A sound field modulation device and method based on a multifunctional acoustic metasurface

Abstract

This invention discloses a sound field modulation device and method based on a multifunctional acoustic metasurface. The acoustic metasurface is installed at the acoustic radiation end of a partitioned piezoelectric transducer for phase modulation of the sound waves excited by the transducer. The partitioned piezoelectric transducer includes partitioned piezoelectric ceramics and a control circuit. The partitioned piezoelectric ceramics are circular and radially divided into an inner circular electrode partition and an outer annular electrode partition. Each electrode partition is electrically connected to the control circuit to independently excite different electrode partitions to generate sound waves. The acoustic metasurface is radially divided into phase modulation regions corresponding one-to-one with the electrode partitions of the partitioned piezoelectric ceramics. Each phase modulation region is equipped with a different phase coding pattern to form sound fields with different functions under different electrode partition excitation states. This invention achieves a multifunctional sound field by switching the partitioned electrodes, which can significantly improve the efficiency of detection and treatment in non-destructive testing and medical ultrasound, and broaden the utilization rate of planar ultrasound transducers.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic nondestructive testing technology, and in particular to a sound field modulation device and method based on a multifunctional acoustic metasurface. Background Technology

[0002] Ultrasound plays a vital role in numerous industrial and biomedical applications, ranging from high-resolution imaging to in vivo bioprinting and brain ultrasound stimulation. However, these technologies require programmable wavefront control, typically achieved through phased array transducers composed of hundreds of individually addressable elements. The complex and costly driving electronics required for phased array ultrasound transducers severely limit element density, consequently restricting achievable resolution and information capacity. In contrast, acoustic holography, which can be integrated with single-element ultrasound transducers, offers a simple and low-cost alternative. Complex sound fields can be constructed using simple acoustic holograms. However, current acoustic holograms lack dynamic adjustment capabilities, failing to meet the demands of complex applications or multifunctional sound field reconstruction.

[0003] Focused sound fields are extremely important in both non-destructive testing (NDT) and medicine. In NDT, focused sound waves not only increase the energy of the target scanning area and enhance the echo of small defects, but also significantly increase the resolution of the inspected area. In medicine, they are widely used for various novel medical procedures such as tissue ablation, brain nerve stimulation, and opening the blood-brain barrier. Currently, focused sound fields are achieved using concave transducers. However, concave transducers are often expensive to manufacture, have a fixed shape, cannot adjust the focal length, and are inefficient. Vortex sound fields also play an important role in micromanipulation and are currently widely used for the manipulation and capture of particles or for transferring acoustic angular momentum to target areas in a medium. However, existing planar ultrasonic transducers cannot achieve effective ultrasonic vortices.

[0004] To meet the demands for multifunctional sound fields, such as detection scenarios requiring multiple focal length scans or scenarios in ultrasonic manipulation requiring focused activation, a sound field with only a single transducer is insufficient. Using multiple independent transducers, however, cannot guarantee operational accuracy due to the constraints of the operating space. Therefore, there is an urgent need to develop a device that can be customized to meet specific requirements and adapt to planar ultrasonic probes to achieve multifunctional sound fields. This would significantly compensate for the lack of multifunctional sound fields with a single transducer. Summary of the Invention

[0005] To address the aforementioned issues, and considering the limitations of existing conventional probes in achieving multifunctional sound fields and the singular functionality of current acoustic metasurfaces, this invention provides a sound field modulation device and method based on a multifunctional acoustic metasurface. Depending on the target sound field orientation, an acoustic metasurface can be designed as needed. Simultaneously, piezoelectric ceramics of appropriate frequencies and sizes can be selected to construct partitioned piezoelectric transducers. The assembled multifunctional acoustic excitation device can achieve independent or nested excitation of various sound fields, overcoming the shortcomings of existing metasurface devices in realizing multifunctional sound fields.

[0006] The technical solution adopted in this invention is:

[0007] This invention includes an acoustic metasurface and a partitioned piezoelectric transducer. The acoustic metasurface is installed at the acoustic radiation end of the partitioned piezoelectric transducer and is used to perform phase modulation on the acoustic waves excited by the partitioned piezoelectric transducer.

[0008] The partitioned piezoelectric transducer includes partitioned piezoelectric ceramics and a control circuit. The partitioned piezoelectric ceramics are circular and radially divided into an inner circular electrode partition and an outer annular electrode partition. Each electrode partition is electrically connected to the control circuit to independently excite different electrode partitions to generate sound waves.

