Ultrasonic transducer housing

Abstract

A piezoelectric micromachined ultrasonic transducer (PMUT) (302) interfaces with an amorphous medium such that, in use, an ultrasonic signal reaching or from the PMUT (302) passes through the amorphous medium. The amorphous medium has a plurality of discrete reflectors (110a, 110b, 111a, 111b) distributed therein. A method of imaging using a PMUT or PMUT array (302) comprises the steps of: determining an acoustic transfer function corresponding to an influence of a discrete reflector (110a, 110b, 111a, 111b) positioned between the PMUT or PMUT array (302) and a scene to be imaged; imaging the scene using a PMUT or PMUT array (302) by transmitting an ultrasound signal and receiving the ultrasound signal at the PMUT or PMUT array (302) after the ultrasound signal undergoes one or more reflections; and processing the received ultrasound signal by applying an inverse function of the acoustic transfer function to the received ultrasound signal to generate an image.

Description

Technical Field

[0001] The present invention relates to housings for ultrasonic transducers. Ultrasonic transducers are devices that generate and receive sound waves at frequencies above those audible to humans. They can be used in many applications, from simple distance-finding applications, where the distance to an object can be estimated by measuring the time between transmitting an ultrasonic signal and receiving a reflected echo signal, to complex medical imaging applications. Background Art

[0002] In many applications, it is important to make the transducers as small as possible, either because they are to be fitted into small devices, or to allow the use of large arrays. One technology that has been developed for this purpose is the piezoelectric micromachined ultrasonic transducer (PMUT), where each PMUT element typically acts as both a transmitter and a receiver when coupled to appropriate circuitry.

[0003] The housing of the ultrasound transducer may be used to protect the PMUT from external wear and tear. Summary of the invention

[0004] It is an object of the present invention to improve upon currently available PMUTs in certain respects.

[0005] Viewed from a first aspect, the present invention provides a piezoelectric micromachined ultrasonic transducer (PMUT) arranged to interface with an acoustic resonant cavity, wherein the acoustic resonant cavity has at least one acoustic characteristic that is adjustable in use according to a signal transmitted or received by the PMUT.

[0006] The present invention also relates to a method for imaging using the PMUT.

[0007] Therefore, those skilled in the art will appreciate that, according to the present invention, the acoustic properties of the acoustic resonant cavity interfaced with the PMUT are adjustable. By adjusting the properties of the acoustic resonant cavity, the outgoing or incoming ultrasonic pulses or signals can be modified. Applicants have recognized that this may be beneficial, for example, to improve ultrasonic imaging by increasing the efficiency of the PMUT in producing images.

[0008] In one set of embodiments, the adjustable property is the acoustic resonant volume of the acoustic resonant cavity. For example, the acoustic resonant volume of the acoustic resonant cavity can be adjusted to match its resonant frequency to the outgoing frequency of the transmitted ultrasound signal. This allows the cavity to be optimized even when the frequency used is not constant (as it usually is in typical applications). By matching the resonant frequency of the cavity to the outgoing frequency, the effective signal strength can be maximized for a given drive power. Similarly, matching the resonant frequency to the resonant frequency of the incoming signal can maximize the effective received signal strength of the ultrasound receiver.

[0009] The acoustic resonance volume can be adjusted in a variety of ways. In one set of embodiments, the acoustic resonance cavity includes a deformable diaphragm, wherein the position and / or shape of the diaphragm is adjustable to adjust the acoustic resonance volume of the cavity. In some embodiments, the PMUT is disposed on the deformable diaphragm such that: the PMUT itself also moves with the diaphragm to adjust the volume within the acoustic resonance cavity.

[0010] Alternatively, in order to adjust the characteristics of the acoustic resonance cavity, in one group of embodiments, the acoustic resonance cavity includes: an amorphous medium for the ultrasonic signal to pass through when in use, the amorphous medium including a plurality of discrete reflectors distributed therein, wherein the positions of the discrete reflectors are adjustable during use to adjust the acoustic characteristics of the acoustic resonance cavity.

[0011] The applicant has recognised that having a plurality of discrete reflectors in an amorphous medium is itself novel and inventive, and therefore, according to a second aspect of the invention, there is provided a piezoelectric micromachined ultrasonic transducer (PMUT) arranged to interface with an amorphous medium such that: in use, an ultrasonic signal to or from the PMUT passes through the amorphous medium comprising a plurality of discrete reflectors distributed therein.

[0012] The present invention also relates to a method for imaging using the PMUT.

[0013] The discrete reflectors may be physically separated multiple reflectors, such as physically completely separated reflectors, such as distributed in an amorphous medium. However, the discrete reflectors may be discrete parts of a structure. One or more discrete reflectors may be in contact with at least one other discrete reflector, such as one or more discrete reflectors may be in contact or physically connected. For example, multiple discrete reflectors may form a structure having multiple holes. Therefore, in one set of embodiments, the multiple discrete reflectors are elements of a structure having multiple holes.

[0014] Thus, in some embodiments, the discrete reflectors form a mesh, such as a fiber mesh, such that a plurality of discrete reflectors are elongated, such as fibers. The mesh may include overlapping discrete reflectors. The mesh may be a woven mesh.

[0015] In other embodiments, the discrete reflectors form a porous membrane, and the plurality of discrete reflectors are the material located between the pores of the membrane. The porous membrane may be synthetic or natural, and may be formed by perforation.

[0016] The discrete reflector may be rigid. Alternatively, the discrete reflector may be deformable, such as flexible or elastic.

[0017] The structure may take the form of a relatively thin layer so that the reflectors are distributed over the surface in two dimensions. Such a surface may (but need not be) substantially flat. However, in some embodiments, the discrete reflectors are distributed in three dimensions.

[0018] The holes need not be uniform, for example, they may have uneven spacing and be unevenly distributed throughout the structure.

[0019] The structure (eg, a mesh or a porous membrane) may introduce sources of diffraction and / or reflection, thereby affecting the ultrasound signals transmitted from and / or received by the PMUT. The structure may also beneficially provide environmental protection, particularly when the structure is a mesh or a porous membrane.

[0020] When the PMUT is used for imaging, as described above, the structure with the hole is preferably positioned between the PMUT and the scene to be imaged, for example, in the signal path transmitted or received by the PMUT. Those skilled in the art will appreciate that the structure may help to effectively broaden the field of view of the PMUT due to the disturbance caused by the discrete reflectors in the structure.

[0021] This can be achieved through the beam spreading effect of discrete reflectors on the ultrasonic signal as it is transmitted through the amorphous medium. When the ultrasonic beam is transmitted through the amorphous medium, reflections and diffractions at the discrete reflectors cause the directional expansion of the ultrasonic signal, thereby increasing the overall divergence of the ultrasonic beam as it propagates through the amorphous medium. This effectively spreads out the ultrasonic signal to provide a more omnidirectional output, thereby expanding the field of view. This effect is also frequency-dependent, as components of the ultrasonic signal with different frequencies will be reflected at different angles. In addition, understanding the effect of the structure on the ultrasonic signal (e.g., by understanding its transfer function) helps provide more information for signal processing when imaging using PMUT.

[0022] The amorphous medium may be acoustically reflective or non-reflective, and in one set of embodiments, the amorphous medium comprises a gel. The amorphous medium may alternatively comprise a liquid or a gas, such as within an acoustic resonant cavity. For example, the amorphous medium may comprise air.

[0023] In one set of embodiments of the second aspect of the invention, the position of the discrete reflector is adjustable in use to adjust the acoustic characteristics of the acoustic resonant cavity. This may provide the advantages described in accordance with the first aspect of the invention.

[0024] Furthermore, by adjusting the position of the reflector, the direction of any output signal can be adjusted, as well as the density of the medium in front of the PMUT, thereby producing a local sound speed variation, which in turn can be used, for example, to produce a lens effect in front of the PMUT.

[0025] The position of the discrete reflector can be adjusted in a variety of ways. In one set of embodiments, the discrete reflector is metal and a magnetic field is used to adjust the position of the discrete reflector. In another set of embodiments, a piezoelectric contraction element is arranged around the acoustic resonant cavity. When current is applied to such a piezoelectric contraction element, it will contract and thus act to squeeze the acoustic resonant cavity, thereby adjusting the position of the reflector within the cavity by the force transmitted from the contraction force via the amorphous medium.

