Systems and methods for targeted and localized wave-based audio delivery and noise control

Abstract

Embodiments relate to devices, systems, and methods for creating highly localized, remote audible zones or noise control zones by utilizing nonlinear interactions of ultrasonic beams. Ultrasonic sources may produce inaudible, straight or curved trajectories that can bypass obstacles, such as human heads or barriers or follow direct paths in open space. When intersecting at a designated target zone, the nonlinear acoustic interaction generates an audible difference-frequency wave within the human audible range, delivering targeted sound content without disturbing surrounding areas. Alternatively, the ultrasonic sources may produce beams to control and / or cancel audible content in a designated zone. These approaches enable precise, scalable, and obstacle-agnostic spatial audio and noise control with broad bandwidth, compact size, and high robustness even in reverberant environments, expanding possibilities in private communication, immersive audio, sound masking, and environmental noise mitigation.

Description

Atty. Ref. No. 0073605-001179SYSTEMS AND METHODS FOR TARGETED AND LOCALIZED WAVE-BASED AUDIO DELIVERY AND NOISE CONTROLCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 760,929, which was filed on February 20, 2025. The entirety of this application is incorporated by reference herein.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH DEVELOPMENT

[0002] This invention was made with government support under Grant No. CMMI2401236 awarded by the National Science Foundation. The Government has certain rights in the inventionFIELD

[0003] The present disclosure generally relates to devices, systems, and methods configured to deliver targeted audible content to a remote location, such as behind obstacles, without disturbing other areas or exposing an entire environment to audible sound. The present disclosure further relates to devices, systems, and methods configured to control or cancel audible content at a remote location.BACKGROUND

[0004] Recent advancements in digital signal processing and loudspeaker array design have significantly improved the capabilities of audio engineering, enabling precise manipulation and high-fidelity reproduction of sound. These technological developments have facilitated the creation of immersive audio experiences, which have broad applications across entertainment, communication, and spatial audio systems. A key objective in modern sound reproduction is toAtty. Ref. No. 0073605-001179deliver personalized, interface-free audio to multiple listeners within a shared environment, such as rooms or vehicle cabins, while minimizing auditory interference and spillover effects.Achieving this goal is particularly challenging in reverberant spaces where reflections and obstacles, such as human heads, scatter sound waves and complicate sound localization and privacy.

[0005] To address these challenges, various wavefront engineering techniques have been explored, including the use of self-bending beams, which are waves capable of following curved trajectories and navigating around obstacles. These beams have demonstrated potential in applications such as contactless object manipulation and noninvasive biomedical imaging. In the context of audio engineering, self-bending acoustic beams have been shown to deliver sound around obstacles like human heads, offering a pathway toward more targeted and private sound delivery. However, the physical properties of acoustic waves, especially at lower frequencies, impose fundamental limitations. The diffraction of long-wavelength sound waves necessitates large source sizes and complex digital processing, which can be impractical and costly.Additionally, the audible presence of sound along the beam’s path can be undesirable in privacysensitive applications.

[0006] Various approaches have been proposed to overcome the diffraction limit in acoustic wave control, including metamaterials, superoscillation, and time reversal focusing. More recently, nonlinear acoustics has emerged as a promising avenue for subdiffraction control of sound waves. Nonlinear effects, inherent to the physics of acoustic wave propagation, can generate secondary waves, such as difference-frequency waves, that fall within the audible range while bypassing the diffraction constraints typical of linear acoustics. These effects include both cumulative nonlinearities, which depend on the medium’s properties, and local nonlinearities,Atty. Ref. No. 0073605-001179related to the local energy density of primary waves. Despite their potential, the integration of nonlinear acoustic effects with advanced wavefront shaping techniques like self-bending beams remains largely unexplored, representing a frontier for future research and technological development.

[0007] Additionally, an important aspect of controlling acoustic energy at a distance can involve not only the delivery of sound but also the suppression or cancellation of unwanted audible content at specified locations. Achieving remote noise cancellation or sound suppression can enable privacy, reduce environmental noise pollution, and improve the quality of spatial audio systems. Conventional methods often require complex and bulky arrays and extensive digital processing, or are limited to linear wave control, which may not be effective in cluttered or reverberant environments.SUMMARY

[0008] We have developed a versatile approach that employs the interaction of multiple ultrasonic beams (e.g., two or more ultrasonic beams) to generate highly localized, remote audible spots, referred to as “audible enclaves.” The ultrasonic beams may be created and directed through various means, including acoustic metasurfaces, phased array transducers, or conventional sources. These ultrasonic beams can be emitted as straight or curved trajectories, depending on the source configuration. The key concept, though, is the intersection of two or more ultrasonic beams, regardless of their shape or propagation path, to produce an audible difference-frequency wave at the intersection point. This enables targeted sound zones, such as behind obstacles or within complex environments, without disturbing surrounding areas.Atty. Ref. No. 0073605-001179

[0009] In addition to delivering targeted audible content, the system can also be configured for remote noise control through sound cancellation. Using multiple ultrasonic sources, ultrasonic beams can be specifically tailored to cancel audible content at specified locations.

[0010] This approach is broadly applicable, encompassing passive or active beam generation techniques. Passive methods may include acoustic metasurfaces, which shape and direct ultrasonic waves without active energy input, while active methods may involve phased array transducers capable of electronically steering and shaping the beams in real time. Importantly, for generating localized audible spots with conventional, straightforward ultrasonic sources, complex metasurfaces or phased arrays may not be necessary, and simply using multiple aligned ultrasonic transducers emitting beams that intersect can suffice.

[0011] These ultrasonic beams, whether straight or curved, passive or active, and regardless of their shape, can be engineered to intersect at specific locations in space. At each intersection, the local nonlinear acoustic interaction produces a difference-frequency wave within the human audible range, forming an audible enclave for sound delivery or a quiet zone for noise suppression. The system’s ultrabroadband performance allows operation across most of the audible spectrum, with practical implementation sizes that support real-world deployment in diverse settings.

[0012] In an exemplary embodiment, a system includes a first ultrasonic source configured to emit a first ultrasonic beam having a first frequency f1, wherein the first ultrasonic beam is inaudible along its trajectory; and a second ultrasonic source configured to emit a second ultrasonic beam having a second frequency f2, wherein the second ultrasonic beam is inaudible along its trajectory. The first ultrasonic beam is configured to intersect with the second ultrasonic beam and create audible content at a target sound zone.Atty. Ref. No. 0073605-001179

[0013] In some embodiments, prior to intersecting, the first ultrasonic beam bypasses a first side of an obstacle and the second ultrasonic beam bypasses a second side of the obstacle.

[0014] In some embodiments, the first ultrasonic beam and the second ultrasonic beam follow straight trajectories.

[0015] In some embodiments, the first ultrasonic beam and the second ultrasonic beam follow curved trajectories.

[0016] In some embodiments, the first ultrasonic source and the second ultrasonic source include acoustic metasurfaces.

[0017] In some embodiments, the first ultrasonic source and the second ultrasonic source include phased array transducers.

[0018] In some embodiments, the audible content at the target sound zone has a difference frequency f = f2 – f1.

[0019] In some embodiments, the first ultrasonic source and the second ultrasonic source have sizes no greater than 0.50 m.

