DC voltage signal to the first piezoelectric converter and / or to the second piezoelectric converter and / or to the capacitive converter. As a result, a mechanical (pre-) tension of the first and / or the second membrane can be changed, whereby a resonance frequency of the first membrane and / or the second membrane can in turn change or be set in a targeted manner. It goes without saying that the direct voltage signal can be applied independently of the alternating voltage signal (s) and therefore represents a so-called bias voltage (bias voltage).

Optionally, if the acoustic wave has a specific frequency, the control unit can be designed to select the DC voltage signal in such a way that the acoustic wave with the specific frequency can both be efficiently generated and efficiently received. This is possible because the DC voltage signal shifts the resonance frequency so that the different frequency sensitivities (when sending and receiving) can be compensated. This makes it possible that a transmitted signal of a certain frequency can also be efficiently received again. This eliminates or at least alleviates the problem mentioned at the beginning of the different sensitivities when transmitting and receiving acoustic waves. The transducer can therefore be changed adaptronically or adaptively so that it is always operated at the optimal frequency (when transmitting and receiving).

According to further exemplary embodiments, it is also possible, for example in a targeted manner, to change a transmission frequency in order, for example, to increase the resolution. The transmission frequency can also be reduced in a targeted manner, for example to change the range of the acoustic wave (e.g. to increase it). This can be used, for example, for material testing in order to examine specific structures in a targeted manner and to make further details visible by increasing the frequency.

Optionally, the control unit is further designed to apply the DC voltage signal to only one of the transducers, to use only one transducer to generate (receive) the acoustic wave and to use at least one of the remaining transducers to receive (generate) the acoustic wave.

Optionally, the control unit is further designed to apply the DC voltage signal to at least one of the transducers and to use the at least one of the transducers to generate and receive the acoustic wave.

Optionally, the control unit is further designed to apply the DC voltage signal only during a transmission of the acoustic wave or only during a subsequent reception of a reflection of the acoustic wave. Or each to apply other DC voltage signals when sending or receiving.

According to exemplary embodiments, it is thus possible to operate the piezoelectric converter (s) and the capacitive converter in parallel at the same time and to flexibly adapt the resonance frequencies. The term “simultaneously” can also include the case where a transducer still has to wait for a reflection signal so that the transducers are active for a fraction of a second later or earlier.

Embodiments also relate to a method for generating or receiving an acoustic wave, the method using one of the acoustic transducers described above. All of the functional features described above can therefore be implemented as further optional method steps.

In particular, the method can include the formation of a mechanical preload in the first membrane and / or in the second membrane in order to enable an acoustic wave of a predetermined frequency to be effectively generated and received.

Optionally, the method can also include changing a mechanical preload in the first membrane and / or in the second membrane in order to enable transmission and / or reception of acoustic waves of different frequencies. Sending / receiving can also take place at the same time, but does not have to be.

• - dass ein effektives Aussenden der akustischen Welle durch einen der Wandler und, nach einer Reflexion der akustischen Welle(z.B. an einem Objekt oder einem Materialartefakt o.ä.), ein effektives Empfangen der akustischen Welle durch den einen Wandler oder durch einen anderen Wandler erreicht wird; oder
• - dass eine gewünschte Reichweitenänderung der akustischen Welle oder eine gewünschte Auflösungsänderung für die akustische Welle erreicht wird.

Optionally, the step of developing the mechanical prestress can be carried out in the method as follows:

• - that an effective emission of the acoustic wave by one of the transducers and, after a reflection of the acoustic wave (e.g. on an object or a material artifact, etc.), an effective reception of the acoustic wave by one transducer or by another transducer is achieved becomes; or
• - That a desired change in range of the acoustic wave or a desired change in resolution for the acoustic wave is achieved.

• - Anregen des ersten und/oder des zweiten piezoelektrischen Wandlers; und
• - Messen einer Auslenkung der ersten und/oder der zweiten Membrane, die durch das Anregen des ersten und des zweiten piezoelektrischen Wandlers verursacht wurde, durch den kapazitiven Wandler (d.h. elektrostatisch).