[0026] In one set of embodiments, the PMUT includes an ultrasonic transmitter, and the acoustic resonant volume is adjusted to match the transmitted signal. For example, when using the PMUT to transmit a signal with a widely varying frequency, the acoustic resonant volume can be adjusted so that the resonant frequency of the cavity matches the resonant frequency of the current transmitted signal to optimize the transmission. As the frequency of the transmitted signal changes, the volume of the acoustic resonant cavity can be varied to match. In contrast to the prior art (non-adjustable cavities), high power variable frequency signals can be more easily achieved using cavities according to the present invention.

[0027] Typically, the prior art (methods for generating broadband signals using PMUTs) modifies the output energy of the PMUT when adjusting the frequency of the signal emitted by the PMUT. However, this is not energy-efficient because to emit a chirp from frequency F0 to F1, the resonance peak may be located at (F1+F0) / 2. In order to achieve a flat output spectrum, less energy may need to be output at this resonance frequency, which is inefficient. Therefore, the total output energy may be reduced, and the efficacy of the PMUT in high-sensitivity imaging applications may be reduced.

[0028] In contrast, according to the present invention, the acoustic resonance volume of the cavity can be adjusted as the frequency of the signal transmitted by the PMUT changes during the chirped transmission. This can reduce the extent to which the output energy needs to be reduced, thereby allowing a relatively flatter output spectrum to be achieved and having a higher total output energy compared to the above-mentioned prior art methods. Therefore, the output energy may not need to be adjusted to the same extent as the frequency is changed in order to achieve a flat broadband output signal, so the PMUT can be used for applications requiring high output energy (such as long-range imaging) or imaging requiring good SNR (such as super-resolution imaging). The output signal to be transmitted is preferably pre-calculated and stored in a memory before transmission, rather than being adjusted during transmission.

[0029] However, other parameters can be adjusted to reduce the output signal energy - such as the PMUT itself and the "deformed" housing.

[0030] In one set of embodiments, the PMUT includes an ultrasound receiver and the acoustic resonance volume is adjusted to match the received signal. If the PMUT is used to receive the reflected chirp, then any output frequency can be received at any time, since echoes from objects at different distances are caused by the outgoing chirp signal. If the imprecise distance to the reflecting object of interest is known, the approximate expected time of the reflected echo can also be known. Therefore, according to the present invention, the volume of the acoustic resonance cavity can be adjusted at this time to amplify the incoming signal when it is expected to arrive, thereby achieving better signal reception.

[0031] In one set of embodiments, the PMUT comprises: a dedicated ultrasound transmitter and at least one separate ultrasound receiver on a single common semiconductor die. This allows for simultaneous transmission and reception of signals, so there is no need to switch electronics to switch between "transmit mode" and "receive mode". This reduces the complexity of the system electronics. Other benefits of having a dedicated ultrasound transmitter and at least one separate ultrasound receiver on a single common semiconductor die are listed in WO 2021 / 079160.

[0032] In one set of embodiments the cavity comprises an opening for outputting and / or receiving ultrasound signals.In such embodiments the acoustic resonant cavity may form a Helmholtz resonator.

[0033] In one set of embodiments, the PMUT is mounted so as to be movable by an actuator (e.g., a motor). The actuator can be used to move the PMUT so as to transmit signals in different directions, for example when understanding the effect of an acoustic resonant cavity on any transmitted or received signal.

[0034] The present invention also provides a system for transmitting and receiving ultrasonic signals, the system comprising: at least a first PMUT and a second PMUT as described in any aspect or embodiment above; a transmitter circuit arranged to drive the first PMUT as an ultrasonic transmitter; and a receiver circuit arranged to detect a signal from the second PMUT as an ultrasonic receiver.

[0035] In one set of embodiments of the first or second aspect of the present invention, there is provided an arrangement structure comprising a plurality of said PMUTs. In one set of such embodiments, the plurality of PMUTs are arranged in a mosaic array.

[0036] It will be appreciated that the PMUTs in a mosaic array may be separated by any length, however, in one set of embodiments, the PMUTs are spaced apart by λ / 2, where λ is the wavelength of the center frequency in the frequency range transmitted or received by the PMUTs. As will be appreciated by those skilled in the art of array signal processing, this is the optimal spacing for beamforming and the like. Thus, while the array can be used as "one common sensor", i.e., by summing or averaging the signals from them, or by using them to transmit the same signal alternately, their inputs or outputs can be used individually as part of an array processing method that processes each PMUT element individually. This has certain benefits, such as being able to better focus or cancel sounds coming from a particular direction.

[0037] In one set of embodiments, a PMUT array is arranged to interface with an acoustic resonant cavity comprising an acoustically non-reflective amorphous medium comprising a plurality of discrete acoustic reflectors.

[0038] The characteristics of the acoustic resonant cavity for a PMUT array may be adjusted in a manner similar to the acoustic resonant cavity described above for PMUTs.

[0039] The determined phase adjustment can be applied to the signal from the corresponding transmitter or receiver to allow them to act as a coherent array, such as for beamforming. Beam steering can be used for transmitted ultrasonic signals, reflected ultrasonic signals, or both. In order to steer the transmitted ultrasonic signal, the determined phase adjustment can be added to the signal emitted by each PMUT in the array so that the resulting transmitted ultrasonic signal is disturbed, thereby generating an overall signal emitted in the desired direction. The reflected ultrasonic signal received can be steered in a similar manner. The determined phase adjustment can be applied to the signal received from all directions to determine the reflected signal from a single direction in the surrounding structure. Compared with using the array as "a common sensor" as described above (wherein the signal is enhanced by using multiple PMUTs, but the signal is only transmitted in one direction), the determined phase adjustment applied to the transmit / receive signal also allows the transmit / receive signal to be steered.

[0040] Changing the position of the acoustic reflector can be used to "steer" the transmitted or received ultrasound signal through the cavity. In order to achieve high quality signal transmission and reception, it is usually necessary to move the position of the PMUT during transmission and reception, but this is obviously impractical. Adjusting the characteristics of the signal transmission or reception medium by adjusting the position of the acoustic reflector may be able to achieve a net effect similar to adjusting the position of the PMUT itself.

[0041] According to the present invention, when a chirp signal is transmitted from F0 to F1, the position of the acoustic reflector within the medium can be adjusted so that: at any given time, the PMUT is "spaced" half a wavelength relative to the current frequency. Therefore, better imaging capabilities can be achieved at all frequencies by adjusting the acoustic reflector. Modifying the position of the acoustic reflector in front of the PMUT array can produce a lens effect, thereby steering the ultrasound signal.

[0042] In one set of embodiments, one or more shell layers are arranged above an acoustic resonant cavity comprising a PMUT array. One or more shell layers can be compressed, for example by means of piezoelectric contraction elements surrounding them, thereby deforming the shell layer or each such shell layer. This will change the pressure in each layer, and the change in pressure will produce an acoustic gradient that can provide a "lensing effect".

[0043] According to another aspect of the invention, a plurality of acoustic resonant cavities are provided, each of which includes an array of PMUTs arranged to interface with the acoustic resonant cavity and also includes an amorphous medium with discrete acoustic reflectors. This "array of arrays" provides additional benefits because individual drive electronics can be provided for each "microarray", each of which, as described above, is, for example, located in an acoustic resonant cavity including an amorphous medium with discrete acoustic reflectors. Therefore, the only information that can be provided for each array is the direction and intensity of the energy. This is typically less than the information provided for the signal waveform for each element in the array.

[0044] In one set of embodiments, each cavity in the plurality of cavities is coupled to a solid substrate. In one set of alternative embodiments, each cavity in the plurality of cavities is disposed on a common damping medium. In another set of alternative embodiments, each cavity in the plurality of cavities is disposed within a common damping medium. The damping medium may be an amorphous material, a semi-solid material, an acoustic dielectric material, or a gel, among others.

[0045] An "array of arrays" also reduces the density of PMUTs in the overall array, making it easier to reduce crosstalk as well, since each "microarray" can be isolated from each other. Since the number of PMUTs is reduced compared to a single array where each PMUT is spaced λ / 2 apart, an "array of arrays" can reduce the overall PMUT density, since the arrays do not need to be so closely spaced. For example, arrays coupled to a solid substrate can be mounted separately on "pillars" so that they are separated from the solid substrate to which they are connected, so that energy does not propagate between arrays. Alternatively, the medium on which the PMUTs can be arranged can be a foam with minimal acoustic transmission capabilities.