[0020] In some embodiments, the system further includes a third ultrasonic source configured to emit a third ultrasonic beam having a third frequency, wherein the third ultrasonic beam is inaudible along its trajectory. The third ultrasonic beam is configured to intersect with either the first ultrasonic beam and the second ultrasonic beam and create audible content at a second target sound zone.

[0021] In an exemplary embodiment, a method of delivering audible content to a remote target sound zone includes emitting a first ultrasonic beam having a first frequency f1 from a first ultrasonic source, wherein the first ultrasonic beam is inaudible along its trajectory; and emitting a second ultrasonic beam having a second frequency f2 from a second ultrasonic source, whereinAtty. Ref. No. 0073605-001179the second ultrasonic beam is inaudible along its trajectory. The first ultrasonic beam is configured to intersect with the second ultrasonic beam and create audible content at the target sound zone.

[0022] In some embodiments, prior to intersecting, the first ultrasonic beam bypasses a first side of an obstacle and the second ultrasonic beam bypasses a second side of the obstacle.

[0023] In some embodiments, the first ultrasonic beam and the second ultrasonic beam follow straight trajectories.

[0024] In some embodiments, the first ultrasonic beam and the second ultrasonic beam follow curved trajectories.

[0025] In some embodiments, the first ultrasonic source and the second ultrasonic source method acoustic metasurfaces.

[0026] In some embodiments, the first ultrasonic source and the second ultrasonic source include phased array transducers.

[0027] In some embodiments, the audible content at the target sound zone has a difference frequency f = f2 – f1.

[0028] In some embodiments, the method further includes emitting a third ultrasonic beam having a third frequency from a third ultrasonic source, wherein the third ultrasonic beam is inaudible along its trajectory. The third ultrasonic beam is configured to intersect with either the first ultrasonic beam and the second ultrasonic beam and create audible content at a second target sound zone.

[0029] In an exemplary embodiment, a system includes a first ultrasonic source configured to emit a first ultrasonic beam having a first frequency f1, wherein the first ultrasonic beam is inaudible along its trajectory; and a second ultrasonic source configured to emit a secondAtty. Ref. No. 0073605-001179ultrasonic beam having a second frequency f2, wherein the second ultrasonic beam is inaudible along its trajectory. The first ultrasonic beam is configured to intersect with the second ultrasonic beam and create a difference frequency that is 180 degrees out-of-phase with target audible content to be canceled out in a target quiet zone.

[0030] In some embodiments, prior to intersecting, the first ultrasonic beam bypasses a first side of an obstacle and the second ultrasonic beam bypasses a second side of the obstacle.

[0031] In some embodiments, the first ultrasonic beam and the second ultrasonic beam follow straight trajectories.

[0032] In some embodiments, the first ultrasonic beam and the second ultrasonic beam follow curved trajectories.

[0033] In some embodiments, the first ultrasonic source and the second ultrasonic source include acoustic metasurfaces.

[0034] In some embodiments, the first ultrasonic source and the second ultrasonic source include phased array transducers.

[0035] In some embodiments, the first ultrasonic source and the second ultrasonic source have sizes no greater than 0.50 m.

[0036] In an exemplary embodiment, a method of canceling audible content at a remote target quiet zone includes emitting a first ultrasonic beam having a first frequency / i from a first ultrasonic source, wherein the first ultrasonic beam is inaudible along its trajectory; and emitting a second ultrasonic beam having a second frequency f2 from a second ultrasonic source, wherein the second ultrasonic beam is inaudible along its trajectory. The first ultrasonic beam is configured to intersect with the second ultrasonic beam and create a difference frequency that is 180 degrees out-of-phase with target audible content to be canceled out in a target quiet zone.Atty. Ref. No. 0073605-001179

[0037] In some embodiments, prior to intersecting, the first ultrasonic beam bypasses a first side of an obstacle and the second ultrasonic beam bypasses a second side of the obstacle.

[0038] In some embodiments, the first ultrasonic beam and the second ultrasonic beam follow straight trajectories.

[0039] In some embodiments, the first ultrasonic beam and the second ultrasonic beam follow curved trajectories.

[0040] In some embodiments, the first ultrasonic source and the second ultrasonic source method acoustic metasurfaces.

[0041] In some embodiments, the first ultrasonic source and the second ultrasonic source include phased array transducers.

[0042] Further features, aspects, objects, advantages, and possible applications of the present disclosure will become apparent from a study of the exemplary embodiments and examples described below, in combination with the Figures, and the appended claims.BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The above and other objects, aspects, features, advantages and possible applications of the present innovation will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings. Like reference numbers used in the drawings may identify like components.

[0044] FIG. 1 is a block diagram demonstrating a first exemplary embodiment of a device and system configured to deliver audible content to a remote target sound zone.

[0045] FIG. 2 is a block diagram demonstrating a second exemplary embodiment of a device and system configured to deliver audible content to a remote target sound zone.Atty. Ref. No. 0073605-001179

[0046] FIG. 3 is a block diagram demonstrating a third exemplary embodiment of a device and system configured to deliver audible content to more than one remote target sound zone.

[0047] FIG. 4 is a block diagram demonstrating a first exemplary embodiment of a device and system configured to cancel or control audible content at a remote target quiet zone.

[0048] FIG. 5 is a block diagram demonstrating a second exemplary embodiment of a device and system configured to cancel of control audible content at a remote target quiet zone.

[0049] FIG. 6 is a schematic illustration depicting the remote creation of an audible enclave at frequency f = f2 – f1 by leveraging the local nonlinear interactions of two self-bending ultrasonic beams at frequencies f1 and f2. Metasurfaces covering ultrasound sources enable generation of the two self-bending ultrasonic beams, culminating in an intersection area behind an obstacle.

[0050] FIG. 7 is a three-dimensional (3D) model of a metasurface, and a schematic illustration showing the dimensions of an air channel of a unit cell.

[0051] FIG. 8 is a sample photo of a metasurface.

[0052] FIG. 9 shows (left) amplitude and (right) phase (in π) of the transmission coefficient of a unit cell as a function of the geometric parameters w1 and l1 at (top) 39.5 kHz and (bottom) 40 kHz.

[0053] FIG. 10 is a graph showing the amplitude and phase of the transmission coefficient of a unit cell as a function of the geometric parameter l1. Solid and dashed lines represent the metasurfaces designed at 39.5 kHz and 40 kHz, respectively.

[0054] FIG. 11 is a graph showing continuous and discrete phase distributions of the metasurfaces. Metasurfaces located in x < 0 and x > 0 were designed at 39.5 kHz and 40 kHz, respectively.Atty. Ref. No. 0073605-001179

[0055] FIG. 12 shows sound field distributions (in pascals, Pa) for a pure-tone audio signal excitation, (top left and right) Audio sound fields at 500 Hz with an observable audible enclave centered at (x, y) = (0, 325 mm). Self-bending ultrasonic beams at (middle left and right) 39.5 kHz and (bottom left and right) 40 kHz directed toward the +x and -x directions, respectively. A circular acoustically hard obstacle was placed with its center at (0, 90 mm) and a radius of 90 mm. Ultrasonic sources at 39.5 kHz and 40 kHz are denoted by two solid lines below y = 0. Simulations in (middle right and bottom right) were obtained using COMSOL Multiphysics, while the distribution in (top right) was calculated using Equation (1). (top left, middle left, and bottom left) Measured and (top right, middle right, and bottom right) simulated results.

