Membrane Transducer with Improved Bandwidth

Abstract

The effective bandwidth of a membrane-based ultrasonic transducer is improved by a control element (C). The control element (C) is disposed on a first side (10a) of the first membrane (10) of the transducer to increase or decrease the displacement amplitude of the first membrane (10) toward the first side (10a) and / or the opposite, second side (10b). This induces a displacement asymmetry (Za<>Zb) in the movement of the first membrane (10) toward the first side (10a) compared to the second side (10b) during a first vibration (V1) of the first membrane (10). This displacement asymmetry can result in improved bandwidth.

Description

Technical Field

[0001] Technical Field and Background The present disclosure relates to membrane-based ultrasonic transducers and methods for enhancing the effective bandwidth of such transducers.

Background Art

[0002] Ultrasonic transducers, for example, as a source and / or receiver, have various applications such as medical imaging, flow meters, and so on. To enhance transmission and / or reception efficiency, resonance-based ultrasonic sources / receivers such as membranes can be used. However, if the transducer is only effective near resonance, the bandwidth and performance of the system may be limited. For example, the accuracy or image resolution of such a transducer may depend on the system bandwidth.

Summary of the Invention

Problems to be Solved by the Invention

[0003] It is still necessary to improve the bandwidth of the membrane-based transducer while maintaining at least a certain degree of resonance-based efficiency.

Means for Solving the Problems

[0004] Overview Some aspects of the present disclosure relate to ultrasonic transducers. The transducer includes at least a first membrane configured to exhibit a first vibration at or near its resonant frequency, and the first membrane is configured to transmit and receive (i.e., transmit and / or receive) ultrasonic waves that interact (resonantly), for example. The electronic circuit is coupled to the first membrane and transmits and receives electrical signals that cause or are caused by the first vibration. The control element is disposed on a first side of the first membrane and is configured to induce displacement asymmetry in the movement of the first membrane during the first vibration to the first side as compared to the opposite, second side. Other aspects or further aspects relate to a method of enhancing the effective bandwidth of a membrane-based ultrasonic transducer. For example, the control element is disposed on a first side of the first membrane of the transducer and increases or decreases the displacement amplitude of the first membrane toward the second side on the first side and / or the opposite side, inducing displacement asymmetry in the movement of the first membrane toward the first side as compared to the second side during the first vibration of the first membrane.

[0005] As described herein, the inventors have found that by forcing the non-linear displacement, particularly the movement of the membrane to one side during resonant vibration, to be asymmetric compared to the movement to the other side, the bandwidth can be improved. The asymmetry can be induced, for example, by applying an asymmetric force to the membrane during its vibration cycle. Such forces may involve, for example, a pressure increase, an electrostatic force, and / or a physical connection. Various combinations can be used to provide synergistic advantages as described herein.

[0006] Brief Description of the Drawings These and other features, aspects, and advantages of the devices, systems, and methods of the present disclosure will become better understood from the following description, the appended claims, and the accompanying drawings.

Brief Description of the Drawings

[0007]

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Best Mode for Carrying Out the Invention

[0008] Description of Embodiments The terminology used to describe particular embodiments is not intended to be limiting of the invention. As used herein, the singular forms "a", "an", and "the" are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term "and / or" includes any and all combinations of one or more of the associated listed items. It will be understood that the terms "comprises" and / or "comprising", while specifying the presence of stated features, do not preclude the presence or addition of one or more other features. When a particular step of a method is recited as following another step, unless otherwise specified, it may follow immediately after the other step or one or more intermediate steps may be performed before this particular step. Similarly, when a connection between structures or components is described, unless otherwise specified, this connection may be established directly or through intermediate structures or components.

[0009] The present invention will be described more fully hereinafter with reference to the accompanying drawings in which embodiments of the invention are shown. In the drawings, the absolute and relative sizes of systems, components, layers, and regions may be exaggerated for clarity. Embodiments may be described with reference to schematic illustrations and / or cross-sectional illustrations of idealized embodiments and intermediate structures in some cases. In the description and the drawings, like numerals refer to like elements throughout. Relative terms as well as their derivatives are to be construed to refer to the orientation as then described or as shown in the drawings under consideration. These relative terms are for convenience of description only and do not require that the system be constructed or operate in a particular orientation unless otherwise specified.