Optionally, the method can further comprise:

• - Exciting the first and / or the second piezoelectric transducer; and
• - Measuring a deflection of the first and / or the second membrane, which was caused by the excitation of the first and the second piezoelectric transducer, by the capacitive transducer (ie electrostatic).

In this way, a piezoelectric excitation can be analyzed, i.e. it can be found out which deflections the excitation has led to.

This method or at least parts thereof can also be implemented or stored in the form of instructions in software or on a computer program product, with stored instructions being able to carry out the steps according to the method when the method runs on a processor. The present invention therefore also relates to a computer program product with software code (software instructions) stored thereon, which is designed to carry out one of the methods described above when the software code is carried out by a processing unit. The processing unit can be any form of computer or control unit that has a corresponding microprocessor capable of executing software code.

Figure list

• 1 zeigt einen akustischen Wandler zum Erzeugen oder Empfangen einer akustischen Welle gemäß einem Ausführungsbeispiel der vorliegenden Erfindung.
• 2 veranschaulicht das Verschieben der Resonanzfrequenz beim Anlegen einer Vorspannung, wie es in Ausführungsbeispielen genutzt wird.
• 3a,3b zeigen akustische Wandler gemäß weiteren Ausführungsbeispielen der vorliegenden Erfindung.
• 4a,4b zeigen einen Aufbau von konventionellen Wandlern.
• 5a,5b zeigen eine elektrische Impedanz eines konventionellen Ultraschallwandlers als Funktion der Frequenz, aus denen die optimale Sende- und Empfangsfrequenzen ermittelbar sind.

The exemplary embodiments of the present invention will be better understood with reference to the following detailed description and the accompanying drawings of the various exemplary embodiments, which, however, should not be understood in such a way that they restrict the disclosure to the specific embodiments, but merely serve for explanation and understanding.

• 1 shows an acoustic transducer for generating or receiving an acoustic wave according to an embodiment of the present invention.
• 2 illustrates the shift in the resonance frequency when a bias voltage is applied, as used in exemplary embodiments.
• 3a , 3b show acoustic transducers according to further exemplary embodiments of the present invention.
• 4a , 4b show a structure of conventional converters.
• 5a , 5b show the electrical impedance of a conventional ultrasonic transducer as a function of the frequency, from which the optimal transmission and reception frequencies can be determined.

DETAILED DESCRIPTION

1 shows an acoustic transducer for generating and / or receiving an acoustic wave 50 according to an embodiment of the present invention. The transducer includes a first diaphragm 110 on which a first piezoelectric transducer 210 is trained. The acoustic transducer also includes a second diaphragm 120 , to which a second piezoelectric transducer 220 is trained. The first membrane 110 and the second membrane 120 delimit a cavity on opposite sides 115 that by an appropriate frame or housing 240 is laterally limited. The acoustic transducer can be rotationally symmetrical about an axis R. be formed and thus circular membrane 110 , 120 have in a plan view. However, the invention is not intended to be limited to any particular form.

In the cavity 115 can be air, a gas or a vacuum and the first membrane 110 and the second membrane 120 can be at a predetermined distance d be formed from each other. If in the cavity 115 Air is present, creating the first membrane 110 and the second membrane 120 acoustic waves 50 in both directions, ie away from the transducer and into the cavity 115 into it. Therefore it can be beneficial to keep the distance d to choose such that the acoustic waves 50 amplify accordingly in order to increase the sound pressure (if they are to be transmitted with the same frequency). If in the cavity 115 a vacuum is formed, the distance can d can also be chosen differently (e.g. smaller), since the acoustic waves in this case are in the 1 are radiated in the vertical direction up and down, but not or hardly in the cavity 115 into it.

If air or some other gas in the cavity 115 is present, a small opening (not shown in the 1 ) for pressure equalization of the cavity 115 be provided to the outside (a so-called "venting channel", as is also used, for example, with every electrostatic microphone).

