Optimization of acoustic membrane arrays

Abstract

An acoustic device (100) includes an array of acoustic membranes (1, 2, 3, 4) formed on a foil (10). Each of the acoustic membranes (1, 2, 3, 4) is configured to vibrate at a resonant frequency (Fr) of the acoustic membrane (1, 2, 3, 4) to generate a corresponding sound wave (W1, W2, W3, W4). A relative phase (ΔΦ12, ΔΦ34) is determined at which the acoustic membranes (1, 2, 4, 5) are actuated to generate a predetermined interference pattern (C) between the sound waves (W1, W2, W3, W4). A Lamb wavelength (λs) of a Lamb wave (Ws) is determined, which passes through a middle portion (10i, 10j) of the foil (10) between adjacent acoustic membranes (1, 2; 3, 4) at the resonant frequency (Fr). The distance (X12, X34) of the middle part (10i, 10j) between adjacent acoustic membranes (1, 2; 3, 4) in the layout is determined based on the relative phase (ΔΦ12, ΔΦ34) and the Lamb wavelength (λs) so that the Lamb wave (Ws) generated by the acoustic membrane (1, 3) arrives in phase with the adjacent acoustic membrane (2, 4).

Description

Technical Field

[0001] The present disclosure relates to acoustic devices including arrays of acoustic membranes, and methods for optimizing the design and manufacture of such devices. Background Art

[0002] There is great interest in the construction and miniaturization of multi-element acoustic arrays, for example, ultrasonic transducers for use in medical diagnostics, non-destructive testing, mid-air haptics, and other applications. An important aspect in the design and manufacture of acoustic arrays is to have all elements (e.g., membranes) have a predefined phase at which they vibrate for optimal focusing. However, inter-element mechanical crosstalk between the elements in the array can degrade performance, for example, because actuation of one elementary transducer can also affect adjacent transducers. One way to avoid crosstalk is to add further acoustic isolation between the transducers. However, this can increase manufacturing costs and result in a bulkier design. Another way to avoid crosstalk is to increase the distance between the transducers. However, this also reduces the number of transducers that can be mounted on a given surface.

[0003] Further improvements in the design and manufacture of acoustic arrays remain desirable, for example, enabling the mounting of densely packed arrays of acoustic membranes on relatively thin (flexible) substrates (such as foils). Summary of the Invention

[0004] Without being bound by theory, the inventors have found that the main source of mechanical crosstalk between adjacent acoustic membranes on a relatively thin substrate or foil can be traced back to antisymmetric Lamb waves passing through the middle portion of such a substrate. Various aspects of the present disclosure are directed to designing an acoustic array in which the middle distance between corresponding pairs of adjacent acoustic membranes is predetermined so that the Lamb waves generated through the middle portion of the substrate at the resonant frequency of the membrane arrive in phase with the adjacent membrane. For membrane pairs or adjacent (in-phase) membranes configured to vibrate with the same phase, the distance is preferably an integer times the Lamb wavelength (optionally, allowing for small fractional deviations). In this way, the sound waves passing through the substrate can actually enhance the actuation of adjacent transducers. Additionally, or alternatively, some pairs of acoustic transducers can actually be designed to vibrate with a specific phase difference. For example, in a focused array it may be desirable that transducers closer to the focus of the sound wave are actuated with a phase delay compared to transducers further away from the focus. The distance between a pair of membranes or adjacent (phase-delaying) membranes configured to vibrate with a relative phase difference is preferably an integer plus a predetermined decimal times the Lamb wavelength. In this case, the decimal is selected based on the specific phase difference. For example, a fractional multiple of the wavelength can correspond to a fractional period of the phase difference.

[0005] In one implementation, the design of the membrane transducer array includes characterizing the carrier substrate or foil to determine its material properties. Since the membrane transducer preferably uses a specific membrane resonant frequency, the Lamb wave dispersion curve for the foil associated with the desired frequency can be determined based on, for example, experiments or calculations. For example, the phase difference can be determined by the phase velocity of the dispersed Lamb wave and the distance between the individual vibrating membranes. For example, the phase velocity at a specific frequency (resonance of the membrane) can be determined based on, for example, the thickness of the foil and the material properties of the foil (density, Poisson's ratio and Young's modulus). Additionally or alternatively, the phase velocity and / or Lamb wavelength in the foil can also be determined experimentally. The array can then be designed so that the Lamb waves arrive in phase between adjacent vibrating membranes (based on the expected phase) to avoid destructive interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The foregoing and other features, aspects, and advantages of the apparatus, systems, and methods of the present disclosure will become better understood from the following description, appended claims, and accompanying drawings, in which:

[0007] Figure 1A shows a top view of an acoustic device including an array of acoustic membranes formed on a foil;

[0008] Figure 1B shows a transducer in a mutually opposite cross-sectional view;

[0009] Figure 1C showing a cross-sectional view of a phase-delayed pair of transducers having a predetermined phase difference;

[0010] Figure 2 An apparatus having an array of acoustic membranes configured to constructively interfere at predetermined locations is shown;

[0011] Figure 3A and Figure 3B A top view of the corresponding acoustic membrane array is shown;

[0012] Figure 4A shows a top view of the membrane arranged in a concentric circle pattern;

[0013] Figure 4B A photograph of an actual device with a similar pattern is shown;

[0014] Figure 5A An acoustic device having a membrane distributed along a spiral pattern is shown;

