Acoustic sensing and communication using metasurfaces

Abstract

A system performs a search to adjust dimensions and distributions of superatoms in a passive acoustic metasurface with respect to a plurality of predetermined input signal attribute sets of an acoustic signal to provide adjusted propagation characteristics of aggregated superatoms, and forms the superatoms using the dimensions and distributions. Each superatom modulates an incident acoustic wavefront to form a corresponding emergent acoustic wave exiting the passive acoustic metasurface. For each input signal attribute set, the aggregated adjusted propagation characteristics support a plurality of predetermined input signal attribute sets of the incident acoustic wavefront. The physical dimension and distribution of the superatoms are adjusted according to the adjusted propagation characteristics to modulate the incident acoustic wavefront to generate a predetermined beam pattern of acoustic signals exiting the passive acoustic metasurface corresponding to a selected one of the predetermined set of input signal attributes.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent No. 63 / 453,057, filed March 17, 2023, entitled “Adaptive Metasurface for Low Earth Orbit Satellite Communications and Acoustic Sensing and Communication,” which is specifically directed to the entire disclosure and teachings thereof, which are incorporated by reference.

[0002] This application is related to U.S. Patent Application No., entitled “Passive Metasurface for Interacting with Electromagnetic Signals,” which is filed concurrently with this application and is specifically directed to the entire disclosure and teachings thereof, which are incorporated by reference. BACKGROUND

[0003] Acoustic sensing and communication is becoming increasingly popular due to the wide availability of devices that support such technologies, including smart phones, smart speakers, and many Internet of Things (IoT) devices. For example, such technologies can be employed to develop a smart phone based solution that transmits inaudible acoustic signals to track the distance, location, and movement of a target to enable more accurate sensing by leveraging the microphone array on a smart speaker, to develop an acoustic communication system as an alternative to NFC, to design an underwater messaging system using acoustic signals due to their slower decay compared to RF signals. Despite significant progress in acoustic sensing, there are fundamental limitations in its sensing range and resolution, as indicated by the Cramer-Rao bound, which indicates that the sensing resolution is limited by the signal-to-noise ratio (SNR) in the prior art and the number of transmitters and receivers required in existing solutions. Similarly, acoustic communication also faces similar challenges in terms of the Shannon capacity. SUMMARY

[0004] In some aspects, the technology described herein relates to a method of designing a passive acoustic metasurface for interacting with an acoustic signal from an acoustic transmitter received at the passive acoustic metasurface, the method comprising: performing a search to adjust physical dimensions and distributions of meta-atoms in the passive acoustic metasurface with respect to a plurality of predetermined input signal property sets of the acoustic signal to provide an adjusted profile of the aggregated meta-atoms; and forming the meta-atoms on the passive acoustic metasurface with the physical dimensions and distributions determined by the search, wherein each meta-atom is configured to modulate an incident acoustic wavefront to form a corresponding outgoing acoustic wave from the passive acoustic metasurface, wherein the adjusted profile of the aggregated meta-atoms supports the plurality of predetermined input signal property sets of the incident acoustic wavefront, and for each input signal property set, the physical dimensions and distributions of the meta-atoms are adjusted according to the adjusted profile to modulate the incident acoustic wavefront to generate a predetermined beam pattern of the acoustic signal from the passive acoustic metasurface corresponding to a selected input signal property set of the plurality of predetermined input signal property sets.

[0005] In some aspects, the technology described herein relates to a passive acoustic metasurface system for interacting with an acoustic signal from an acoustic transmitter received at the passive acoustic metasurface system, the passive acoustic metasurface system comprising: a passive acoustic metasurface designed by performing a search to adjust physical dimensions and distributions of meta-atoms in the passive acoustic metasurface with respect to a plurality of predetermined input signal property sets of the acoustic signal to provide an adjusted profile of the aggregated meta-atoms, and manufactured by forming the meta-atoms on the passive acoustic metasurface with the physical dimensions and distributions determined by the search, wherein each meta-atom is configured to modulate an incident acoustic wavefront to form a corresponding outgoing acoustic wave from the passive acoustic metasurface, wherein the adjusted profile of the aggregated meta-atoms supports the plurality of predetermined input signal property sets of the incident acoustic wavefront, and for each input signal property set, the physical dimensions and distributions of the meta-atoms are adjusted according to the adjusted profile to modulate the incident acoustic wavefront to generate a predetermined beam pattern of the acoustic signal from the passive acoustic metasurface corresponding to a selected input signal property set of the plurality of predetermined input signal property sets.

[0006] In some aspects, the technology described herein relates to one or more tangible processor-readable storage media embodied with instructions for execution on one or more processors and circuits of a computing device for a process for designing a passive acoustic metasurface for interaction with an acoustic signal received at the passive acoustic metasurface from an acoustic transmitter, the process comprising: performing a search to adjust physical dimensions and distribution of meta-atoms in the passive acoustic metasurface with respect to a plurality of predetermined input signal property sets of the acoustic signal to provide an adjusted propagation property of the aggregated meta-atoms; wherein the meta-atoms of the passive acoustic metasurface are formed on the passive acoustic metasurface with the physical dimensions and distribution determined by the search, wherein each meta-atom is configured to modulate an incident acoustic wavefront to form a corresponding outgoing acoustic wave from the passive acoustic metasurface, wherein the adjusted propagation property of the aggregated meta-atoms supports the plurality of predetermined input signal property sets of the incident acoustic wavefront, and for each input signal property set, the physical dimensions and distribution of the meta-atoms are adjusted according to the adjusted propagation property to modulate the incident acoustic wavefront to generate a predetermined beam pattern of the acoustic signal from the passive acoustic metasurface corresponding to a selected input signal property set of the plurality of predetermined input signal property sets.

[0007] In some aspects, the technology described herein relates to a passive acoustic metasurface for interaction with an acoustic signal received at the passive acoustic metasurface, the passive acoustic metasurface comprising: a matrix of meta-atoms distributed throughout the passive acoustic metasurface, each meta-atom positioned in the passive acoustic metasurface to provide an adjusted propagation property of the aggregated meta-atoms, each meta-atom providing a propagation path for at least one beam of the acoustic signal, each meta-atom interacting with the acoustic signal to modulate an incident acoustic wavefront of the acoustic signal received by the meta-atom to form a corresponding outgoing acoustic wavefront of the acoustic signal from the passive acoustic metasurface, wherein the adjusted propagation property of the aggregated meta-atoms supports a plurality of predetermined input signal property sets of the incident acoustic wavefront, and for each input signal property set, physical dimensions and distribution of the meta-atoms in the passive acoustic metasurface are adjusted according to the adjusted propagation property to phase shift the incident acoustic wavefront to generate a predetermined beam pattern of the acoustic signal from the passive acoustic metasurface corresponding to the input signal property set.

[0008] In some aspects, the technology described herein relates to a method of manufacturing a passive acoustic metasurface for interacting with an acoustic signal received at the passive acoustic metasurface, the method comprising: performing a search to adjust a beamforming weight and a position of each of a plurality of meta-atoms with respect to a steering vector corresponding to an angle of incidence of a beam of the acoustic signal; and forming a matrix of meta-atoms distributed throughout the passive acoustic metasurface, each meta-atom positioned in the passive acoustic metasurface to provide an adjusted propagation characteristic of the aggregated meta-atoms, each meta-atom providing a propagation path for at least one beam of the acoustic signal, each meta-atom interacting with the acoustic signal to modulate an incident acoustic wavefront of the acoustic signal received by the meta-atom to form a corresponding outgoing acoustic wavefront of the acoustic signal off the passive acoustic metasurface, wherein the adjusted propagation characteristic of the aggregated meta-atoms supports a plurality of predetermined input signal property sets of the incident acoustic wavefront, and for each input signal property set, physical dimensions and distribution of the meta-atoms in the passive acoustic metasurface are adjusted according to the adjusted propagation characteristic to phase shift the incident acoustic wavefront to generate a predetermined beam pattern of the acoustic signal off the passive acoustic metasurface corresponding to the input signal property set.

[0009] In some aspects, the technology described herein relates to a method of using a passive acoustic metasurface for interacting with an acoustic signal received at the passive acoustic metasurface, the method comprising: modifying at least one input property of the acoustic signal in a plurality of predetermined input property sets, wherein the passive acoustic metasurface is formed as a matrix of meta-atoms distributed throughout the passive acoustic metasurface, each meta-atom positioned in the passive acoustic metasurface to provide an adjusted propagation characteristic of the aggregated meta-atoms, each meta-atom providing a propagation path for at least one beam of the acoustic signal; and steering the acoustic signal off the passive acoustic metasurface, each meta-atom modulating an incident acoustic wavefront of the acoustic signal received by the meta-atom to form a corresponding outgoing acoustic wavefront of the acoustic signal off the passive acoustic metasurface, wherein the adjusted propagation characteristic of the aggregated meta-atoms supports a plurality of predetermined input signal property sets of the incident acoustic wavefront, and for each input signal property set, physical dimensions and distribution of the meta-atoms in the passive acoustic metasurface are adjusted according to the adjusted propagation characteristic to phase shift the incident acoustic wavefront to generate a predetermined beam pattern of the acoustic signal off the passive acoustic metasurface corresponding to the input signal property set.

[0010] This Summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description. This Summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter.

[0011] Other implementations are also described and recited herein. BRIEF DESCRIPTION OF DRAWINGS

[0012] Figure 1 An example environment for acoustic sensing and communication is shown.

[0013] Figure 2 An example dynamic acoustic beam steering system with a loudspeaker phased array and a passive acoustic metasurface is shown.

[0014] Figure 3 An example passive acoustic metasurface composed of multiple unit cells and beamforming propagating to / from a focal point is shown.

[0015] Figure 4 A side view of an example passive acoustic metasurface and a unit cell characterized by a length parameter is shown.

[0016] Figure 5 An example unit cell in a passive acoustic metasurface composed of 16x16 unit cells based on described techniques is shown.

[0017] Figure 6 An example passive acoustic metasurface composed of multiple unit cells and beamforming propagating to / from a focal point by appropriate configuration of unit cells is shown.

[0018] Figure 7 An example structure of signals received at various angles is shown.

[0019] Figure 8 An example beam pattern when steered to a particular angle during optimization or adjustment is shown.

[0020] Figure 9 Symmetry properties of a 16x16 metasurface are shown.

[0021] Figure 10 An example of a sound channel matrix with 4 metasurface units and 3 loudspeakers with different loudspeaker distribution is shown.

[0022] Figure 11 A plot showing (a) amplitudes and (b) phases of a codebook that demonstrates optimization, with a first loudspeaker set as a reference and aligned to zero phase is shown.

[0023] Figure 12 A plot showing example results of (a) phase distribution and (b) cell index for an optimized metasurface design is shown.

[0024] Figure 13 An example operation for designing a passive acoustic metasurface is shown.

[0025] Figure 14 An example operation for manufacturing a passive acoustic metasurface is shown.

[0026] Figure 15 Example operations for using a passive acoustic metasurface are shown.

[0027] Figure 16 Example computing devices for use in implementing the described technology are shown. DETAILED DESCRIPTION

[0028] Acoustic sensing and communication are increasingly popular due to the widely available devices that support them, such as smartphones, smart speakers, and other acoustic systems. However, the sensing resolution and range are still limited due to the limited bandwidth and sharp roll-off in the signal at inaudible frequencies. The described technology applies passive acoustic metasurfaces to acoustic sensing and communication solutions. The described passive acoustic metasurface technology can enable a significant SNR increase while maintaining a compact size compared to existing technologies.