[0009] The acoustic metasurface is radially divided into a circular phase modulation region and an annular phase modulation region. The phase modulation region of the acoustic metasurface corresponds one-to-one with the electrode partition of the partitioned piezoelectric ceramic. Each phase modulation region is equipped with different types of phase coding patterns to form sound fields with different functions under different electrode partition excitation states.

[0010] The partitioned piezoelectric transducer further includes a matching layer, a backing, a housing, and leads. The backing, partitioned piezoelectric ceramic, and matching layer are sequentially installed inside the housing. The positive electrode surface of the partitioned piezoelectric ceramic serves as the acoustic radiation surface, and the negative electrode surface of the partitioned piezoelectric ceramic is covered with a backing for absorbing reflected waves. The partitioned piezoelectric ceramic is electrically connected to the control circuit through leads passing through the housing. The acoustic metasurface is installed outside the housing and contacts the side of the matching layer away from the partitioned piezoelectric ceramic, and is used to modulate the spatial phase distribution of the transmitted sound waves.

[0011] The size of the acoustic metasurface is the same as that of the partitioned piezoelectric ceramic, and the phase encoding pattern of each phase modulation region of the acoustic metasurface specifically includes a focused sound field phase pattern or a vortex sound field phase pattern.

[0012] The maximum thickness of the acoustic metasurface is specifically defined as the minimum thickness that satisfies the condition of π phase delay after sound waves pass through the acoustic metasurface.

[0013] The thickness of the matching layer is equal to one-quarter of the acoustic wavelength corresponding to the center frequency of the partitioned piezoelectric ceramic.

[0014] When the internal circular electrode partition and the external annular electrode partition in the partitioned piezoelectric ceramic have the same operating frequency, the acoustic radiation surface of the partitioned piezoelectric ceramic is divided into electrode areas by laser cutting or dicing machine cutting.

[0015] When the internal circular electrode partition and the external annular electrode partition in a partitioned piezoelectric ceramic have different operating frequencies, the partitioned piezoelectric ceramic is composed of circular piezoelectric ceramics and annular piezoelectric ceramics with different operating frequencies coaxially nested together.

[0016] A sound field modulation method based on a multifunctional acoustic metasurface includes the following steps:

[0017] S1. Determine the phase coding pattern type of each phase modulation region of the acoustic metasurface according to the type of the target sound field;

[0018] S2. At the preset operating frequency of the partitioned piezoelectric ceramic, the thickness distribution of each phase modulation region of the acoustic metasurface is obtained by processing according to the phase-thickness mapping relationship of the target acoustic field.

[0019] S3. Prepare acoustic metasurfaces based on the phase coding pattern type and thickness distribution of the acoustic metasurfaces;

[0020] S4. Controlling the electrode partitioning of the partitioned piezoelectric ceramic causes the partitioned piezoelectric ceramic to emit ultrasonic waves. After being modulated by the acoustic metasurface, the ultrasonic waves form a target sound field at a preset position.

[0021] The phase coding pattern of the acoustic metasurface adopts a binary phase coding method, and the phase modulation region has only a first phase state or a second phase state, with a phase difference of π between the first phase state and the second phase state.

[0022] The beneficial effects of this invention are:

[0023] This invention allows for the customization of acoustic metasurfaces and partitioned piezoelectric transducers to meet specific industrial or medical needs, enabling the creation of multifunctional sound fields through the switching of partitioned electrodes. This significantly improves the efficiency of non-destructive testing and medical ultrasound in detection and treatment, and expands the utilization rate of planar ultrasonic transducers.

[0024] In the field of acoustic manipulation, this invention can capture and manipulate both microscopic and macroscopic particles. It also allows for focusing on the manipulated object during manipulation. In the field of nondestructive testing, switching the sound field enables variable-focus ultrasonic testing. To a certain extent, it overcomes the limitation of existing ultrasonic transducers that only have a single sound field, effectively solving the technical challenge of multifunctional composite acoustic metasurface devices. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of a sound field modulation device based on a multifunctional acoustic metasurface.

[0026] Figure 2 This is an exploded view of a sound field modulation device based on a multifunctional acoustic metasurface.

[0027] Figure 3 This is the wiring diagram of the partitioned piezoelectric ceramics in a partitioned electrode transducer.

[0028] Figure 4 This is a schematic diagram of a multifunctional acoustic metasurface device.

[0029] Figure 5 This is a flowchart of the working process of a sound field modulation device based on a multifunctional acoustic metasurface.

[0030] Figure 6 This is a schematic diagram of focused sound field calculation based on a sound field modulation device.

[0031] Figure 7 This is a phase distribution diagram of an acoustic metasurface focusing and vortex in an embodiment of a sound field modulation device.

[0032] Figure 8 This is a simulation diagram of the focused and vortex sound field in Example 1.