[0015] Figure 5B A corresponding isometric view of an apparatus for generating acoustic waves to form a focus is shown;

[0016] Figure 6A shows the Lamb wave dispersion curve of a typical substrate (foil) used to construct membrane arrays;

[0017] Figure 6B A graph showing the sound pressure level produced by a transducer array as a function of frequency for different distances between the transducers is shown. DETAILED DESCRIPTION

[0018] The terms used to describe specific embodiments are not intended to limit the invention. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms, unless the context clearly indicates otherwise. The term "and / or" includes any and all combinations of one or more of the listed related items. It will be understood that the terms "comprises" and / or "comprising" specify the presence of the features described, but do not exclude the presence or addition of one or more other features. It will be further understood that when a particular step of a method is referred to as a subsequent step of another step, unless otherwise stated, the particular step may directly follow the other step, or one or more intermediate steps may be performed before performing the particular step. Similarly, it will be understood that when describing a connection between structures or components, unless otherwise stated, the connection may be established directly or may be established through an intermediate structure or component.

[0019] The present invention is described more fully below 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. The embodiments may be described with reference to schematic and / or cross-sectional views of possible idealized embodiments and intermediate structures of the invention. Throughout the specification and drawings, like numbers refer to like elements. Relative terms and their derivatives should be interpreted as referring to orientations as subsequently described or as shown in the drawings under discussion. These relative terms are for ease of description and do not require that the system be constructed or operated in a particular orientation unless otherwise specified.

[0020] Figure 1A A top view of an acoustic device 100 comprising an array of acoustic membranes 1 , 2 , 3 , 4 formed on a foil 10 is shown. Figure 1B A co-opposing cross-section of the transducers 1 , 2 is shown. Figure 1C A cross-sectional view of a phase-delayed pair of transducers 3 , 4 having a predetermined phase difference ΔΦ13 is shown.

[0021] Some aspects of the present disclosure relate to an acoustic device 100 comprising an array of acoustic membranes 1, 2, 3, 4 formed on a foil 10. In a preferred embodiment, each of the acoustic membranes 1, 2, 3, 4 is configured to vibrate at a resonant frequency Fr of the acoustic membrane 1, 2, 3, 4 for generating a corresponding sound wave W1, W2, W3, W4.

[0022] In some embodiments, at least a first subset of the array is formed by co-phase pairs of adjacent acoustic membranes 1, 2. For example, each co-phase pair includes a corresponding first acoustic membrane 1 and an adjacent second acoustic membrane 2. In one embodiment, for example, as shown in the figure, the first acoustic membrane 1 and the second acoustic membrane 2 are separated by a first intermediate portion 10i of the foil 10 therebetween. Preferably, a first distance X12 of the first intermediate portion 10i between the first acoustic membrane 1 and the second acoustic membrane 2 is a first integer N12 times a predetermined Lamb wavelength λs of a Lamb wave Ws generated by the acoustic membranes 1, 2 passing through the intermediate portion 10i between the adjacent acoustic membranes 1, 2 at a resonant frequency Fr.

[0023] In some embodiments, a smaller deviation may be allowed. For example, the distance X12 may be an integer multiple of the Lamb wavelength (λs) plus or minus a first decimal d12 that is less than one tenth of the Lamb wavelength (λs). This may be expressed as X 12 =(N 12 ±d 12 )·λ s In order to minimize crosstalk interference between the same pairs of adjacent films 1, 2, the decimal d12 is preferably relatively small, for example, less than one fifth (<0.2), less than one tenth (<0.1), less than one twentieth (<0.05), less than one fiftieth (<0.02), or even less than one hundredth (<0.01). Most preferably, the decimal d12 is as low as possible, i.e., zero (within measurement or manufacturing tolerances). The smaller the decimal d12, the smaller the effect of destructive interference between the pairs.

[0024] In some embodiments, at least a second subset of the array is formed by phase-delayed pairs of adjacent acoustic membranes 3 and 4. For example, each phase-delayed pair includes a third acoustic membrane 3 and an adjacent fourth acoustic membrane 4. In one embodiment, for example, as shown in the figure, the third acoustic membrane 3 and the fourth acoustic membrane 4 are separated by a second intermediate portion 10j of the foil 10 therebetween. Preferably, the second distance X34 of the second intermediate portion 10j between the third acoustic membrane 3 and the fourth acoustic membrane 4 is a second integer N34 plus or minus a non-zero second decimal d34, multiplied by a predetermined Lamb wavelength λs of the Lamb wave Ws, wherein the Lamb wave is generated by the acoustic membranes 3 and 4 passing through the intermediate portion 10i between the adjacent acoustic membranes 3 and 4 at the resonant frequency Fr. This can be expressed as X 34 =(N 45±d 34 )·λ s Preferably, the second decimal d34 is a value corresponding to the phase delay between the third acoustic membrane 3 and the fourth acoustic membrane 4. Predetermined.

[0025] In principle, the integer N12, N34 that counts the number of Lamb wavelengths fitted between the films can be values ​​of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc. However, preferably, the distance X12 or X34 between the transducers remains relatively small. For example, the first integer N12 and / or the second integer N34 are preferably less than or equal to three, two, or even one. The distance between the transducers is smaller, and each surface area of ​​foil 10 can be equipped with more transducers. It will be understood that, particularly for relatively small distances, this teaching can provide benefits in avoiding undesirable crosstalk. In certain embodiments, it may be desirable to have enough distances and materials between the transducers so that at least some isolation is achieved between the transducers. Therefore, it may be desirable to set the integer to at least one or two.