[0010] Figures 1 to 4 illustrate increasing the effective bandwidth of the membrane-based ultrasonic transducer 100. In the embodiments described herein, the ultrasonic transducer 100 includes at least a first membrane 10. For example, the first membrane 10 exhibits a first vibration V1 (at or near its resonance frequency) and is configured to transmit and receive (i.e., transmit and / or receive) ultrasonic waves W that interact (resonate) with, for example, the first membrane 10. Advantageously, a control element C can be provided on one or both sides of the membrane to induce displacement asymmetry Za<>Zb in the movement of the first membrane 10. For example, the asymmetry is induced on the first side 10a during the first vibration V1 as compared to the opposite, second side 10b.

[0011] In some embodiments, for example, in the embodiments shown, the first membrane 10 is configured to vibrate in the direction Z transverse to the plane XY of the first membrane 10 with respective amplitudes Za, Zb towards the first side and the second side. In some embodiments, the first vibration V1 has a first amplitude Za between the (central) equilibrium position Z1 of the first membrane 10 and the maximum expansion position of the first membrane 10 towards the first side 10a. In other or further embodiments, the first vibration V1 has a different second amplitude Zb between the equilibrium position and the maximum expansion position of the first membrane 10 towards the second side 10b. Preferably, the control element C is configured to affect the movement of the first membrane 10 to induce a difference between the first amplitude Za and the second amplitude Zb. For example, this difference is at least 5 percent, preferably at least 10 percent, and further exceeds 20 percent, and can be, for example, up to 50 percent, and even up to 100 percent (double). For example, the amplitude represents the range of movement of the center point of the membrane from the equilibrium position (when the membrane is not actuated) to each side (when the membrane is actuated by an electrical signal E or ultrasonic wave W).

[0012] In one embodiment, the control element C is configured to reduce (e.g., resist, restrain, and / or limit) the movement of the first membrane 10 in one of the directions towards the first side 10a or the second side 10b as compared to the opposite direction. For example, the range of movement is reduced to at least 1 / 1.05 times, 1 / 1.1 times, 1 / 1.2 times or more, for example, up to 1 / 1.5 times, and even up to 1 / 2 times (i.e., the second amplitude Zb is at least 10 percent higher than the first amplitude Za). In some embodiments, the control element C exclusively reduces the membrane displacement in one direction, for example, by applying resistance, while having little or no effect in the other direction. In other or further embodiments, the control element C can reduce the membrane displacement in both directions, but to different extents, for example, by making the resistance applied in one direction greater than that in the other direction. Instead of, or in addition to, reducing the displacement in one direction, the control element C can also be envisioned to enhance the membrane displacement in the other direction, for example, by active control as described hereinafter.

[0013] Preferably, the electronic circuit 30 is coupled to the first membrane 10. In one embodiment, the electronic circuit 30 is configured to transmit an electrical signal E1 that causes the first vibration V1. In another or further embodiment, the electronic circuit 30 is configured to receive an electrical signal E1 caused by the first vibration V1. In some embodiments, the electronic circuit 30 includes a signal generator (not shown) configured to generate an electrical signal E1 that includes one or more frequencies at or near the resonance frequency of the first membrane 10. In other or further embodiments, the electronic circuit 30 includes a signal detector (not shown) configured to detect an electrical signal E1 that includes one or more frequencies at or near the resonance frequency of the first membrane 10.