[0046] According to another aspect of the present invention, there is provided an arrangement comprising a plurality of PMUTs arranged to interface with corresponding acoustic tubes, the PMUTs being arranged in a mosaic array.

[0047] In any of the above PMUT arrays, in one set of embodiments, the array is mounted to be movable by an actuator (e.g., a motor that moves the array). Similar to the above actuators that move the PMUTs, the actuator can be used to change the position of the array to learn directional impulse responses in different directions.

[0048] In any of the above arrays, the array may be 3D, i.e. not planar. A 3D array structure may allow more acoustic output energy to be generated on the surface, since the signal generated by each PMUT transmitter is summed with the signals from the other transmitters.

[0049] Additionally, different PMUTs in the array may have different sizes so that each PMUT has its own, different resonant frequency.

[0050] For example, if the properties of the acoustic resonant cavity or medium interfacing with the PMUT array are tuned, a motor can be used to “learn” how this shaping affects the array acoustic response and this information can then be further used during transmission to better focus the ultrasound signal, as the effect of the tuned cavity on the transmitted signal will have been learned.

[0051] In one set of embodiments an input power signal is provided to each array and further information such as signal direction / pattern, strength and calibration information is provided wirelessly so that multiple arrays provide a sensor network.

[0052] The reflected signals received at the PMUT array may be signal processed, for example using any suitable image reconstruction technique to produce an image. The signal processing preferably includes beamforming and may be performed in the digital domain. The signal processing may be performed using any suitable processor.

[0053] According to a third aspect of the present invention, there is provided a method for imaging using a PMUT or a PMUT array, comprising:

[0054] determining an acoustic transfer function corresponding to the acoustic impact of a plurality of discrete reflectors located between the PMUT or PMUT array and a scene to be imaged;

[0055] imaging a scene using a PMUT or a PMUT array by transmitting an ultrasound signal and receiving the ultrasound signal at the PMUT or PMUT array after the ultrasound signal has been reflected one or more times;

[0056] The received ultrasound signal is processed by applying the inverse of the acoustic transfer function to the received ultrasound signal to generate an image.

[0057] In some embodiments, the method is applied to a PMUT array comprising a plurality of PMUTs according to the second aspect of the invention. In one set of embodiments, the plurality of PMUTs are arranged in a mosaic array.

[0058] Those skilled in the art will appreciate that the acoustic transfer function is a mathematical function of the effect of multiple discrete reflectors on the image generated by a PMUT or PMUT array. When processing received signals, a clearer image can be formed using a determined acoustic transfer function. As described above, due to the presence of discrete reflectors (e.g., in front of the PMUT), the PMUT or PMUT array can have a wider field of view. Therefore, the method provides imaging that achieves a wider field of view without sacrificing image quality.

[0059] The acoustic transfer function may be determined in various ways. The acoustic transfer function may be predetermined and stored in a memory of the processor. In one set of embodiments, the acoustic transfer function is determined using, for example, an iterative algorithm and stored in a memory of the processor.

[0060] The acoustic transfer function may include a directional filter, such as a directional impulse response.

[0061] In one set of embodiments, the determining step of the third aspect is implemented by a method comprising the following steps:

[0062] (a) selecting an acoustic transfer function that is applied to the received signal to generate an image;

[0063] (b) performing imaging using a PMUT or a PMUT array by transmitting an ultrasound signal and receiving the ultrasound signal at the PMUT or PMUT array after the ultrasound signal has undergone one or more reflections;

[0064] (c) processing the received signal using the inverse of the acoustic transfer function to generate an image;

[0065] (d) determining a sharpness parameter of the image, and when the determined sharpness parameter:

[0066] (i) if it is not above a predetermined threshold, adjusting the transfer function before repeating steps (b)-(d);

[0067] (i) When the value is higher than a predetermined threshold, the method is terminated.

[0068] According to another aspect, the present invention provides a method for determining an acoustic transfer function for imaging using a PMUT or a PMUT array, comprising:

[0069] (a) selecting an acoustic transfer function that is applied to the received signal to generate an image;

[0070] (b) performing imaging using a PMUT or a PMUT array by transmitting an ultrasound signal and receiving an ultrasound signal at the PMUT or PMUT array after the ultrasound signal has undergone one or more reflections;

[0071] (c) processing the received signal using the inverse function of the acoustic transfer function to generate an image;

[0072] (d) determining a sharpness parameter of the image, and when the determined sharpness parameter:

[0073] (i) if it is not above a predetermined threshold, adjusting the transfer function before repeating steps (b)-(d);

[0074] (i) When the value is higher than a predetermined threshold, the method is terminated.

[0075] Thus, the method may allow for effective "tuning" of the acoustic transfer function to improve the quality of images obtained using multiple discrete reflectors. For example, if the "wrong" acoustic transfer function is selected, the images obtained from ultrasound imaging will almost always be "blurry". Thus, the sharpness of the image may be used as a criterion to update the acoustic transfer function selected to obtain the image.

[0076] The sharpness parameter may be a measure such as image sharpness, see https: / / ieeexplore.ieee.org / document / 6783859. Alternatively, the sharpness parameter may be calculated using the ratio between low reflector values ​​(close to 0) and high reflector values.

[0077] The acoustic transfer function may be adjusted using an old acoustic transfer function stored in a memory (eg, a server).

[0078] The features of any aspect or embodiment described herein may be applied to any other aspect or embodiment described herein where appropriate. When different embodiments or groups of embodiments are mentioned, it should be understood that these embodiments or groups of embodiments are not necessarily different, but may overlap. BRIEF DESCRIPTION OF THE DRAWINGS

[0079] Certain embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

[0080] Figure 1 is a view of a PMUT according to a first embodiment of the present invention;

[0081] Figure 2A is a view of a PMUT according to a second embodiment of the present invention;

[0082] Figure 2B is another view of a PMUT according to a second embodiment of the present invention;

[0083] Figure 3 is a view of a PMUT according to a third embodiment of the present invention;

[0084] Figure 4A Shows Figure 1 a PMUT wherein a chirped signal having a first cavity volume is transmitted;

[0085] Figure 4B Shows Figure 1 a PMUT wherein a chirped signal having a second cavity volume is transmitted;

[0086] Figure 5A A plurality of PMUTs are shown arranged in a mosaic array and interfaced with an amorphous medium including random reflectors;

[0087] Figure 5B A plurality of PMUTs are shown, arranged in a mosaic array and interfaced with an amorphous medium containing regularly spaced reflectors;

[0088] Fig. 6A A plurality of PMUTs are shown, arranged in a mosaic array within an acoustic resonant cavity and interfaced with an amorphous medium including random reflectors;

[0089] Figure 6B A plurality of PMUTs are shown, arranged in a mosaic array within an acoustic resonant cavity and interfaced with an amorphous medium including regularly spaced reflectors;

[0090] Fig. 7A A plurality of PMUTs are shown, arranged in a mosaic array and interfaced with an amorphous medium including randomly moving reflectors;

[0091] Figure 7B shows a plurality of PMUTs arranged in a mosaic array interfacing with an amorphous medium including regularly spaced reflectors that are moved to tune the properties of the medium;

[0092] Fig. 8A Shows Figure 6B PMUT array and cavity, and a plot of the acoustic transfer function used to simulate the reflector effect;

[0093] Figure 8B Shows Figure 8B PMUT array and modified acoustic transfer function;

[0094] Fig. 9 shows a method for imaging a known object. Figure 6B PMUT array in;

[0095] Fig.10A single transmitter and a single receiver are shown for imaging a single reflector;

[0096] Fig.11 A PMUT array is shown interfaced with a cavity that is larger than the PMUT array;

[0097] Fig. 12A An array of arrays coupled to a solid substrate is shown;

[0098] Fig. 12B An array of arrays arranged on a medium is shown;

[0099] Fig. 12C An array of arrays disposed within a medium is shown;

[0100] Fig.13 The method for imaging an object when used is shown Fig. 12A an array of arrays of;

[0101] Fig.14 A non-planar PMUT array is shown;

[0102] Fig.15 An array of arrays is shown, wherein each array is interfaced with an acoustic port;

[0103] Fig.16A shows a PMUT array arranged in a stacked manner, wherein a plurality of layers with different impedances are arranged in front of the PMUT array;

[0104] Fig. 16B yes Fig.16A Exploded view of;

[0105] Fig. 16C Shows Fig.16A The force exerted by the piezoelectric strip shown;

[0106] Fig.16D Shows Fig.16D Deformations of the layers caused by the forces shown;

[0107] Fig.17 is a flow chart illustrating a method of updating a directional impulse response to improve the quality of an acquired image;

[0108] Fig.18 Shows Figure 5A a three-dimensional representation of the embodiment shown;

[0109] Fig.19 Shows Figure 5A A three-dimensional representation of a variation of the embodiment shown;

[0110] Fig. 20A series of graphs are shown demonstrating how the frequency response of the PMUT and the housing affects the outgoing signal. DETAILED DESCRIPTION

[0111] Figure 1 A highly schematic diagram of a PMUT 2 arranged in an acoustic resonant cavity 4 according to an embodiment of the present invention is shown. The acoustic resonant cavity 4 has two openings 6a, 6b through which ultrasound signals can be transmitted or received. The acoustic resonant volume 7 of the cavity 4 can be adjusted using a deformable diaphragm 8.