[0026] Although in principle the membrane can support different resonant vibrations, preferably the fundamental mode (u01, 1s) with the lowest resonant frequency is used to efficiently generate the sound waves. Typically, the resonant frequency Fr is determined by, for example, one or more of the diameter of the acoustic membrane and the membrane material properties. Other or additional parameters may also be used, such as density, Poisson's ratio and Young's modulus. In some embodiments, the fundamental frequency Fr (Hz) may be determined by the membrane tension T (N / m), density σ (kg / m 2 ), diameter D(m) is expressed as Alternatively, or in addition, the fundamental frequency of the membrane can be determined by any other analytical or numerical modeling. The Lamb wavelength can also be determined experimentally, for example, by actuating the foil at the resonant frequency and recording the wave. In one embodiment, the specific resonant frequency Fr is determined by setting a specific diameter D that is related to the tension and density of the membrane. For example, the diameter D can correspond to half the wavelength of a wave propagating in the membrane at the resonant frequency to generate a standing wave.

[0027] Typically, the Lamb wavelength λs is determined by, for example, the frequency at which the Lamb wave Ws is generated (e.g., the resonant frequency Fr of the membrane) and the material properties and thickness of the intermediate portion 10i. Other or similar parameters, such as the density of the foil (including the base foil and any additional layers), Poisson's ratio, and Young's modulus, may also be used. For example, the wavelength may be determined as a function of the phase velocity of the Lamb wave (at the resonant frequency) divided by the resonant frequency. Alternatively, or in addition, the fundamental frequency of the membrane may be determined by any other analytical or numerical modeling. Preferably, the distance of the intermediate portions between the nearest adjacent membranes is between half and twice the membrane diameter and is fine-tuned according to the specifications for the relative phase described in the present disclosure.

[0028] In a preferred embodiment, the acoustic membranes 1, 2, 3, 4 are formed as an integral part of the foil 10. For example, the actuating surface of the acoustic membranes 1, 2, 3, 4 comprises a layer 10b of foil. For example, the middle portion 10i, 10j of the foil between the membranes may be provided with one or more further layers 10a to provide definition of the edges of the acoustic membrane and / or to provide at least some acoustic insulation between the membranes. In some embodiments, the acoustic membranes themselves may comprise further layers (not shown), for example a piezoelectric layer sandwiched between respective bottom and top electrode layers. By energizing the piezoelectric layer, for example by applying a voltage to the electrodes, the piezoelectric layer and the membrane may be deformed. For example, an AC voltage signal may be applied to the electrodes, wherein the signal comprises a frequency component that coincides with the resonant frequency Fr. Actuation of the membranes may also be provided in other ways, for example by a separate transducer.

[0029] Typically, the foil 10 is relatively thin. In principle, the foil can be formed by a thin sheet of any solid material, for example, the thickness of the solid material is less than the wavelength of the compression / shear waves that can be generated in the material (by the transducer), or the thickness of the solid material has the same order of magnitude as the wavelength of the compression / shear waves. Preferably, the total thickness of the middle part of the foil between the membranes (including any additional layers 10a, 10b) is less than two millimeters, less than one millimeter, or even less than half a millimeter. The membrane forming the corresponding acoustic transducer can be thinner, for example, less than eighty percent of the middle part of the foil, preferably less than sixty percent, or even thinner, for example, at least two or three times thinner. In some embodiments, the foil 10 can be relatively flexible, for example, so that the foil (including the membrane) can be bent on a radius of less than 20 centimeters, less than 10 centimeters or even less than 5 centimeters, without the acoustic device 100 losing its basic (electrical / acoustic) function.

[0030] In some embodiments, the thickness of the middle portions 10i, 10j of the foil 10 can be varied to influence the propagation of the Lamb waves, for example, so that the Lamb waves arrive in phase with adjacent membranes. It is also conceivable to add further thickness or acoustic insulation to the middle portions between at least some transducers that cannot be set at a desired distance and would otherwise interfere destructively with each other. Combinations are also possible, for example, where membranes along a common radius or circle are set at a distance apart so that the Lamb waves interfere constructively, while membranes on different circles are insulated from each other by additional material or by a foil clamped between the membranes on the different circles.

[0031] As described in the present disclosure, the membranes in the array are preferably distributed in a predetermined layout to avoid destructive interference between adjacent membranes, for example, wherein the separation distance is determined so that the Lamb waves arrive in phase with the vibrating membranes. Accordingly, various aspects of the present disclosure may be embodied as a method of manufacturing an acoustic device as described in the present disclosure, or embodied in other ways.

[0032] Some embodiments include determining a layout of an array of acoustic membranes 1, 2, 3, 4 formed on a foil 10, wherein each of the acoustic membranes 1, 2, 3, 4 is configured to vibrate at a resonant frequency Fr of the acoustic membrane 1, 2, 3, 4 to generate a corresponding acoustic wave W1, W2, W3, W4. Other or additional embodiments include determining relative phases ΔΦ12, ΔΦ34 at which the acoustic membranes 1, 2, 4, 5 are actuated to generate a predetermined interference pattern C between the acoustic waves W1, W2, W3, W4. Other or additional embodiments include determining a Lamb wavelength λs of a Lamb wave Ws that passes through a middle portion 10i, 10j of the foil 10 between adjacent acoustic membranes 1, 2 and 3, 4 in the array at the resonant frequency Fr.