[0029] Furthermore, a major limitation of passive acoustic metasurface technology is its static configuration and operation. The target of an acoustic sensing and / or communication system can be positioned at any possible location and can in fact move within the environment. Therefore, the target is to support scanning in different directions to track the target within the supported angular range. To address this purpose and others, the described technology provides a passive acoustic metasurface that has been designed by jointly optimizing the structural configuration of the passive acoustic metasurface and the selective control of the transmitted signals from the corresponding loudspeakers / microphones to enable low-cost dynamic steering from the passive acoustic metasurface. Thus, the described technology can prove effectiveness in improving SNR, acoustic sensing accuracy, and acoustic communication reliability in a wide range of scenarios.

[0030] To further improve performance, the number of acoustic transceivers can be increased. However, increasing the number of transceivers increases the cost, size, and energy consumption. Furthermore, existing sound cards cannot support more than eight channels. All these factors significantly limit the applicability of increasing the number of transceivers in real-world deployments.

[0031] Another option is to employ acoustic lenses. Like optical lenses, acoustic lenses can steer the direction of acoustic wave propagation and focusing in a certain region. However, due to the large wavelength of acoustic waves, acoustic lenses are typically bulky. In contrast, acoustic metasurfaces provide a more compact design.

[0032] An acoustic metasurface can include many subwavelength units, where each unit can operate like a microtransducer and modify the phase and / or intensity of the incident wave, such that collectively the passive acoustic metasurface can manipulate the wave in a way of interest (e.g., steer the outgoing wave towards a certain direction).

[0033] In one implementation disclosed herein, a passive acoustic metasurface with a beamforming configuration can be used in conjunction with one or more loudspeakers or microphones (collectively, “transceivers”). In one example, beamforming with a passive acoustic metasurface using 3 and 6 loudspeakers can increase the SNR by 4.7 dB and 7.9 dB, respectively. In contrast, another example passive acoustic metasurface with a size of 16x16 cells at 1 loudspeaker can increase the SNR by 15.5 dB. Thus, passive acoustic metasurfaces can significantly increase the SNR using a compact design without consuming power.

[0034] While passive acoustic metasurfaces are an alternative to dynamic acoustic metasurfaces, typical passive acoustic metasurfaces can only support static configurations and operations, e.g., always beamforming towards a fixed angle. Since targets can be at any location, beamforming as a fixed angle will not track moving targets or cannot be adjusted to have an effect on targets outside the fixed angle. Simply moving (e.g., rotating or translating) the passive acoustic metasurface to try to emulate a dynamic beam is not always a practical option. Instead, the described techniques employ dynamic beam steering with passive acoustic metasurfaces by selectively modifying input properties of incident signals, such as by using a phased array, to change the angle of the outgoing beam or modify receiver processing at multiple microphones.

[0035] Figure 1 An example environment 100 for acoustic sensing and communication is shown. An acoustic transceiver system 102 (e.g., a smart speaker) is positioned in the environment 100. In one implementation, the acoustic transceiver system 102 includes a phased array of loudspeakers and / or a phased array of microphones. To enhance the signal-to-noise ratio (SNR) of outgoing acoustic signals and incoming acoustic signals, a passive acoustic metasurface 104 has been placed between the acoustic transceiver system 102 and a sensing target 106 (e.g., a person) and between the acoustic transceiver system 102 and a communication node 108 (e.g., another smart speaker). The acoustic transceiver system 102 is referred to herein as a “source” and / or a “receiver.” The sensing target 106 and the communication node 108 are collectively referred to as “targets,” although both targets can initiate, reflect, or receive acoustic signals. Incoming acoustic waves can be propagated (e.g., transmitted or reflected) in either direction and from either side of the passive acoustic metasurface 104 by (through or from) the passive acoustic metasurface 104, or to and from the targets.

[0036] Because the targets can be positioned at different locations (e.g., at different angles) and can even move relative to the acoustic transceiver system 102 and the passive acoustic metasurface 104, the angle of the acoustic beam 110 between the source and the target is adjustable. For example, as the sensing target 106 moves across the space containing the acoustic transceiver system 102 and the passive acoustic metasurface 104, the acoustic beam is dynamically steerable to track the movement of the sensing target 106, despite the fact that the passive acoustic metasurface 104 is explicitly a passive structure, rather than a dynamic metasurface that can be actively adjusted or reconfigured, such as by applying adjustable voltages to electromagnets attached to a dynamic metasurface membrane to modify the phase and / or intensity of incident acoustic waves.

[0037] Figure 2 An example dynamic acoustic beam steering system 200 is shown having a phased array of loudspeakers 202 and a passive acoustic metasurface 204. Referring to Figure 2 , for example, the passive acoustic metasurface 204 has a number of unit cells (also referred to as meta-atoms) labeled 1-N in Figure 2 , where j is an index, and each unit cell can potentially be viewed as a micro-antenna. In this way, the passive acoustic metasurface 204 effectively increases the number of loudspeakers (and / or microphones), thereby improving the sensing resolution. By controlling the phase and / or amplitude of acoustic wave propagation through each unit cell, the passive acoustic metasurface 204 can manipulate the wavefield. The illustrated example dynamic acoustic beam steering system 200 disclosed herein combines a number of sub-wavelength, pre-fabricated 3D unit cells into a passive acoustic metasurface 204. Each unit cell encodes a specific phase offset. By rearranging these unit cells, a number of different instances of the metasurface can be produced. Since acoustic sensing / communication typically uses inaudible sound with wavelengths much smaller, the curled metasurface is more compact than Helmholtz-resonators and membrane-type structures.

[0038] The use of the passive acoustic metasurface 204 enables sharp beams with a small number of loudspeakers, a large SNR gain, and high resolution. Even with very few loudspeakers, the use of beamforming enables dynamic steering without the need for movement of the passive acoustic metasurface 204 relative to the phased array of loudspeakers 202 and without the need for a dynamic metasurface membrane. A small number of loudspeakers in a phased array with a passive acoustic metasurface 204 can achieve beamforming resolution similar to a large number of loudspeakers. For example, using a passive acoustic metasurface with 16x16 cells and a 6-loudspeaker phased array is comparable in beam width to a 9x16 = 144 phased array.

[0039] In implementations of the described technology, a joint design algorithm can be executed to optimize the configuration of the passive acoustic metasurface 204 and the beamforming weights of the loudspeaker phased array 202. Specifically, the joint design of the passive acoustic metasurface 204 and the configurable beamforming of the loudspeaker phased array 202 can be formulated as an optimization problem with the goal of maximizing or adjusting the acoustic signal strength along each desired angle of operation (e.g., sampled from an angular range) and minimizing or adjusting the performance variation across these angles and energy in the sidelobes.

[0040] The optimization of the metasurface, loudspeaker / microphone phased array processing, and optionally their relative placement (e.g., placement relative to each other) increases the signal-to-noise ratio (SNR). According to Cramer Rao’s bound and Shannon capacity, the increased SNR leads to an improvement in wireless sensing and communication performance.

[0041] In one implementation, the system of the example dynamic acoustic beam steering system 200 includes a 3D printed film of the passive acoustic metasurface 204, six loudspeakers in the loudspeaker phased array 202, and a microphone. A joint design algorithm can be applied to determine the acoustic metasurface configuration and phased array codeword for steering the outgoing beam 206 in real-time dynamically. The passive acoustic metasurface 204 and the loudspeaker phased array 202 are jointly adjusted to achieve dynamic beam steering and high SNR for acoustic sensing and communication. The joint design can be evaluated using (i) the SNR of the received signal, (ii) the sensing performance (e.g., range estimation using frequency-modulated continuous wave (FMCW) and angle estimation using multiple signal classification (MUSIC) algorithm), and (iii) the communication error.

[0042] The example implementations of the acoustic sensing system described herein yield a significant improvement in SNR, range estimation, angle estimation, and communication reliability. Specifically, jointly designing the passive acoustic metasurface and the phased array codeword allows for dynamic steering of the beam to the desired direction and boosts the SNR. The increased SNR in turn increases the acoustic sensing and communication range. This approach increases the sensing range from 1.5 m in a single loudspeaker without an acoustic metasurface to 4 m with a passive acoustic metasurface using 6 loudspeakers; similarly, it increases the communication range from 0.8 m to 3.9 m.

[0043] In example implementations, the passive acoustic metasurface is transparent to the sensing algorithm. Thus, existing range estimation (e.g., FMCW) or angle estimation algorithms (e.g., MUSIC) can be applied to the received signal at the transceiver.

[0044] As noted above, multiple transmitters and / or multiple receivers can be used to enhance the received signal. At the transmitter (e.g., speaker) end, beamforming can be used to generate a transmission that arrives at the receiver at a phase such that the multipath signals are constructively added. At the receiver (e.g., microphone) end, the receiver can compensate for the phase difference of the received signals across different multipath signals to ensure constructive combination.

[0045] In various implementations, a passive acoustic metasurface is a 2D structure composed of many subwavelength 3D unit cells. By carefully designing each of the unit cells, one can manipulate acoustic waves by dynamically changing one or more signal properties of the acoustic signals that interact with the passive acoustic metasurface. Each unit cell can be viewed as a micro acoustic source. To perform beamforming in a certain direction, the paths through different unit cells in the metasurface are constructively added together to enhance the SNR in the direction / angle. This beamforming can be achieved by having each unit cell compensate for the phase difference. For example, without special design, the path through a first unit cell can differ from the path through a second unit cell by To ensure that the signals from the two paths are constructively added, one can design the first unit cell, and one can design the second cell to compensate for the phase difference One way to achieve this is to impose different geometries so that the path through the second cell is longer than the path through the first cell

[0046] Figure 3 An example passive acoustic metasurface 300 is shown that is composed of multiple unit cells (see, e.g., unit cell 302) and beamforming 304 towards a focal point 306. An incident plane wave 308 is focused at the focal point 306 after passing through the passive acoustic metasurface 300. Due to the reciprocity principle, therefore, when a point source is placed at the focal point 306, the signal coming out of the passive acoustic metasurface 300 will be an outgoing plane wave directed in a direction that is generally orthogonal to the metasurface. However, the passive acoustic metasurface 300 has been jointly designed with the code words of the phased array at the focal point 306 so as to allow dynamic steering of the incident plane wave 308 or the outgoing plane wave in response to changes in the phased array at the focal point. In some implementations, this change is due to different code words that control the signal properties via the phased array, where the code words represent a set of analog phase shift values or a set of amplitude plus phase shift values applied to the phased array.

[0047] Figure 4A side view of an example passive acoustic metasurface 400 and unit cell 402 characterized by length parameters dl and d2 is shown. Passive acoustic metasurface 400 is composed of 16x16 unit cells based on the described technology, each unit cell formed of a substantially rigid material 404 (e.g., a thermoplastic material) and defining an acoustic wave propagation path through the unit cell (e.g., from one side of passive acoustic metasurface 400 to the other through the unit cell). In Figure 4 In the middle, the propagation path through unit cell 402 is indicated by the arrow lines traversing from the incident wave to the exit wave from left to right.

[0048] The different lengths of the propagation paths cause different phase delays at the output. The structure and distribution of the unit cells across passive acoustic metasurface 400 are characterized by the adjusted propagation properties of the collective unit cell responses (e.g., according to the internal structure of each unit cell and the distribution of the unit cells on the passive acoustic metasurface), such that the phase shift imposed on the individual wavefronts at each unit cell causes the beam of acoustic signals to be directed at one of a plurality of predetermined steering angles. For example, the selection of this steering angle is controlled by the input signal properties of the incident signal applied to the code word of the phased array. Thus, by changing the signal properties of the incident signal in a set of predetermined input signal properties, the steering angle of the exit signal off the passive acoustic metasurface can be deterministically controlled to change the steering angle, change the code word controlling the signal properties of the incident signal.