[0112] The deformable diaphragm 8 can be made of any suitable material, such as a piezoelectric material. When a voltage is applied, the piezoelectric material will deform, and the degree of deformation depends on the applied voltage and the material used. Common piezoelectric materials include: PZT (lead zirconate titanate), KNN ((K,Na)NbO3), ZnO (zinc oxide), BaTiO3 (barium titanate), PMN-PT (Pb (Mg1 / 3Nb2 / 3)O3-PbTiO3) and aluminum nitride (AlN). The deformable diaphragm will be mounted inside the top of the cavity 4 and bonded to the edge of the cavity 4 so that: when a voltage is applied, the edge of the diaphragm 8 will not move, but the unfixed center of the diaphragm 8 will deform, thereby reducing the volume 7 in the cavity. Therefore, a controllable drive voltage is provided to the diaphragm 8 so that the volume 7 of the cavity 4 can be adjusted.

[0113] The position and / or shape of the deformable membrane 8 may be adjusted, so that by such adjustment the resonance volume of the cavity 4 may be adjusted. The acoustic resonance cavity may be a Helmholtz resonance cavity.

[0114] The PMUT 2 may be an ultrasound transmitter, an ultrasound receiver, or both.

[0115] Figure 2A and Figure 2B A highly schematic diagram of a PMUT 102 arranged within an acoustic resonant cavity 104 according to a second embodiment of the present invention is shown. Figure 2A and Figure 2B The illustrated embodiment has four openings 106a-106d through which ultrasound signals can be transmitted or received. Figure 1 As with the embodiments of the present invention, PMUT 102 may be a transmitter, a receiver, or both.

[0116] The volume of the acoustic resonant cavity 104 is adjustable. The acoustic resonant cavity 104 includes a deformable diaphragm 108 on which the PMUT 102 is arranged. The position or shape of the diaphragm 108 and thus the PMUT 102 can be adjusted to change the volume of the acoustic resonant cavity 104.

[0117] exist Figure 2A, the diaphragm 108 is shown in a deformed position, thereby reducing the volume within the cavity 104. Figure 2B The diaphragm 108 in FIG. 1 is shown in a relaxed position, and the arrows indicate possible upward deformation of the diaphragm 108 and the PMUT 102, as shown in FIG. Figure 2A shown.

[0118] if Figure 1 , Figure 2A and Figure 2B If the PMUT 2, 102 shown in is used to transmit an ultrasonic signal, the acoustic resonant volume of the cavity 4, 104 can be adjusted to match the outgoing frequency of the transmitted ultrasonic signal. This is particularly relevant when PMUT 2, 102 is used to create a variable frequency signal. If PMUT 2, 102 transmits at a frequency different from the resonant frequency of the cavity 4, 104, a variable frequency transmission signal can be more easily achieved compared to a non-adjustable cavity. The system can transmit (e.g., continuously increase / decrease frequency transmission) a chirp signal from frequency F0 to F1 by adjusting the volume of the acoustic resonant cavity 4, 104. Therefore, a flatter output spectrum can be achieved over the frequency range F0 to F1 without adjusting the input energy, so that the transmitted signal can have a high output energy and can be used in applications that require a large range or good SNR, for example.

[0119] if Figure 1 , Figure 2A and Figure 2B The PMUT 2, 102 shown in FIG. 1 is used to receive the reflected chirp signal, and since the outgoing chirp signal causes echoes from objects at different distances, any frequency can be received at any time. If the imprecise distance to the reflecting object of interest is known, the approximate expected time of the reflected echo is also known. Therefore, the volume of the cavity 4, 104 can be adjusted at this time to amplify the incoming signal when it is expected to arrive, thereby achieving better signal reception.

[0120] Figure 3 FIG. 2 shows a highly schematic diagram of a PMUT 202 arranged in an acoustic resonant cavity 204 according to a third embodiment of the present invention. Figure 2A and Figure 2B As in the embodiment shown in , the acoustic resonant cavity 204 has four openings 206a-d. An amorphous medium is also provided in the acoustic resonant cavity 204, and the amorphous medium includes a plurality of discrete reflectors 10. The reflectors 10 can be adjusted during use, for example, the positions of the reflectors 10 can be adjusted to adjust the acoustic characteristics of the acoustic resonant cavity 204.

[0121] For example, the amorphous medium can be a gel, and the reflector 10 includes small magnetized metal balls embedded in the gel. A controllable magnetic field (not shown) can then be applied to the cavity 204, causing the position of the reflector 10 to change. In addition, due to the application of the magnetic field, the density of the medium can be changed by the movement of the metal balls. In this way, the gel can act like a spring, compressing when the reflector is subjected to the magnetic field force and expanding when the force disappears. For example, if the metal balls are very tightly gathered in front of the PMUT using a magnetic field, the density will increase, while if the metal balls are evenly distributed throughout the medium, the density of the medium "in front" of the PMUT will decrease. Changing the density of the medium can change the local sound velocity, which can also be used to create a lens effect for the transmitted ultrasound signal.

[0122] Figure 4A and Figure 4B Shows Figure 1 The PMUT 2 and the acoustic resonant cavity 4 and the transmitted chirp signal 12. Figure 4A In the embodiment, the diaphragm 8 is only slightly deformed, so the volume of the acoustic resonance cavity 4 is relatively large. Therefore, the resonance frequency 14a of the cavity 4 is low frequency, and the frequency shown is similar to the starting frequency of the chirp signal 12.

[0123] In contrast, Figure 4B In the process, the diaphragm 8 has further deformed, so Figure 4A Compared with the acoustic resonance cavity 4, the volume is reduced. Figure 4B The volume of the resonant cavity 4 in the cavity is reduced, and the resonant frequency 14b of the cavity 4 is higher than Figure 4A The frequency of the resonant frequency 14a is shown.

[0124] therefore, Figure 4A and Figure 4BIt is shown how to adjust the resonant frequency of the cavity 4 by adjusting the volume of the acoustic resonant cavity 4. Therefore, when the PMUT 2 is transmitting a chirp signal, the volume of the acoustic resonant cavity 4 can be continuously adjusted using the adjustable diaphragm 8 during the transmission of the chirp signal 12. Therefore, the resonant frequency of the cavity 4 can be matched to the transmission frequency, thereby outputting a relatively flat spectrum with a higher total energy, so that the chirp signal can be used for imaging applications that require long distances or good SNR. For example, super-resolution imaging methods generally rely on high SNR (see Christensen-Jeffries, K. et al., "Super-resolution ultrasound imaging", Ultrasound in Medicine & Biology, 2020, 46 (4), 865-891). Better SNR can lead to better ultrasound detection and better effective beamforming in array beamforming applications. In addition, a sufficiently sensitive ultrasound receiver with a good SNR reduces the need for excessive output power (i.e., no strong signal is required to improve the SNR) and reduces the use of excessive power in the device.

[0125] Figure 5A and Figure 5B An embodiment of another aspect of the present invention is shown, which includes a plurality of PMUTs 302 arranged in a mosaic array. The array of PMUTs 302 is arranged to interface with a cavity 304. The cavity 304 includes a non-reflective amorphous medium 16, which includes a plurality of discrete reflectors 110. The array of PMUTs 302 is coupled to a solid substrate 18, wherein the amorphous medium 16 and reflectors 110a, 110b extend between each PMUT 302 in the array.