[0033] Preferably, the distances X12, X34 of the middle portions 10i, 10j between adjacent acoustic membranes 1, 2 and 3, 4 in the layout are determined based on the relative phases ΔΦ12, ΔΦ34 and the Lamb wavelength λs so that the Lamb wave Ws arrives in phase with the second acoustic membrane 2, 4 in the acoustic membrane pair of the adjacent acoustic membrane, wherein the Lamb wave is generated by actuating the first acoustic membrane 1, 3 in the acoustic membrane pair of the adjacent acoustic membrane and passes through the corresponding middle portions 10i, 10j. Therefore, an acoustic device can be manufactured using a determined layout. In one embodiment, the optimized distance between the membranes is obtained by changing the position of the membranes so that the phase difference between the case where the Lamb wave arrives exactly in phase for each membrane and the initial layout is minimized. For example, a minimizer routine can be used.

[0034] Figure 2 A device having an array of acoustic membranes configured to constructively interfere at predetermined locations is shown.

[0035] In some embodiments, all or at least a subset of the acoustic membranes are actuated to generate sound waves with corresponding phases to constructively interfere at one or more specific locations above (or below) the foil. For example, the sound waves of all membranes are generated to have corresponding phases so as to constructively interfere at a focus C or a focal line (not shown). For example, the acoustic device 100 forms a tactile feedback device in which the membranes are configured to create a tangible point in mid-air above the device by constructively interfering between sound waves W emitted by different membranes.

[0036] In some embodiments, corresponding pairs of acoustic membranes 1, 2 and 3, 4 (e.g. Figure 1B and Figure 1C ) between zero or non-zero phase delay The phases of the acoustic waves W1, W2, W3, W4 generated by at least some (preferably all) of the acoustic membranes 1, 2, 3, 4 are determined so that they constructively interfere at a focal point C above the array. In other or additional embodiments, the relative phases of the respective transducers 3, 4 may be determined based on their respective distances Z3, Z4 from the focal point C. For example, the first total distance Z3 between the first transducer 3 and the focal point C may be expressed as an integer N3 times the wavelength λa of the acoustic wave (e.g., in air) plus a residual fractional wavelength. The residual fractional portion may be expressed as the ratio of the phase difference ΔΦ3 divided by the entire period, for example, expressed as two π radians (2π rad).

[0037] In one embodiment, for example, as shown, at least some (preferably most, or even all) of the acoustic membranes 3, 4 forming respective phase-delay pairs of adjacent membranes (e.g., their centers) are arranged at specific respective distances Z3 and Z4 from a common focus C above the foil 10 (e.g., when the foil is lying flat). For example, the distances Z3 and Z4 are determined as:

[0038] Z3=N3+ΔΦ3 / 2π·λ a And Z4=N4+ΔΦ4 / 2π·λ a ,

[0039] where λa is the wavelength of the acoustic wave generated by membranes 3 and 4, N3 and N4 are integer values ​​determined by the number of full wavelengths fitted between the respective membranes and the focal point, and ΔΦ3 and ΔΦ4 are the respective phases of the membranes (expressed in radians);

[0040] In another or additional embodiment, the distance X34 between the phase delay pairs of films 3, 4 is determined by X 34 =N 34 +ΔΦ 34 / 2π·λ s Sure,

[0041] where λs is the Lamb wavelength λs, N34 is an integer value determined by the number of full wavelengths fitted between the respective transducer and the focal point, and ΔΦ34 is the phase difference (in radians) between the respective pairs of phase retardations of the films 3, 4.

[0042] Preferably, the distance X34 is selected so that the following equation for the relative phase holds:

[0043] ΔΦ 34 / 2π=|ΔΦ3 / 2π-ΔΦ4 / 2π|±d 34 , where d34 is the maximum fractional phase difference allowed between Lamb waves generated by one of the phase delay pairs of membranes 3, 4 and arriving at the other of the phase delay pairs of membranes 3, 4. Preferably, the maximum fractional phase difference allowed d 34 Less than one-fifth, preferably less than one-tenth, or as low as possible, such as zero, to have minimal destructive interference.

[0044] It will be appreciated that in the case where the phase delay at distances Z3 and Z4 to point C is greater than one full cycle (2π), integers may be added or subtracted, for example, by adding or subtracting integers from the sum of the subsequent phase differences; or the integers N3 and N4 may be adjusted, for example, to a maximum. It may also be noted that similar expressions generally hold for the same phase pair of transducers 1 and 2 at equal distances from the focal point (not shown here). For example, this may be expressed as:

[0045] ΔΦ 12 / 2π=|ΔΦ1 / 2π-ΔΦ2 / 2π|±d 12 =0.

[0046] Where d12 is the first decimal or the maximum allowed decimal phase difference.

[0047] In some embodiments, for example, as shown in the figure, the acoustic device 100 includes a controller 50, which is configured to generate corresponding drive signals S1, S2, S3 to actuate the acoustic membranes in the array. For example, the controller may include a signal generator configured to generate an alternating voltage for driving the piezoelectric material on the acoustic membrane. In one embodiment, each of the drive signals S1, S2, S3 includes a corresponding drive frequency corresponding to the resonant frequency Fr of the membrane. In another or additional embodiment, the acoustic membranes 1, 2 in the corresponding in-phase pairs of the membranes are connected to receive the same drive signal S1. In another or additional embodiment, the acoustic membranes 3, 4 in the corresponding phase-delayed pairs are connected to receive phase-delayed drive signals S1, S2.