[0014] In principle, the membrane can respond to various resonant vibrations, but preferably, the fundamental mode having the lowest resonance frequency (e.g., u01 Or as specified as 1s) is used to efficiently generate or receive sound waves. For example, the resonance frequency Fr is determined by, for example, one or more of the material properties of the membrane and the diameter of the acoustic membrane. It is also possible to use other parameters or additional parameters, such as density, Poisson ratio, and Young's modulus. In some embodiments, the fundamental frequency Fr (Hz) can be expressed using parameters such as membrane tension T (N / m), density σ (kg / m 2 ), diameter D (m), etc. It is also possible to use other parameters or additional parameters such as membrane thickness, elastic modulus, etc. Alternatively, or additionally, the fundamental frequency of the membrane can be determined by any other analytical modeling or numerical modeling. In one embodiment, a specific resonance frequency Fr is determined by setting a specific diameter D with respect to the tension and density of the membrane. For example, the diameter D can correspond to half the wavelength at the resonance frequency of the wave that travels through the membrane to generate a standing wave.

[0015] In a preferred embodiment, a piezoelectric transducer is used to operate the membrane. Most preferably, the piezoelectric material is disposed as a layer on the flexible membrane. It is also possible to provide other layers, such as electrode layers, for use in applying respective electrical signals to the piezoelectric layer. As described herein, a capacitive layer and / or a conductive layer for applying an electrostatic charge can also be envisioned. These layers can be charged by other electrical signals or additional electrical signals, for example, by applying an electrostatic charge or by dynamically applying a charge during respective partial cycles of the vibration.

[0016] By driving the transducer at the carrier frequency at each resonance frequency of the transducer, or at a carrier frequency around the resonance frequency, the performance can be improved. For example, the first resonance or ground resonance of the membrane is used. The resonance frequency of the transducer is relatively high, for example, it may exceed 1 kilohertz, it may exceed 10 kilohertz, it may exceed 100 kilohertz, and even may exceed 1 megahertz. Such high frequencies are not necessarily suitable for all applications. For example, frequencies exceeding 800 hertz may be difficult to feel in the case of tactile applications. For example, the optimal frequency for tactile feedback can be between 50 hertz and 500 hertz, preferably between 100 hertz and 300 hertz.

[0017] In some embodiments, the electrical signal includes a plurality of frequencies including a carrier frequency (as good as possible) corresponding to the resonance frequency of the transducer and an envelope frequency or modulation frequency according to the application. For example, a tactile feedback device can use a carrier frequency of 40 kHz that is an amplitude modulated by a modulation frequency of 200 Hz. It is also conceivable to use three or more frequencies, in particular, for example, a bandwidth of frequencies including the resonance frequency of each transducer.

[0018] In some embodiments, the acoustic device is formed including an array of a plurality of acoustic transducers as described herein. For example, the transducer can be formed by a stack patterned on a flexible substrate. In one embodiment, the stack includes a piezoelectric layer sandwiched between a respective lower electrode layer and an upper electrode layer. In some embodiments, the working surface of the acoustic transducer includes a portion of the flexible substrate in the contact area. In other embodiments or further embodiments, the membrane can be separately attached to the surrounding substrate.

[0019] Here, various types of control elements will be described. In some embodiments, the control element C includes passive elements, such as components adjacent to the first membrane 10. Preferably, the adjacent control element C is not in direct contact with the first membrane 10. For example, having a pocket or other layer between the first membrane 10 and the control element C may enable a smoother interaction. In other or further embodiments, the control element C may be actively controlled, for example, its effect on the first membrane 10 is adapted during each cycle of the first vibration V1.

[0020] Figure 1A illustrates inducing displacement asymmetry (in this figure, Za < Zb) by closely stacking two membranes 10 and 20 vertically with respect to each other. In some embodiments, such as the illustrated embodiments, the control element C includes a second membrane 20 disposed parallel to the first membrane, and there is a (closed) pocket 15 therebetween. For example, the displacement asymmetry can be caused by the asymmetry between the expansion and contraction of the pocket 15. Preferably, the pocket 15 is filled with a fluid, such as a gas like air, and when the pocket contracts, it resists compression and causes a non-linear force on the first membrane as a function of the displacement of the pocket towards the second membrane. For example, the fluid in the pocket, such as air, applies an outward pressure to the membrane, while the surrounding medium, such as air, applies an inward pressure, such as atmospheric pressure, to the membrane. Usually, the outward pressure increases when the pocket contracts and decreases when the pocket expands. For example, the outward pressure can be increased non-linearly when the membrane moves inward.