[0049] For the purposes of discussion, assume that an incident acoustic wave enters the unit cell 402 from the left. The curved propagation path increases the time it takes for the incident acoustic wave to traverse the unit cell 402, which essentially introduces a phase shift to the outgoing wave. The unit cell structure formed from the substantially rigid material 404 of the different unit cells in the passive acoustic metasurface 400 forms different propagation paths determined by two dominant parameters dl and d2, which results in different propagation path lengths and thus different phase delays. The parameter dl is shown as the length of the protrusion of the rigid material from the inner wall of the unit cell 402 to the interior or the unit cell 402, and the parameter d2 is shown as the spacing between the protrusions of the rigid material along the axis through the unit cell. A single unit cell can include multiple instances of these parameters (e.g., lengths of other protrusions and / or distances between other protrusions). One way to determine dl and d2 is through numerical methods in a simulator (e.g., COMSOL based on finite element multi-physical simulators). It should be appreciated that the same concept can be applied to signals in a phased array of microphones passing through or reflecting from the passive acoustic metasurface 400 to a focal point based on the reciprocity principle. Other physical dimensions of each unit cell can also be determined during joint design, including but not limited to tunnel length (e.g., axial length of the unit cell or length from input of the unit cell to output of the unit cell), protrusion thickness, number of protrusions, etc.

[0050] By placing each unit cell (which applies a particular designed phase shift) in the appropriate location in the metasurface, the phase shift characteristics (also referred to as adjusted propagation characteristics to reflect that the characteristics can reflect changes in phase and / or amplitude of the acoustic signal interacting with each metasurface) are encoded into the metasurface to provide the desired functionality. The design determines a single phase shift corresponding to each propagation element of each unit cell distributed across the metasurface. The phase shift value applied to each unit cell determines the explicit physical dimensions associated with the propagation element of each unit cell.

[0051] The adjusted (e.g., optimized) propagation characteristics can be achieved by placing the unit cells in the appropriate locations in the metasurface (e.g., based on a joint design with expected signal properties of the incident acoustic signal and expected positioning of the acoustic signal receiver). Each unit cell is designed to provide an aggregated intentionally designed phase shift coverage (with other unit cells) to achieve high transmittance / reflectance. The described techniques can provide specifically designed phase shift characteristics in each propagation direction to achieve dynamic fine-grained focusing and steering using a combination of passive metasurfaces and small phased arrays. Thus, in accordance with the adjusted propagation characteristics, the physical dimensions and distribution of the propagation elements of the unit cells in the passive metasurface are structurally adjusted to modulate the incident acoustic wavefront to generate a defined beam pattern of acoustic signals exiting the passive acoustic metasurface corresponding to a set of input signal properties.

[0052] Figure 5 An example unit cell in a passive acoustic metasurface 504, which is composed of 16x16 unit cells based on the described techniques, is shown (see, e.g., unit cell 500 and unit cell 502). A phased loudspeaker array 506 is located at the focal point in front of the passive acoustic metasurface 504. Incident waves 508 at two different unit cells have different phases. However, each unit cell is constructed according to different dominant parameters di and d2, such that the outgoing waves 510 from each unit cell are at substantially the same phase (i.e., “in phase”). Thus, the structure of each unit cell in the passive acoustic metasurface 504 is adjusted to receive incident waves with different phases and output outgoing waves with the same phase.

[0053] Furthermore, in the context of dynamically steering the beam using the passive acoustic metasurface 504, the structure of each unit cell in the described techniques is also jointly designed in coordination with the signal properties (e.g., phase and / or amplitude) of the code words of the phased array at the focal point (e.g., the location of the audio loudspeaker). In this way, changing the code words of the phased array changes the signal properties of the incident waves 508, causing the beamforming to change the steering angle of the outgoing waves 510 relative to the direction normal to the surface of the passive acoustic metasurface 504. In this way, the outgoing waves 510 are dynamically steered, for example, by the coordinated changing of the signal properties of the incident waves 508 and the structure of the passive acoustic metasurface 504. It should be appreciated that the same concept can be applied to the signals passing through or reflected from the passive acoustic metasurface 504 to microphones in the phased array at the focal point based on the reciprocity principle.

[0054] As shown in FIG. 5B, the unit cell has a complex maze-like internal structure with four parallel strips positioned orthogonal to the direction of the incident acoustic wave. Interestingly, the transmission efficiency is high and reaches 98% on average across all unit cells. Generally, this response is due to at least the following two main reasons: i) the subwavelength unit cells diffract and cause the sound energy to bypass the parallel strips instead of being reflected back; and ii) the strips within each unit cell are curved instead of having sharp angles to reduce the acoustic impedance and maintain high transmission efficiency. In summary, the passive acoustic metasurface 504 has negligible power loss, so power loss does not need to be considered when developing passive acoustic metasurface designs for narrow bandwidths, although for wide bandwidths, power loss can be considered. Figure 5

[0055] Figure 6 ​An example passive acoustic metasurface 600 is shown that is composed of multiple unit cells and beamforming that propagates to / from a focal point through proper configuration of the unit cells. See, for example, unit cell 602. The unit cells can be arranged in a straight line to form a ID metasurface, or arranged in a rectangle to form a 2D metasurface of 3D unit cells. Beamforming can be achieved by introducing proper phase shifts at each unit cell. In one example, the type of unit cell can be quantized to 16 choices, making it easy to assemble / reassemble the metasurface. The unit cell can cover phase shifts from 0 to 2π. Thus, for each position in the array, the unit cell is chosen for the phase shift that is closest to the desired offset.

[0056] Once the passive acoustic metasurface 600 is printed, the mapping from the incident wave to the outgoing wave is fixed. Since the target can be in any direction, a varying codeword of the phased speaker array 604 is employed to steer the direction of the outgoing wave. Given the fixed configuration of the passive acoustic metasurface 600, one way to change the direction of the outgoing wave is to move the passive acoustic metasurface 600 by translational movement or by rotation. While movement is feasible, mechanical motion is slow, power consuming, causes wear and tear, and can even require operator intervention. For practical use, it is desirable to dynamically adjust the direction of the wave coming out of the passive acoustic metasurface 600 by changing the codeword of the phased speaker array 604 to avoid the need for mechanical motion. Thus, the passive acoustic metasurface 600 and the phased speaker array 604 are jointly designed to achieve the desired beamforming for different steering angles based on different codewords, which represent different beam phases and / or amplitudes. It should be appreciated that the same concept can be applied to the signals of the microphones in the phased array that pass through or reflect off the passive acoustic metasurface 600 to the focal point based on the reciprocity principle.

[0057] A phased array uses beamforming to constructively combine signals from multiple speakers. Beamforming can be applied to transmitters or receivers or both. There are multiple beamforming algorithms. They vary in the optimization goal: some maximize the signal, while others minimize the interference. In analog beamforming, beamforming is performed on analog signals at the transmitter before being sent into the air or at the receiver before analog-to-digital conversion. In digital beamforming, beamforming is performed on digital signals at the transmitter before digital-to-analog conversion or at the receiver after analog-to-digital conversion.

[0058] The beamforming capability depends on the number of speakers and their spacing. In one example, a beam pattern corresponding to varying number of speakers m is shown. The beam width in the desired direction is relatively large, and the sidelobes are significant when the number of speakers is within 8. The half-power beam width (HPBW) at 0° (i.e., perpendicular to the speaker array) can be approximated as follows: where λ is the wavelength, m is the number of loudspeakers, and d denotes the loudspeaker spacing, which is typically recommended to be For example, when the number of loudspeakers is 2, 4, 6, and 16, the HPBW will be 59.6°, 25.5°, 16.9°, and 6.3°, respectively. The beamwidth for a general angle can be derived as follows: where θ s is the steering angle and θ 0.5s is the HPBW of the steered beam. This indicates that the scanning range should not be too large, and typically θ s ≤ 60°.

[0059] Once the passive acoustic metasurface is assembled (e.g., 3D printed or manufactured via another method), it cannot be reconfigured on the fly. To provide dynamic adaptation while achieving high resolution and long range, a small number of loudspeakers are used in conjunction with the acoustic metasurface. The beamforming of the loudspeakers is optimized so that the outgoing waves from the passive acoustic metasurface are directed towards the desired angle. More specifically, a phased array can control the direction of the output signal, which serves as the incident signal propagating towards the passive acoustic metasurface. The use of multiple loudspeakers allows for the implementation of fast, dynamic control without the physical movement of components.

[0060] Returning to Figure 2 , there are M loudspeakers. Let w i denote the codeword for the i-th loudspeaker, where w i is a complex number, where the magnitude and phase are the scaling factor and phase shift, respectively, for the i-th transmitted signal. There are N unit cells in the passive acoustic metasurface. The acoustic signal received by the j-th passive acoustic metasurface cell from the i-th loudspeaker S i，j can be computed as follows, where t i is the transmitted signal of the i-th loudspeaker and H ij denotes the acoustic channel between the i-th loudspeaker and the j-th cell: S i,j = H ij w i t i (1)

[0061] Since the relative position between the passive acoustic metasurface unit cell i and the transmitter i is predetermined, one can derive where c is the speed of the acoustic signal, d i,j is the distance from the i-th transmitter to the j-th cell, a(d i,j ) is the signal attenuation amount at distance d i,j , and F(·) is a function that models how the channel attenuates with distance d i,j .

[0062] The placement of the phased array, denoted as x, can be considered and the above relationship rewritten in the following matrix form: S in = H(x)w (2) The transmitted signal t i can be ignored before beamforming, as it is the same at each loudspeaker.

[0063] Each element in the passive acoustic metasurface modifies the incident signal (e.g., by adding a path delay and / or changing the amplitude). Such modifications can be captured using a matrix, denoted as G, as further described herein. Then, the signal coming out of the passive acoustic metasurface becomes S out = GH(x)w (3)

[0064] Finally, R d denotes the signal in a given steering direction d from the passive acoustic metasurface. R d can be derived as follows, where K d denotes the steering vector corresponding to the direction d between the passive acoustic metasurface and the target. R d = K d GH(x)w (4)

[0065] The goal is to jointly design the codebook of the passive acoustic metasurface and the loudspeaker array to maximize the signal strength along each angle of interest. For example, if the scanning angles are supported from -60° to 60°, then the signal strength should be maximized for each angle in the range. Note that the passive acoustic metasurface has a fixed configuration across all angles, while the codebook can be changed for each beamforming angle, as in a typical beamforming scenario. Thus, the signal of interest R can be derived as follows: R = KGH(x)W (5) where R is a d x d matrix (where each row represents the received signal from a given direction d and each column represents a steering direction), K is a d x N matrix that specifies the steering vectors from the N unit-cell passive acoustic metasurface, G is a M x N matrix and its diagonal elements specify how the N-element passive acoustic metasurface converts the incident signal to the outgoing signal, H(x) is a N x M matrix that specifies the channel from the M transmitters to the N-element passive acoustic metasurface, and W is a M x d codebook for the M loudspeakers corresponding to the directions d.

[0066] The channel H and the steering vector K are fixed and can be analytically derived. Given H and K, the goal is to find the optimal static passive acoustic metasurface configuration G and codebook W to perform beamforming across a wide range of angles. Since the power of the beam in each direction is optimized, in the following we use the power P of the received signal R, which is denoted as P = |R| 2 .

[0067] The structure of the received signal P at various angles is denoted in Figure 7 as having high signal strength along the diagonal elements, which indicates that the signal is beamformed towards the desired steering angle.

[0068] In at least one implementation, the objective function includes the following three terms: Sum power : Since the use of static metasurface design and the need to adapt to a wide range of angles, the goal is to maximize the sum of power across all d directions. This can be derived as follows: L power = tr(P) (6) where tr(·) is the trace of a matrix (i.e., the sum of the diagonal elements in the trace). Minimum variance criterion : Maximizing only the total power can introduce some dead zones for certain directions. To avoid this problem, the variance P of the diagonal term is introduced as a penalty term L var to ensure that all directions are covered: L var = var(diag(P)) (7) In general, a weight matrix Q is introduced, which can place different weights on different angles. The result is: L var = var(diag(PQ)) (8) where Q = diag(q1, q2,... q l ) is the set of weights to control. If there is prior knowledge about the approximate location of the target, then the entries in Q corresponding to the locations close to the target can be increased. Minimum side lobe : Suppression of side lobe level (SLL) helps sensing and communication. Nulling and minimization are two common suppression methods. Some methods require prior knowledge about the direction of the side lobe, while other methods minimize the maximum side lobe. Minimizing the average SLL (i.e., minimizing the sum of the absolute values of all non-diagonal peaks in P) is the most effective in this context, although other methods can be employed.