The first and second piezoelectric transducers 210 , 220 each comprise two electrodes, between each of which a piezoelectric material 214 , 224 (as a film or layer) and an (optional) insulating layer in each case 216 , 226 are trained. If the membrane (s) is / are insulating, two electrodes above and below the piezoelectric layer would be necessary for contacting the piezoelectric layers. Even if this case is not shown, it goes without saying that the individual voltage sources (control unit 150) then have to be connected to these electrodes for the piezoelectric transducers. If the first / second membrane 110 , 120 is / are formed from an electrically conductive material, the first membrane 110 and / or the second membrane 120 form one of the two electrodes, while the other electrode is on the piezoelectric materials 214 , 224 can be arranged.

The acoustic transducer further comprises a control unit 150 which is designed to transmit a first alternating voltage signal AC1 to the first piezoelectric transducer 210 to apply and a third AC voltage signal AC3 to the second piezoelectric transducer 220 to be created or tapped accordingly (when receiving). By applying an electric field to the piezoelectric materials 214 , 224 there is a change in length of the piezoelectric material 214 , 224 which causes the first and the second membrane 110 , 120 due to the change in length of the piezoelectric material 214 , 224 bend. When an alternating voltage is applied, this leads to vibrations in the membrane 110 which then, with the appropriate strength, as an acoustic wave 50 be sent out.

The second piezoelectric transducer 220 can be formed in a same manner as the first piezoelectric transducer 210 . Both the first piezoelectric transducer 210 as well as the second piezoelectric transducer 220 can be on one side (inside or outside) of the first or second membrane 110 , 120 to be ordered.

It goes without saying that acoustic waves are received in an analogous manner, ie the incoming acoustic waves excite the membrane 110 , 120 to vibrations, which then generate electrical alternating voltage signals AC1, AC3, which in turn can be evaluated by the control unit 150.

There is also between the first membrane 110 and the second membrane 120 or the electrodes formed thereon (the electrodes of the piezoelectric transducer 210 , 220 can be used) a second alternating voltage signal AC2 can be applied. As a result, there is an electrical attraction between the first and second membranes 110 , 120 can, so that the second alternating voltage signal AC2 also excites the diaphragms to vibrate 110 , 120 leads. The first and second diaphragms form accordingly 110 , 120 along with those stuck to them formed electrode layers (which are also part of the piezoelectric transducer 210 , 220 can be) a capacitive converter 230 . All three converters 210 , 220 , 230 can be excited independently of one another by the AC voltage signals AC1, AC2, AC3. Even if there are three independent options, only two membranes are used for this. So there are only two independent “channels” for sending / receiving sound waves.

In addition to the alternating voltage signals AC1, AC2, AC3, an electrostatic potential or a direct voltage signal DC can be applied, which - depending on the polarity - the membranes 110 , 120 either bent upwards or downwards. It goes without saying that repulsion occurs when the total amount of charge carriers on the membranes 110 , 120 is not equal to zero (ground potential is then not symmetrical between the electrostatic potentials on the membranes 110 , 120 ). This changes the mechanical tension within the membranes 110 , 120 which in turn leads to the fact that the resonance frequencies for the membrane vibrations change. The direct voltage signal DC can in principle be superimposed separately on each alternating voltage signal AC1, AC2, AC3, so that the first membrane 110 and / or the second membrane 120 can be mechanically preloaded separately or together. As in 1 shown, the direct voltage signal DC will work most effectively when both membranes 110 , 120 electrostatically biased relative to each other (linearized and increased with regard to sensitivity). In the 1 is only an example of the direct voltage signal DC for the capacitive converter 230 shown, but, as said, it can also be superimposed on the first and / or the third AC voltage signal AC1, AC3.

The change in the resonance properties of the membranes 110 , 120 The direct voltage signal DC can be used to optimize the sensitivity with regard to the transmission and reception of acoustic waves. Apart from this effect, the preload can also be used to compensate for a deflection due to a vacuum in the cavity 215 be used. When there is a particularly good vacuum to decouple the vibration excitations on the first and second membrane 110 , 120 is to be formed, this can lead to a bending of the membrane, which - at least to a certain extent - can be reversed by applying a positive / negative total amount of charge to the transducers. This has the advantage that the mechanical stress on the fixation of the membrane 110 , 120 is decreased.