[0021] In other embodiments or further embodiments, for example, in the embodiments as shown, parallel membranes are arranged with a separation of only the equilibrium distance Ze therebetween. In a preferred embodiment, the distance Ze is relatively small so as to have a sufficient effect. For example, the distance Ze can be made equivalent to less than twice the total deflection amplitude Za + Zb, for example, this total amplitude. In another preferred embodiment or a further preferred embodiment, the parallel membranes are arranged at a distance Ze such that they do not contact even during operation. Thus, a gap distance Zg can be left between them. For example, the equilibrium distance Ze between the membranes (when not operating) is greater than twice the (first) amplitude Za towards the inside (i.e., Ze > 2 * Za). Therefore, when the amplitude Zc towards the inside of the second membrane 20 is equivalent to the amplitude Za towards the inside of the first membrane 10, they do not contact each other as their respective vibrations V1, V2 progress.

[0022] In some embodiments, the membranes have a diameter between 0.5 millimeters and 0.5 centimeters, preferably between 1 millimeter and 3 millimeters, for example, 2 millimeters. Usually, the deflection or total amplitude of the membrane at resonance is much smaller than the diameter, for example, at least one-tenth or one-hundredth. For example, the total amplitude Za + Zb is between 10 nanometers and 100 micrometers, preferably less than 10 micrometers, and even less than 1 micrometer. In one embodiment, the distance Ze between the membranes is in the range between 5 nanometers and 50 micrometers, preferably less than 10 micrometers, less than 5 micrometers, and even less than 1 micrometer. The smaller the distance, for example, the greater the non-linear effect until the distance at which the membranes start to contact (gap distance Zg = 0) is reached. However, it is preferably not inclusive of this reaching point.

[0023] In a preferred embodiment, the second membrane 20 is actuated to exhibit a second vibration V2 that is out of phase with the first vibration V1. In other words, adjacent membranes are configured to move such that they simultaneously move towards each other or away from each other. As will be appreciated, by moving the second membrane in this way, the effect of the expanding / contracting pocket can be significantly enhanced. In other or further embodiments (not shown), it is also contemplated to replace the second membrane 20 with a stationary or fixed layer / wall. For example, the pocket can be formed between the first membrane and a stationary wall.

[0024] FIG. 1B illustrates an embossing of the membrane to further enhance the effect. In some embodiments, for example, in the embodiments as shown, at least the first membrane 10 has a relatively thick and / or stiff section 10e at the center of the membrane compared to the (radial) edge of the membrane. For example, as illustrated by the comparison between FIGS. 1A and 1B, this makes it possible to have the effect of increasing the total displacement volume compared to the peak out-of-plane displacement of the membrane. For example, the relatively thick or stiff central section of FIG. 1B may have a smaller curvature in deflection (e.g., more blocky than Gaussian), so the effect of the inward contraction extends over a larger area than just the peak at the center compared to FIG. 1A.

[0025] In some embodiments, the center of the membrane is, for example, at least 1.1 times, 1.2 times, 1.5 times, 2 times or more thicker than the edge. In other or further embodiments, the material of the center of the membrane is stiffer than the edge, for example, the bending stiffness [Pa·m 3and / or the Young's modulus [Pa] is at least 1.1 times, 1.2 times, 1.5 times, 2 times or more, and is higher. Preferably, the thickened region and / or the stiffened region extends over sub-regions of the total area, for example, covering 50 percent to 90 percent, preferably 60 percent to 80 percent of that area. In some embodiments, the membrane has a layer or an embossment separately provided on at least one side, preferably on the first side 10a facing in the inner direction. As can be understood, having material separately offset from the center with respect to the central plane of the membrane on one side may also contribute to displacement asymmetry.