[0069] Figure 7An example structure 700 of signals received at various angles is shown. Structure 700 includes high signal strength along diagonal elements (e.g., see diagonal element 702 and diagonal element 704) corresponding to the main beam. Non-diagonal elements (e.g., see non-diagonal element 706 and non-diagonal element 708) are considered to be "side lobes" that can reduce overall performance. Thus, the sum of non-diagonal peaks can be minimized as follows: L sidelobe =∑non-diagonalpeaks (9) To derive L sidelobe , the peaks in the P matrix are identified (e.g., using the findpeak() function), and then the peaks in the non-diagonal entries of the matrix are summed. This process reduces both side lobes and improves the quality of the main lobe.

[0070] Figure 8 An example beam pattern 800 is shown when directed to a particular angle during optimization or adjustment. Minimizing non-diagonal peaks helps to reduce side lobes and increase directivity. If the highest peak is a non-diagonal element, it can be minimized to correct the direction. Putting these concepts together, the following optimization model is obtained: where where μ and γ are parameters that control the importance of variance and side lobe terms, respectively. There are two constraints on the amplitude of the metasurface parameter G and the codebook W. In most implementations, neither G nor W should exceed 1.

[0071] The constraint on the amplitude of the metasurface G is called the constant modulus constraint (CMC). The problem involving the CMC is non-convex and NP-hard. In the described technique, |G ii | = 1 refers to points on the surface of an N-dimensional hypercube that indicate that each metasurface element does not change the amplitude of the incident signal. These are non-convex constraints. |W ij | ≤ 1 is a constraint on the amplitude of the phased array. The set contains the entire hypercube and includes the interior. Thus, it is a convex set. Therefore, for the phased array codebook, the amplitude can be limited to be within 1 rather than exactly equal to 1 to make the problem easier to solve.

[0072] In various implementations, the problem is a non-linear constrained optimization problem. Due to the presence of constraints, a gradient descent scheme cannot be applied directly. Therefore, a gradient projection method can be used, which guarantees that the solution after each gradient descent update still falls within the feasible set Ω. Specifically, if the k+1th update (i.e., x (k+1) = x (k) + α k d (k) ) such that the solution falls outside the feasible region, where αk is the learning rate, and d (k) is the gradient, which can be projected into the feasible set Ω as follows: x (k+1) = Π[ x (k) + a k d (k) ] (10) where Π is the projection operator, and Π[ x ] is called the projection of x into Ω. To this end, G ii is normalized in magnitude after each update, and if it is greater than |W ij | is normalized. The Adam optimizer in Pytorch can be used for optimization. Adam is an extended version of stochastic gradient descent that adapts the learning rate for each parameter. The output from Adam can be modified during each iteration using equation 10 to ensure that the constraints are satisfied.

[0073] Figure 9 The symmetry property of the 16x16 metasurface 900 is shown. As mentioned above, the diagonal of the variable G represents the phase delay for the metasurface unit cell. The passive acoustic metasurface is a 2D structure. The configuration of the passive acoustic metasurface should be left-right symmetric and up-down symmetric, as shown in the example of the 16x16 metasurface 900, because the scanning performance should be the same in the left-right direction in the azimuthal angle direction, and the beam pattern should also be the same in the up-down direction in the elevation angle direction. By exploiting the left-right and up-down symmetry property, 75% of the search dimension can be reduced for G.

[0074] Since the steering angles are from -60° to 60°, the codebook in some implementations is also symmetric between the positive and negative angles. Therefore, half of the codebook can be optimized (i.e., corresponding to the steering angles in (-60°, 0)) and copied to generate the codebook for (0, 60°).

[0075] The location of the metasurface-based loudspeaker and unit cell can determine the channel H(x). Let x = {x1, x2,... x M} represent the loudspeaker locations, and g = {g1, g2,... g N} represent the locations of the metasurface unit cells. The channel can be derived as follows: where ||·|| represents the distance between two points (i.e., the loudspeaker and the metasurface unit cell), and F() represents a function that maps the distance to a wireless channel, including the magnitude and phase.

[0076] Figure 10An example 1000 of a sound channel matrix H with 4 metasurface units and 3 loudspeakers with different loudspeaker distribution x is shown. The distance between each loudspeaker and metasurface unit can be derived to determine the channel H between the phased array and the metasurface.

[0077] In another example implementation, a joint optimization algorithm for metasurface macro configuration and receive beamforming weights is as follows. (The algorithm can be implemented in acoustic systems as well as electromagnetic systems. Such as for low earth orbit (LEO) communications.) For an incident signal x that passes through the metasurface and reaches multiple receiving transceivers / antennas, the angle of arrival (AoA) information between the target and the receiving transceivers / antennas is obtained.

[0078] Returning to the implementation using Equation 11, a given phased array setup (e.g., a uniformly distributed linear array) or an optimized phased array setup can be used as input. In the latter case, x i are treated as optimization variables along with other variables. Note that no constraint is imposed on x due to the symmetric properties of the metasurface G and codebook W, although a constraint can be imposed in some implementations. Equation 11 assumes a single line-of-sight path between the phased array and the metasurface, which is realistic because the metasurface is close to the phased array and there is no obstruction.

[0079] Figure 11 A plot 1100 showing (a) amplitudes and (b) phases of an optimized codebook is shown, where the first loudspeaker is set as the reference and aligned to zero phase. For the example system design, angles from -60° to 60° with 1° interval are sampled. Thus, for a 6-loudspeaker system, the codebook W is a 121 x 6 matrix containing 121 independent code words for 121 directions and 6 loudspeakers. Since the goal is to maximize the sum power of the diagonal elements, the amplitudes of each element in the codebook are close to 1 to achieve maximum transmission power, but since they are constrained ≤ 1, some are slightly less than 1, while the phases are manipulated to generate the desired acoustic field at the metasurface. It should be understood that a phased loudspeaker array can transmit acoustic signals with selected signal properties according to the transmission codebook, and a phased microphone array can receive acoustic signals with selected signal properties according to the receive codebook.

[0080] Figure 12A plot 1200 showing example results of (a) phase distribution and (b) cell index for an optimized 16x16 metasurface design is shown. By exploiting the diagonal elements of G and the symmetry property, the phase distribution of the metasurface is reconstructed. As mentioned above, the phase shift of each passive acoustic metasurface unit cell is quantized to 16 levels for flexible design and assembly / disassembly. The numbers in the top left corner represent the cell index for the top left metasurface, and quadrants are omitted for brevity due to left-right and top-bottom symmetry. The final passive acoustic metasurface can then be assembled by selecting the unit cells with the nearest phase shift, where the color reflects the unit cell index, and a higher index indicates a larger phase shift. The loudspeakers can be placed uniformly or arbitrarily in the phased array, and the placement can be fed to the optimization algorithm, or the algorithm can optimize the placement along with other configuration parameters.

[0081] An example experimental setup can be used for evaluation. The system can be divided into three parts: loudspeakers, microphones, and passive acoustic metasurfaces. Uniform placement of components can be used as a default configuration. In this case, six (6) identical microphones (16Ω, 0.25W) can be provided as transmitters. Each loudspeaker is connected with an operational amplifier THS 4001 to amplify the voltage and a power amplifier LM 386 to amplify the current. The distance between the centers of adjacent loudspeakers can be 8.6mm, which is half the wavelength of 20kHz sound. Four (4) microphones can be used to form a microphone array as receivers. The distance between the four (4) microphones can be 3.06cm, 2.04cm, and 3.06cm to reduce ambiguity and obtain better performance. All loudspeakers and microphones can be connected to the same Bela board for signal synchronization. The loudspeaker placement can also be optimized using the above-described scheme.

[0082] The passive acoustic metasurfaces are constructed according to the optimization process described above. The passive acoustic metasurfaces are composed of 256 (16x16) unit cells across 15cmx15cm. Since the unit cells are quantized to 16 choices, 16 different types of unit cells are 3D printed and assembled to the acoustic lens according to the evaluation scenarios. For example, a passive acoustic metasurface is assembled for 1 loudspeaker setup, different passive acoustic metasurfaces are assembled for 6 loudspeakers with uniform spacing, and another passive acoustic metasurface is assembled for 6 loudspeakers with non-uniform spacing. Each is designed in conjunction with the loudspeaker array. To ensure that most of the signals emitted by the loudspeakers pass through the passive acoustic metasurface, the passive acoustic metasurface is placed 2cm away from the loudspeaker array. For a single loudspeaker, the passive acoustic metasurface is placed 10cm away from the loudspeaker.

[0083] The scheme was evaluated in terms of (i) SNR, (ii) sensing accuracy, and (iii) communication performance. For acoustic sensing, a Kinect V3 was used to determine live distance and AoA. The loudspeaker transmitted the following FMCW signal: where f = 16 kHz, B = 4 kHz, and T = 0.1 s. Distance error and AoA error were used to quantify sensing accuracy. min

[0084] 1D MUSIC is an AoA estimation algorithm that computes the autocorrelation matrix R of the received signal x as R = x H x, where x is a 1 x N vector and x H is the conjugate transpose of x, and then performs eigenvalue decomposition on R. Let R N denote the noise space matrix, which is the space spanned by the N-M smallest eigenvectors, where M is the number of signals. Peaks in the pseudo-spectrum correspond to AoA.

[0085] For acoustic communication, data was encoded using OFDM. Each OFDM frame contained 180 binary phase shift keying (BPSK) symbols, which were banded onto 12 subcarriers spanning 18 kHz - 20 kHz. CDMA was used as an FEC code to improve resilience, and the code rate was 50%. Bit error rate (BER) and frame error rate (FER) were used to quantify communication performance. While there are other encoding schemes for acoustic communication, the benefits of this scheme (i.e., passive acoustic metasurface with loudspeaker array) can be similar across different acoustic encoding schemes.

[0086] Unless otherwise stated, all results reported herein are from testbed experiments. In one example, a 6-loudspeaker array with equal spacing of 9.4 mm between adjacent loudspeakers and the 16 x 16 passive acoustic metasurface was used. In the no-device acoustic sensing experiment, the microphone array was placed 3 cm above the passive acoustic metasurface to track the distance and AoA to a person’s hand, such that the signal from the loudspeaker to the target passes through the metasurface, and the signal reflects from the target (hand) and is received by the microphone array without passing through the metasurface. In the acoustic communication experiment, the receiver was placed 1.5 m away from the loudspeaker array. The impact of various parameters was also evaluated by changing their values.

[0087] Figure 13 ​Example operations 1300 for designing a passive acoustic metasurface are shown. The passive acoustic metasurface is designed to interact with an acoustic signal received at the passive acoustic metasurface from an acoustic transmitter. A search operation 1302 performs a search to adjust physical dimensions and distributions of super-atoms in the passive acoustic metasurface with respect to a plurality of predetermined input signal property sets of the acoustic signal to provide an adjusted propagation characteristic of the aggregated super-atoms. A shaping operation 1304 forms the super-atoms on the passive acoustic metasurface with the physical dimensions and distributions determined by the search. Each super-atom is configured to modulate an incident acoustic wavefront to form a corresponding outgoing acoustic wave from the passive acoustic metasurface. The adjusted propagation characteristic of the aggregated super-atoms supports the plurality of predetermined input signal property sets of the incident acoustic wavefront, and for each input signal property set, the physical dimensions and distributions of the super-atoms are adjusted according to the adjusted propagation characteristic to modulate the incident acoustic wavefront to generate a predetermined beam pattern of the acoustic signal from the passive acoustic metasurface corresponding to a selected input signal property set of the plurality of predetermined input signal property sets.