[0033] Figure 9 This is the phase distribution diagram of the acoustic metasurface vortex plus vortex in Embodiment 2 of the sound field modulation device.

[0034] Figure 10 This is a schematic diagram of the simulation of the vortex plus vortex sound field in Example 2.

[0035] Figure 11 This is the phase distribution diagram of acoustic metasurface focusing plus focusing in Embodiment 3 of the sound field modulation device.

[0036] Figure 12 This is a simulation diagram of the focused sound field in Example 3.

[0037] Figure reference numerals: 1 Acoustic metasurface, 2 Matching layer, 3 Zoned piezoelectric ceramic, 4 Backing, 5 Housing, 6 Leads. Detailed Implementation

[0038] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the scope of protection of this invention.

[0040] like Figure 1 and Figure 2 As shown, this embodiment includes an acoustic metasurface 1 and a partitioned piezoelectric transducer. The acoustic metasurface 1 is installed at the acoustic radiation end of the partitioned piezoelectric transducer and is used to perform phase modulation on the acoustic waves excited by the partitioned piezoelectric transducer.

[0041] Specifically, the acoustic metasurface 1 is a flat plate structure with a corresponding phase-encoded pattern. Furthermore, the acoustic metasurface 1 and the partitioned piezoelectric transducer can be assembled by means of water immersion adsorption, bonding, mechanical structure, etc.

[0042] The partitioned piezoelectric transducer includes a partitioned piezoelectric ceramic 3 and a control circuit. The partitioned piezoelectric ceramic 3 is circular and is divided into an inner circular electrode partition and an outer ring electrode partition along the radial direction. The inner circular electrode partition is located in the center area, and the outer ring electrode partition surrounds the inner circular electrode partition. The inner and outer piezoelectric ceramics can be selected to have the same or different center frequencies. Each electrode partition is electrically connected to the control circuit to independently excite different electrode partitions to generate sound waves.

[0043] The acoustic metasurface 1 is radially divided into circular phase modulation regions and annular phase modulation regions. Each phase modulation region of the acoustic metasurface 1 corresponds one-to-one with the electrode regions of the segmented piezoelectric ceramic 3; that is, the inner circular electrode regions correspond to the circular phase modulation regions, and the outer annular electrode regions correspond to the annular phase modulation regions. Each phase modulation region is configured with a different phase coding pattern to create sound fields with different functions under different electrode region excitation states. The multifunctional sound field of the acoustic metasurface can be achieved using piezoelectric ceramic sheets of different frequencies; for example, a high-frequency piezoelectric transducer can be used for the inner ring, and a low-frequency piezoelectric transducer for the outer ring. This allows for the realization of multiple functional sound fields.

[0044] In other words, piezoelectric ceramics can be segmented using lasers or other physical methods. After assembly with an acoustic metasurface, each segment corresponds to a specific area of ​​the acoustic metasurface. The acoustic metasurface can be programmed with various acoustic field types, such as focused sound fields and vortex sound fields, simultaneously in different areas. By switching the back-end circuitry of the piezoelectric ceramic, multifunctional sound field switching can be achieved, and multiple sound fields can be realized simultaneously.

[0045] The partitioned piezoelectric transducer also includes a matching layer 2, a backing 4, a housing 5, and leads 6. The backing 4, the partitioned piezoelectric ceramic 3, and the matching layer 2 are sequentially installed inside the housing 5. The positive electrode surface of the partitioned piezoelectric ceramic 3 serves as the sound radiation surface, and the negative electrode surface of the partitioned piezoelectric ceramic 3 is covered with the backing 4 for absorbing reflected waves. The partitioned piezoelectric ceramic 3 is electrically connected to the control circuit through the leads 6 passing through the housing 5. The acoustic metasurface 1 is installed outside the housing 5 and contacts the side of the matching layer 2 away from the partitioned piezoelectric ceramic 3, and is used to modulate the spatial phase distribution of the transmitted sound waves.

[0046] like Figure 3 As shown, the zoned piezoelectric transducer, designed to achieve a multi-functional sound field, is divided into an inner ring and an outer ring, each with independent electrode leads. The inner and outer rings can use piezoelectric ceramics with the same or different center frequencies, depending on the function. The transducer housing is connected to the back of the piezoelectric ceramic, with a back-side connection provided as the negative electrode.

[0047] The size of the acoustic metasurface 1 is the same as that of the partitioned piezoelectric ceramic 3. The phase encoding pattern of each phase modulation region of the acoustic metasurface 1 specifically includes a focused sound field phase pattern or a vortex sound field phase pattern.