2 illustrates the shift of the resonance frequency when a bias voltage is applied, whereby a large and a small signal for different DC voltage values DC were used in a simulation. Specifically, the deflection of the center of a membrane (equivalent to the surface speed) is shown during the oscillation, with the resonance correlating with the maximum deflection.

First represents the solid line 250 represents the piezoelectric excitation signal. The dashed line 260 shows the superposition of the piezoelectric with the capacitive excitation signal. Both lines show the case without a bias (DC = 0).

Lines 270 show the corresponding resonance curves for a first bias voltage, which is 50% of a so-called “pull-in” voltage (eg 1352 V), while lines 280 show the corresponding resonance curves for a bias voltage of 60% and lines 290 the resonance curves for a preload equal to 70% of the pull-in tension. For each case two lines are shown corresponding to a stronger and a weaker signal.

As the electrical bias DC increases, the resonance frequency and the surface speed decrease and the converter efficiency increases during transmission. The bias voltage DC can therefore, on the one hand, increase the efficiency and, on the other hand, set the optimum transmission frequency if the increase in converter efficiency is compensated for by a lower excitation voltage.

The following values were taken as examples for this simulation: d = 10 µm, AC1 = AC3 = 10 volts, AC2 = 0 volts. How to continue the right side of the 2 can be seen, the converter is rotationally symmetrical about the axis R. , the piezoelectric transducer 210 , 220 have a radial extension of approx. 3 mm and the membrane of approx. 3.7 mm. The layer thickness of the piezoelectric layer is 210 μm, for example, and comprises a material: PZT 7B. The membrane is 290 µm thick and consists of a material: CuNi ₁₈ Zn ₂₇ .

It goes without saying that these geometry / materials are only an example to demonstrate the functionality of the acoustic transducer, i.e. the selected materials and geometries are only intended to illustrate that the resonance frequency shifts to lower frequencies with increasing bias.

According to further exemplary embodiments, a different bias voltage can therefore be used during transmission than during reception, so that a acoustic wave 50 can be transmitted with a certain frequency and can be received efficiently at the same time with the same transducer (for example after a reflection on a body or a material structure; neglecting Doppler shifts).

But it is also possible that one of the three converters 210 , 220 , 230 for sending and another transducer is used for receiving, the bias voltage being used accordingly to make both transducers as sensitive as possible for sending and receiving. As described above, the resonance frequency of each transducer can be adjusted adaptively by means of a plurality of bias voltages.

3a shows another embodiment in which the acoustic transducer has at least one acoustic reflector 310 comprises acoustic waves emitted in different directions 50 in a preferred direction V to reflect. The at least one reflector 310 can be on both sides of the membranes 110 , 120 be formed (there can also be two separate reflectors 310 be) to those of the membranes 110 , 120 emitted acoustic waves 50 redirect (e.g. in the desired direction V ).

According to further exemplary embodiments, below the second membrane 120 also a parabolic reflector may be present to pick up the acoustic wave 50 from the second membrane 120 in the same direction as the acoustic wave 50 that from the first membrane 110 is transmitted (vertically upwards). In this case needs above the first membrane 110 no further reflector be available.

It goes without saying that the same arrangement is also advantageous for the reception of acoustic waves 50 can be used. Here are incoming acoustic waves 50 separated on the two membranes 110 , 120 steered.

3b shows a further embodiment for the acoustic transducer, which differs from the embodiment from FIG 1 differs in that the acoustic transducer is located above a resonator cavity 215 is trained. The resonator cavity 215 is in a resonator housing 320 and is formed by the second membrane 120 limited or closed so that the second membrane 120 between the resonator cavity 215 and the cavity 115 is arranged and separates both cavities from each other.

The resonator cavity 215 causes the vertically downward (ie into the resonator cavity 215 ) emitted acoustic waves in the resonator cavity 215 be reflected and fed back. Then they can also spread upwards. For this purpose, for example, in the cavity 115 air should also be present to allow the spread.