[0088] Figure 14 Example operations 1400 for manufacturing a passive acoustic metasurface are shown. The passive acoustic metasurface is manufactured to interact with an acoustic signal received at the passive acoustic metasurface. A search operation 1402 performs a search to adjust beamforming weights and locations of each super-atom of a plurality of super-atoms with respect to a steering vector corresponding to an angle of incidence of a beam of the acoustic signal. A row operation 1404 forms a matrix of super-atoms distributed across the passive acoustic metasurface, each super-atom positioned in the passive acoustic metasurface to provide an adjusted propagation characteristic of the aggregated super-atoms. Each super-atom provides a propagation path for at least a beam of the acoustic signal. Each super-atom interacts with the acoustic signal to modulate an incident acoustic wavefront of the acoustic signal received by the super-atom to form a corresponding outgoing acoustic wavefront of the acoustic signal from the passive acoustic metasurface. The adjusted propagation characteristic of the aggregated super-atoms supports a plurality of predetermined input signal property sets of the incident acoustic wavefront, and for each input signal property set, the physical dimensions and distributions of the super-atoms in the passive acoustic metasurface are adjusted according to the adjusted propagation characteristic to phase shift the incident acoustic wavefront to generate a predetermined beam pattern of the acoustic signal from the passive acoustic metasurface corresponding to the input signal property set.

[0089] Figure 15Example operations 1500 for using a passive acoustic metasurface are shown. A passive acoustic metasurface is fabricated to interact with acoustic signals received at the passive acoustic metasurface. A signal modification operation 1502 modifies at least one input property of the acoustic signals in a plurality of predetermined input property sets. The passive acoustic metasurface is formed as a matrix of superatoms distributed throughout the passive acoustic metasurface, each superatom positioned in the passive acoustic metasurface to provide an adjusted propagation property of the aggregated superatoms, each superatom providing a propagation path for at least one beam of the acoustic signals. A steering operation 1504 steers the acoustic signals away from the passive acoustic metasurface, each superatom modulating an incident acoustic wavefront of the acoustic signals received by the superatom to form a corresponding outgoing acoustic wavefront of the acoustic signals away from the passive acoustic metasurface. The adjusted propagation property of the aggregated superatoms supports a plurality of predetermined input signal property sets of the incident acoustic wavefront, and for each input signal property set, physical dimensions and distribution of the superatoms in the passive acoustic metasurface are adjusted according to the adjusted propagation property to phase shift the incident acoustic wavefront to generate a predetermined beam pattern of the acoustic signals away from the passive acoustic metasurface corresponding to the input signal property set.

[0090] Figure 16 Example computing device 1600 for implementing in the described technologies is shown. Computing device 1600 can be a client computing device (such as a laptop computer, a desktop computer, or a tablet computer), a server / cloud computing device, an Internet of Things (IoT), any other type of computing device, or a combination of these options. Computing device 1600 includes one or more hardware processors 1602 and memory 1604. Memory 1604 typically includes both volatile memory (e.g., RAM), and non-volatile memory (e.g., flash memory), although one or other type of memory can be omitted. An operating system 1610 resides in memory 1604 and is executed by processor(s) 1602. In some implementations, computing device 1600 includes storage 1620 and / or is communicatively coupled to storage 1620.

[0091] In example computing device 1600, as Figure 16As shown, one or more software modules, segments, and / or processors, such as the application 1650, various types of simulation software, numerical modeling software, phased array transmitter / receiver control software, and other program code and modules are loaded into the operating system 1610 on the memory 1604 and / or storage 1620 and executed by the processor(s) 1602. The storage 1620 can store codebooks, codewords, phase shift parameters, amplitude parameters, steering angles, and other data, and be local to the computing device 1600, or can be remote and communicatively connected to the computing device 1600. Specifically, in one implementation, components of a system for designing, manufacturing, and / or using a passive acoustic metasurface can be implemented entirely in hardware or a combination of hardware circuitry and software.

[0092] The computing device 1600 includes a power source 1616, which can include or be connected to one or more batteries or other power sources, and which provides power to the other components of the computing device 1600. The power source 1616 can also be connected to an external power source that covers or recharges the internal battery or other power source.

[0093] The computing device 1600 can include one or more communication transceivers 1630, which can be connected to one or more antennas 1632 to provide network connectivity to one or more other servers, client devices, IoT devices, and other computing and communication devices (e.g., mobile phone networks, Wi-Fi®, Bluetooth®, and other wireless networks, and wired networks). The computing device 1600 can also include a communication interface 1636, such as a network adapter or I / O port, which is any type of communication device. The computing device 1600 can use the adapter and any other type of communication device to establish a connection to a wide area network (WAN) or local area network (LAN). It should be appreciated that the network connections illustrated are exemplary and other communications devices and means for establishing a communications link between the computing device 1600 and other devices can be used.

[0094] The computing device 1600 can include one or more input devices 1634 so that a user can input commands and information (e.g., a keyboard, a touchpad, or a mouse). These and other input devices can be coupled through one or more interfaces 1638, such as a serial port interface, a parallel port, or a universal serial bus (USB) to the server. The computing device 1600 can also include a display 1622, such as a touchscreen display.

[0095] The computing device 1600 can include various tangible processor-readable storage devices and intangible processor-readable communication signals. Tangible processor-readable storage devices can be embodied by any available media or means including storage devices and storage media accessible by the computing device 1600 and can include both volatile and nonvolatile storage mediums, as well as removable and non-removable storage media. Tangible processor-readable storage media excludes intangible and transitory communications signals and includes volatile and non-volatile, removable and non-removable storage media implemented in any method or technology for storage of information such as processor-readable instructions, data structures, program modules or other data. Tangible processor-readable storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CDROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other tangible medium which can be used to store the desires information and which can be accessed by the computing device 1600. Intangible processor-readable communication signals, in contrast to tangible processor- readable storage media, can embody processor-readable instructions, data structures, program modules or other data resident in modulated data signals such as carrier waves or other signal transmission mechanisms. The term "modulated data signal" means a signal that has one or more of its characteristics set or changed in such a manner as to encode a signal. By way of example, and not limitation, intangible communication signals include signals through wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared and other wireless media.

[0096] Clause 1. A method of designing a passive acoustic metasurface for interacting with an acoustic signal from an acoustic transmitter received at the passive acoustic metasurface, the method comprising: performing a search to adjust physical dimensions and distributions of meta-atoms in the passive acoustic metasurface with respect to a plurality of predetermined input signal property sets of the acoustic signal to provide an adjusted propagation property of the aggregated meta-atoms; and forming the meta-atoms on the passive acoustic metasurface with the physical dimensions and distributions determined by the search, wherein each meta-atom is configured to modulate an incident acoustic wavefront to form a corresponding outgoing acoustic wave off the passive acoustic metasurface, wherein the adjusted propagation property supports the plurality of predetermined input signal property sets of the incident acoustic wavefront, and for each input signal property set, the physical dimensions and distributions of the meta-atoms are adjusted according to the adjusted propagation property to modulate the incident acoustic wavefront to generate a predetermined beam pattern of the acoustic signal off the passive acoustic metasurface corresponding to a selected input signal property set of the plurality of predetermined input signal property sets.

[0097] Clause 2. The method of clause 1, wherein each predetermined input signal property set of the plurality of predetermined input signal property sets comprises an incident angle of an incident beam of the acoustic signal.

[0098] Clause 3. The method of clause 1, wherein the acoustic transmitter comprises a plurality of acoustic transmitters forming a phased array to transmit acoustic signals according to a codebook of the transmission codebook to the passive acoustic metasurface to generate a predetermined beam pattern for the passive acoustic metasurface corresponding to one of the predetermined input signal property sets, wherein the transmission codebook of the phased array and the meta-atoms of the passive acoustic metasurface are adjusted to achieve the corresponding predetermined output beam pattern.

[0099] Clause 4. The method of clause 3, wherein the search is configured to optimize a user-defined function or a function of signal-to-noise ratio (SNR) or sum capacity at a set of specified angles.

[0100] Clause 5. The method of clause 1, wherein a plurality of acoustic receivers forming a phased array to receive acoustic signals from the passive acoustic metasurface according to a codebook of the reception codebook to combine the signals received at the plurality of receivers from the passive acoustic metasurface, and the codebook corresponds to one of the predetermined input signal property sets, wherein the reception codebook of the phased array and the meta-atoms of the passive acoustic metasurface are adjusted to achieve the corresponding predetermined target.

[0101] Clause 6. The method of clause 5, wherein the search is configured to optimize a user-defined function or a function of signal-to-noise ratio (SNR) or sum capacity at a set of specified angles.

[0102] Clause 7. The method of clause 1, wherein the acoustic transmitter comprises a plurality of acoustic transmitters to form a phased transmitter array and a plurality of acoustic receivers to form a phased receiver array configured to receive acoustic signals from the passive acoustic metasurface, wherein the plurality of acoustic transmitters uses codebooks from a transmission codebook and the plurality of acoustic receivers uses codebooks from a reception codebook, and the transmission codebook, the reception codebook, and the passive acoustic metasurface are jointly adjusted to achieve a predetermined target.

[0103] Clause 8. The method of clause 7, wherein the search is configured to optimize a user-defined function or a function of signal-to-noise ratio (SNR) or sum capacity at a set of specified angles.

[0104] Clause 9. The method of clause 1, wherein the passive metasurface is designed for acoustic sensing including range estimation or angle-of-arrival estimation or for acoustic communication.

[0105] Clause 10. A passive acoustic metasurface system for interacting with an acoustic signal from an acoustic transmitter received at the passive acoustic metasurface system, the passive acoustic metasurface system comprising: a passive acoustic metasurface designed by performing a search to adjust physical dimensions and distributions of meta-atoms in the passive acoustic metasurface with respect to a plurality of predetermined input signal property sets of the acoustic signal to provide adjusted propagation properties of the aggregated meta-atoms, and fabricated by forming the meta-atoms on the passive acoustic metasurface with the physical dimensions and distributions determined by the search, wherein each meta-atom is configured to modulate an incident acoustic wavefront to form a corresponding outgoing acoustic wave from the passive acoustic metasurface, wherein the adjusted propagation properties support the plurality of predetermined input signal property sets of the incident acoustic wavefront, and for each input signal property set, the physical dimensions and distributions of the meta-atoms are adjusted according to the adjusted propagation properties to modulate the incident acoustic wavefront to generate a predetermined beam pattern of the acoustic signal from the passive acoustic metasurface corresponding to a selected input signal property set of the plurality of predetermined input signal property sets.

[0106] Clause 11. The passive acoustic metasurface system of clause 10, wherein each predetermined input signal property set of the plurality of predetermined input signal property sets comprises an incident angle of an incident beam of the acoustic signal.

[0107] Clause 12. The passive acoustic metasurface system of clause 10, wherein the acoustic transmitter comprises a plurality of acoustic transmitters forming a phased array to transmit the acoustic signal to the passive acoustic metasurface according to a code word of a transmission codebook to generate a predetermined beam pattern for the passive acoustic metasurface, and the code word corresponds to one of the predetermined input signal property sets, wherein the transmission codebook of the phased array and the meta-atoms of the passive acoustic metasurface are adjusted to achieve the corresponding predetermined output beam pattern.

[0108] Clause 13. The passive acoustic metasurface system of clause 12, wherein the search is configured to optimize a user-defined function or a function of signal-to-noise ratio (SNR) or sum capacity at a specified set of angles.

[0109] Clause 14. The passive acoustic metasurface system of clause 10, wherein a plurality of acoustic receivers forming a phased array to receive the acoustic signal from the passive acoustic metasurface according to a code word of a reception codebook to combine the signals received at the plurality of receivers from the passive acoustic metasurface, and the code word corresponds to one of the predetermined input signal property sets, wherein the reception codebook of the phased array and the meta-atoms of the passive acoustic metasurface are adjusted to achieve the corresponding predetermined target.