[0048] like Figure 4 As shown, the surface pattern of the acoustic metasurface needs to be designed according to the sound field requirements. The inner and outer rings can be independently designed as focused or vortex sound field phase patterns. Depending on the configuration of the inner and outer ring electrodes, sound fields with multiple functions such as dual focusing, dual vortex, and focused + vortex sound fields can be realized.

[0049] The phase coding pattern of an acoustic metasurface is a continuous phase distribution or a binary phase distribution calculated based on the generalized Snell's law, the Fresnel lens principle, or the angular spectrum method.

[0050] Acoustic metasurfaces can be constructed from a variety of materials, generally choosing those with low sound attenuation coefficients, including but not limited to epoxy resin, acrylic resin, and other polymeric materials. The maximum thickness of the acoustic metasurface needs to be designed based on the sound velocity of the material to ensure a maximum phase delay of π. Acoustic metasurfaces can be manufactured using various additive or subtractive manufacturing methods, such as 3D printing, injection molding, and machining.

[0051] The focused acoustic field phase pattern consists of several concentric ring structures, with the rings spaced at intervals of 0 or π. The number and width of the concentric rings depend primarily on the selected ultrasonic frequency and the target focal length. For a given ultrasonic frequency, the greater the focal length, the fewer the number of concentric rings; for a given focal length, the lower the frequency, the fewer the number of concentric rings.

[0052] The vortex acoustic field phase pattern is as follows: topological charges are superimposed on the focusing phase of the corresponding ultrasonic frequency and target focal length. The size and rotation polarity of the vortex acoustic field depend on the size of the topological charges. The larger the number of topological charges, the larger the diameter of the vortex acoustic field.

[0053] The maximum thickness of acoustic metasurface 1 is specifically defined as the minimum thickness that satisfies the condition for generating a π phase delay after sound waves pass through acoustic metasurface 1.

[0054] The thickness of the matching layer 2 is equal to one-quarter of the acoustic wavelength corresponding to the center frequency of the partitioned piezoelectric ceramic 3.

[0055] When the internal circular electrode partition and the external annular electrode partition in the partitioned piezoelectric ceramic 3 have the same operating frequency, the acoustic radiation surface of the partitioned piezoelectric ceramic 3 is divided into electrode areas by laser cutting or dicing machine cutting.

[0056] When the internal circular electrode partition and the external annular electrode partition in the partitioned piezoelectric ceramic 3 have different operating frequencies, the partitioned piezoelectric ceramic 3 is composed of a combination of circular piezoelectric ceramics with different operating frequencies and coaxially nested annular piezoelectric ceramics.

[0057] The backing 4 is made of a material with strong sound absorption capacity, including but not limited to epoxy resin filled with tungsten powder and epoxy resin filled with glass microspheres.

[0058] When the inner and outer partitions of the piezoelectric transducer are selected with piezoelectric ceramics of the same center frequency, the acoustic radiation surface of the partitioned piezoelectric ceramic 3 is divided into several electrode regions in any of the following ways: laser cutting, dicing machine cutting, etc.

[0059] When piezoelectric transducers are selected using piezoelectric ceramics with different center frequencies, circular piezoelectric ceramics and ring-shaped piezoelectric ceramics can be used for transducer nesting. The negative electrodes of the inner and outer ring electrodes of the piezoelectric ceramics can be connected to the transducer housing.

[0060] To ensure the quality of sound field reconstruction, transducer partitions are generally limited to no more than two, but are not limited to multi-layer partition designs along the axis. The size and number of electrode partitions can be adjusted according to target needs. It should be noted that electrode partitioning is irreversible; once selected, it cannot be changed.

[0061] The acoustic radiation surface of the partitioned piezoelectric ceramic 3 is provided with a multi-electrode flexible circuit board or a needle-shaped electrode.

[0062] like Figure 5 As shown, the sound field modulation method based on a multifunctional acoustic metasurface includes the following steps:

[0063] S1. Determine the phase coding pattern type of each phase modulation region of acoustic metasurface 1 according to the type of target sound field;

[0064] That is, select an appropriate strategy based on the target sound field requirements, such as dual focus, dual vortex, or vortex focusing nested sound field.

[0065] S2. At the preset working frequency of the partitioned piezoelectric ceramic 3, the thickness distribution of the acoustic metasurface 1 is obtained by processing the phase-thickness mapping relationship of the target sound field.

[0066] This involves calculating the phase pattern of the acoustic metasurface based on the target strategy. The calculation of the target phase distribution pattern of the acoustic metasurface is generally derived using the generalized Snell's law, but is not limited to Fresnel lens ring distribution, Airy waves, angular spectrum methods, etc.