[0026] Figure 2A illustrates inducing displacement asymmetry using electrostatic charges. In some embodiments, for example, in the embodiments as shown, the control element C includes an electrostatic device (not shown) configured to generate electrostatic charges on the surface of the first membrane 10 and on another opposing surface adjacent to the first membrane 10. As can be understood, the attractive and / or repulsive forces (+-, ++,--) between the electrostatic charges may contribute to an asymmetric force on the first membrane 10 that affects its displacement in one or both directions. This figure shows repelling (similar) charges, but it is also possible to use attracting charges, for example, if asymmetry is to be induced in the opposite direction. Combinations are also possible.

[0027] In some embodiments, for example, in the embodiments as shown in this figure and similarly in other embodiments applicable to those described herein, the first membrane 10 includes a piezoelectric layer 10p. For example, the piezoelectric layer 10p is coupled to an electronic circuit 30 for receiving and / or generating an electrical signal E1. For example, applying an alternating electrical signal to the piezoelectric layer 10p can cause the piezoelectric material that actuates the membrane to contract / expand, and vice versa.

[0028] In other embodiments or further embodiments, for example, in the embodiments as shown, the first membrane 10 includes an electrostatic layer 10s made of, for example, a conductive material for applying an electrostatic charge. Preferably, as shown, the electrostatic layer 10s is on the first side 10a of the first membrane 10, for example, facing an adjacent second electrostatic layer 10t. Most preferably, as shown, the electrostatic layer 10s is disposed on the first side 10a of the first membrane 10, while the piezoelectric layer 10p can be disposed on, for example, the opposite second side 10b. Other configurations are also possible.

[0029] In some embodiments, the electrostatic device is configured to generate an alternating current (AC) signal of electrostatic charge. For example, the application of the electrostatic charge is synchronized with the vibration of the membrane. In one embodiment, the alternating electrical signal E1 can be used to actuate the piezoelectric layer 10p of the first membrane 10, while the alternating charge is applied to the (separate) electrostatic layers 10s, 10t to induce displacement asymmetry. For example, the electrical (electrostatic) signals E3 and / or E4 can be applied to the respective electrostatic layers 10s, 10t. Preferably, the electrostatic charge or signals E3, E4 are applied asymmetrically during each cycle of the vibrating membrane, for example, only during half of the cycle when the membranes are together or only during half of the cycle when they are apart.

[0030] In other embodiments or further embodiments, the control element C is configured to dynamically affect the membrane displacement during each vibration cycle. For example, dynamically change the electrostatic charge and apply a force only during a part of the vibration cycle. In one embodiment, the electrostatic charge affects at least the stiffness of the first membrane 10.

[0031] Figure 2B illustrates the use of electrostatic charge in combination with a second membrane. In some embodiments, the electrostatic charge is generated on the second membrane 20. Such a combination can provide a synergistic advantage of inducing the asymmetry according to the previous embodiments. Alternatively, or additionally, further effects can even be realized by combining with the first membrane 10 and / or the second membrane 20 having a relatively thick and / or stiff section 10e relative to the central part of each membrane. As can be understood, the relatively flat part of the vibrating membrane not only increases the displacement in the pocket, but also enlarges the area where the charges can enter within an effective distance from each other. Other advantageous combinations are also possible, for example, only thickening the section of the first membrane 10. For example, this can be applied to the single membrane 10 of FIG. 2A in combination with a fixed wall instead of the second membrane 20.

[0032] Instead of using, or in addition to using, an alternating current (AC) signal to generate an electrostatic charge, it is also conceivable to apply a continuous signal (DC). In some embodiments, the electrostatic device is configured to include a continuous signal (DC) or include a DC component (offset) in the alternating current (AC) signal for applying an electrostatic charge, and the electrostatic charge is configured to change at least the equilibrium position of the first membrane 10. For example, a fixed or offset electrostatic charge on one or more membranes can be used to adjust the equilibrium distance that may deviate from the center. Also in this case, the effect may be greater when combined with a thickened or stiffened central section, for example, resulting in a more blocky deflection.