[0048] While the membrane is preferably actuated at a drive frequency at or near the resonant frequency Fr, other or additional drive frequencies may be used. In some embodiments, the drive signal comprises a plurality of frequencies, including a carrier frequency Fc corresponding to the resonant frequency Fr of the membrane (preferably as possible); and including an envelope or modulation frequency Fm depending on the application. For example, a tactile feedback device may use a carrier frequency at 40 kHz that is amplitude modulated by a modulation frequency at 200 Hz. It is also conceivable to use more than two frequencies, or even a bandwidth of frequencies, for example including the bandwidth of the resonant frequency of the respective transducer.

[0049] In some embodiments, the drive signal comprises a carrier frequency above 10 kHz, e.g., by modulating tens or hundreds of kHz at least 10 times lower, e.g., below 800 Hz. Without being bound by theory, it is noted that in order to induce tactile feedback in a linear sense (i.e., using sound frequencies below 800 Hz directly), the required sound intensity is so high that it can cause deafness. Furthermore, since the wavelength of sound at these low frequencies is large (6.8 m (50 Hz) - 0.4 m (800 Hz)), this means that very large transducers (the size of multiple wavelengths) are required to produce sound of any effectiveness. Furthermore, in order to produce these frequencies using an array of transducers, the size of the focal point can only be on the order of one wavelength at best: this means a lateral width of 0.4-6.8 m. Thus, there is little choice as to which part of the subject is excited.

[0050] Figure 3A A top view of an array comprising only in-phase acoustic membranes is shown. Figure 3B Shown is a top view of an array comprising a mixture of in-phase acoustic membranes along the rows of the array and phase delay membranes between the rows. In some embodiments, an acoustic membrane array is provided, wherein each of the adjacent (closest) pairs of membranes is designed to vibrate in phase with each other. For example, in the configuration shown, each membrane can be spaced apart from the (closest) adjacent membrane by a predetermined distance Xi, which can be the same distance as shown in the figure, or can be a variable distance, for example, an integer multiple of the wavelength within the row is different from an integer multiple of the wavelength between the rows (not shown). In other or additional embodiments, for example, as shown in the figure, the acoustic membrane is configured as a hexagonal pattern, wherein each corner of the hexagon is occupied by a membrane, and a membrane is provided at the center of the hexagon. This can also be described as a triangular pattern, wherein the membrane is provided at the corner of the triangle. Typically, the triangle is an isosceles triangle, for example, wherein the distance (for example, Xo) from one membrane to at least two adjacent membranes is the same (for example, providing the same phase difference). Figure 3A and Figure 3BAs a special case, the membranes can be arranged in a pattern of equilateral hexagons or equilateral triangles, e.g. Figure 3A Other patterns are also possible, as described below.

[0051] Figure 4A A top view of the membrane arranged along a pattern of concentric circles R1 , R2, R3, R4 is shown. Figure 4B A photograph of an actual device with a similar pattern is shown.

[0052] In a preferred embodiment, the acoustic membranes are arranged along a pattern of concentric circles R1, R2, R3, and R4. In some embodiments, adjacent membranes 1, 2, and at least a subset (preferably all) of 2, 3 on the same circle R1 form a phase-delayed pair that is configured to vibrate with the same phase. For example, each phase-delayed pair has a corresponding first distance X12, X23 between them to provide constructive interference of Lamb waves that propagate through the middle portion of the foil at the first distance and arrive at the adjacent in-phase membrane. In other or additional embodiments, adjacent membranes 2, 4, and at least a subset (preferably all) of 3, 4 on the adjacent circles R1, R2 form a phase-delayed pair that is configured to vibrate with a predetermined phase difference. For example, each phase-delayed pair has a corresponding second distance X24, X34 between them to provide favorable interference of Lamb waves that propagate through the middle portion of the foil at the second distance and arrive at the adjacent phase-delayed membrane.

[0053] In some embodiments, for example, as shown, at least some of the adjacent membranes 3, 4 and 3, 5 on adjacent circles R1, R2 form phase delay pairs with different distances X34 and X35 between them. For example, the distances differ by an integer number of wavelengths. In one embodiment, each of the membranes 1, 2, 3 on the first circle R1 is configured to vibrate at a first phase. In another or additional embodiment, each of the membranes 4, 5 on the second circle R2 adjacent to the first circle R1 is configured to vibrate at a different second phase. In another or additional embodiment, each of the membranes 6, 7 on the third circle R3 adjacent to the second circle R2 is configured to vibrate at a third phase. In some embodiments, the phase delay between the first phase and the second phase is different from the phase delay between the second phase and the third phase. For example, the phase delay can be determined so that the corresponding delay pairs compensate for different distances (through the air) to the common focus C, for example with reference to Figure 2 described.

[0054] As previously mentioned, in some embodiments, small fractional deviations from the ideal of an integer number of wavelengths can be tolerated, for example, by adding or subtracting a fractional d12 as previously shown. For example, a fractional d12 less than one tenth may correspond to minimal destructive interference. On the one hand, the smaller the fractional d12, the less undesirable crosstalk / destructive interference between adjacent pairs. On the other hand, the presence of a smaller fractional d12 can provide greater design freedom for different configurations.