[0067] S3. Prepare acoustic metasurface 1 according to the phase coding pattern type and thickness distribution of acoustic metasurface 1, and assemble acoustic metasurface 1 with partitioned piezoelectric transducers to form a sound field modulation device.

[0068] That is, based on the calculation results, a suitable processing method is selected for preparation, and piezoelectric ceramics with corresponding frequency and aperture size are selected for transducer preparation, and the assembly of the prepared acoustic metasurface and partitioned transducer is completed.

[0069] S4. Selectively control the corresponding electrode partitions of the partitioned piezoelectric ceramic 3 so that the partitioned piezoelectric ceramic 3 emits ultrasonic waves. After being modulated by the acoustic metasurface 1, the ultrasonic waves form a single sound field or a target sound field superimposed with multiple sound fields at a preset position.

[0070] Step S2 specifically involves: the maximum material thickness is determined by the phase delay Φ=k after the sound wave passes through the material. i *L is used for design, where k i The wave number in different media (typically water and lens materials) can be expressed as λ=C. i / f performs the calculation, C i Let f be the wave velocity in different media and f be the frequency parameter of the adapted probe. Plane waves of the same frequency have different phase delays when passing through a medium of thickness L. When the phase of the transmitted wave between media is π, multiple lens thickness values ​​can be determined. Generally, the smallest thickness value d in the series can be selected; after determining the maximum thickness, the thickness distribution in different regions of the metasurface depends on the mapping relationship between the phase pattern and the thickness. Considering the convenience of processing, the phase pattern can be binary, i.e., phase 0 or phase π; at this time, the thickness region of the metasurface can be binaryly distributed, i.e., height 0 or height d.

[0071] Once the maximum thickness of a metasurface material is determined, the thickness distribution in different regions of the metasurface depends on the mapping relationship between the phase pattern and the thickness. For ease of fabrication, the phase pattern can also be binary, resulting in a binary distribution of the metasurface thickness regions.

[0072] The maximum thickness of the material is determined by the phase delay Φ=k after the sound wave passes through the material. i *L is used for design, where k i The wavenumbers in different media (generally water and lens materials) can be represented by λ=C. i / f performs the calculation, C i Let f represent the wave velocity in different media, and f be the frequency parameter of the adapted probe. Plane waves of the same frequency will have different phase delays when passing through a medium of thickness L. When the phase of the transmitted wave between the media is π, multiple lens thickness values ​​can be determined. Generally, the smallest thickness value in the series can be selected.

[0073] Acoustic metasurface devices are primarily used to modulate ultrasonic waves excited by partitioned electrode transducers. The acoustic metasurface itself is designed according to requirements, and its structure must correspond to the partitions of the partitioned electrode transducer (the inner and outer rings of the metasurface must correspond to the partitions of the piezoelectric ceramic in the partitioned electrode transducer). Acoustic metasurfaces are generally made of materials with acoustic impedance well-matched to water and low acoustic attenuation coefficients, including but not limited to photosensitive resins, PLA, and other common polymer materials. Their maximum thickness depends on the sound velocity of the material and the sound velocity of the medium in the application environment. Generally, water is chosen as the coupling medium for the ultrasound.

[0074] Generally, the phase delay of a sound wave after it passes through a material can be calculated as Φ=k i *L, where k i Given the wavenumbers in different media (water and lens materials), the wavelength of the sound wave is λ=C. i / f, C i Let f be the wave velocity in different media, and f be the center frequency of the piezoelectric transducer. The phase delay of the plane wave excited by the piezoelectric transducer as it passes through the medium (thickness L) is different. Multiple lens thickness values ​​can be determined based on the phase difference π between the media. Furthermore, the smallest thickness value d in the series is selected as the maximum thickness value of the acoustic metasurface.

[0075] Furthermore, the thickness of other parts of the acoustic metasurface is related to the phase pattern calculation results. For the phase pattern of partitioned metasurfaces, the generalized Snell's law is generally used for calculation. Figure 6 As shown, taking the calculation of the phase pattern of a focused + vortex sound field as an example, the phase pattern of the focused sound field needs to be calculated first, where the focal coordinates are (x0, z0). At this time, the phase pattern distribution Φ(x) of the acoustic metasurface should satisfy: dΦ(x) / dx=k i *sinθ(x)+C, where sinθ(x) is the refraction angle of the transmitted sound wave along the x-axis, and the refraction angle sinθ(x) = (x-x0) / ((x-x0)). 2 +z0 2 ) 1 / 2Substituting the angle of refraction, the phase distribution on the x-axis plane can be calculated as Φ(x) = k i *((x-x0) 2 +z0 2 ) 1 / 2 +C; Based on the calculated phase pattern, a rotating phase with a topological charge of L is superimposed to obtain the vortex phase pattern. The topological charge L controls the size of the vortex center; the larger L is, the larger the diameter of the vortex center. The smaller L is, the smaller the diameter of the vortex center. Further, the phase patterns of the focusing and vortex fields are axially segmented, and the phase patterns of the focusing and vortex fields are superimposed as inner and outer rings respectively. This yields the complete metasurface phase pattern.