[0056] FIG. 13 is a photograph of an experimental setup, where sources L and R emitted ultrasonic beams at frequencies f1 = 39.5 kHz and f2 = 40 kHz, respectively. An acoustically hard circular cylinder with a radius of 90 mm was placed to obstruct the beams.

[0057] FIG. 14 shows measured audio sound (f= 500 Hz) and ultrasound (39.5 kHz and 40 kHz) fields. An audible enclave was not formed.

[0058] FIG. 15 shows measured audio sound (f= 500 Hz) and ultrasound (39.5 kHz and 40 kHz) fields. An audible enclave was not formed. Instead, two directional audio beams were generated.

[0059] FIG. 16 is a photograph of an experimental setup, where sources L and R emitted ultrasonic beams at frequencies f1 = 39.5 kHz and f2 = 40 kHz, respectively. An acoustically hard circular cylinder with a radius of 90mm was placed to obstruct the beams.

[0060] FIG. 17 shows measured audio sound (f= 500 Hz) and ultrasound (39.5 kHz and 40 kHz) fields. An audible enclave was not formed behind the obstacle. Instead, significant audible signals were observed near the sources.Atty. Ref. No. 0073605-001179

[0061] FIG. 18 shows self-bending ultrasonic beams at frequencies of (left) 39.5 kHz and (right) 40 kHz.

[0062] FIG. 19 shows corresponding audio sound fields at 500 Hz generated using (left) cumulative nonlinear effects only, (middle) local nonlinear effects only, and (right) both cumulative and local nonlinear effects.

[0063] FIG. 20 shows self-bending ultrasonic beams at frequencies of (left) 39.5 kHz and (right) 40 kHz.

[0064] FIG. 21 shows corresponding audio sound fields at 500 Hz generated using (left) cumulative nonlinear effects only, (middle) local nonlinear effects only, and (right) both cumulative and local nonlinear effects.

[0065] FIG. 22 is a schematic illustration showing the formation of an audible enclave and parameter definitions. Obstacle radius ro: Varied to examine the effects of head size. Obstacle displacement xcAdjusted to analyze the impact of head position. Source separation Aa: Modified as a potential solution to maintain robust audible enclave formation. Bending radius Ro Optimized to improve the robustness of self-bending beams. Source size a: Increased to further enhance the robustness.

[0066] FIG. 23 shows simulated sound field distributions (Pa) with a larger obstacle radius of ro = 100 mm. Other parameters defined in FIG. 22 are: rc= 0 mm, Aa= 25 mm, Ro = 80 mm, and a = 16 cm. Self-bending ultrasonic beams at (middle) 39.5 kHz and (right) 40 kHz.

[0067] FIG. 24 shows measured sound field distributions (Pa) with a larger obstacle radius of ro = 100 mm. Other parameters defined in FIG. 22 are: xc= 0 mm, Aa= 25 mm, Ro = 80 mm, and a = 16 cm. Self-bending ultrasonic beams at (middle) 39.5 kHz and (right) 40 kHz.Atty. Ref. No. 0073605-001179

[0068] FIG. 25 shows simulated sound field distributions (Pa) with a larger obstacle radius of ro = 100 mm. Other parameters defined in FIG. 22 are: xc= 0 mm, Aa= 25 mm, Ro = 80 mm, and a = 16 cm. Self-bending ultrasonic beams at (middle) 39.5 kHz and (right) 40 kHz.

[0069] FIG. 26 shows measured sound field distributions (Pa) with a larger obstacle radius of ro = 100 mm. Other parameters defined in FIG. 22 are: xc= 0 mm, Aa= 25 mm, Ro = 80 mm, and a = 16 cm. Self-bending ultrasonic beams at (middle) 39.5 kHz and (right) 40 kHz.

[0070] FIG. 27 shows simulated sound field distributions (Pa) with a head position of xc= -30 mm. Other parameters defined in FIG. 22 are: ro= 90 mm, Aa= 50 mm, Ro = 80 mm, and a = 16 cm. Self-bending ultrasonic beams at (middle) 39.5 kHz and (right) 40 kHz.

[0071] FIG. 28 shows measured sound field distributions (Pa) with a head position of xc= -30 mm. Other parameters defined in FIG. 22 are: ro = 90 mm, Aa= 50 mm, Ro = 80 mm, and a = 16 cm. Self-bending ultrasonic beams at (middle) 39.5 kHz and (right) 40 kHz.

[0072] FIG. 29 shows simulated sound field distributions (Pa) with a head position of xc= -30 mm. Other parameters defined in FIG. 22 are: ro = 90 mm, Aa= 50 mm, Ro = 80 mm, and a = 16 cm. Self-bending ultrasonic beams at (middle) 39.5 kHz and (right) 40 kHz.

[0073] FIG. 30 shows measured sound field distributions (Pa) with a head position of xc= -30 mm. Other parameters defined in FIG. 22 are: ro = 90 mm, Aa= 50 mm, Ro = 80 mm, and a = 16 cm. Self-bending ultrasonic beams at (middle) 39.5 kHz and (right) 40 kHz.

[0074] FIG. 31 shows simulated sound field distributions (Pa) with a larger bending radius of Ro = 90 mm. Other parameters defined in FIG. 22 are: Aa= 25 mm, a = 16 cm, xc= 0, ro = 100 mm. (left) Audio sound fields at 500 Hz. Self-bending ultrasonic beams at (middle) 39.5 kHz and (right) 40 kHz.Atty. Ref. No. 0073605-001179

[0075] FIG. 32 shows simulated sound field distributions (Pa) with a larger bending radius of Ro = 90 mm. Other parameters defined in FIG. 22 are: Aa= 25 mm, a = 16 cm, xc= -30 mm, ro = 90 mm. (left) Audio sound fields at 500 Hz. Self-bending ultrasonic beams at (middle) 39.5 kHz and (right) 40 kHz.

[0076] FIG. 33 shows simulated sound field distributions (Pa) with a larger source size a = 24 cm. Other parameters defined in FIG. 22 are: Aa= 25 mm, Ro = 90 mm, xc= 0, ro= 100 mm. (left) Audio sound fields at 500 Hz. Self-bending ultrasonic beams at (middle) 39.5 kHz and (right) 40 kHz.

[0077] FIG. 34 shows simulated sound field distributions (Pa) with a larger source size a = 24 cm. Other parameters defined in FIG. 22 are: Aa= 25 mm, Ro = 90 mm, xc= -30 mm, ro= 90 mm. (left) Audio sound fields at 500 Hz. Self-bending ultrasonic beams at (middle) 39.5 kHz and (right) 40 kHz.

[0078] FIG. 35 shows measured audio sound field distributions (in Pa) for pure-tone audio signal excitations in the presence of a circular acoustically hard obstacle with a radius of 90 mm at (top left) 125 Hz, (top right) 250 Hz, (middle left) 500 Hz, (middle right) 1 kHz, (bottom left) 2 kHz, and (bottom right) 4 kHz. In all cases, the center ultrasonic frequency was 40 kHz, and the same metasurfaces used in FIG. 12 were employed.

[0079] FIG. 36 shows (top) right and (bottom) left profile views of measurement setup in the presence of a head and torso simulator.

[0080] FIG. 37 is a graph showing the spectral density of excitation signals.