[0126] The reflectors 110a, 110b may be randomly spaced throughout the amorphous medium 16, such as Figure 5A , or they may be arranged in a regular pattern, such as Figure 5B As shown in the reflector 110b.

[0127] Fig.18 Shows Figure 5A A three-dimensional representation of the embodiment shown in FIG. Fig.18 Shown are a PMUT array 302, a substrate 18, and an amorphous medium 16 including random reflectors 110a.

[0128] Fig.19 Shows Fig.18 A variation of the embodiment shown. Fig.19 Shown as Fig.18The PMUT array 302, substrate 18 and amorphous medium 16 are shown with random reflectors in the form of overlapping optical fibers 111a, 111b that form an irregular structure, i.e., a network or "web" of discrete optical fiber reflectors 111a, 111b. Fig.19 It can be seen that the mesh has a plurality of holes to allow the signal to pass through the amorphous medium 16. Fig.19 The beam spreading effect provided by the reticle helps to increase the field of view of the PMUT array 302, thereby allowing more information to be captured when imaging using the PMUT array 302.

[0129] Fig. 6A and Figure 6B An array of PMUTs 302 is shown, which is similar to Figure 5A and Figure 5B , however, the cavity 404 extends over the amorphous medium 16 and the reflectors 110a, 110b, having an acoustically transparent opening 306 through which ultrasound signals can be transmitted or received.

[0130] Fig. 7A and Figure 7B An array of PMUTs 302 is shown, which is FIG. 5A to FIG. 6B The array of PMUTs 302 shown in FIG. 3 is similar and is arranged to interface with the cavity 304 .

[0131] Fig. 7A Discrete reflectors 210a are shown, which can move freely throughout the amorphous medium 16. For example, if the discrete reflectors 210a are metallic, they can move, for example, by mutual induction from an external magnetic field.

[0132] Figure 7B Discrete reflectors 210b are shown arranged in a regular pattern throughout the amorphous medium 16. The cavity 304 may be circular, and an external inward force may be applied to the outer edge of the cavity 304 to compress it. Figure 7B As shown, this causes the peripheral reflector 210b to move inward. This can have the effect of "shaping" the volume of the cavity 304. For example, a piezoelectric material (not shown) can surround the cavity 304. When a voltage is applied, the piezoelectric material (e.g., in the form of a strip) contracts, causing the cavity 304 to be compressed, and the medium 16 is also compressed. This has the effect of moving the reflector 210b inward, thereby creating a "lens" effect.

[0133] exist FIG. 5A to FIG. 7BIn the array shown, the individual PMUTs can be spaced apart so that: in operation, the ultrasound array of PMUT 302 transmits a steered ultrasound beam. A determined phase adjustment can be applied to the signals from the corresponding transmitters or receivers to allow them to act as a coherent array - for example, for beamforming. Beam steering can be used for transmitted ultrasound signals, reflected ultrasound signals, or both. In order to steer the transmitted ultrasound signal, a determined phase adjustment can be added to the signal transmitted by each PMUT 302 in the array so that the resulting transmitted ultrasound signal is interfered, thereby producing an overall signal transmitted in the desired direction. The received reflected ultrasound signal can be steered in a similar manner. A determined phase adjustment can be applied to the received signals from all directions to determine the reflected signal from a single direction in the surrounding structure.

[0134] Most standard beamforming algorithms benefit from half-wavelength spacing of the PMUT 302, as this enables each incident wavefront to be distinguished from other incident wavefronts with different angles or wavenumbers, thereby preventing the "grating lobe" problem. Classical beamforming methods that benefit from half-wavelength (or tighter) spacing include: (weighted) delay and sum beamformers, adaptive beamformers (e.g., MVDR / Capon), direction finding methods (e.g., MUSIC and ESPRIT), and blind source estimation methods (e.g., DUET), as well as wireless communication methods, and ultrasound imaging methods with additional constraints (e.g., entropy or information maximization).

[0135] Changing the position of the reflectors 210a, 210b can be used to "steer" the ultrasound signal transmitted or received through the cavity 304. To achieve high quality signal transmission and reception, it is often desirable to move the position of the PMUT 302 during transmission and recording, but this is often impractical. Adjusting the properties of the medium 16 through which the signal is transmitted or received by adjusting the position of the reflectors 210a, 210b has the same net effect as adjusting the position of the PMUT 302 itself.

[0136] When transmitting frequency-converting signals, a typical disadvantage of array design is that the position of PMUT element 302 is optimal for only one frequency (which is usually the center frequency of the broadband signal), so that PMUT 302 has a half-wavelength spacing of the center frequency. Therefore, the PMUT spacing may not be the optimal spacing for other frequencies in the broadband signal. According to the present invention, when transmitting a chirped signal from F0 to F1, the position of reflectors 210a, 210b is adjusted in the medium so that: at any given moment, PMUT 302 is "spaced apart" by half a wavelength relative to the current frequency. Therefore, by adjusting reflectors 210a, 210b, better imaging capabilities can be achieved at all frequencies. Modifying the position of reflectors 210a, 210b in front of the array of PMUT 302 may produce a lens effect. Having a half-wavelength spacing allows for easy use of relatively simple beamforming methods. In terms of transmission, half-wavelength spacing is beneficial because it directly determines the extent to which the focused beam can be prevented from "leaking" into other unintended directions. On the reception side the problem is usually slightly better, especially when working in air where there is usually a lot of "space" and some sharp reflectors (as opposed to e.g. medical imaging where everything is on the continuous spectrum).

[0137] If the elements are spaced other than λ / 2 on the processing side of the receive array, a combination of the following two aspects can be exploited: (a) the scene is usually relatively sparse, and (b) so-called "grating lobes" occur at different angles at different frequencies. Therefore, using a broadband signal may help reduce the need for λ / 2 spacing.

[0138] Using broadband signals, multiple frequencies can be matched and used as a protection against mutual errors. Specifically, suppose an array is 1 Below λ 1 / 2. The array will have grating lobes at a specific angle β relative to the main beam (at angle α). This means that when looking at an object, there is no way to tell whether the reflector is at angle α or angle β - because the incident waves from these two angles will look exactly the same on the array sensor.

[0139] This is a result of spatial undersampling, similar to the aliasing phenomenon in time domain signal processing. However, if we also consider another wavelength λ 2 , and consider the same main beam at angle α - then the associated grating lobes are now typically at different angles Ω.

[0140] If the object is at an angle β, then for the second wavelength λ 2, the response in the direction of α and / or Ω (the two directions are indistinguishable) will be low. If not, then the object is likely at angle α. The same logic can be used to discern multiple objects at multiple angles, until a certain point where there are points almost everywhere and the scene is no longer sparse enough to exploit the possibility of such broadband inheritance. In practice, compressed sensing methods will exploit these broadband features in sparse scenes where undersampled arrays are present, and generally do not have to resort to search or cancel-one-out approaches such as those outlined above.

[0141] Now we will refer to Figure 8B and Fig. 8A describe Figure 5B and Figure 6B The operation of the embodiment shown in . Fig. 8A Shows Figure 6B 4, and a graph of the PMUT array 302 and cavity 404 in FIG. 4, and transfer functions F(θ, ω) and F(γ, ω) used to simulate the expected effect of the reflector 110 on the transmitted ultrasound signal (e.g., chirp). The transfer function is a mathematical function that theoretically simulates the output of the PMUT array 302 as a function of the position of the reflector 110. Figure 8B The PMUT array 302 and cavity 304 with modified transfer functions F'(θ,ω) and F'(γ,ω) Figure 1 It is shown that the transfer function is modified due to the movement of reflector 210b.

[0142] Fig. 9 An array of PMUTs 302 is shown for imaging a known object 20 in order to accurately simulate the impulse response of the transmitted signal. The object 20 may also be an active element rather than a passive reflector, such as a microphone, so that it emits its own signal 22.

[0143] The following formulas provide more details on the processing performed for imaging using the PMUT described above. The processing may be performed using any suitable processor.

[0144] First, consider Fig.10 The simplified scenario shown here assumes a single reflector, transmitter, and receiver. Then, assume that a band-limited Dirac pulse is emitted from the transmitter. The received signal is:

[0145]

[0146] x i (t) is the transmitted signal, is the reflected signal, f i (α,t) is the filter applied to the transmitted signal, and gj (β,t) is the filter applied to the received signal.