In addition, the resonator cavity 215 in the direction of propagation of the acoustic wave 50 a depth 1 have half the wavelength of the acoustic wave 50 amounts, so that after a reflection on the bottom surface of the resonator cavity 215 a constructive overlay (so-called resonance exaggeration) of the second membrane 120 generated acoustic wave and the reflected wave arises, which then both together towards the first membrane 110 be sent.

Also, the distance can d between the first membrane 110 and the second membrane 120 be chosen so that the in the direction of the first membrane 110 acoustic wave propagating through that of the first membrane 110 generated wave is reinforced (constructively superimpose). In this way the acoustic wave can 50 that are in the 3 is sent vertically upwards, have a maximum sound pressure.

In this exemplary embodiment, too, a preload can for example be applied between the first membrane 110 and the second membrane 120 be formed, the two membranes 110 , 120 holds under a mechanical bias, which in turn shifts the resonance frequency or anti-resonance frequency.

All other features in connection with the exemplary embodiment of 1 have been described, can optionally also be present in this exemplary embodiment.

• Die Erfindung betrifft einen neuartigen Ultraschallwandler, bei dem die beiden bekannten Aktorprinzipien der elektrostatischen und der piezoelektrischen Anregung in einer Doppelstruktur kombiniert werden. Die Kombination ermöglicht die gleichzeitige Wandlung und/oder die gegenseitige Beeinflussung beider Wandlungsprinzipien. Damit wird weiter Folgendes ermöglicht
  • - elektrostatische Wandlung in entgegengesetzten Raumrichtungen, beim Senden und Empfangen;
  • - piezoelektrische Wandlung in entgegengesetzten Raumrichtungen, beim Senden und Empfangen;
  • - dieselbe piezoelektrische Wandlung mit mechanischer Vorspannung durch elektrisches Feld, z.B. um adaptronisch zwischen optimaler Sende- und Empfangsfrequenz umzuschalten (z.B. zum Ausgleich von Fertigungstoleranzen oder sogar dem gezielten Senden und Empfangen unterschiedlicher Frequenzen);
  • - piezoelektrische Anregung mit gleichzeitigem elektrostatischem Empfang, z.B. um die Funktion des piezoelektrischen Systems zu überwachen;
  • - elektrostatische Anregung mit piezoelektrischem Empfang, z.B. um die Funktion des elektrostatischen Systems zu überwachen;
  • - elektrostatische Anregung mit zusätzlicher piezoelektrischer Vorspannung, z.B. um den möglichen Frequenzbereich gegenüber der reinen elektrischen Vorspannung weiter zu vergrößern;
  • - gleichzeitige Anregung mit beiden Wandlungsprinzipien, z.B. um einen höheren Schalldruck zu erzeugen;
  • - wird die Doppelstruktur auf einer Seite mit einer entsprechend abgestimmten Resonatorkavität ergänzt, kann die rückseitig erzeugte Schalleistung auf die Vorderseite reflektiert werden und damit ein höherer Schalldruck erzeugt werden.
  • - zumindest ein Reflektor kann genutzt werden, um die in verschiedene Richtungen ausgesendeten akustischen Wellen in eine Vorzugsrichtung zu reflektieren.

Advantageous aspects of exemplary embodiments can be summarized as follows:

• The invention relates to a novel ultrasonic transducer in which the two known actuator principles of electrostatic and piezoelectric excitation are combined in a double structure. The combination enables the simultaneous conversion and / or the mutual influencing of both conversion principles. This also enables the following
  • - Electrostatic conversion in opposite spatial directions, when sending and receiving;
  • - Piezoelectric conversion in opposite spatial directions, when sending and receiving;
  • - the same piezoelectric conversion with mechanical bias by electrical Field, for example to switch adaptronically between the optimal transmission and reception frequency (e.g. to compensate for manufacturing tolerances or even the targeted transmission and reception of different frequencies);
  • - Piezoelectric excitation with simultaneous electrostatic reception, for example to monitor the function of the piezoelectric system;
  • - electrostatic excitation with piezoelectric reception, for example to monitor the function of the electrostatic system;
  • - Electrostatic excitation with additional piezoelectric bias, for example to further enlarge the possible frequency range compared to the pure electrical bias;
  • - Simultaneous excitation with both conversion principles, eg to generate a higher sound pressure;
  • - If the double structure is supplemented on one side with a correspondingly matched resonator cavity, the sound power generated on the rear side can be reflected onto the front side and thus a higher sound pressure can be generated.
  • - At least one reflector can be used to reflect the acoustic waves emitted in different directions in a preferred direction.