[0081] FIG. 38 shows spectrograms (dB / Hz): (top) the transient wideband audio excitation signal; (top-middle) measured signals at the target spot; (bottom-middle) measured signals at ear L; (bottom) measured signals at ear R.Atty. Ref. No. 0073605-001179DETAILED DESCRIPTION

[0082] The following description illustrates exemplary embodiments and methods of use that are presently contemplated for implementing the present invention. This description is not intended to be limiting, but rather to elucidate the general principles and features of various aspects of the invention. The scope of the invention is not restricted by this description.

[0083] Embodiments relate to devices, systems, and methods configured to deliver targeted audible content to a designated target sound zone without disturbing other areas or exposing an entire environment to audible sound, or to control and / or cancel audible content in a designated target quiet zone. These techniques can operate with various wavefront shapes, such as conventional straight beams or self-bending beams, with the key feature being the intersection of ultrasonic beams at a specific target zone. The target zone may be in open space, behind obstacles, or within obstructed environments.

[0084] The approach employs ultrasonic beams that are generally inaudible to humans as they propagate through space. Self-bending beams may be created via passive or active means.Passive methods may include engineered acoustic metasurfaces, while active methods may utilize phased array transducers capable of electronically steering and shaping ultrasonic beams in real time. Straight beams may be generated via conventional ultrasonic sources, such as using ultrasonic sources without metasurfaces or phased arrays.

[0085] Regarding the delivery of targeted audible content, a plurality of ultrasonic beams (e.g., two or more ultrasonic beams) may be directed to intersect at one or more precise target sound zones. Upon intersection of the beams, local nonlinear acoustic interactions can occur, transforming the ultrasonic energy into an audible wave within the human audible range. For example, the audible wave can be formed based on a difference frequency f= \f —. / i |, where / i isAtty. Ref. No. 0073605-001179the frequency of a first ultrasonic beam and f is the frequency of a second ultrasonic beam, though embodiments are not limited to only two beams.

[0086] Regarding the control and / or cancellation of audible content in a specified zone, the system may detect and collect sound or noise within a target quiet zone, and then generate ultrasonic beams with phase profiles designed to produce destructive interference or phase cancellation at that location. These beams may be generated passively via metasurfaces or actively via phased arrays, and their phases can be precisely tuned to cancel out unwanted sound or noise. This creates a target quiet zone, or a noise cancellation zone, where the audible content is significantly reduced or eliminated. The same wave manipulation principles apply, with the difference being that the ultrasonic sources are configured to emit waves with phases that are the inverse or canceling of the collected sound, thus actively reducing the acoustic energy at the target zone. This approach allows for localized noise suppression without affecting adjacent and surrounding areas.

[0087] Delivery of Targeted Audible Content

[0088] Devices and systems can include a plurality (e.g., two or more) ultrasonic sources.

[0089] In one embodiment, referring to FIG. 1, a first ultrasonic source 100 is configured to emit ultrasonic waves at a selected frequency or frequency range ( / i). The waves may be modulated or shaped to form a first self-bending beam 102 that follows a curved, predetermined trajectory. A second ultrasonic source 110 may be similarly configured to emit ultrasonic waves at a different frequency or frequency range (fi), which differs from f. These waves may also be modulated or shaped to form a second self-bending beam 112 that follows a curved, predetermined trajectory. The first and second ultrasonic sources 102, 112 may be configured to module the phase of the emitted waves in either a passive or active or active manner. Passive techniques include acousticAtty. Ref. No. 0073605-001179metasurfaces, which can shape and direct ultrasonic waves without active energy input, by imparting fixed phase shifts determined during manufacturing. Such metasurfaces may be fabricated via multilayer 3D printing, microfabrication, or other advanced techniques, allowing precise control over wavefront shaping and trajectory control. Active techniques include phased array transducers, which can dynamically steer and shape ultrasonic beams by controlling the phase and amplitude of individual elements in real time.

[0090] The self-bending beams 102, 112 may follow predetermined curved trajectories, such that they eventually intersect at a target sound zone 120 at a remote location. As used herein, the terms “remote” or “remote location” refer to a spatial position separated from the ultrasonic sources.

[0091] Due to their curved trajectories, the beams 102, 112 may optionally, circumvent an obstacle 130. For example, the beams 102, 112 may curve around the obstacle 130, such that the first beam 102 curves around one side of the obstacle 130 and the second beam 112 curves around an opposite or different side of the obstacle 130. After bypassing the obstacle 130, the beams 102, 112 may intersect at the target sound zone 120.

[0092] In another embodiment, referring to FIG. 2, a first ultrasonic source 100 is configured to emit ultrasonic waves at a selected frequency or frequency range ( / i). The waves may form a first beam 102 that follows a straight or substantially straight trajectory. A second ultrasonic source 110 is configured to emit ultrasonic waves at a selected frequency or frequency range fi). The waves may form a second beam 112 that follows a straight or substantially straight trajectory. It is understood that in this embodiment, the first and second ultrasonic sources 100, 110 may not include metasurfaces, phased arrays, etc., as such components are not required for the generation of straight ultrasonic beams.Atty. Ref. No. 0073605-001179

[0093] The ultrasonic sources may be angled or otherwise positioned such that the beams 102, 112 eventually intersect at a target sound zone 120 at a remote location.

[0094] In some embodiments, the beams 102, 112 may be configured to avoid or bypass an obstacle 130. No matter whether the beams are configured to be self-bending or straight, the frequencies / and f may be selected such that the beams are inaudible or substantially inaudible to humans along their respective propagation paths. For example, these frequencies may be chosen within the ultrasonic range above approximately 20 kHz, ensuring privacy and minimal disturbance within the environment. Alternatively, frequency selection may be based on application-specific parameters to optimize beam formation, bypassing obstacles, and nonlinear interaction efficiency.

[0095] Although the beams are designed to be inaudible along their curved or straight trajectories, when the beams intersect at the target sound zone, their nonlinear acoustic interaction at the target sound zone may transform ultrasonic energy into an audible wave at a difference frequency (e.g., / wherein / =- 1 |) that is within the human audible range. In some embodiments, / is between 125 Hz and 8 kHz, though it is contemplated that / may be any frequency within the human audible range and is not particularly limited. Since the beams are inaudible along their trajectories but may generate audible content upon intersecting, such as after bypassing an obstacle, a remote, audible enclave may effectively be created at the target sound zone.

[0096] The nonlinear interaction predominantly occurs at the target sound zone, where the beams converge. Due to the high spatial localization of the ultrasonic beams, whose dimensions can be on the order of a fraction of the ultrasonic wavelength, the resulting difference-frequency wave is likewise highly localized, forming an audible enclave with a size significantly smallerAtty. Ref. No. 0073605-001179than the wavelength of the audible sound. This high degree of localization allows for precise targeting and minimal spillover, creating a “private sound bubble.”

[0097] As noted above, devices and systems can include a plurality of ultrasonic sound sources. Embodiments may include two ultrasonic sound sources, three ultrasonic sound sources, four ultrasonic sound sources, five ultrasonic sound sources, six ultrasonic sound sources, seven ultrasonic sound sources, eight ultrasonic sound sources, nine ultrasonic sound sources, ten ultrasonic sound sources, etc. The number of ultrasonic sound sources is not particularly limited.

[0098] As seen in FIG. 3, devices and systems can include a first ultrasonic source 100 configured to emit ultrasonic waves at a selected frequency or frequency range ( i), a second ultrasonic source 110 configured to emit ultrasonic waves at a selected frequency or frequency range (fi), and a third ultrasonic source 140 configured to emit ultrasonic waves at a selected frequency or frequency range (fi). The waves may form beams 102, 112, 142 that follow straight or curved trajectories.