[0076] Furthermore, the phase range of the metasurface phase pattern is 0 to π, where phase π corresponds to the maximum thickness d of the material, and the remaining thickness can be mapped according to the phase distribution range. Acoustic metasurfaces can be fabricated using various methods, including but not limited to 3D printing and laser subtractive processing, depending on the frequency of use and the complexity of the pattern. For ease of processing, the phase pattern can also be simplified to a binary distribution, meaning the phase pattern encoding range is limited to only two types: 0 and π.

[0077] Once the acoustic metasurface has been processed, it can be assembled with the partitioned electrode probe to form a multifunctional acoustic metasurface device.

[0078] In use, taking the focusing + vortex acoustic field device as an example, the assembled multifunctional acoustic metasurface device is immersed in water. When the outer electrode path is selected, the outer ring ultrasonic transducer is excited to achieve a vortex acoustic field. After the vortex acoustic field has completed its function, the middle electrode path is selected to excite the inner ring ultrasonic transducer to achieve a focused acoustic field. After connecting the inner and outer electrode paths, both the inner and outer ring ultrasonic transducers can be excited simultaneously to achieve a dual-function focused + vortex acoustic field.

[0079] like Figure 4 As shown, the assembled multifunctional acoustic metasurface device must first be immersed in water. When the outer electrode path is selected, the outer ring planar ultrasonic transducer excites ultrasonic waves, which are modulated by the outer ring metasurface to form sound field one. At this time, the outer ring planar ultrasonic transducer can be turned off or on as needed. When the inner electrode path is selected, the inner ring planar ultrasonic transducer excites ultrasonic waves, which are modulated by the inner ring metasurface to form sound field two. The two sound fields can exist simultaneously or alternate as needed, and a multifunctional sound field can be achieved by combining and multiplexing them.

[0080] In the field of acoustic manipulation, multifunctional sound fields can capture and manipulate both microscopic and macroscopic particles. Focusing can also be used during manipulation to concentrate the manipulated object. In the field of nondestructive testing, switching sound fields enables variable-focus ultrasonic testing. This, to some extent, compensates for the limitation of existing ultrasonic transducers that only have a single sound field. It effectively solves the technical challenge of multifunctional composite acoustic metasurface devices.

[0081] The basic implementation involves first determining the target sound field, then selecting an ultrasonic transducer of appropriate size and frequency based on the target sound field, and designing a corresponding sound field phase pattern according to the transducer frequency. The material required for fabricating the acoustic metasurface is selected, and the sound velocity of the material is measured and recorded. Based on the selected material's sound velocity and the appropriate probe frequency, the thickness of the focusing acoustic lens is calculated when the transmitted wave phase delay π occurs at different sound velocities. After completing the fabrication of the acoustic metasurface, it is assembled into a multifunctional acoustic excitation device.

[0082] Example 1:

[0083] like Figure 7 and Figure 8 As shown, a circular piezoelectric ceramic with a center frequency of 2MHz and an aperture of 50mm was selected. The surface of the piezoelectric ceramic was radially segmented using a laser, with a 25mm diameter region designated as the inner ring and the area outside the 25mm diameter region designated as the outer ring. Further, corresponding electrode wires were led out. The negative electrode of the piezoelectric ceramic was directly connected to the transducer housing using a common ground lead. After completing the lead wires, the backplane and matching layer of the transducer were sequentially encapsulated to complete the fabrication of the partitioned ultrasonic transducer. Further, a photosensitive resin was used to prepare the acoustic metasurface, with a sound velocity of 2350m / s. Phase calculations revealed that the optimal thickness range for the metasurface was 0~0.85mm. Further, the target focal length for the focusing and vortex fields was set to 50mm. The phase distribution required for the focusing sound field was obtained through the first calculation. By superimposing the focusing phase and the rotational phase of the topological charge L=2, the phase distribution required for the vortex sound field was obtained. Based on the dimensions of the inner and outer ring segments, the phase distribution patterns for the focusing and vortex fields were respectively cut. The inner ring is a focused phase pattern, and the outer ring is a topological charge L=2 vortex phase pattern. After assembly, the phase distribution range is mapped to the thickness range to complete the design of the acoustic metasurface. Lens manufacturing can be completed using 3D printing technology.