[0110] Clause 15. The passive acoustic metasurface system of clause 14, wherein the search is configured to optimize a user-defined function or a function of signal-to-noise ratio (SNR) or sum capacity at a set of specified angles.

[0111] Clause 16. The passive acoustic metasurface system of clause 10, wherein the acoustic transmitter comprises a plurality of acoustic transmitters to form a phased transmitter array and a plurality of acoustic receivers to form a phased receiver array configured to receive acoustic signals from the passive acoustic metasurface, wherein the plurality of acoustic transmitters use codewords from a transmission codebook and the plurality of acoustic receivers use codewords from a receive codebook, and the transmission codebook, the receive codebook, and the passive acoustic metasurface are jointly adjusted to achieve a predetermined target.

[0112] Clause 17. The passive acoustic metasurface system of clause 16, wherein the search is configured to optimize a user-defined function or a function of signal-to-noise ratio (SNR) or sum capacity at a set of specified angles.

[0113] Clause 18. The passive acoustic metasurface system of clause 10, wherein the passive acoustic metasurface is used for one or more of motion tracking, respiration monitoring, or communication.

[0114] Clause 19. The passive acoustic metasurface system of clause 10, wherein the passive metasurface is designed for acoustic sensing including range estimation or angle of arrival estimation or for acoustic communication.

[0115] Clause 20. One or more tangible processor-readable storage media embodied with instructions for execution on one or more processors and circuits of a computing device for a process for designing a passive acoustic metasurface for interaction with acoustic signals from an acoustic transmitter received at the passive acoustic metasurface, the process comprising: performing a search to adjust physical dimensions and distributions of meta-atoms in the passive acoustic metasurface with respect to a plurality of predetermined input signal property sets of the acoustic signals to provide an adjusted propagation property of the aggregated meta-atoms; wherein the meta-atoms of the passive acoustic metasurface are formed on the passive acoustic metasurface with the physical dimensions and distributions determined by the search, wherein each meta-atom is configured to modulate an incident acoustic wavefront to form a corresponding outgoing acoustic wave from the passive acoustic metasurface, wherein the adjusted propagation property supports the plurality of predetermined input signal property sets of the incident acoustic wavefront, and for each input signal property set, the physical dimensions and distributions of the meta-atoms are adjusted according to the adjusted propagation property to modulate the incident acoustic wavefront to generate a predetermined beam pattern of the acoustic signal from the passive acoustic metasurface corresponding to a selected input signal property set of the plurality of predetermined input signal property sets.

[0116] Clause 21. The one or more tangible processor-readable storage mediums of Clause 20, wherein each of the plurality of predetermined input signal property sets comprises an angle of incidence of an incident beam of acoustic signals.

[0117] Clause 22. The one or more tangible processor-readable storage mediums of Clause 20, wherein the acoustic transmitter comprises a plurality of acoustic transmitters forming a phased array to transmit acoustic signals according to a codebook of codewords of a transmission codebook to the passive acoustic metasurface to generate a predetermined beam pattern for the passive acoustic metasurface, and a codeword corresponds to one of the predetermined input signal property sets, wherein the transmission codebook of the phased array and the meta-atoms of the passive acoustic metasurface are adjusted to achieve the corresponding predetermined output beam pattern.

[0118] Clause 23. The one or more tangible processor-readable storage mediums of Clause 20, wherein the search is configured to optimize a user-defined function or a function of signal-to-noise ratio (SNR) or sum capacity at a set of specified angles.

[0119] Clause 24. The one or more tangible processor-readable storage mediums of Clause 20, wherein the plurality of acoustic receivers forming a phased array to receive acoustic signals according to a codebook of codewords of a reception codebook from the passive acoustic metasurface to combine signals received at the plurality of receivers from the passive acoustic metasurface, and a codeword corresponds to one of the predetermined input signal property sets, wherein the reception codebook of the phased array and the meta-atoms of the passive acoustic metasurface are adjusted to achieve the corresponding predetermined target.

[0120] Clause 25. The one or more tangible processor-readable storage mediums of Clause 24, wherein the search is configured to optimize a user-defined function or a function of signal-to-noise ratio (SNR) or sum capacity at a set of specified angles.

[0121] Clause 26. The one or more tangible processor-readable storage mediums of Clause 20, wherein the acoustic transmitter comprises a plurality of acoustic transmitters to form a phased transmitter array and a plurality of acoustic receivers to form a phased receiver array configured to receive acoustic signals from the passive acoustic metasurface, wherein the plurality of acoustic transmitters use codewords from a transmission codebook and the plurality of acoustic receivers use codewords from a reception codebook, and the transmission codebook, the reception codebook, and the passive acoustic metasurface are jointly adjusted to achieve a predetermined target.

[0122] Clause 27. The one or more tangible processor-readable storage mediums of Clause 26, wherein the search is configured to optimize a user-defined function or a function of signal-to-noise ratio (SNR) or sum capacity at a set of specified angles.

[0123] Clause 28. The one or more tangible processor-readable storage mediums of Clause 20, wherein the passive metasurface is designed for acoustic sensing or for acoustic communication including range estimation or angle of arrival estimation.

[0124] Clause 29. A passive acoustic metasurface for interacting with an acoustic signal received at the passive acoustic metasurface, the passive acoustic metasurface comprising: a matrix of meta-atoms distributed throughout the passive acoustic metasurface, each meta-atom positioned in the passive acoustic metasurface to provide an adjusted propagation property of the collective meta-atoms, each meta-atom providing a propagation path for at least one beam of the acoustic signal, each meta-atom interacting with the acoustic signal to modulate an incident acoustic wavefront of the acoustic signal received by the meta-atom to form an outgoing acoustic wavefront of the acoustic signal off the passive acoustic metasurface corresponding to the incident acoustic wavefront, wherein the adjusted propagation property of the collective meta-atoms supports a plurality of predetermined sets of input signal properties of the incident acoustic wavefront, and for each set of input signal properties, physical dimensions and distribution of the meta-atoms in the passive acoustic metasurface are adjusted according to the adjusted propagation property to phase shift the incident acoustic wavefront to generate a predetermined beam pattern of the acoustic signal off the passive acoustic metasurface corresponding to the set of input signal properties.

[0125] Clause 30. The passive acoustic metasurface of Clause 29, wherein the adjusted propagation property of the collective meta-atoms is based on a search for beamforming weights corresponding to different angles of arrival.

[0126] Clause 31. The passive acoustic metasurface of Clause 29, wherein the adjusted propagation property of the collective meta-atoms is based on a search for phase delays for each metasurface cell of the passive acoustic metasurface.

[0127] Clause 32. The passive acoustic metasurface of Clause 29, wherein each predetermined set of input signal properties of the plurality of predetermined sets of input signal properties includes an angle of incidence of a beam of the acoustic signal.

[0128] Clause 33. The passive acoustic metasurface of Clause 29, wherein each predetermined set of input signal properties of the plurality of predetermined sets of input signal properties includes a phase of a beam of the acoustic signal.

[0129] Clause 34. The passive acoustic metasurface of Clause 29, wherein each predetermined set of input signal properties of the plurality of predetermined sets of input signal properties includes an amplitude of a beam of the acoustic signal.

[0130] Clause 35. The passive acoustic metasurface of clause 29, wherein the acoustic transmitters comprise a plurality of acoustic transmit transceivers forming a phased array to transmit acoustic signals to the passive acoustic metasurface according to code words of a transmission codebook to generate a predetermined beam pattern for the passive acoustic metasurface, and the code words correspond to one of the predetermined input signal property sets, wherein the transmission codebook of the phased array and the meta-atoms of the passive acoustic metasurface are adjusted to achieve the corresponding predetermined output beam pattern.

[0131] Clause 36. The passive acoustic metasurface of clause 29, wherein a plurality of acoustic receivers forming a phased array to receive acoustic signals from the passive acoustic metasurface according to code words of a reception codebook to combine the signals received at the plurality of receivers from the passive acoustic metasurface, and the code words correspond to one of the predetermined input signal property sets, wherein the reception codebook of the phased array and the meta-atoms of the passive acoustic metasurface are adjusted to achieve the corresponding predetermined target.

[0132] Clause 37. The passive acoustic metasurface of clause 29, wherein the acoustic transmitters comprise a plurality of acoustic transmit transceivers and a plurality of acoustic receive transceivers forming another phased array configured to receive acoustic signals from the passive acoustic metasurface, wherein the plurality of acoustic transmit transceivers use code words from a transmission codebook and the plurality of acoustic receive transceivers use code words from a reception codebook, and the transmission codebook, the reception codebook, and the passive acoustic metasurface are jointly adjusted to achieve a predetermined target.

[0133] Clause 38. A method of manufacturing a passive acoustic metasurface for interacting with acoustic signals received at the passive acoustic metasurface, the method comprising: performing a search to adjust a beamforming weight and a position of each meta-atom of a plurality of meta-atoms with respect to a steering vector corresponding to an angle of incidence of a beam of the acoustic signals; and forming a matrix of the meta-atoms distributed across the passive acoustic metasurface, each meta-atom positioned in the passive acoustic metasurface to provide an adjusted propagation characteristic of the collective meta-atoms, each meta-atom providing a propagation path for at least one beam of the acoustic signals, each meta-atom interacting with the acoustic signals to modulate an incident acoustic wavefront received by the meta-atom to form a corresponding outgoing acoustic wavefront of the acoustic signals exiting the passive acoustic metasurface, wherein the adjusted propagation characteristic of the collective meta-atoms supports a plurality of predetermined input signal property sets of the incident acoustic wavefront, and for each input signal property set, the physical dimensions and distribution of the meta-atoms in the passive acoustic metasurface are adjusted according to the adjusted propagation characteristic to phase shift the incident acoustic wavefront to generate a predetermined beam pattern of the acoustic signals exiting the passive acoustic metasurface corresponding to the input signal property set.

[0134] Clause 39. The method of clause 38, wherein the adjusted propagation properties of the clustered meta-atoms are based on a search for beamforming weights corresponding to different angles of arrival.

[0135] Clause 40. The method of clause 38, wherein the adjusted propagation properties of the clustered meta-atoms are based on a search for phase delays for each meta-surface unit of the passive acoustic metasurface.

[0136] Clause 41. The method of clause 38, wherein each of the plurality of predetermined input signal property sets comprises an angle of incidence of a beam of acoustic signals.

[0137] Clause 42. The method of clause 38, wherein each of the plurality of predetermined input signal property sets comprises a phase of a beam of acoustic signals.

[0138] Clause 43. The method of clause 38, wherein each of the plurality of predetermined input signal property sets comprises an amplitude of a beam of acoustic signals.

[0139] Clause 44. The method of clause 38, wherein the acoustic transmitter comprises a plurality of acoustic transmit transceivers forming a phased array to transmit acoustic signals to the passive acoustic metasurface according to code words of a transmission codebook to generate a predetermined beam pattern for the passive acoustic metasurface, and a code word corresponds to one of the predetermined input signal property sets, wherein the transmission codebook of the phased array and the meta-atoms of the passive acoustic metasurface are adjusted to achieve the corresponding predetermined output beam pattern.

[0140] Clause 45. The method of clause 38, wherein a plurality of acoustic receivers forming a phased array to receive acoustic signals from the passive acoustic metasurface according to code words of a reception codebook to combine signals received at the plurality of receivers from the passive acoustic metasurface, and a code word corresponds to one of the predetermined input signal property sets, wherein the reception codebook of the phased array and the meta-atoms of the passive acoustic metasurface are adjusted to achieve the corresponding predetermined target.

[0141] Clause 46. The method of clause 38, wherein the acoustic transmitter comprises a plurality of acoustic transmit transceivers and a plurality of acoustic receive transceivers forming another phased array configured to receive acoustic signals from the passive acoustic metasurface, wherein the plurality of acoustic transmit transceivers uses code words from a transmission codebook and the plurality of acoustic receive transceivers uses code words from a reception codebook, and the transmission codebook, the reception codebook, and the passive acoustic metasurface are jointly adjusted to achieve a predetermined target.