[0099] The first beam 102 and the second beam 112 may intersect at a first target sound zone 120, and the first beam 102 and the third beam 142 may intersect at a second target sound zone 150. When the first and second beams 102, 112 intersect, their nonlinear acoustic interaction at the target sound zone 120 may transform ultrasonic energy into an audible wave at a difference frequency (f wherein / =- / i|) that is within the human audible range. Similarly, when the first and third beams 102, 142 intersect, their nonlinear acoustic interaction at the target sound zone 150 may transform ultrasonic energy into an audible wave at a difference frequency (f wherein / = ] j - / i |) that is within the human audible range.

[0100] The devices and systems may be configured to deliver any type of audible content to the target sound zone, and the audible content is not particularly limited. NonlimitingAtty. Ref. No. 0073605-001179examples include speech, music, alarms, environmental sounds, or other audio signals suitable for applications such as private communication, immersive spatial audio, or sensory guidance.

[0101] The obstacle optionally bypassed by the beams can be any physical object or structure. Nonlimiting examples include human bodies or body parts (e.g., human heads), walls, furniture, or other objects that may obstruct direct line-of-sight or sound propagation. The system’s ability to circumvent such obstacles enhances its versatility and applicability in complex environments.

[0102] In embodiments in which the ultrasonic sources incorporate metasurfaces, the metasurfaces may be fabricated using a multilayer three-dimensional (3D) printing process or other advanced manufacturing techniques. Such techniques may allow for precise control over the phase profile across the metasurface surface. The phase profile across each metasurface can be designed based on the desired beam trajectory, obstacle geometry, and application-specific parameters. The phase shifts are typically discretized into multiple elements, each imparting a specific phase delay to produce a continuous phase profile approximated by a series of discrete steps.

[0103] The phase profiles of the metasurfaces can be tailored to direct the self-bending ultrasonic beams along specific trajectories to reach the desired intersection point. By modifying the phase distribution across the metasurface, the beams can be precisely controlled to intersect at any chosen location behind obstacles, enabling flexible and adaptable targeting of the target sound zone.

[0104] This capability allows the system to be configured for various applications, such as targeting specific individuals, creating localized sound environments within a room, or delivering audio content at arbitrary positions in space. The trajectories can be optimized toAtty. Ref. No. 0073605-001179avoid environmental obstructions, minimize interference, and enhance nonlinear interaction efficiency.

[0105] Control or Cancellation of Audible Content

[0106] Referring to FIGS. 4 and 5, a system may be configured to detect and suppress noise within a specific, localized target quiet zone. The target quiet zone can be in open space or behind obstacles, and the system may be designed to create a targeted noise cancellation region where audible content is significantly reduced or eliminated.

[0107] The process begins with the system collecting data related to the target audible content. This data may include parameters such as sound frequency, phase, etc. One or more sensors 250, such as microphones, may be placed in or near a target quiet zone 220 to detect the target audible content, and this data can be transmitted to a plurality (e.g., two or more) ultrasonic sources. The sources may be then configured to emit waves with specific phase profiles designed to counteract or cancel the target audible content within the target quiet zone 220.

[0108] A first ultrasonic source 200 may be configured to emit ultrasonic waves at a first frequency / i, and a second ultrasonic source 210 may be configured to emit ultrasonic waves at a second frequency f. As seen in FIG. 4, the waves may be modulated or shaped (e.g., using metasurfaces, phased arrays, or other wavefront control techniques) to produce self-bending beams 202, 212. Alternatively, as seen in FIG. 5, the waves may form beams 202, 212 that follow a straight or substantially straight trajectories. In any case, the two ultrasound waves are configured to generate a difference frequency f= ] / i — _ / z| that is 180 degrees out-of-phase with the target audible content to be canceled out in the quiet zone. The system can dynamically adjustAtty. Ref. No. 0073605-001179the frequencies of the waves in real-time, based on the collected data, to generate a destructive interference pattern precisely at the target quiet zone 220.

[0109] When the ultrasonic beams 202, 212 reach the target quiet zone 220, the nonlinearly generated difference-frequency audible sound interacts with the target audible content. Specifically, the phase of the difference-frequency sound may be engineered to destructively interfere with the target audible content. This interference effectively reduces the amplitude of the target audible content, creating a sound suppression or noise-cancellation zone.

[0110] The system can be configured to adaptively monitor and respond to changing acoustic environments. For example, if the noise level or frequency content varies over time, the sensors continuously update the sound profile, and the ultrasonic sources dynamically adjust their frequency, phase, and amplitude profiles to maintain optimal cancellation. This real-time feedback loop enables the creation of a stable, highly localized quiet zone that can be shifted or expanded as needed, even in complex or reverberant environments.

[0111] In some embodiments, the beams 202, 212 may be configured to avoid or bypass obstacle(s) 230 by following predetermined trajectories that circumvent physical obstructions.

[0112] In some embodiments, the beams 202, 212 may be selected such that they are inaudible or substantially inaudible to humans along their respective propagation paths.

[0113] The system’s capability to generate multiple ultrasonic beams with adjustable phases and trajectories enables control of both sound delivery and noise suppression. For example, the same hardware can switch between or simultaneously perform targeted audio delivery and active noise cancellation.

[0114] Applications and UsesAtty. Ref. No. 0073605-001179

[0115] Embodiments further relate to various applications and methods of utilizing the described devices, systems, and methods for targeted audio delivery and noise control.

[0116] In one example, systems can enable personalized audio experiences in public and shared spaces without the need for headphones or earbuds. For instance, museums could provide individual visitors with tailored audio guides that are delivered directly to their designated zones, allowing multiple visitors to experience different content simultaneously in the same space. Similarly, libraries or study areas could employ these systems to offer audio lessons or ambient sounds for individual students, minimizing disturbance to others and enhancing privacy.

[0117] In automotive environments, systems could be used to allow each passenger to listen to personal audio, such as music or podcasts, within their seat or zone, without distracting the driver. Navigation instructions could be delivered directly to the driver’s auditory zone, ensuring clear communication while maintaining overall focus on driving. This targeted delivery enhances safety and comfort for all occupants.

[0118] Additionally, in office buildings or military settings, the system could establish localized speech zones for confidential conversations or sensitive communications. By precisely directing ultrasonic beams to generate speech or information zones, personnel can communicate privately even within open-plan environments, without the need for physical barriers or headsets.

[0119] The technology can also be adapted for active noise cancellation by creating quiet zones in noisy environments. For example, in workplaces or urban areas, designated zones could be established where ambient noise, such as traffic or machinery, is actively suppressed through ultrasonic wave interference, thereby improving concentration, comfort, and safety. This noise control approach can be dynamically adjusted in real time to respond to changing noise sources or environmental conditions.Atty. Ref. No. 0073605-001179

[0120] These applications are only exemplary and are highly adaptable.

[0121] Overall, the described system offers a versatile platform for enhancing personal and environmental acoustic experiences, delivering content directly to specific locations, reducing unwanted noise, and enabling private communication.