[0033] Figures 3A - 3C illustrate inducing displacement asymmetry by using a foldable structure to constrain one - way movement above a threshold.

[0034] In some embodiments, for example, in the embodiments as shown, the control element C includes a (physical) connection to the center of the first membrane 10 on the first side 10a. For example, this connection enables displacement (inward) towards the first side 10a of the first membrane 10, but displacement towards the second side 10b is restricted. In one embodiment, the displacement is restricted by the physical connection beyond a threshold displacement in the direction of the second side 10b, for example, beyond the central position or further. In one embodiment, the connection resists displacement beyond the threshold or substantially impedes displacement beyond the threshold. Examples of such connections may include, for example, a flexible thread / rope, a stiffer element such as a strut, an elastic element such as a spring, etc. In some embodiments, the connection includes a foldable structure configured to be folded (or relaxed) in one direction and tightly pulled beyond a threshold displacement in the other direction.

[0035] In one embodiment, for example, in the embodiments illustrated in FIGS. 3A and 3B, the connection connects the first membrane 10 to the second membrane 20 (at the center). In another or further embodiment, for example, in the embodiment shown in FIG. 3C, the connection connects the first membrane 10 to an electrostatic layer. It is also possible to envision other or further embodiments having connection structures.

[0036] FIG. 4A illustrates inducing displacement asymmetry by using a second piezoelectric layer 10q on the first membrane 10 to asymmetrically affect membrane displacement. In some embodiments, the membrane includes a first piezoelectric layer 10p for transmitting and receiving an electrical signal E1 related to the first vibration V1 of the first membrane 10. In other or further embodiments, the control element C includes a second piezoelectric layer 10q, and the electronic circuit is configured to operate the second piezoelectric layer 10q to dynamically change the characteristics of the first membrane 10 during a part of its vibration cycle V1.

[0037] Figure 4B illustrates the application of different electrical signals E1, E2, and the resulting vibration V1 as a function of time T. In some embodiments, the first electrical signal is transmitted to (or received from) the first piezoelectric layer 10p, and a different, second electrical signal E2 is transmitted to the second piezoelectric layer 10q. In other or further embodiments, the second electrical signal E2 is configured to activate the second piezoelectric layer 10q during a particular portion of the first vibration V1. In one embodiment, the second electrical signal E2 exclusively activates the membrane during each half-cycle in one of the directions of the vibration cycle. For example, the second piezoelectric layer is activated to cancel or damp the displacement in one direction Za. In this way, the pressure pulse generated by the membrane actuated via the first piezoelectric layer 10p can be (non-linearly) deformed in said one direction as compared to the other direction. Preferably, the second piezoelectric layer is disposed on the opposite side of the membrane with respect to the first piezoelectric layer. For example, a flexible membrane material is disposed between the piezoelectric layers 10p, 10q.

[0038] Figures 5A and 5B illustrate a comparison between a symmetric pressure pulse (P) and an asymmetric pressure pulse (P) as a function of time (T) and the intensity (I) of the associated frequency spectrum (F). In one preferred embodiment, in the asymmetric pulse (Figure 5B), the effective bandwidth can be broadened, for example, by forcing the membrane displacement to be more non-linear, specifically, by inducing displacement asymmetry.

[0039] Aspects of the present disclosure can be embodied as a method for enhancing the effective bandwidth of a membrane-based ultrasonic transducer. Some embodiments utilize control elements C disposed on one or both sides of the membrane to increase or decrease the displacement amplitude of the membrane towards that side and / or the opposite side. Thereby, during its vibration, displacement asymmetry can be induced on either side of the membrane's movement.

[0040] In some embodiments, for example, in the embodiments described with reference to FIGS. 1A and 1B, the control element C changes, for example, decreases the displacement amplitude Za of the first membrane 10 towards the first side 10a, as compared to the second side 10b, by the pressure of the fluid compressed by the displacement of the pocket formed on the first side 10a.