[0142] Clause 47. A method of using a passive acoustic metasurface for interacting with acoustic signals received at the passive acoustic metasurface, the method comprising: modifying at least one input property of the acoustic signals in a plurality of predetermined input property sets, wherein the passive acoustic metasurface is formed as a matrix of meta-atoms distributed throughout the passive acoustic metasurface, each meta-atom positioned in the passive acoustic metasurface to provide an adjusted propagation property of the collective meta-atoms, each meta-atom providing a propagation path for at least one beam of the acoustic signals; and directing the acoustic signals away from the passive acoustic metasurface, each meta-atom modulating an incident acoustic wavefront of the acoustic signals received by the meta-atom to form a corresponding outgoing acoustic wavefront of the acoustic signals away from the passive acoustic metasurface, wherein the adjusted propagation property of the collective meta-atoms supports a plurality of predetermined input signal property sets of the incident acoustic wavefront, and for each input signal property set, physical dimensions and distribution of the meta-atoms in the passive acoustic metasurface are adjusted according to the adjusted propagation property to phase shift the incident acoustic wavefront to generate a predetermined beam pattern of the acoustic signals away from the passive acoustic metasurface corresponding to the input signal property set.

[0143] Clause 48. The method of clause 47, wherein the adjusted propagation property of the collective meta-atoms is based on a search for beamforming weights corresponding to different angles of arrival.

[0144] Clause 49. The method of clause 47, wherein the adjusted propagation property of the collective meta-atoms is based on a search for phase delays for each metasurface element of the passive acoustic metasurface.

[0145] Clause 50. The method of clause 47, wherein each predetermined input signal property set in the plurality of predetermined input signal property sets comprises an angle of incidence of a beam of the acoustic signals.

[0146] Clause 51. The method of clause 47, wherein each predetermined input signal property set in the plurality of predetermined input signal property sets comprises a phase of a beam of the acoustic signals.

[0147] Clause 52. The method of clause 47, wherein each predetermined input signal property set in the plurality of predetermined input signal property sets comprises an amplitude of a beam of the acoustic signals.

[0148] Clause 53. The method of clause 47, wherein the acoustic transmitter comprises a plurality of acoustic transmit transceivers forming a phased array to transmit the acoustic signals to the passive acoustic metasurface according to a codebook of code words to generate a predetermined beam pattern for the passive acoustic metasurface, and the code word corresponds to one of the predetermined input signal property sets, wherein the transmission codebook of the phased array and the meta-atoms of the passive acoustic metasurface are adjusted to achieve the corresponding predetermined output beam pattern.

[0149] Clause 54. The method of clause 47, wherein the plurality of acoustic receivers forming a phased array are to receive acoustic signals from the passive acoustic metasurface according to a receive codebook of codewords, to combine signals received at the plurality of receivers from the passive acoustic metasurface, and a codeword corresponding to one of a set of predetermined input signal properties, wherein the receive codebook of the phased array and the meta-atoms of the passive acoustic metasurface are adjusted to achieve the corresponding predetermined target.

[0150] Clause 55. The method of clause 47, wherein the acoustic transmitter comprises a plurality of acoustic transmit transceivers, and a plurality of acoustic receive transceivers form another phased array configured to receive acoustic signals from the passive acoustic metasurface, wherein the plurality of acoustic transmit transceivers use codewords from a transmit codebook and the plurality of acoustic receive transceivers use codewords from a receive codebook, and the transmit codebook, the receive codebook, and the passive acoustic metasurface are jointly adjusted to achieve a predetermined target.

[0151] Clause 56. A system for designing a passive acoustic metasurface for interaction with acoustic signals from an acoustic transmitter received at the passive acoustic metasurface, the method comprising: means for performing a search to adjust physical dimensions and distributions of meta-atoms in the passive acoustic metasurface with respect to a plurality of sets of predetermined input signal properties of the acoustic signals to provide adjusted propagation properties of the collective meta-atoms; and means for forming the meta-atoms on the passive acoustic metasurface with the physical dimensions and distributions determined by the search, wherein each meta-atom is configured to modulate an incident acoustic wavefront to form a corresponding outgoing acoustic wave from the passive acoustic metasurface, wherein the adjusted propagation properties support the plurality of sets of predetermined input signal properties of the incident acoustic wavefront, and for each set of input signal properties, the physical dimensions and distributions of the meta-atoms are adjusted according to the adjusted propagation properties to modulate the incident acoustic wavefront to generate a predetermined beam pattern of the acoustic signals from the passive acoustic metasurface corresponding to a selected set of input signal properties of the plurality of sets of predetermined input signal properties.

[0152] Clause 57. The system of any preceding clause, wherein each set of predetermined input signal properties of the plurality of sets of predetermined input signal properties comprises an angle of incidence of an incident beam of the acoustic signals.

[0153] Clause 58. The system of clause 3, wherein the acoustic transmitter comprises a plurality of acoustic transmitters forming a phased array to transmit acoustic signals to the passive acoustic metasurface according to a codebook of transmission codes to generate a predetermined beam pattern for the passive acoustic metasurface corresponding to one of the predetermined input signal property sets, wherein the transmission codebook of the phased array and the meta-atoms of the passive acoustic metasurface are adjusted to achieve the corresponding predetermined output beam pattern.

[0154] Clause 59. The system of clause 3, wherein the search is configured to optimize a user-defined function or a function of signal-to-noise ratio (SNR) or sum capacity at the specified set of angles.

[0155] Clause 60. The system of any preceding clause, wherein a plurality of acoustic receivers forming a phased array to receive acoustic signals from the passive acoustic metasurface according to a codebook of reception codes to combine the signals received at the plurality of receivers from the passive acoustic metasurface, and the reception codebook of the phased array and the meta-atoms of the passive acoustic metasurface are adjusted to achieve the corresponding predetermined target.

[0156] Clause 61. The system of any preceding clause, wherein the search is configured to optimize a user-defined function or a function of signal-to-noise ratio (SNR) or sum capacity at the specified set of angles.

[0157] Clause 62. The system of any preceding clause, wherein the acoustic transmitter comprises a plurality of acoustic transmit transceivers and a plurality of acoustic receive transceivers forming another phased array configured to receive acoustic signals from the passive acoustic metasurface, wherein the plurality of acoustic transmit transceivers use codes from a transmission codebook and the plurality of acoustic receive transceivers use codes from a reception codebook, and the transmission codebook, the reception codebook, and the passive acoustic metasurface are jointly adjusted to achieve a predetermined target.

[0158] Clause 63. The system of any preceding clause, wherein the search is configured to optimize a user-defined function or a function of signal-to-noise ratio (SNR) or sum capacity at the specified set of angles.

[0159] Clause 64. The system of any preceding clause, wherein the passive metasurface is designed for acoustic sensing including range estimation or angle of arrival estimation or for acoustic communication.

[0160] Clause 65. A system for fabricating a passive acoustic metasurface for interacting with acoustic signals received at the passive acoustic metasurface, the method comprising: means for performing a search to adjust a beamforming weight and a position of each of a plurality of meta-atoms with respect to a steering vector corresponding to an angle of incidence of a beam of the acoustic signals; and means for forming a matrix of meta-atoms distributed throughout the passive acoustic metasurface, each meta-atom positioned in the passive acoustic metasurface to provide an adjusted propagation characteristic of the aggregated meta-atoms, each meta-atom providing a propagation path for at least one beam of the acoustic signals, each meta-atom interacting with the acoustic signals to modulate an incident acoustic wavefront of the acoustic signals received by the meta-atom to form a corresponding outgoing acoustic wavefront of the acoustic signals off the passive acoustic metasurface, wherein the adjusted propagation characteristic of the aggregated meta-atoms supports a plurality of predetermined sets of input signal properties of the incident acoustic wavefront, and for each set of input signal properties, physical dimensions and distribution of the meta-atoms in the passive acoustic metasurface are adjusted according to the adjusted propagation characteristic to phase shift the incident acoustic wavefront to generate a predetermined beam pattern of the acoustic signals off the passive acoustic metasurface corresponding to the set of input signal properties.

[0161] Clause 66. The system of any preceding Clause, wherein the adjusted propagation characteristic of the aggregated meta-atoms is based on a search for beamforming weights corresponding to different angles of arrival.

[0162] Clause 67. The system of any preceding Clause, wherein the adjusted propagation characteristic of the aggregated meta-atoms is based on a search for phase delays for each metasurface cell of the passive acoustic metasurface.

[0163] Clause 68. The system of any preceding Clause, wherein each predetermined set of input signal properties of the plurality of predetermined sets of input signal properties comprises an angle of incidence of a beam of the acoustic signals.

[0164] Clause 69. The system of any preceding Clause, wherein each predetermined set of input signal properties of the plurality of predetermined sets of input signal properties comprises a phase of a beam of the acoustic signals.

[0165] Clause 70. The system of any preceding Clause, wherein each predetermined set of input signal properties of the plurality of predetermined sets of input signal properties comprises an amplitude of a beam of the acoustic signals.

[0166] Clause 71. The system of any preceding Clause, wherein the acoustic transmitter comprises a plurality of acoustic transmit transceivers forming a phased array to transmit acoustic signals to the passive acoustic metasurface according to code words of a transmission codebook to generate a predetermined beam pattern for the passive acoustic metasurface corresponding to one of a set of predetermined input signal properties, and the code words correspond to the one of the set of predetermined input signal properties, wherein the transmission codebook of the phased array and the meta-atoms of the passive acoustic metasurface are adjusted to achieve the corresponding predetermined output beam pattern.

[0167] Clause 72. The system of any preceding Clause, wherein a plurality of acoustic receivers forming a phased array to receive acoustic signals from the passive acoustic metasurface according to code words of a reception codebook to combine the signals received at the plurality of receivers from the passive acoustic metasurface, and the code words correspond to one of a set of predetermined input signal properties, wherein the reception codebook of the phased array and the meta-atoms of the passive acoustic metasurface are adjusted to achieve the corresponding predetermined target.

[0168] Clause 73. The system of any preceding Clause, wherein the acoustic transmitter comprises a plurality of acoustic transmit transceivers and a plurality of acoustic receive transceivers forming another phased array configured to receive acoustic signals from the passive acoustic metasurface, wherein the plurality of acoustic transmit transceivers use code words from a transmission codebook and the plurality of acoustic receive transceivers use code words from a reception codebook, and the transmission codebook, the reception codebook, and the passive acoustic metasurface are jointly adjusted to achieve a predetermined target.

[0169] Clause 74. A system for using a passive acoustic metasurface for interacting with acoustic signals received at the passive acoustic metasurface, the method comprising: means for modifying at least one input property of the acoustic signals in a plurality of sets of predetermined input properties, wherein the passive acoustic metasurface is formed as a matrix of meta-atoms distributed throughout the passive acoustic metasurface, each meta-atom positioned in the passive acoustic metasurface to provide an adjusted propagation property of the collective meta-atoms, each meta-atom providing a propagation path for at least one beam of the acoustic signals; and means for directing the acoustic signals away from the passive acoustic metasurface, each meta-atom modulating an incident acoustic wavefront of the acoustic signals received by the meta-atom to form a corresponding outgoing acoustic wavefront of the acoustic signals away from the passive acoustic metasurface, wherein the adjusted propagation property of the collective meta-atoms supports a plurality of sets of predetermined input signal properties of the incident acoustic wavefront, and for each set of input signal properties, the physical dimensions and distribution of the meta-atoms in the passive acoustic metasurface are adjusted according to the adjusted propagation property to phase shift the incident acoustic wavefront to generate a predetermined beam pattern of the acoustic signals away from the passive acoustic metasurface corresponding to the set of input signal properties.