[0055] In a preferred embodiment, for example, as shown in the figure, the acoustic membrane forms a regular pattern. In one embodiment, for example, as shown in the figure, each of the concentric circles R1-R4 includes an integer multiple of six membranes equidistantly distributed around the corresponding circle. For example, the first circle includes six membranes, the second circle includes twelve membranes, the third circle includes eighteen membranes, and so on. As shown in the figure, a single membrane can also be set at the center. Of course, other patterns are also possible. For example, other multiples other than six can be used, membranes can be omitted at specific locations (as shown in the next figure), or completely different patterns can be envisioned.

[0056] Figure 5A An acoustic device 100 is shown having membranes distributed along a spiral pattern. Figure 5B Shown is the corresponding isometric view of the device that produces sound wave W to form focus C.In one embodiment, for example, as shown in the figure, the film in the array is arranged along a spiral pattern.Advantageously, fixed or variable distance X12 can be used between each subsequent film along the spiral.For example, distance X12 can be selected according to the phase difference between the subsequent film that causes due to the difference of the corresponding path length of film to common focus C.For example, the difference of path length can (for example, using the Pythagorean theorem) be calculated according to the difference of radius R1, R2 and axial distance Z.In certain embodiments, spiral pattern can be determined according to Archimedean spiral, wherein, the distance DR between the subsequent winding (winding) is constant.In other or additional embodiments, distance DR can change, for example, changes according to the desired phase delay between the subsequent winding.

[0057] Figure 6A The Lamb wave dispersion curve of a typical substrate (foil) used to construct a membrane array is shown. For example, at a typical resonant frequency FR = 40 kHz, the Lamb wave velocity in the substrate Vs = 70 m / s. In this case, the Lamb wavelength in the substrate λs = 1.75 mm.

[0058] Figure 6BA graph of the sound pressure level (SPL) generated by a transducer array and as a function of frequency (F) at different distances X12 between the transducers is shown. It can be observed that for a resonant frequency of 40 kHz, the optimal sound pressure level is obtained with a distance X12 = 1.01·λs (i.e. close to an integer number of wavelengths, in this example N12 = 1, with the decimal within d12 = ±0.01). Note that the scale is expressed in decibels (dB), i.e. calculated logarithmically. Without knowing the present invention, it would be surprising to find that a lower peak SPL is obtained for a higher density of transducers (e.g. a smaller distance X12 = 0.71·λs). For X12 = 0.91·λs, the SPL peak is only slightly reduced, but there may be additional effects that still have a negative impact on performance.

[0059] In some embodiments, for example, as shown in the figure, it can be noted that for deviating values ​​of X12 (i.e., not an ideal integer number of wavelengths), the SPL peak is not only smaller, but also shifted in frequency. For example, the peak for X12 < λs is shifted to a higher frequency away from the actual resonant frequency (Fr) of the membrane. Without being bound by theory, lower wavelengths corresponding to higher (non-resonant) frequencies can better fit the distance between the transducers. Undesirable shifts in frequency away from the expected resonant frequency can lead to further problems. For example, if different transducers vibrate at different frequencies, this can lead to periodic destructive interference. Therefore, it is most preferred that all transducers have the same resonant frequency Fr, and / or that steps are taken to periodically reset the phase of the transducers before the transducers lose synchronization.

[0060] For the sake of clarity and brevity, features are described herein as being part of the same or separate embodiments, however, it will be understood that the scope of the invention may include embodiments having all or some combinations of the features described. Although some embodiments described in this disclosure relate to a device configured to form a single focus, other shapes may also be produced, for example, a straight line or curve producing a focus. It is also conceivable to provide a variable focus, line or other shape depending on the corresponding phase of the drive signal. The elements of the acoustic membrane or foil may be combined or split into one or more alternative components. The various elements of the embodiments discussed and illustrated provide specific advantages, such as improving the efficiency of the acoustic array. Of course, it will be understood that any of the above embodiments or processes can be combined with one or more other embodiments or processes to provide further improvements and advantages in finding and matching designs. It will be understood that the present disclosure provides particular advantages for acoustic membrane arrays formed on relatively thin (e.g., flexible) foils or substrates or acoustic membrane arrays formed in the foils or substrates, and can generally be applied to any application for reducing crosstalk between acoustic transducers in an array formed on a substrate or other applications.

[0061] In interpreting the appended claims, it should be understood that the word "comprising" does not exclude the presence of other elements or activities than those listed in a given claim; the word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements; any reference signs in a claim do not limit the scope of the claim; multiple "means" may be represented by the same or different items or structures or functions; and any disclosed device or part of the device may be combined together or separated into further parts unless otherwise specifically stated. When one claim refers to another claim, this may indicate a synergistic advantage achieved by combining the respective features of these claims. However, the fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to advantage. Therefore, the embodiments described may include all valid combinations of claims, wherein each claim may in principle refer to any preceding claim unless the context clearly excludes it.