[0084] Furthermore, a simulated ultrasonic incident model of a planar ultrasonic transducer with partitioned electrodes was established using the numerical calculation software MATLAB. The inner loop circuit was activated, the outer loop circuit was activated, and both loops were activated simultaneously. It was observed that the transmitted wave formed a multifunctional sound field in the preset area. Experiments also verified the realization of the multifunctional sound field. The vortex sound field can be used to capture particles whose diameter matches the vortex center, and the focusing sound field can focus the particles. This significantly expands the capabilities of existing equipment that cannot simultaneously capture and focus particles.

[0085] Example 2:

[0086] like Figure 9 and Figure 10 As shown, a circular piezoelectric ceramic with a center frequency of 2MHz and an aperture of 50mm was selected. The surface of the piezoelectric ceramic was radially segmented using a laser, with a 25mm diameter region designated as the inner ring and the area outside the 25mm diameter region designated as the outer ring. Further, corresponding electrode lines were led out. The negative electrode of the piezoelectric ceramic was directly connected to the transducer housing using a common ground lead. After completing the lead wires, the backplane and matching layer of the transducer were sequentially encapsulated to complete the fabrication of the partitioned ultrasonic transducer. Further, a photosensitive resin was used to prepare the acoustic metasurface, with a sound velocity of 2350m / s. Phase calculations revealed that the optimal thickness range for the metasurface was 0~0.85mm. Further, the target focal lengths of the vortex fields were set to 20mm and 50mm respectively, and the phase distribution required for the focused sound field was obtained through the first calculation. Further still, the phase distributions required for the two vortex sound fields were obtained by superimposing the focusing phase and the rotational phase of the topological charge L=3. Based on the dimensions of the inner and outer ring segments, the phase distribution patterns of the vortices were cut. The inner ring consists of two vortex phase patterns: one with topological charge L=3 and a focal length of 20mm, and the other with topological charge L=3 and a focal length of 50mm. After assembly, mapping the phase distribution intervals to the thickness intervals completes the design of the acoustic metasurface. For ease of fabrication, the phase distribution is simplified to a binary distribution of 0 and π. Lens manufacturing can then be achieved using 3D printing technology.

[0087] Furthermore, a simulated ultrasonic incident model of a planar ultrasonic transducer with partitioned electrodes was established using the numerical calculation software MATLAB. The inner loop circuit was activated, the outer loop circuit was activated, and both loops were activated simultaneously. It was observed that the transmitted wave formed a multifunctional sound field within the preset area. Experiments further verified the realization of this multifunctional sound field.

[0088] Example 3:

[0089] like Figure 11 and Figure 12As shown, a circular piezoelectric ceramic with a center frequency of 2MHz and an aperture of 25mm and a ring-shaped piezoelectric ceramic with a center frequency of 3MHz, an inner diameter of 25mm, and an outer diameter of 50mm were selected, respectively. The circular piezoelectric ceramic with a diameter of 25mm is the inner ring part, and the area outside the ring with both inner and outer diameters of 25mm is the outer ring part.

[0090] Furthermore, corresponding electrode lines are led out. The negative electrodes of the two piezoelectric ceramics are directly connected to the transducer housing using a common ground lead. After the lead is completed, the backplane and matching layer of the transducer are encapsulated sequentially to complete the fabrication of the partitioned ultrasonic transducer. Further, photosensitive resin is selected for the fabrication of the acoustic metasurface, with a sound velocity of 2350 m / s. Through phase calculation, the optimal thickness range for the metasurface is found to be 0~0.85 mm. Further, the target focal lengths of the inner and outer ring focusing sound fields are set to 20 mm and 50 mm, respectively. The required phase distribution for the focusing sound field is obtained through calculation. Based on the dimensions of the inner and outer rings, the focusing phase distribution patterns are cut. The inner ring is a focusing phase pattern with a focal length of 20 mm, and the outer ring is a focusing phase pattern with a focal length of 50 mm. After assembly, mapping with the thickness range completes the design of the acoustic metasurface. Considering ease of processing, the phase distribution is simplified to a binary distribution of 0 and π. Lens manufacturing can be completed using 3D printing technology.

[0091] Furthermore, a simulated ultrasonic incident model of a planar ultrasonic transducer with partitioned electrodes was established using the numerical calculation software MATLAB. The inner loop circuit was activated, the outer loop circuit was activated, and both loops were activated simultaneously. It was observed that the transmitted wave formed a multifunctional sound field within the preset area. Experiments also verified the realization of this multifunctional sound field, where focused sound fields with different focal lengths can scan defects of varying depths. This significantly expands the existing limitations of variable-focal-length ultrasonic scanning.