[0147] Then, for a single transmitter, a single receiver, and multiple reflectors, the received signal is:

[0148]

[0149] Among them, the received signal r k is the sum of the signals of all reflectors k.

[0150] For multiple transmitters, a single receiver, and multiple reflectors, the received signal is:

[0151]

[0152] Among them, the transmitted signal x i (t) is the sum of the signals of all transmitters i, and the received signal r k is the sum of the signals of all reflectors k.

[0153] When the array of PMUTs is used for both transmission and reception of ultrasound signals, the received signal r k is minimized, and the real data y j (t s ) and estimated image data are input to the processor together.

[0154]

[0155] The directional filters F, G are learned by calculating the reflectivity, focusing on image quality:

[0156]

[0157] r={r k}

[0158] F={f i (α a ,β b )}

[0159] G = {g i (α a ,β b )}

[0160] This is then further refined by adding additional restrictions related to the transfer functions F and G as follows:

[0161]

[0162] Then in multiple scenarios R = {r k Learn F and G in

[0163]

[0164] Therefore, this is a blind study of the array impulse response in multiple scenarios.

[0165] contrast(r p ) can be calculated as the L1 norm of the vector r, or alternatively as the L1 norm in some transform domain Br, where B can contain: a codebook vector that represents a specific type of information related to the acoustic scene (such as an edge filter in the depth direction or the angular direction). It can also be related to the distribution of coefficients in r, such as rewarding many zeros and some positive coefficients. Or it can be the L0 norm of r, or any other method based on compressed transmission or sparsity, Bayesian methods, linear programming-based methods, or other methods.

[0166] The component continuity (F) can be a measure of the rate of change of the acoustic transfer function between closely spaced angles. If f i ,f j is the vector of the matrix F representing the directional impulse response in direction I,j, then:

[0167]

[0168] Where d(i,j) is f i ,f j A measure of the angular distance between the impulse responses represented. S is the set of all relevant angle pairs to be considered.

[0169] The calculations listed above relate to standard ultrasound imaging with known directional filters F, G and a known reflector r.

[0170] The following calculations include modifications to the calculations shown above for when the "medium" in front of the PMUT used for imaging changes. Examples of these changes are: changes in the volume of the acoustic resonant cavity or changes in the position of the reflectors (which change the density of the medium in front of the PMUT).

[0171] For multiple transmitters, a single receiver, and multiple reflectors, the received signal is now:

[0172]

[0173] Among them, the transmitted signal x i (t) is the sum of the signals on all transmitters i, and the received signal r k is the sum of the signals on all reflectors k. Directional filter f i ,g j It also depends on the state vector w as well as the angles α, β and the time dependency t.

[0174] Receive signal r k is minimized, and the real data y j (t s ) together with the estimated image data Together, the estimated image data is input to the processor and now also depends on the state vector w.

[0175]

[0176] As before, the directional filters F, G are learned by computing the reflections, focusing on image quality:

[0177]

[0178] As shown in the following equations, the transfer functions F and G also depend on the state vector w, which provides information about the changes in the medium in front of the PMUT used to transmit or receive ultrasound signals.

[0179] r={r k}

[0180] F={f i (α α ,β b ,w)}

[0181] G = {g i (α a ,β b ,w)}

[0182] This is then further improved by adding additional restrictions related to the transfer functions F and G, which now also depend on the state vector w as shown below, and exploit the knowledge that the transfer functions F and G change gradually with angle:

[0183]

[0184] Then in multiple scenarios R = {r k} to learn F and G:

[0185]

[0186] Coming back to the equation for receiving the signal:

[0187]

[0188] The angles (α, β) do not need to be explicit parameters, since they can be based on the reflection intensity r k Calculated based on knowledge of the reflector position.

[0189] Therefore, the equation can be simplified to:

[0190]

[0191] Where x = {x 1 (t),x 2 (t),…} is a set of driving signal functions.

[0192] This can be further simplified using the drive signal matrix:

[0193]

[0194] Therefore, the received signal equation becomes:

[0195]

[0196] The reflectance vector that provides information about the "image" produced during the imaging process can be determined:

[0197]

[0198] Therefore, the received signal equation can be further simplified as shown below:

[0199]

[0200] As the number N increases, the system of equations becomes more adaptive and, therefore, the results (images) will also be better.

[0201] Increasing N increases the number of ways to launch the signal (X) and the number of ways to modify the aperture (w), such as by adjusting the acoustic cavity volume or by adjusting the position of a reflector in the medium in front of the PMUT.

[0202] By transmitting ultrasound signals through different media (such as amorphous media with reflectors), the above equation can be used to "learn" how the sound is affected by the medium, and then use the equation to steer the sound during transmission and reception. The output signal of each array element can be pre-conditioned, and the received signal can then be processed and used to acquire an image of the surrounding environment.

[0203] Therefore, by arranging the reflectors so that they are randomly positioned relative to each other, a better image can be obtained. For example, when the reflectors include metal spheres randomly placed within a gel (such as Figure 3 This is possible when the reflectors are positioned randomly and / or moved (randomly) in many different directions (as shown). This has a similar effect to taking images from many different angles with a camera. Randomly positioning the reflectors and / or moving them (randomly) in many different directions allows the PMUT array 302 to determine more information as more camera angles are being observed.

[0204] The PMUT 302 array may also be mounted on a motor (not shown) and moved during observation of a single (or multiple) reflector. Thus, the directional impulse response may be sampled in all directions. The sampling may be performed before the PMUT array 302 is used for imaging, such as in a test lab environment, or during use, such as when the array 302 is mounted on a robot or other device capable of controlling the physical position and angle of the array 302. This allows the PMUT array 302 to obtain multiple views of its surroundings.

[0205] By simulating the impulse response of the transmitted signal with a known reflector, the effect of position adjustment of reflector 210b can be simulated to improve imaging.

[0206] Now go to Fig.11 , showing the PMUT array 302 interfaced with the cavity 504. The amorphous medium 16 and the reflector 110b are arranged in the cavity, in front of the PMUT array 302. It is obvious that the cavity 504 is much larger than the array 302, which is different from the cavity and array shown in the previous figures. The larger cavity 504 provides a "larger aperture" for imaging using the PMUT array 302, while also reducing the cost, which would be much higher if the PMUT array 302 filled the entire cavity 504. Having a "larger aperture" ensures that the PMUT array 302 has better near-field focusing capabilities.

[0207] In reality, not all frequencies have optimal beam patterns or focusing, but by utilizing all frequencies simultaneously (i.e., using multiple frequencies for imaging) and through the knowledge that: (a) all frequencies reflect similarly to some extent, and (b) the acoustic scene in air is generally sparse (minimal reflections), good focusing can be achieved at all frequencies.

[0208] FIG. 12A to FIG. 12C Various configurations of multiple arrays are shown, each with Figure 6B The configuration in is similar, thus forming an "array of arrays".

[0209] Fig. 12A Each array 402 is shown disposed within a corresponding cavity 604. Each cavity 604 is coupled to the solid substrate 24 through a corresponding support post 25.

[0210] exist Fig. 12B In FIG. 6 , similar cavities 604 ′ are arranged on the damping medium 26 , which may be any suitable damping medium, such as a semi-solid or amorphous medium, a gel or an acoustic dielectric.

[0211] Fig. 12CEach array 402 is arranged in a cavity 604", and the cavity 604" is arranged in a damping medium 28, which can also be any suitable damping medium, such as an amorphous medium similar to the medium in the cavity 604".

[0212] Fig.13 Shown by Fig. 12A A system formed by an array 40 of arrays of arrays, the array 40 of arrays being used to image an object 30. The figure shows the width indication of the steered ultrasonic signal 32 and the transmitted ultrasonic signal 34 emitted from each array 402a, 402b, 402c, and also shows the grating lobe 36. The grating lobe 36 is a secondary main lobe that appears when a phased array is used (the main lobe is the ultrasonic signal 32). The grating lobe 36 appears when the array spacing is greater than λ / 2, where λ is the wavelength of the transmitted ultrasonic signal. The grating lobe 36 spreads out from the arrays 402a, 402b, 402c at an angle other than the main path, which is shown by the steered ultrasonic signal 32. The ultrasonic signal 32 is steered and shaped by adding a determined phase adjustment to the signal emitted by each PMUT in each array 402a, 402b, 402c, so that the generated transmitted ultrasonic signal from each PMUT in each PMUT array 402 is interfered, thereby producing an overall steered signal 32 emitted in the desired direction. As shown Fig.13 As is clearly shown in FIG. 4 , the transmit signals 32 from each array 402a, 402b, 402c are steered in different directions towards the object 30 being imaged. In this way, the object 30 may be imaged from multiple directions due to the directional signals 32 from the arrays.