[0122] Possible applications are further expanded due to the possible compact implementation size of the described devices and systems. In particular, each ultrasonic source may be no greater than 0.50 m, allowing for compact implementation. In nonlimiting embodiments, an ultrasonic source may be no greater than 0.50 m, 0.40 m, 0.30 m, 0.20 m, 0.15 m, 0.10 m, and / or the like. It is understood that embodiments described herein are not limited to such sizes, and the sources sizes may exceed these limits, especially as the distance between a target zone and sources increases.EXAMPLES

[0123] The below example describes a study and testing related to audible content delivery. The scope of the present disclosure is in no way limited to the specific embodiments described in this example.Materials and Methods

[0124] Hardware of Ultrasound Sources'. Two ultrasound arrays, labeled as sources L and R in FIG. 36, were constructed. Each array consisted of 16 x 16 = 256 PZT-based ultrasonic transducers (Murata MA40S4S) with a diameter of 10 mm and a center frequency of 40 kHz. During experiments, however, only the central 8 rows ultrasonic transducers are activated and covered by metasurfaces, as shown in FIG. 36. All activated transducers emitted in-phase ultrasound waves, with their initial phases calibrated using a field-programmable gate array (Xilinx XC7A100T).Atty. Ref. No. 0073605-001179

[0125] Fabrication of Metasurfaces: The samples were fabricated using a commercial stereolithography 3D printer (Formlabs Form 3L, the lateral resolution is 0.025 mm). The 3D printed samples were rinsed in IPA in Form Wash for 30 min and then postcured by 405 nm and 375 nm light in Form Cure for 1 h.

[0126] Simulations'. The simulations in the ultrasonic frequency range were conducted using the commercial finite element analysis software COMSOL Multiphysics v6.0 with the “Pressure Acoustics, Frequency Domain” module. The thermoviscous loss inside the metasurface was modeled using “Thermoviscous Boundary Layer Impedance” boundary condition. Acoustically rigid boundaries were assigned to the walls of the solid materials in the metasurfaces. The background medium was considered to be air with a mass density (po) of 1.21 kg / m3and a sound speed (co) of 343 m / s. Due to memory constraints, only one unit cell along the z-direction was simulated. A “Periodic Condition” with “Continuity” was applied along the z-direction to approximate the 20 repeats in experiments. The audio sound field was obtained by substituting the ultrasound fields obtained in COMSOL into Equation (1).

[0127] Experimental Settings and Sound Measurement'. The experiments were conducted in a laboratory, which was approximately a cuboid room with dimensions of 11.1 m x 5.3 mx 2.4 m. Spatial sound field distributions depicted in FIGS. 12 and 35 were measured using a single microphone (GRAS Type 40BF), which was mounted on a programmable scanning stage to scan the sound field. The measurement region formed a rectangle lying in the horizontal plane intersecting the center of the sources. As shown in FIG. 12, two ultrasonic sources were located along the line y = 0 within the region -185 mm < x < -25 mm and 25 mm < x < 185 mm. The measurement region covered an area of -360 mm < x < 360 mm and 0 < y < 600 mm, with a spatial resolution of 5 mm in both the x- and y-directions. A section within a rectangle (-105 mmAtty. Ref. No. 0073605-001179< x < 105 mm and 0 < y < 185 mm) was not measured due to the presence of the obstacle, left blank in FIGS. 12 and 35. All signals were acquired using National Instruments Data Acquisition hardware PCIe-6353. To simulate a listener, a head and torso simulator (HATS, Bruel and Kjser Type 4128) was employed, as shown in FIG. 36. Two microphones were positioned at both the Left and Right ears of the HATS to capture the transient audio signal, as depicted in FIG. 38. Results

[0128] Creation of Audible Enclaves by Nonlinear Self-bending Beams. FIG. 6 depicts the schematic of our concept for creating audible enclaves by harnessing nonlinear self-bending beams. We employ two acoustic sources emitting ultrasonic waves at frequencies / i and / 2, each covered by metasurfaces to facilitate the generation of self-bending ultrasonic beams and the formation of an intersection zone behind an obstacle (illustrated as a human head in FIG. 6). When this intersection zone is small compared to the audio wavelength, the cumulative nonlinear interaction between ultrasonic beams is negligible. Instead, the local nonlinear interaction dominates, resulting in highly localized audible waves within the intersection zone. The resultant audio sound pressure at frequency f = \fi - / i|can be approximated using Equation (1),<>)

[0129] wherein the superscript * denotes the complex conjugate,0is air density, c0is the linear sound speed, pj(r) and Vj(r) are the sound pressure and particle velocity of ultrasound at frequency of (z = 1,2), respectively.

[0130] From Equation (1), it is seen that the audio sound pressure along the trajectories of the two self-bending beams, except within their intersection zone, is minimal due to the negligible overlap of the ultrasound fields• Consequently, an audible enclave is remotely generated behind an obstacle with inaudible trajectories from the sound source,Atty. Ref. No. 0073605-001179meaning that the human head (obstacle) in front of the sound source cannot perceive audible signals. Notably, a major advantage of the concept is its ability to overcome the limit due to diffraction in linear acoustics. Specifically, the spatial resolution (size) of audible enclaves is determined by the ultrasonic waves, which possess much smaller wavelengths compared to the audio waves of interest. Furthermore, a subwavelength aperture size source can create the audible enclaves in the far field defined by the Rayleigh distance, resulting in a compact real-world implementation of this technique.

[0131] Design of the Metasurface for Self-bending Ultrasonic Beams'. As illustrated in FIG. 6, two metasurfaces were used to precisely control the phase of two ultrasonic beams emitted by two sound sources. The 3D model and sample photo of one metasurface are shown in FIGS. 7 and 8, respectively. Each acoustic metasurface was discretized along the x-direction into 40 unit cells to achieve the required phase profile and repeated along the z-direction for 20 times. The schematic of the air channel of the unit cell, with walls 0.6 mm thick, is depicted in FIG. 7. Here, the periodicity of unit cell in the xz-plane was set to 4 mm (approximately half the wavelength at fu= 40 kHz), while the air channel widthwas 2.8 mm. The total height H = Hs+ H1+ H2was set to satisfy the Fabry-Perot resonance condition for maximizing the transmission. Specifically, the total height of the unit cell, H. was chosen to be approximately twice the first working wavelength, i.e., H = 18 mm ~ 2c0 / fu. The zig-zag channel with a height of Hs= 10.2 mm was tuned with the parameter / 1 between 1.1 mm and 2.7 mm, modulating the transmitted phase across a complete 2n range as shown in FIG. 10. While sweeping Zi, the channel width n1was fixed as 1 mm to avoid excess thermoviscous loss. The channels labeled with H1= 6.4 mm and H2= 1.4 mm were designed by including a wider air channel that matches well with the impedance of free space. As a result, the pressure transmission coefficient wasAtty. Ref. No. 0073605-001179approximately 70% for the frequency of interest, as shown in FIG. 10. The phase profile provided by the metasurfaces for the self-bending ultrasonic beams is shown in FIG. 10, where the solid lines represent the continuous phase profile characterized by Equation (2),0) = [| x| - 2R0arctan(^)] wt / c0(2)Ko

[0132] where = 2πfi, i = 1,2, and the bending radius Ro= 80 mm (which is close to a human head size) and the markers exhibit the discrete phases of 80 elements (40 elements for 39.5 kHz and the other 40 elements for 40 kHz). The self-bending beams used in this study possess a nonparaxial circular trajectory, enabling them to efficiently bypass a human head.Eight different types of elements are chosen to cover the phase shift of 2TT range at intervals of 7t / 4.