• - einen Wandler bestehend aus einer Kombination von mindestens zwei piezoelektrischen Wandlern zu einem neuartigen Wandler, der zusätzlich nach dem kapazitiven Wandlungsprinzip arbeiten kann;
• - einen Wandler, der außerdem elektrostatisch vorgespannt und piezoelektrisch ausgelenkt wird;
• - einen Wandler, der außerdem piezoelektrisch vorgespannt und elektrostatisch ausgelenkt wird;
• - einen Wandler, der außerdem elektrostatisch vorgespannt und ausgelenkt wird und bei dem die Auslenkung piezoelektrisch beeinflusst wird;
• - einen Wandler, der außerdem piezoelektrisch ausgelenkt wird und dessen Auslenkung elektrostatisch gemessen wird;
• - einen Wandler, der außerdem kombiniert piezoelektrisch und elektrostatisch ausgelenkt wird;
• - einen Wandler, der außerdem elektrostatisch vorgespannt und piezoelektrisch empfängt;
• - einen Wandler, der außerdem piezoelektrisch vorgespannt wird und elektrostatisch empfängt;
• - einen Wandler, der außerdem auf der Rückseite eine Kavität aufweist, die akustische Energie reflektiert.

Embodiments thus relate in particular to the following subjects:

• - A converter consisting of a combination of at least two piezoelectric converters to form a new type of converter, which can also work according to the capacitive conversion principle;
• a transducer which is also electrostatically biased and piezoelectrically deflected;
• a transducer which is also piezoelectrically biased and electrostatically deflected;
• a transducer which is also electrostatically biased and deflected and in which the deflection is piezoelectrically influenced;
• a transducer which is also deflected piezoelectrically and whose deflection is measured electrostatically;
• a transducer which is also deflected in a combined piezoelectric and electrostatic manner;
• a transducer which is also electrostatically biased and receives piezoelectrically;
• a transducer which is also piezoelectrically biased and receives electrostatically;
• - A transducer, which also has a cavity on the back that reflects acoustic energy.

The features of the invention disclosed in the description, the claims and the figures can be essential for the implementation of the invention both individually and in any combination.

List of reference symbols

50

acoustic wave

110, 120, 410

Membranes

115, 415

cavity

210

first piezoelectric transducer

220

second piezoelectric transducer

215

Resonator cavity

230

capacitive converter

240, 420

frame

214, 224, 441

piezoelectric materials

216, 226

Insulation layers

250, 260, ...

Membrane rash

310

acoustic reflector (s)

320

Housing of the resonator cavity

431

Plate electrode

432

Back electrode

442

Buffer layer / insulation layer

d

Distance between the membranes

1

Depth of the resonator cavity

R.

Rotational axis of rotation

V.

Preferred direction of acoustic waves

QUOTES INCLUDED IN THE DESCRIPTION

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

Patent literature cited

• DE 102010042875 A1 [0003]

Claims (15)