[0041] In other or further embodiments, for example, in the embodiments described with reference to FIGS. 2A and 2B, the control element C changes, for example, decreases or increases, or vice versa, the equilibrium position and / or the displacement amplitude Za of the first membrane 10 towards the first side 10a, as compared to the second side 10b, by the continuous electrostatic force and / or the alternating (dynamic) electrostatic force applied to the first membrane 10 by the control element C.

[0042] In other or further embodiments, for example, in the embodiments described with reference to FIGS. 3A and 3B, the control element C changes the equilibrium position and / or the displacement amplitude Zb of the first membrane 10 towards the second side 10b, as compared to the first side 10a, by an (exclusive) physical connection to the central part of the first membrane 10 on the first side 10a, thereby enabling the displacement of the first membrane 10 towards the inner side towards the first side 10a, but restricting the displacement towards the second side 10b.

[0043] In other or further embodiments, the control element dynamically affects the force and / or the stiffness of the first membrane 10 using, for example, a plurality of piezoelectric layers 10p, 10q that are operated differently during each respective vibration cycle, as described with reference to FIGS. 4A and 4B, or by a variable electrostatic force as described with reference to FIGS. 2A and 2B.

[0044] For the purpose of a clear and concise description, although features are described herein as part of the same embodiment or separate embodiments, it will be understood that the scope of the invention may include embodiments having all the described features or combinations of some of the features. Of course, any one of the above embodiments or processes may be combined with one or more other embodiments or processes to provide further improvements when finding and matching designs and advantages. It is understood that the present disclosure presents certain advantages in increasing the bandwidth of a membrane-based transducer and can generally be applied to any application using a resonant transducer.

[0045] When interpreting the appended claims, unless specifically stated otherwise, the word "comprising" does not exclude the existence of other elements or acts than those listed in a given claim, and the words "a" or "an" preceding an element do not exclude the presence of a plurality of such elements, and any reference signs in the claims do not limit the scope, and some "means" may be represented by the same or different items (including plural), or the implemented structure or function, and it is understood that any of the disclosed devices or parts thereof may be combined together or separated into further parts. When one claim refers to another claim, this may indicate a synergistic advantage realized by a combination of the respective features. However, just because a particular means is cited in different claims does not mean that the combination of these means cannot be used to obtain an advantage. Therefore, the present embodiment may include all valid combinations of the claims, and each claim may, in principle, refer to any preceding claim unless clearly excluded by the context.

Claims

**Claim 1** An ultrasonic transducer (100), comprising: - at least a first membrane (10) including a first piezoelectric layer (10p) and configured to exhibit a first vibration (V1) for transmitting and receiving ultrasonic waves (W); - an electronic circuit (30) coupled to the first membrane (10) and configured to transmit and receive an electrical signal (E1) that causes the first vibration (V1) or is caused by the first vibration (V1) to or from the first piezoelectric layer (10p); - a control element (C) disposed on a first side (10a) of the first membrane (10) and configured to induce displacement asymmetry (Za<>Zb) in the movement of the first membrane (10) during the first vibration (V1) to the first side (10a) as compared to an opposite second side (10b); The ultrasonic transducer (100) comprising the above. **Claim 2** The control element (C) includes a second membrane (20) disposed parallel to the first membrane and having a closed pocket (15) therebetween, and in order to induce the displacement asymmetry, the closed pocket (15) contains a fluid, and when the closed pocket (15) contracts, it resists compression and causes a non-linear force on the first membrane (10) as a function of its displacement towards the second membrane (20). The ultrasonic transducer according to claim 1. **Claim 3** The electronic circuit (30) is configured to operate the second membrane (20) to exhibit a second vibration (V2) that is out of phase with the first vibration (V1), and the membranes are configured to move away from each other simultaneously or to move towards each other without direct contact. The ultrasonic transducer according to claim 2. **Claim 4** At least the first membrane (10) has a relatively thick and / or stiff section (10e) that covers a small section of the membrane between 50% and 90% of the total area of the membrane at the center of the membrane, and the center of the membrane has a thickness and / or rigidity that is at least 1.1 times that of the edge of the membrane. The ultrasonic transducer according to any one of claims 1 to 3. **Claim 5** The electronic circuit (30) is configured to transmit a first electrical signal (E1) to the first membrane (10) to cause the first vibration (V1), and the electronic circuit (30) is configured to dynamically affect the displacement of the membrane during each vibration cycle of the first vibration (V1) caused by the first electrical signal (E1) by transmitting a different, second electrical signal (E2) to the control element (C). The ultrasonic transducer according to any one of claims 1 to 4.