[0133] Spatial Sound Field Distributions for Pure-tone Audio Signal Excitations'.

[0134] We examined the spatial distribution of the sound field for a pure-tone audio signal excitation. FIG. 12 shows both the measured and simulated sound field distributions. The setup involved two line sources, each with a length of a = 0.16 m, positioned at line y = 0 and covered by the metasurfaces. The ultrasound waves emitted by the source located in the region -a- Ea<x < Sa (Sa <x < + a) were directed towards the +x (-x) direction at 39.5 kHz (40 kHz), through the wavefront shaping effects of metasurfaces, forming self-bending beams. Here, Ac / = 25 mm is a small separation chosen for the practical and convenient setup of the experiment. The audible DFW at frequency / = 500 Hz was generated in the air due to quadratic acoustic nonlinearity. To obstruct the beams, we placed an acoustically rigid cylinder in front of the sources. The cylinder has a radius of ro = 90 mm, a dimension comparable to that of a human head.Atty. Ref. No. 0073605-001179

[0135] FIG. 12 presents the measured ultrasound fields, displaying clearly observable self-bending beams as predicted in the simulated results. At (x,y) = (0, 325 mm), we observed a highly localized audio spot at the intersection of the main lobes of two ultrasonic beams behind the obstacle. This spot exhibited a deep subwavelength size (0.06 m full width at half maximum sound energy) compared to the audio wavelength at 500 Hz (0.68 m). Such localization arises from local nonlinearity, with the measured results aligning with the predicted ones as shown in FIG. 12. Notably, the trajectories of two self-bending ultrasonic beams to form audible enclaves remained inaudible. Specifically, the center of the audible enclave (0, 325 mm) measured 58.3 mPa (66.3 dB re 20μPa), while the audio sound pressure at two typical points in the trajectories x = -105 mm, = 90 mm and x = 105 mm,j = 90 mm was only 0.55 mPa (25.8 dB) and 1.7 mPa (35.6 dB), respectively, showcasing remarkable acoustic contrast of 40.5 dB and 30.7 dB. In contrast, as shown in FIGS. 13 and 14, the audible enclave could not be generated without using metasurfaces to form the self-bending ultrasonic beams. It is also noted that this approach utilized the local nonlinearity, which differs from the conventional parametric array FIGS. 15-21, where the audible enclave was not observed.

[0136] It is worth noting that the sound fields were measured in a common room with dimensions of 11.1 m x 5.3 m x 2.4 m, ensuring robust performance in the formation of audible enclaves in reverberant environments. The control of long- wavelength audio waves in such indoor environments was crucial yet challenging due to multiple scattering by walls, furniture, and human bodies. However, the effects of reverberation on high-frequency ultrasound waves were less significant, as they were rapidly attenuated in air due to thermoviscous and relaxation-induced absorptions. Consequently, reflected and scattered ultrasound waves contributed insignificantly to the total sound fields, ensuring that the formation of audible enclaves based onAtty. Ref. No. 0073605-001179local nonlinear interactions of self-bending ultrasonic beams remained less susceptible to reverberation. Furthermore, the robustness of the audible enclave formation under varying head sizes and displacements was examined, and potential solutions are presented in FIGS. 22-33.

[0137] We proceeded to evaluate the wideband performance of the proposed audible enclave creation. While humans can detect sound waves across a range from 20 Hz to 20 kHz, the major energy in real-world applications, such as speech communications, is typically found within the 100 Hz to 4 kHz range. Therefore, sound fields were measured at the center frequencies of six typical octave bands, ranging from 125 Hz to 4 kHz, as presented in FIG. 35. Remarkably, despite using the same metasurfaces designed at around 40 kHz across different audio frequencies, the audible enclaves were consistently formed at the same location with similar size. Although some small sidelobes formed behind the audible enclave, the trajectory of self-bending ultrasonic beams remained inaudible.

[0138] The bandwidth performance of the proposed audible enclaves was determined by both ultrasonic beams and metasurfaces. The diffraction ability of the local-nonlinearity-enabled generation of the DFW depend on short- wavelength ultrasound waves. This indicated that the resolution of the generation of the audible enclave was determined by the ultrasound wavelength and could be further enhanced by increasing the ultrasound frequency. In linear acoustics, the working frequency bandwidth of metasurfaces is commonly constrained due to resonance-based mechanisms. However, a narrow bandwidth at high frequencies can result in a wide bandwidth at low frequencies. For instance, even though only a 10% bandwidth at 40 kHz was observed in this Example, it translated to 40 kHz x 10% = 4 kHz, which is sufficient for the audible frequency range. The bandwidth limited by metasurfaces can potentially be further improved using more sophisticated designs.Atty. Ref. No. 0073605-001179

[0139] Another observation in FIG. 35 was that the energy in audible enclaves decreases as the audible frequency increases. This phenomenon can be attributed to the PZT-based ultrasonic emitters (Murata MA40S4S) used in experiments, which feature a narrowband frequency response around 40 kHz. This issue could potentially be addressed by employing high-power wideband micromachined ultrasound transducers.

[0140] Performance for Transient Wideband Audio Signal Excitations'.

[0141] In real-world audio applications, it is essential to emit transient wideband audio signals, denoted as s(t), such as music reproduction. To create a transient audible enclave, we utilize double sideband amplitude modulation to modulate audio signals onto a pure-tone ultrasound signal with a frequency of fu, although there exists more sophisticated modulation techniques. As shown in FIG. 36, in the design, the signal fed into the right ultrasonic source (referred to as “source R”) is s^ft) = cos (2TT Z), where t is the time. For any arbitrary transient audio signal, s(t), the signal fed into the left ultrasonic source (referred to as “source L”) is set as sift) = s(t) cos (2nfuf). Through Fourier analysis, we find that the spectrum of sift) is sLf) oc s( ) * [d'( / — fu) + 8(J + fu], where * is the linear convolution in the frequency domain and <5 denotes the Dirac-delta function. Each audio component in s(f) at frequency f contributes to the spectrum s-ff), which includes lower and upper sideband components at frequencies, - / and / , I / respectively. Consequently, for a transient audio signal with a maximal frequency of fm, sidebands ranging from fu+ fm) are emitted, as illustrated in FIG. 37. When the maximal audible frequency is small compared to the carrier frequency, such as / OT= 4 kHz and fu= 40 kHz, the transient ultrasonic beams can still effectively interact with the metasurfaces. At the intersection of two ultrasonic self-bending beams, the local nonlinear interactions of theAtty. Ref. No. 0073605-001179ultrasound at frequency fugenerated by source R and that at sidebandsemitted by source L form a transient audible enclave.

[0142] To assess the performance of transient wideband excitation, we utilized a 9-s sample of audio signal (loaded built-in data ‘handel’ in MATLAB R2023a) with its spectrogram depicted in FIG. 38. Additionally, as shown in FIG. 36, we placed a head and torso simulator (HATS, Brüel and Kjær Type 4128) in front of the source to simulate a listener as the obstacle. In FIG. 38, a spectrogram resembling that of the excitation signal was measured at the target spot situated at the center of the audible enclave. The attenuation of amplitude at higher frequencies, compared to lower frequencies, was attributed to the narrow frequency bandwidth of the PZT-based ultrasonic transducers, as discussed previously. Notably, the audio energy measured at both ears of the HATS, shown in FIG. 38, was significantly lower than that at the audible enclave across the wideband frequency range. Some weak audio energies were observed at the Left ear (FIG. 38), primarily due to the nonlinear interaction of sidebands themselves generated by the left source. This can be further mitigated by reducing the energy of sideband signals while increasing the energy of the carrier signal. Nonetheless, these components (FIG. 38) were already at least 20 dB lower than those measured at the target spot in the audible enclave (FIG.38), which suffices for most audio applications.