An acoustic transducer for generating or receiving an acoustic wave (50), the transducer comprising: a first diaphragm (110) having a first piezoelectric transducer (210); and a second diaphragm (120) with a second piezoelectric transducer (220), the first diaphragm (110) and the second diaphragm (120) being oscillatable and separated from one another by a cavity (115) to excite the acoustic wave (50) the first piezoelectric transducer (210) and / or the second piezoelectric transducer (220) to generate or receive. Acoustic converter according to Claim 1 , wherein the first membrane (110) and the second membrane (120) are exposed on both sides and the cavity (115) has air or another gas or is evacuated, so that the acoustic transducer is able to transmit acoustic waves in two opposite directions to send or receive from there. Acoustic converter according to Claim 2 wherein the first diaphragm (110) and the second diaphragm (120) have a predetermined distance (d) in order to amplify an acoustic pressure due to a constructive interference between the generated acoustic waves (50). Acoustic transducer according to one of the preceding claims, which further comprises at least one acoustic reflector in order to reflect acoustic waves (50) emitted in different directions in a preferred direction (V). Acoustic transducer according to one of the preceding claims, further comprising a resonator cavity (215), wherein the second membrane (120) is formed between the first membrane (110) and the resonator cavity (215) to at least partially absorb acoustic waves to transmit or receive the resonator cavity (215), and the resonator cavity (215) is designed to reflect the generated acoustic waves (50) and thus to increase a sound pressure of radiated acoustic waves. Acoustic transducer according to one of the preceding claims, which further comprises a control unit (150) which is designed to apply or tap at least one of the following AC voltage signals (AC1, AC2, AC3) for generating / receiving the acoustic wave (s) (50) : - A first alternating voltage signal (AC1) to / from the first piezoelectric transducer (210), - A second alternating voltage signal (AC2) between the first membrane (110) and the second membrane (120) in order to form an additional capacitive transducer, - A third alternating voltage signal (AC3) to / from the second piezoelectric transducer (220). Acoustic converter according to Claim 6 , wherein the control unit (150) is further designed to apply a direct voltage signal (DC) as a bias voltage to at least one of the following converters (210, 220, 230): - the first piezoelectric converter (210), - the second piezoelectric converter (220 ), - the capacitive transducer (230) in order to change a resonance frequency of the first membrane (110) and / or the second membrane (120) by changing a mechanical preload. Acoustic converter according to Claim 7 , wherein the acoustic wave has a specific frequency and the control unit (150) is further designed to select the direct voltage signal (DC) in such a way that the acoustic wave (50) with the specific frequency can be efficiently generated as well as efficiently received. Acoustic converter according to Claim 7 or Claim 8 , wherein the control unit (150) is further designed to apply the direct voltage signal (DC) to only one of the transducers (210, 220, 230) in order to use the one transducer to generate / receive the acoustic wave, and to use at least one of the to use the remaining transducer for receiving / generating the acoustic wave. Acoustic converter according to Claim 7 or Claim 8 , wherein the control unit (150) is further designed to apply the direct voltage signal (DC) to at least one of the converters (210, 220, 230) and the at least one of the converters (210, 220, 230) to generate and receive the acoustic Use shaft (50). Acoustic converter according to one of the Claims 7 to 10 , wherein the control unit (150) is further designed to apply the direct voltage signal (DC) only during a transmission of the acoustic wave (50) or only during a subsequent reception of a reflection of the acoustic wave (50). Method for generating or receiving an acoustic wave using an acoustic transducer according to one of the Claims 1 to 11 . Procedure according to Claim 12 which further comprises at least one of the following steps: forming a mechanical preload in the first diaphragm (110) and / or in the second diaphragm (120) in order to produce an effective to enable effective reception of an acoustic wave (50) of a predetermined frequency, changing a mechanical preload in the first membrane (110) and / or in the second membrane (120) in order to simultaneously transmit and / or receive acoustic waves ( 50) of different frequencies. Procedure according to Claim 13 wherein the step of establishing the mechanical preload is carried out in such a way: - that an effective emission of the acoustic wave (50) by one of the transducers (210, 220, 230) and, after a reflection of the acoustic wave (50), an effective reception the acoustic wave (50) is reached by the one transducer or by another transducer; or - that a desired change in range of the acoustic wave (50) or a desired change in resolution for the acoustic wave is achieved. Method according to one of the Claims 12 to 13th which further comprises: - exciting the first and / or second piezoelectric transducer (210, 220); and - measuring a deflection of the first and / or the second membrane (110, 120), which was caused by the excitation of the first and / or the second piezoelectric transducer (210, 220), by the capacitive transducer (230).

Images