6. The ultrasonic transducer according to any one of claims 1 to 5, wherein the control element (C) includes an electrostatic device configured to generate an electrostatic charge on the surface of the first membrane (10) and on another opposite surface adjacent to the first membrane (10).

7. The ultrasonic transducer according to claim 6, wherein the electrostatic charge is generated on a second membrane (20).

8. The ultrasonic transducer according to claim 6 or 7, wherein the electrostatic device is configured to generate an alternating current signal of the electrostatic charge, and the application of the electrostatic charge is synchronized with the first vibration (V1) of the first membrane (10).

9. The ultrasonic transducer according to any one of claims 6 to 8, wherein the electrostatic device is configured to include an offset in a continuous signal or an alternating current signal to apply the electrostatic charge, and the electrostatic charge is configured to change at least the equilibrium position of the first membrane (10).

10. The control element (C) includes a second piezoelectric layer (10q), and the electronic circuit (30) is configured to operate the second piezoelectric layer (10q) to dynamically change the characteristics of the first membrane (10) during a part of its vibration cycle (V1). A first electrical signal is sent to the first piezoelectric layer (10p), and a different second electrical signal (E2) is sent to the second piezoelectric layer (10q). The ultrasonic transducer according to any one of claims 1 to 9.

11. The ultrasonic transducer according to any one of claims 6 to 9, wherein the electrostatic charge affects the rigidity of the first membrane (10).

12. The ultrasonic transducer according to claim 10, wherein the second piezoelectric layer (10q) affects the rigidity of the first membrane (10).

13. The ultrasonic transducer according to any one of claims 1 to 12, wherein the control element (C) is configured to reduce the amplitude (Za, Zb) of the first membrane (10) in one of the directions toward the first side (10a) or the second side (10b) of the first membrane (10) as compared to the opposite direction.

14. The ultrasonic transducer according to any one of claims 1 to 13, wherein the control element (C) includes a connection structure that is exclusively connected to the first side (10a) and exclusively to the central portion of the first membrane (10), and the connection structure enables displacement of the first membrane (10) toward the first side (10a) but restricts displacement toward the second side (10b).

15. The first vibration (V1) is - a first amplitude (Za) between the equilibrium position (Z1) of the first membrane (10) and the maximum expansion position of the first membrane (10) toward the first side (10a), - a second amplitude (Zb) between the equilibrium position and the maximum expansion position of the first membrane (10) toward the second side (10b), and - the control element (C) is configured to affect the movement of the first membrane (10) to induce a difference of at least 5 percent between the first amplitude (Za) and the second amplitude (Zb). The ultrasonic transducer according to any one of claims 1 to 14.

16. A method for enhancing the effective bandwidth of a piezoelectric membrane-based ultrasonic transducer, comprising transmitting and receiving an electrical signal (E1) to or from a first piezoelectric layer (10p) included in a first membrane (10) of the ultrasonic transducer, the electrical signal (E1) causing a first vibration (V1) of the first membrane (10) or being caused by the first vibration (V1). Using a control element (C) arranged on a first side (10a) of the first membrane (10), increasing or decreasing the displacement amplitude of the first membrane (10) towards a second side (10b) of the first side (10a) and / or the opposite side, and during the first vibration (V1) of the first membrane (10), inducing a displacement asymmetry (Za<>Zb) in the movement of the first membrane (10) towards the first side (10a) as compared to the second side (10b), thereby enhancing the effective bandwidth; A method comprising this.

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