[0143] It should be understood that modifications to the embodiments disclosed herein can be made to meet a particular set of design criteria. For instance, the number of or configuration of components or parameters may be used to meet a particular objective.

[0144] It will be apparent to those skilled in the art that numerous modifications and variations of the described examples and embodiments are possible in light of the above teachings of the disclosure. The disclosed examples and embodiments are presented for purposesAtty. Ref. No. 0073605-001179of illustration only. Other alternative embodiments may include some or all of the features of the various embodiments disclosed herein. For instance, it is contemplated that a particular feature described, either individually or as part of an embodiment, can be combined with other individually described features, or parts of other embodiments. The elements and acts of the various embodiments described herein can therefore be combined to provide further embodiments.

[0145] It is the intent to cover all such modifications and alternative embodiments as may come within the true scope of this invention, which is to be given the full breadth thereof.Additionally, the disclosure of a range of values is a disclosure of every numerical value within that range, including the end points. Thus, while certain exemplary embodiments of the device and methods of making and using the same have been discussed and illustrated herein, it is to be distinctly understood that the invention is not limited thereto but may be otherwise variously embodied and practiced within the scope of the following claims.

Claims

Atty. Ref. No. 0073605-001179WHAT IS CLAIMED IS:

1. A system comprising:a first ultrasonic source configured to emit a first ultrasonic beam having a first frequency f₁, wherein the first ultrasonic beam is inaudible along its trajectory; anda second ultrasonic source configured to emit a second ultrasonic beam having a second frequency f₂, wherein the second ultrasonic beam is inaudible along its trajectory,wherein the first ultrasonic beam is configured to intersect with the second ultrasonic beam and create audible content at a target sound zone.

2. The system of claim 1, wherein, prior to intersecting, the first ultrasonic beam bypasses a first side of an obstacle and the second ultrasonic beam bypasses a second side of the obstacle.

3. The system of claim 1, wherein the first ultrasonic beam and the second ultrasonic beam follow straight trajectories.

4. The system of claim 1, wherein the first ultrasonic beam and the second ultrasonic beam follow curved trajectories.

5. The system of claim 4, wherein the first ultrasonic source and the second ultrasonic source include acoustic metasurfaces.Atty. Ref. No. 0073605-0011796. The system of claim 4, wherein the first ultrasonic source and the second ultrasonic source include phased array transducers.

7. The system of claim 1, wherein the audible content at the target sound zone has a difference frequency f=f2- f1.

8. The system of claim 1, wherein the first ultrasonic source and the second ultrasonic source have sizes no greater than 0.50 m.

9. The system of claim 1, further comprising:a third ultrasonic source configured to emit a third ultrasonic beam having a third frequency f₃, wherein the third ultrasonic beam is inaudible along its trajectory, andwherein the third ultrasonic beam is configured to intersect with either the first ultrasonic beam and the second ultrasonic beam and create audible content at a second target sound zone.

10. A method of delivering audible content to a remote target sound zone, the method comprising:emitting a first ultrasonic beam having a first frequency f₁ from a first ultrasonic source, wherein the first ultrasonic beam is inaudible along its trajectory; andemitting a second ultrasonic beam having a second frequency f₂ from a second ultrasonic source, wherein the second ultrasonic beam is inaudible along its trajectory,wherein the first ultrasonic beam is configured to intersect with the second ultrasonic beam and create audible content at the target sound zone.Atty. Ref. No. 0073605-00117911. The method of claim 10, wherein, prior to intersecting, the first ultrasonic beam bypasses a first side of an obstacle and the second ultrasonic beam bypasses a second side of the obstacle.

12. The method of claim 10, wherein the first ultrasonic beam and the second ultrasonic beam follow straight trajectories.

13. The method of claim 12, wherein the first ultrasonic beam and the second ultrasonic beam follow curved trajectories.

14. The method of claim 13, wherein the first ultrasonic source and the second ultrasonic source method acoustic metasurfaces.

15. The method of claim 13, wherein the first ultrasonic source and the second ultrasonic source include phased array transducers.

16. The method of claim 10, wherein the audible content at the target sound zone has a difference frequency f=f1- f2.

17. The method of claim 10, further comprising:emitting a third ultrasonic beam having a third frequency f₃, from a third ultrasonic source, wherein the third ultrasonic beam is inaudible along its trajectory, andAtty. Ref. No. 0073605-001179wherein the third ultrasonic beam is configured to intersect with either the first ultrasonic beam and the second ultrasonic beam and create audible content at a second target sound zone.

18. A system comprising:a first ultrasonic source configured to emit a first ultrasonic beam having a first frequency f₁, wherein the first ultrasonic beam is inaudible along its trajectory; anda second ultrasonic source configured to emit a second ultrasonic beam having a second frequency f₂, wherein the second ultrasonic beam is inaudible along its trajectory,wherein the first ultrasonic beam is configured to intersect with the second ultrasonic beam and create a difference frequency that is 180 degrees out-of-phase with target audible content to be canceled out in a target quiet zone.

19. The system of claim 18, wherein, prior to intersecting, the first ultrasonic beam bypasses a first side of an obstacle and the second ultrasonic beam bypasses a second side of the obstacle.

20. The system of claim 18, wherein the first ultrasonic beam and the second ultrasonic beam follow straight trajectories.

21. The system of claim 18, wherein the first ultrasonic beam and the second ultrasonic beam follow curved trajectories.

22. The system of claim 21, wherein the first ultrasonic source and the second ultrasonic source include acoustic metasurfaces.Atty. Ref. No. 0073605-00117923. The system of claim 21, wherein the first ultrasonic source and the second ultrasonic source include phased array transducers.

24. The system of claim 18, wherein the first ultrasonic source and the second ultrasonic source have sizes no greater than 0.50 m.

25. A method of canceling audible content at a remote target quiet zone, the method comprising:emitting a first ultrasonic beam having a first frequency f₁ from a first ultrasonic source, wherein the first ultrasonic beam is inaudible along its trajectory; andemitting a second ultrasonic beam having a second frequency f₂ from a second ultrasonic source, wherein the second ultrasonic beam is inaudible along its trajectory,wherein the first ultrasonic beam is configured to intersect with the second ultrasonic beam and create a difference frequency that is 180 degrees out-of-phase with target audible content to be canceled out in a target quiet zone.

26. The method of claim 25, wherein, prior to intersecting, the first ultrasonic beam bypasses a first side of an obstacle and the second ultrasonic beam bypasses a second side of the obstacle.

27. The method of claim 25, wherein the first ultrasonic beam and the second ultrasonic beam follow straight trajectories.Atty. Ref. No. 0073605-00117928. The method of claim 25, wherein the first ultrasonic beam and the second ultrasonic beam follow curved trajectories.

29. The method of claim 28, wherein the first ultrasonic source and the second ultrasonic source method acoustic metasurfaces.

30. The method of claim 28, wherein the first ultrasonic source and the second ultrasonic source include phased array transducers.

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