[0170] Clause 75. The system of any preceding Clause, wherein the adjusted propagation properties of the assembled meta-atoms are based on a search for beamforming weights corresponding to different angles of arrival.

[0171] Clause 76. The system of any preceding Clause, wherein the adjusted propagation properties of the assembled meta-atoms are based on a search for phase delays for each metasurface unit of the passive acoustic metasurface.

[0172] Clause 77. The system of any preceding Clause, wherein each of the plurality of predetermined input signal property sets includes an angle of incidence of a beam of acoustic signals.

[0173] Clause 78. The system of any preceding Clause, wherein each of the plurality of predetermined input signal property sets includes a phase of a beam of acoustic signals.

[0174] Clause 79. The system of any preceding Clause, wherein each of the plurality of predetermined input signal property sets includes an amplitude of a beam of acoustic signals.

[0175] Clause 80. The system of any preceding Clause, wherein the acoustic transmitter includes a plurality of acoustic transmit transceivers forming a phased array to transmit acoustic signals to the passive acoustic metasurface according to a codebook of codes to generate a predetermined beam pattern for the passive acoustic metasurface, and a code of the codebook corresponds to one of the predetermined input signal property sets, wherein the codebook of the phased array and the meta-atoms of the passive acoustic metasurface are adjusted to achieve the corresponding predetermined output beam pattern.

[0176] Clause 81. The system of any preceding Clause, wherein a plurality of acoustic receivers forming a phased array to receive acoustic signals from the passive acoustic metasurface according to a codebook of codes to combine signals received at the plurality of receivers from the passive acoustic metasurface, and a code of the codebook corresponds to one of the predetermined input signal property sets, wherein the codebook of the phased array and the meta-atoms of the passive acoustic metasurface are adjusted to achieve the corresponding predetermined target.

[0177] Clause 82. The system of any preceding Clause, wherein the acoustic transmitter includes a plurality of acoustic transmit transceivers and a plurality of acoustic receive transceivers forming another phased array configured to receive acoustic signals from the passive acoustic metasurface, wherein the plurality of acoustic transmit transceivers uses codes from a transmission codebook and the plurality of acoustic receive transceivers uses codes from a receive codebook, and the transmission codebook, the receive codebook, and the passive acoustic metasurface are jointly adjusted to achieve a predetermined target.

[0178] Some implementations can include an article of manufacture that includes a tangible storage medium to store or retrieve instructions that when executed by a machine, hardware, or software, cause the machine, hardware, or software to operate like a computer including the described embodiments. The instructions can comprise one or more programs, routines, sub-routines, programs, computer programs, applications, software modules, applications, application modules, application programs, system programs, machine programs, operating system software, middleware, firmware, software modules, routines, sub-routines, objects, methods, processes, software interfaces, application program interfaces (API), instruction sets, computing code, computer code, code segments, computer code segments, words, values, symbols, or any combination thereof. In one implementation, for example, an article of manufacture can store executable computer program instructions that when executed by a computer cause the computer to perform a method and / or operations according to described embodiments. The executable computer program instructions can include any suitable type of code, such as source code, compiled code, interpreted code, executable code, static code, dynamic code, and the like. The executable computer program instructions can be implemented according to a predetermined computer language, manner or syntax, for instructing a computer to perform a certain operation. The instructions can be implemented using any suitable high-level, low-level, object-oriented, visual, compiled and / or interpreted programming language.

[0179] The implementations described herein are implemented as logical steps in one or more computer systems. The logical steps can be implemented as (1) a sequence of processor-implemented steps executing in one or more computer systems and (2) interconnected machine or circuit modules within one or more computer systems. The implementation is a matter of choice dependent on the performance requirements of the computer system being utilized. Accordingly, the logical operations making up the implementations described herein are referred to variously as operations, steps, objects, or modules. Furthermore, it should be understood that logical operations can be performed in any order, unless explicitly claimed otherwise, or otherwise explicitly specified in the claim language.

Claims

1. A passive acoustic metasurface for interacting with an acoustic signal received at the passive acoustic metasurface, the passive acoustic metasurface comprising: a matrix of meta-atoms distributed throughout the passive acoustic metasurface, each meta-atom positioned in the passive acoustic metasurface to provide an adjusted propagation characteristic of the meta-atoms in aggregate, each meta-atom providing a propagation path for at least one beam of the acoustic signal, each meta-atom interacting with the acoustic signal to modulate an incident acoustic wavefront of the acoustic signal received by the meta-atom to form a corresponding outgoing acoustic wavefront of the acoustic signal off the passive acoustic metasurface, wherein the adjusted propagation characteristic of the meta-atoms in aggregate supports a plurality of predetermined input signal attribute sets of the incident acoustic wavefront, and for each input signal attribute set, the physical dimensions and distribution of the meta-atoms in the passive acoustic metasurface are adjusted according to the adjusted propagation characteristic to phase shift the incident acoustic wavefront to generate a predetermined beam pattern of the acoustic signal off the passive acoustic metasurface corresponding to the input signal attribute set.

2. The passive acoustic metasurface of claim 1, wherein the adjusted propagation characteristic of the meta-atoms in aggregate is based on a search for beamforming weights corresponding to different angles of arrival.

3. The passive acoustic metasurface of claim 1, wherein the adjusted propagation characteristic of the meta-atoms in aggregate is based on a search for phase delays for each metasurface element of the passive acoustic metasurface.

4. The passive acoustic metasurface of claim 1, wherein each predetermined input signal attribute set of the plurality of predetermined input signal attribute sets includes an angle of incidence of the beam of the acoustic signal.

5. The passive acoustic metasurface of claim 1, wherein each predetermined input signal attribute set of the plurality of predetermined input signal attribute sets includes a phase of the beam of the acoustic signal.

6. The passive acoustic metasurface of claim 1, wherein each predetermined input signal attribute set of the plurality of predetermined input signal attribute sets includes an amplitude of the beam of the acoustic signal.

7. The passive acoustic metasurface of claim 1, wherein an acoustic transmitter includes a plurality of acoustic transmit transceivers forming a phased array to transmit the acoustic signal to the passive acoustic metasurface according to a code word of a transmission codebook to generate the predetermined beam pattern for the passive acoustic metasurface, and the code word corresponds to one of the predetermined input signal attribute sets, wherein the transmission codebook of the phased array and the meta-atoms of the passive acoustic metasurface are adjusted to achieve a corresponding predetermined output beam pattern.

8. The passive acoustic metasurface of claim 1, wherein a plurality of acoustic receivers forming a phased array are to receive the acoustic signal from the passive acoustic metasurface according to a codebook of codewords, to combine signals received at the plurality of receivers from the passive acoustic metasurface, and the codewords correspond to one of the set of predetermined input signal properties, wherein the receive codebook of the phased array and the meta-atoms of the passive acoustic metasurface are adjusted to achieve a corresponding predetermined target.

9. The passive acoustic metasurface of claim 1, wherein acoustic transmitters comprise a plurality of acoustic transmit transceivers, and a plurality of acoustic receive transceivers form another phased array configured to receive the acoustic signal from the passive acoustic metasurface, wherein the plurality of acoustic transmit transceivers use codewords from a transmit codebook and the plurality of acoustic receive transceivers use codewords from a receive codebook, and the transmit codebook, the receive codebook, and the passive acoustic metasurface are jointly adjusted to achieve a predetermined target.

10. A method of manufacturing a passive acoustic metasurface for interacting with an acoustic signal received at the passive acoustic metasurface, the method comprising: performing a search to adjust a beamforming weight and a position of each meta-atom of a plurality of meta-atoms with respect to a steering vector corresponding to an angle of incidence of a beam of the acoustic signal; and forming a matrix of the meta-atoms distributed throughout the passive acoustic metasurface, each meta-atom positioned in the passive acoustic metasurface to provide an adjusted propagation property of the collective meta-atoms, each meta-atom providing a propagation path for at least one beam of the acoustic signal, each meta-atom interacting with the acoustic signal to modulate an incident acoustic wavefront of the acoustic signal received by the meta-atom to form a corresponding outgoing acoustic wavefront of the acoustic signal exiting the passive acoustic metasurface, wherein the adjusted propagation property of the collective meta-atoms supports a plurality of predetermined sets of input signal properties of the incident acoustic wavefront, and for each set of input signal properties, the physical dimensions and distribution of the meta-atoms in the passive acoustic metasurface are adjusted according to the adjusted propagation property to phase shift the incident acoustic wavefront to generate a predetermined beam pattern of the acoustic signal exiting the passive acoustic metasurface corresponding to the set of input signal properties.

11. The method of claim 10, wherein the adjusted propagation property of the collective meta-atoms is based on a search for beamforming weights corresponding to different angles of arrival.

12. The method of claim 10, wherein the adjusted propagation property of the collective meta-atoms is based on a search for phase delays for each metasurface element of the passive acoustic metasurface.

13. The method of claim 10, wherein each predetermined set of input signal properties of the plurality of predetermined sets of input signal properties comprises an angle of incidence of the beam of the acoustic signal.

14. The method of claim 10, wherein each of the plurality of predetermined input signal property sets comprises a phase of the beams of the acoustic signal.

15. The method of claim 10, wherein each of the plurality of predetermined input signal property sets comprises an amplitude of the beams of the acoustic signal.

16. A method of using a passive acoustic metasurface for interacting with an acoustic signal received at the passive acoustic metasurface, the method comprising: modifying at least one input property of the acoustic signal in a plurality of predetermined input property sets, wherein the passive acoustic metasurface is formed as a matrix of meta-atoms distributed throughout the passive acoustic metasurface, each meta-atom positioned in the passive acoustic metasurface to provide an adjusted propagation property of the aggregated meta-atoms, each meta-atom providing a propagation path for at least one beam of the acoustic signal; and steering the acoustic signal away from the passive acoustic metasurface, each meta-atom modulating an incident acoustic wavefront of the acoustic signal received by the meta-atom to form a corresponding outgoing acoustic wavefront of the acoustic signal away from the passive acoustic metasurface, wherein the adjusted propagation property of the aggregated meta-atoms supports the plurality of predetermined input signal property sets of the incident acoustic wavefront, and for each input signal property set, the physical dimensions and distribution of the meta-atoms in the passive acoustic metasurface are adjusted according to the adjusted propagation property to phase shift the incident acoustic wavefront to generate a predetermined beam pattern of the acoustic signal away from the passive acoustic metasurface corresponding to the input signal property set.

17. The method of claim 16, wherein the adjusted propagation property of the aggregated meta-atoms is based on a search for a phase delay for each metasurface cell of the passive acoustic metasurface.

18. The method of claim 16, wherein an acoustic transmitter comprises a plurality of acoustic transmit transceivers forming a phased array to transmit the acoustic signal to the passive acoustic metasurface according to a code word of a transmission codebook to generate the predetermined beam pattern for the passive acoustic metasurface, and the code word corresponds to one of the predetermined input signal property sets, wherein the transmission codebook of the phased array and the meta-atoms of the passive acoustic metasurface are adjusted to achieve a corresponding predetermined output beam pattern.

19. The method of claim 16, wherein a plurality of acoustic receivers forming a phased array to receive the acoustic signal from the passive acoustic metasurface according to a code word of a reception codebook to combine signals received at the plurality of receivers from the passive acoustic metasurface, and the code word corresponds to one of the predetermined input signal property sets, wherein the reception codebook of the phased array and the meta-atoms of the passive acoustic metasurface are adjusted to achieve a corresponding predetermined target.

20. The method of claim 16, wherein acoustic transmitters comprise a plurality of acoustic transmit transceivers and a plurality of acoustic receive transceivers form another phased array configured to receive the acoustic signals from the passive acoustic metasurface, wherein the plurality of acoustic transmit transceivers use codewords from a transmit codebook and the plurality of acoustic receive transceivers use codewords from a receive codebook, and the transmit codebook, the receive codebook, and the passive acoustic metasurface are jointly adjusted to achieve a predetermined target.

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