[0213] In certain imaging situations, such as in high intensity near-field acoustics (e.g. object levitation or haptic feedback), it is desirable to have a wide overall array baseline and to have the object of interest close to the surface. This allows the energy to be focused not only in a general direction, but also to a "spot". It is beneficial to focus the energy to that spot and "fade" it away from it. For this, a long array baseline is required. Manufacturing large arrays of PMUTs is both expensive and difficult because the drive electronics require large FPGAs with many ports.

[0214] Fig.13 The system 40 in provides an additional benefit for this wide array baseline: individual driver electronics can be provided for each array 402 within the system 40. Each array 402 can be provided with parameters indicating the direction of energy and the strength of the signal to be transmitted. Alternatively, in some cases (e.g., multi-touch), a "directional map" with multiple directions can be included, and the processing required to create this map can be performed at the ASIC of each array 402.

[0215] Providing multiple arrays 402 in system 40 also makes the entire array "thinner" due to the reduction in the number of PMUTs, thereby reducing the occurrence of crosstalk. Each array 402 can be isolated from the other arrays, that is, so that they are not in physical contact with each other so that energy does not propagate between them. Each array 402 can be as Fig. 12A The mounting shown utilizes rods 25 raised above the substrate 24 so that they are separated from the base substrate 24 to which they are connected. Alternatively, the array 402 may be arranged on a foam medium having minimal acoustic emission capabilities.

[0216] It is also easier to fabricate a smaller array 402 in a single cavity 604 than a larger array which is more difficult to manipulate. A larger PMUT array may require bonding wires to each individual element which is difficult to fabricate.

[0217] The spacing between arrays 402 in system 40 may also be used to place additional sensors, such as 2D or 3D cameras, to provide additional viewing angles for objects to be imaged and focused on.

[0218] In some embodiments, power is provided only to each array 402. Signal direction / pattern, signal strength, and other information used for calibration may be provided wirelessly to the array 402. Thus, the entire system 40 is a sensor network of arrays 402, with an input power source.

[0219] Alternatively, in some embodiments, additional information may be provided to system 40 via a wired connection.

[0220] Each PMUT array 402 is interfaced with a cavity 604. D / A converters and / or A / D converters may also be provided if desired, as well as an ASIC and wireless chip if signal direction / mode, signal strength, and other information used for calibration is provided wirelessly to the array 402.

[0221] It should be understood that the "array of arrays" shown above may include any array or PMUT shown in any of the figures, for example, the medium may not contain reflectors. In addition, the array may be non-planar, for example Fig.14 704. Alternatively, as shown in FIG. Fig.15 As shown, the system 140 may use an acoustic tube / port 42 without an amorphous medium in the cavity 804 within which the PMUT array 602 is located. However, the acoustic tube 42 may become clogged with dust, thereby adversely affecting the transmitted ultrasound signal.

[0222] Fig.16A The PMUT array 702 is shown arranged in a stack 44 , wherein a plurality of layers of different impedances are arranged in front of the PMUT array 702 . Fig. 16B yes Fig.16A Exploded view of.

[0223] A housing layer 46 is arranged above the PMUT array 702. The housing layer 46 is made of gel and has a good impedance match with the PMUT array 702. A second layer 48 is arranged above the housing layer 46 and has a different impedance than the housing layer 46. Finally, a third layer 50 is arranged on top and forms an outer layer. The outer layer 50 can be quite hard and lightweight to protect the PMUT stack 44.

[0224] Piezoelectric strips 52 are glued around the outside of the stack 44 (one for each layer 46, 48, 50). When current is applied to the piezoelectric strip 52, it changes its thickness and can apply a different force to each layer in the stack, such as Fig. 16C This results in deformation of the layers in the stack, which results in pressure variations between each layer 46, 48, 50, such that: the pressure variations can be used to control and guide Fig.16D The wavefront 56 shown in FIG. The pressure change creates an acoustic gradient, which provides a "lensing effect" as described above, which has the same effect as changing the position of the PMUT element itself.

[0225] Layers 46, 48, 50 become increasingly harder away from the PMUT and toward the outside. The layer 46 above the PMUT is usually relatively soft (e.g., gel or even air). The gradual transition in hardness ensures a good impedance matching strategy. If a hard surface is laid above the gel or air layer 46, all transmitted energy from the PMUT array 702 will be reflected back.

[0226] If the outer layer 50 is solid, this can protect the PMUT array 702. The piezoelectric strips 52 can move and flex the PMUT array 702. This can be used to create a "crack-free" dirt and dust layer, and also to "check" the state of the array when imaging under different conditions.

[0227] The layers 46, 48, 50 may wear over time, thereby changing the acoustic transfer function. However, according to the present invention, the acoustic transfer function can be modified "in situ". For example, a previous acoustic transfer function can be used to acquire an image. This stored acoustic transfer function can then be modified to obtain a clearer image. Fig.15 Arranging multiple reflectors around the array (eg, in one of the layers 46, 48, 50) makes the imaging less susceptible to variations in the shape of the housing around the PMUTs since the acoustic transfer function can be modified, compared to the acoustic ports shown.

[0228] Fig.17is a flow chart showing a method for updating a directional impulse response to improve the quality of an acquired image using any of the above embodiments with a reflector in an acoustic resonant cavity. i ,ω j ), the images obtained from ultrasound imaging are almost always "blurry". Therefore, the sharpness of the image can be used as a criterion to update the filter selected to obtain the image.

[0229] In step 58, the original filter F(θ i ,ω j ), and then use these selected raw filters to image the scene in step 60. The scene will be imaged using a PMUT or PMUT array, which transmits an ultrasound signal that is reflected and received, and the received signal is processed by a processor locally on the PMUT or on a cloud server.

[0230] In step 62, the sharpness of the image is evaluated. This sharpness can be calculated using a metric such as image sharpness (see https: / / ieeexplore.ieee.org / document / 6783859) or the ratio between low reflectance values ​​(close to 0) and high reflectance values.

[0231] If the sharpness is above the predetermined threshold in step 64 , the process will terminate in step 66 .

[0232] However, if the sharpness is not above the threshold, the filter will be adjusted in step 68. The filter may be adjusted using an old filter 70 stored in a memory (e.g., a server). The scene will then be imaged using the adjusted filter, and the sharpness of the scene will be assessed using the new filter.

[0233] Fig. 20shows how the PMUT and the housing change the signal output from the transducer. The top graph shows the original chirp signal s(t) 900, which will be output from the PMUT and ideally amplified into the air. The frequency response 901 (A(ω)) of the PMUT element itself is shown in the second graph, where ω is the wavelength. The third graph shows the signal 902 generated by driving the chirp s(t) through the PMUT. As can be seen, the center frequency is amplified. The dotted lines 903 and 904 show the energy levels (windows) that can be achieved for a flat spectrum, that is, if the signal s(t) is modified to reduce the power of the center frequency, or in other words, replace s(t) with a modified signal s'(t) so that for some positive number K and all ω, S(ω)A(ω)=K. The fourth graph 905 shows the effect of driving the chirp signal s(t) through a housing with a frequency response of B(ω) (not shown), which has a resonant frequency different from A(ω) (the PMUT element itself). The bottom graph 906 shows the effect of driving s(t) through both the PMUT and the transducer, where both the PMUT and housing frequencies are amplified.

[0234] Adjustments can be made to help achieve Fig. 20 The spectrum 906 shown in FIG. 9 is a flatter output spectrum than the spectrum 906 shown in FIG. The method by which this is achieved will now be described.

[0235] Let s(t) be the output signal (usually chirp). Ideally, the output would be the original (with noise added):

[0236] y(t)=s(t)+n(t)

[0237] In practice, the result will also be affected by the PMUT element itself which has a transfer function f(t).

[0238] t(t)=s(t)*f(t)+n(t)

[0239] Typically, the frequency response F(ω) of the filter f(t) has one or more resonant peaks. It is also necessary to include the effect of the enclosure as g(t). If the enclosure is not adaptive, then:

[0240] y(t)=s(t)*f(t)*g(t)+n(t)

[0241] The design goal may be to create a valid output signal y(t) that supports both standards or some combination of the two standards.