Claims

1. An acoustic device (100), comprising: - an array of a plurality of acoustic membranes (1, 2, 3, 4) formed on a foil (10); as well as - a controller (50) configured to generate corresponding drive signals to make the plurality of acoustic membranes (1, 2, 3, 4) vibrate at corresponding resonant frequencies (Fr) of the acoustic membranes to generate corresponding sound waves (W1, W2, W3, W4), wherein at least a first subset of the array is formed by in-phase pairs of first adjacent acoustic membranes (1, 2) of the plurality of acoustic membranes (1, 2, 3, 4), the in-phase pairs of the first adjacent acoustic membranes being connected to receive the same drive signal (S1) from the controller (50), wherein each in-phase pair comprises a respective first acoustic membrane (1) and an adjacent second acoustic membrane (2), wherein the first acoustic membrane (1) is spaced apart from the second acoustic membrane (2) by a first intermediate portion (10i) of the foil (10) therebetween, Wherein, the first distance (X) of the first middle portion (10i) between the first acoustic membrane (1) and the second acoustic membrane (2) is 12 ) is: the first integer (N 12 ) plus or minus the first decimal less than one tenth (d 12 ), multiplied by the predetermined Lamb wavelength (λ s ), the Lamb wave is generated by the first acoustic membrane (1) and the second acoustic membrane (2) passing through the first middle part (10i) between the first acoustic membrane (1) and the second acoustic membrane (2) at the resonant frequency (Fr).

2. The device according to claim 1, wherein At least a second subset of the array is formed by phase-delayed pairs of second adjacent acoustic membranes (3, 4) of the plurality of acoustic membranes (1, 2, 3, 4), the phase-delayed pairs of the second adjacent acoustic membranes being connected to receive phase-delayed drive signals (S1, S2) from the controller (50), wherein each phase-delayed pair comprises a third acoustic membrane (3) and an adjacent fourth acoustic membrane (4), wherein the third acoustic membrane (3) is spaced apart from the fourth acoustic membrane (4) by a second intermediate portion (10j) of the foil (10) therebetween, Wherein, the second distance (X) of the second middle portion (10j) between the third acoustic membrane (3) and the fourth acoustic membrane (4) is 34 ) is: the second integer (N 34 ) plus or minus the non-zero second decimal (d 34 ), multiplied by the predetermined Lamb wavelength (λ s ), wherein the Lamb wave is generated by the third acoustic membrane (3) and the fourth acoustic membrane (4) through the second middle portion (10j) between the third acoustic membrane (3) and the fourth acoustic membrane (4) at the resonant frequency (Fr), wherein the second decimal (d 34 ) is based on the phase delay between the third acoustic membrane (3) and the fourth acoustic membrane (4) Predetermined.

3. The device according to claim 2, wherein Zero or non-zero phase delay between the first acoustic membrane (1) and the second acoustic membrane (2) Zero or non-zero phase delay between the third acoustic membrane (3) and the fourth acoustic membrane (4) The array is determined so that corresponding acoustic waves (W1, W2, W3, W4) generated by the plurality of acoustic membranes (1, 2, 3, 4) constructively interfere at a focal point (C) above the array.

4. The device according to claim 2, wherein the third acoustic membrane (3) and the fourth acoustic membrane (4) forming respective phase-delay pairs of the second adjacent acoustic membranes (3, 4) being arranged above the foil (10) at respective distances Z3 and Z4 from a common focus (C), The distances Z3 and Z4 are determined as Z3=N3+ΔΦ3 / 2π·λ a and Z4=N4+ΔΦ4 / 2π·λ a , Among them, λ a is the wavelength of the sound wave generated by the third acoustic membrane (3) and the fourth acoustic membrane (4), N3 is an integer value determined by the number of full wavelengths fitted between the third acoustic membrane (3) and the common focus (C), N4 is an integer value determined by the number of full wavelengths fitted between the fourth acoustic membrane (4) and the common focus (C), ΔΦ3 is the phase of the third acoustic membrane (3), and ΔΦ4 is the phase of the fourth acoustic membrane (4); Wherein, the distance X between the phase delay pair of the third acoustic membrane (3) and the fourth acoustic membrane (4) is 34 It is through X 34 =N 34 +ΔΦ 34 / 2π·λ s Sure, Among them, λ s is the Lamb wavelength (λ s ), N 34 is an integer value determined by the number of full wavelengths fitted between the third acoustic membrane (3) and the common focus (C) and the number of full wavelengths fitted between the fourth acoustic membrane (4) and the common focus (C), and ΔΦ 34 is the phase difference between the corresponding phase delay pairs of the third acoustic membrane (3) and the fourth acoustic membrane (4); Wherein, the distance X 34 is chosen such that: (DF 34 / 2π)=|(ΔΦ3 / 2π)-(ΔΦ4 / 2π)|±d 34 , Among them, d 34 is the maximum allowable fractional phase difference, the value of which is less than one tenth.

5. The device according to claim 1 or 2, wherein: Each respective one of the drive signals (S1, S2, S3) for driving a respective membrane comprises a respective drive frequency corresponding to a resonant frequency (Fr) of the respective membrane.

6. The device according to claim 1 or 2, wherein: The plurality of acoustic membranes (1, 2, 3, 4) are arranged along a pattern of concentric circles (R1, R2, R3, R4), wherein at least a subset of adjacent acoustic membranes (1, 2; 2, 3) on the same circle (R1) form a pair of same phases, the pairs being configured to vibrate in the same phase, each pair having a corresponding first distance (X) between them 12 , X 23 ) to provide constructive interference of Lamb waves which pass through the middle portion of the foil over the first distance and arrive at an adjacent in-phase acoustic membrane.

7. The device according to claim 6, wherein At least a subset of adjacent acoustic membranes (2, 4; 3, 4) on adjacent circles (R1, R2) form phase-delayed pairs configured to vibrate with a predetermined phase difference, with a corresponding second distance (X) between each phase-delayed pair. 24 , X 34 ) to provide constructive interference of Lamb waves, which pass through the middle portion of the foil over the second distance and arrive at the adjacent phase delay acoustic membrane.