[0092] The above detailed embodiments illustrate the technical solution and beneficial effects of the present invention. It should be understood that the above description is only the most preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A sound field modulation device based on a multifunctional acoustic metasurface, characterized in that: It includes an acoustic metasurface (1) and a partitioned piezoelectric transducer. The acoustic metasurface (1) is installed at the acoustic radiation end of the partitioned piezoelectric transducer and is used to modulate the phase of the acoustic wave excited by the partitioned piezoelectric transducer. The partitioned piezoelectric transducer includes a partitioned piezoelectric ceramic (3) and a control circuit. The partitioned piezoelectric ceramic (3) is circular and is divided into an inner circular electrode partition and an outer ring electrode partition along the radial direction. Each electrode partition is electrically connected to the control circuit to independently excite different electrode partitions to generate sound waves. The acoustic metasurface (1) is divided into a circular phase modulation region and an annular phase modulation region along the radial direction. The phase modulation region of the acoustic metasurface (1) corresponds one-to-one with the electrode partition of the partitioned piezoelectric ceramic (3). Each phase modulation region is equipped with different types of phase coding patterns to form sound fields with different functions under different electrode partition excitation states.

2. The sound field modulation device based on a multifunctional acoustic metasurface according to claim 1, characterized in that: The partitioned piezoelectric transducer also includes a matching layer (2), a backing (4), a housing (5), and leads (6). The backing (4), the partitioned piezoelectric ceramic (3), and the matching layer (2) are sequentially installed inside the housing (5). The positive electrode surface of the partitioned piezoelectric ceramic (3) serves as the sound radiation surface, and the negative electrode surface of the partitioned piezoelectric ceramic (3) is provided with a backing (4) for absorbing reflected waves. The partitioned piezoelectric ceramic (3) is electrically connected to the control circuit through the leads (6) passing through the housing (5). The acoustic metasurface (1) is installed outside the housing (5) and contacts the side of the matching layer (2) away from the partitioned piezoelectric ceramic (3), and is used to modulate the spatial phase distribution of the transmitted sound waves.

3. The sound field modulation device based on a multifunctional acoustic metasurface according to claim 1, characterized in that: The size of the acoustic metasurface (1) is the same as that of the partitioned piezoelectric ceramic (3). The phase encoding pattern of each phase modulation region of the acoustic metasurface (1) specifically includes a focused sound field phase pattern or a vortex sound field phase pattern.

4. The sound field modulation device based on a multifunctional acoustic metasurface according to claim 1, characterized in that: The maximum thickness of the acoustic metasurface (1) is specifically the minimum thickness that satisfies the condition of π phase delay after sound waves pass through the acoustic metasurface (1).

5. The sound field modulation device based on a multifunctional acoustic metasurface according to claim 1, characterized in that: The thickness of the matching layer (2) is equal to one-quarter of the acoustic wavelength corresponding to the center frequency of the partitioned piezoelectric ceramic (3).

6. The sound field modulation device based on a multifunctional acoustic metasurface according to claim 1, characterized in that: When the internal circular electrode partition and the external ring electrode partition in the partitioned piezoelectric ceramic (3) have the same working frequency, the acoustic radiation surface of the partitioned piezoelectric ceramic (3) is divided into electrode areas according to laser cutting or dicing machine cutting. When the internal circular electrode partition and the external annular electrode partition in the partitioned piezoelectric ceramic (3) have different operating frequencies, the partitioned piezoelectric ceramic (3) is formed by coaxially combining circular piezoelectric ceramics and annular piezoelectric ceramics with different operating frequencies.

7. A sound field modulation method based on a multifunctional acoustic metasurface as described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Determine the phase coding pattern type of each phase modulation region of the acoustic metasurface (1) according to the type of the target sound field; S2. At the preset working frequency of the partitioned piezoelectric ceramic (3), the thickness distribution of each phase modulation region of the acoustic metasurface (1) is obtained by processing according to the phase-thickness mapping relationship of the target sound field. S3. Prepare acoustic metasurface (1) according to the phase coding pattern type and thickness distribution of acoustic metasurface (1); S4. Controlling the electrode partitioning of the partitioned piezoelectric ceramic (3) causes the partitioned piezoelectric ceramic (3) to emit ultrasonic waves. After the ultrasonic waves are modulated by the acoustic metasurface (1), a target sound field is formed at the preset position.

8. The sound field modulation method based on a multifunctional acoustic metasurface according to claim 7, characterized in that: The phase coding pattern of the acoustic metasurface (1) adopts a binary phase coding method. The phase modulation region has only a first phase state or a second phase state, and the phase difference between the first phase state and the second phase state is π.

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