[0242] The first criterion (a) is that |Y(ω)| is as large as possible, which indirectly means that the magnitude of the term s(t)*f(t)*g(t) is also as large as possible, assuming that the expected noise magnitude is constant, E|N(ω)| = K. Therefore, (a) is essentially an SNR maximization criterion.

[0243] The second criterion (b) is that |Y(ω)| remains as constant as possible for all values ​​of ω, i.e., the flat output spectrum criterion. Some parameters can be changed to try to optimize each criterion, or to create some useful compromise between the two.

[0244] The following equation can be rewritten as:

[0245] y(t)=s(t)*f(t)*g(t)+n(t)=z(t)*g(t)+n(t))

[0246] Note: s(t)*f(t)=z(t)

[0247] This can be written in the time domain as:

[0248]

[0249] Recall that adjusting the characteristics of the enclosure effectively changes the enclosure filter or enclosure transfer function g(t), so for each sample of y(t):

[0250]

[0251]

[0252] Varying filter g i (.) are not fixed - they can be designed to change shape by adjusting the electrical parameters associated with changing the shell. Therefore, it is possible to define g i (.) = f(α(t i )), where α(t i ) is some physical parameter associated with the shell (e.g., current), which in turn defines g i (.). Assuming there is a functional model of how this happens, there are now two tools that can be used to satisfy these two goals:

[0253] One approach is to adjust z(k) = s(t) * f(t). This can be done indirectly by changing the drive signal s(t) - the PMUT response f(t) may not change.

[0254] Another approach is to adjust the shell characteristics and thus the shell transfer function at a specific time: g i (.) = f(α(t i )).

[0255] As an example, consider the case where s(t) is a linear chirp from frequency F0 to F1. There is a resonance peak in the middle (F0+F1) / 2, with three times the energy of other typical frequencies.

[0256] Time-specific filter g i (.) can also be adjusted—where i is the time window index—to amplify a certain frequency by a factor of three.

[0257] Then we can do two things. First, we can modify s(t) to become z(t), where the middle frequency of z(t) is attenuated to 1 / 3 the level of the other frequencies at frequency (F0+F1) / 2.

[0258] Secondly, when chirping upward from frequency F0, the time-specific filter g i (.) will continue to track the frequency of the chirp such that: each frequency upwards is amplified by a factor of 3 until it approaches the center frequency (F0+F1) / 2. The filter then does not change until the chirp moves beyond the center peak, at which point it resumes tracking the chirp signal again. Remember that near the center frequency, the PMUT itself will amplify the amplitude by a factor of 3, so the enclosure does not need to do this.

[0259] The end result is a flat frequency output spectrum of the signal y(t) that is amplified by a factor of three across the spectrum.

[0260] In practice, achieving both criteria perfectly (flat spectrum and maximum SNR) can be difficult, so various receptive regions and optimization strategies can be employed. Gradient descent, linear programming, nonlinear programming, or neural networks can be used to provide acceptance or penalty regions for deviations beyond certain target values.

[0261] It will be appreciated by those skilled in the art that the invention has been described by describing one or more specific embodiments thereof, but the invention is not limited to these embodiments; many variations and modifications are possible within the scope of the appended claims.

Claims

1. A piezoelectric micromachined ultrasonic transducer (PMUT) arranged to interface with an amorphous medium such that: in use, an ultrasonic signal to or from the PMUT passes through the amorphous medium, the amorphous medium comprising a plurality of discrete reflectors distributed therein.

2. The PMUT of claim 1, arranged to interface with an acoustic resonant cavity, the acoustic resonant cavity comprising the amorphous medium.

3. The PMUT according to claim 1 or 2, wherein: The discrete reflectors form a mesh or a porous membrane.

4. A PMUT according to any one of the preceding claims, wherein: The discrete reflectors are distributed in two dimensions.

5. A PMUT according to any one of the preceding claims, wherein: The position of the discrete reflectors is adjustable in use to adjust the acoustic properties of the acoustic resonant cavity.

6. A PMUT according to any one of the preceding claims, wherein: The discrete reflectors are metallic and a magnetic field is used to adjust the position of the discrete reflectors.

7. The PMUT according to any one of claims 2 to 7, wherein: The piezoelectric contraction element is arranged around the acoustic resonance cavity.

8. A PMUT according to any one of the preceding claims, wherein: The characteristics of the cavity are arranged to be adjusted as the frequency of the signal transmitted by the PMUT changes during chirped transmission.

9. A PMUT according to any one of the preceding claims, wherein: The PMUT includes a dedicated ultrasound transmitter and at least one separate ultrasound receiver on a single common semiconductor die.

10. A PMUT according to any one of the preceding claims, wherein: The PMUT is mounted so as to be movable by an actuator.

11. A method for imaging using a PMUT as claimed in the preceding claim or a PMUT array comprising a plurality of PMUTs as claimed in any one of the preceding claims, the method comprising: determining an acoustic transfer function corresponding to the effects of a plurality of discrete reflectors positioned between the PMUT or the array of PMUTs and a scene to be imaged; imaging the scene using the PMUT or the PMUT array by transmitting an ultrasound signal and receiving the ultrasound signal at the PMUT or the PMUT array after the ultrasound signal has undergone one or more reflections; The received ultrasound signals are processed by applying an inverse function of the acoustic transfer function to the received ultrasound signals to generate an image.

12. The method according to claim 11, wherein: The determining step comprises: (a) selecting an acoustic transfer function that is applied to a received signal to generate an image; (b) performing imaging using the PMUT or the PMUT array by transmitting an ultrasound signal and receiving the ultrasound signal at the PMUT or the PMUT array after the ultrasound signal has undergone one or more reflections; (c) processing the received signal using an inverse function of the acoustic transfer function to generate an image; (d) determining a sharpness parameter of the image, and when the determined sharpness parameter: (i) if it is not above a predetermined threshold, adjusting the transfer function before repeating steps (b)-(d); (i) When the value is higher than a predetermined threshold, the method is terminated.

13. The method according to claim 11 or 12, wherein: The acoustic transfer function includes a directional impulse response.

14. A method for imaging using a piezoelectric micromachined ultrasonic transducer, a PMUT or a PMUT array, comprising: determining an acoustic transfer function corresponding to the effects of a plurality of discrete reflectors positioned between the PMUT or the array of PMUTs and a scene to be imaged; imaging the scene using the PMUT or the PMUT array by transmitting an ultrasound signal and receiving the ultrasound signal at the PMUT or the PMUT array after the ultrasound signal has undergone one or more reflections; The received ultrasound signals are processed by applying an inverse function of the acoustic transfer function to the received ultrasound signals to generate an image.

15. A system for transmitting and receiving ultrasonic signals, comprising: At least a first PMUT and a second PMUT according to any one of claims 1 to 10, a transmitter circuit arranged to drive the first PMUT as an ultrasound transmitter, and A receiver circuit is arranged to detect a signal from the second PMUT as an ultrasound receiver.

16. An arrangement structure comprising: A plurality of PMUTs according to any one of claims 1 to 10.

17. The arrangement of claim 16, wherein: The plurality of PMUTs are arranged in an array.

18. An arrangement according to claim 16 or 17, wherein: The PMUTs are spaced apart by λ / 2, where λ is the wavelength of the center frequency within the frequency range transmitted or received by the PMUTs.

19. An arrangement according to claim 17 or 18, wherein: The array is mounted so as to be movable by means of an actuator.

20. An arrangement according to any one of claims 17 to 19, wherein: The array is not flat.

21. An arrangement according to any one of claims 17 to 20, wherein: Different PMUTs in the array have different sizes.

22. A method of imaging using the PMUT of any one of claims 1 to 10.

23. A piezoelectric micromachined ultrasonic transducer (PMUT) arranged to interface with an acoustic resonant cavity, wherein: The acoustic resonant cavity has at least one acoustic characteristic, and the acoustic characteristic can be adjusted according to the signal transmitted or received by the PMUT during use.

24. An arrangement structure comprising: A plurality of PMUTs are arranged to interface with corresponding acoustic tubes, the PMUTs being arranged in a mosaic array.

25. A plurality of acoustic resonant cavities, each acoustic resonant cavity comprising an array of PMUTs arranged to interface with the acoustic resonant cavity and further comprising an amorphous medium having discrete acoustic reflectors.

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