8. The device according to claim 6, wherein At least some adjacent acoustic membranes (3, 4; 3, 5) on adjacent circles (R1, R2) form phase delay pairs with different distances (X) between them. 34 , X 35 ), wherein the distances differ by an integer number of wavelengths.

9. The device according to claim 1 or 2, wherein: The plurality of acoustic membranes (1, 2, 3, 4) are formed as an integral part of the foil (10), wherein an actuating surface of the plurality of acoustic membranes (1, 2, 3, 4) comprises a layer (10b) of the foil.

10. The device according to claim 1 or 2, wherein: The resonant frequency (Fr) is determined by one or more of the membrane material properties and diameters of the plurality of acoustic membranes (1, 2, 3, 4), wherein the Lamb wavelength (λ s ) is determined by the resonant frequency (Fr) generating the Lamb wave (Ws) and the material properties and thickness of the middle portion of the foil (10), wherein the total thickness of the middle portion of the foil (10) is less than one millimeter and the total thickness of the plurality of acoustic membranes (1, 2, 3, 4) is at least two times lower than the thickness of the middle portion of the foil (10).

11. A method for manufacturing an acoustic device (100), the method comprising: - determining a layout of an array of a plurality of acoustic membranes (1, 2, 3, 4) formed on a foil (10), wherein each of the plurality of acoustic membranes (1, 2, 3, 4) is configured to vibrate at a resonant frequency (Fr) of the plurality of acoustic membranes (1, 2, 3, 4) for generating a corresponding sound wave (W1, W2, W3, W4); - Determine the relative phase (ΔΦ 12 , ΔΦ 34 ), at said relative phases, said plurality of acoustic membranes (1, 2, 3, 4) will be actuated to generate a predetermined interference pattern (C) between said acoustic waves (W1, W2, W3, W4); -Determine the Lamb wavelength (λ) of the Lamb wave (Ws) s ), the Lamb waves passing through the middle portion (10i, 10j) of the foil (10) between adjacent acoustic membranes (1, 2; 3, 4) in the array at the resonant frequency (Fr); According to the relative phase (ΔΦ 12 , ΔΦ 34 ) and the Lamb wavelength (λ s ) determines the distance (X) of the intermediate portions (10i, 10j) between the adjacent acoustic membranes (1, 2; 3, 4) in the layout 12 , X 34 ) so that the Lamb wave (Ws) arrives in phase with at least one of the second acoustic membrane (2) and the fourth acoustic membrane (4) in the acoustic membrane pair of adjacent acoustic membranes (1, 2; 3, 4), wherein the Lamb wave is generated by actuating at least one of the first acoustic membrane (1) and the third acoustic membrane (3) in the acoustic membrane pair of adjacent acoustic membranes (1, 2; 3, 4) and passing through the corresponding intermediate portion (10i, 10j).

12. The method according to claim 11, wherein At least a first subset of the array is formed by co-phase pairs of first adjacent acoustic membranes (1, 2) of a plurality of acoustic membranes (1, 2, 3, 4), wherein each co-phase pair comprises a respective first acoustic membrane (1) and an adjacent second acoustic membrane (2), wherein the first acoustic membrane (1) is spaced apart from the second acoustic membrane (2) by a first intermediate portion (10i) of the foil (10) therebetween, wherein a first distance (X) of the first intermediate portion (10i) between the first acoustic membrane (1) and the second acoustic membrane (2) is 12 ) is: the first integer (N 12 ) plus or minus the first decimal less than one tenth (d 12 ), multiplied by the predetermined Lamb wavelength (λ s ), the Lamb wave is generated by the first acoustic membrane (1) and the second acoustic membrane (2) passing through the first middle part (10i) between the first acoustic membrane (1) and the second acoustic membrane (2) at the resonant frequency (Fr).

13. The method according to claim 11 or 12, wherein: At least a second subset of the array is formed by phase-delayed pairs of second adjacent acoustic membranes (3, 4) of the plurality of acoustic membranes (1, 2, 3, 4), wherein each phase-delayed pair comprises a third acoustic membrane (3) and an adjacent fourth acoustic membrane (4), wherein the third acoustic membrane (3) is spaced apart from the fourth acoustic membrane (4) by a second intermediate portion (10j) of the foil (10) therebetween, and wherein a second distance (X) of the second intermediate portion (10j) between the third acoustic membrane (3) and the fourth acoustic membrane (4) is 34 ) is: the second integer (N 34 ) plus or minus the non-zero second decimal (d 34 ), multiplied by the predetermined Lamb wavelength (λ s ), the Lamb wave is generated by the third acoustic membrane (3) and the fourth acoustic membrane (4) at the resonant frequency (Fr) through the second middle portion (10j) between the third acoustic membrane (3) and the fourth acoustic membrane (4), wherein the second decimal (d 34 ) is based on the phase delay between the third acoustic membrane (3) and the fourth acoustic membrane (4) Predetermined.

14. The method according to claim 11 or 12, wherein: The thickness of the middle portion of the foil between corresponding pairs of multiple acoustic membranes (1, 2, 3, 4) is changed to affect the propagation of Lamb waves (Ws) so that the Lamb waves generated by one acoustic membrane in the corresponding pair arrive in phase with the other acoustic membrane in the corresponding pair.

15. The method according to claim 11 or 12, wherein: The plurality of acoustic membranes (1, 2, 3, 4) in the array are arranged along a spiral pattern.

Images