Holographic sound field reconstruction method based on amplitude modulation and forward optimization

Abstract

The invention discloses a holographic sound field reconstruction method based on amplitude modulation and forward optimization, and belongs to the technical field of acoustical holography. Comprising the following steps: building a binary matrix network, and randomly generating an initial value of the binary matrix network; and based on the binary matrix network, transmitting sound waves through an angular spectrum method, calculating an intensity difference between an image plane amplitude and a target pattern amplitude, when the intensity difference does not reach a preset value or does not meet an iteration termination condition, regenerating a value of the binary matrix network by using a genetic algorithm, updating the binary matrix network, and obtaining a target image. Next iteration is carried out until the optimal value of the binary matrix network is found; and manufacturing a metasurface corresponding to the optimal value of the binary matrix network by using a metal cutting process, and carrying out acoustical hologram reconstruction on the acoustical hologram to be detected.

Description

Technical Field

[0001] The present invention belongs to the technical field of acoustic holography, and more specifically, relates to a holographic sound field reconstruction method with amplitude modulation and forward optimization. Background Art

[0002] Implementing sound field customization underwater has important application prospects. For example, it can improve imaging accuracy and resolution, precisely control energy transfer, achieve special functions, and adapt to complex environments. Currently, there are mainly two schemes for realizing underwater customized sound field design, namely, based on active phased arrays and based on metasurface controlled regulation. Active devices can independently and dynamically control the amplitude and phase of each vibration source, thereby generating a sound field that changes in real time in space. Using the acoustic radiation force provided by the sound field makes it possible to non-contact dynamically manipulate particles. Active arrays require the combination of a high-density transducer array and a complex drive circuit. When projecting a complex customized sound field, such as a patterned sound field, since the pattern contains tens of thousands or even hundreds of thousands of pixels, it is difficult for an active phased array to provide such a large number of vibration sources at this time. For this reason, researchers have introduced acoustic metasurfaces into the design of patterned sound fields. Currently, there are mainly three schemes for realizing acoustic holography based on acoustic metasurfaces, namely, phase regulation, amplitude regulation, and simultaneous amplitude and phase regulation. The first one usually requires repeated iteration in the source plane and the image plane to restore the incident phase, and then provides the required phase profile according to the material thickness. Since the impedance of the sample and the background medium is different, different phase distributions will be obtained when sound waves pass through materials with different thicknesses, thereby realizing sound field regulation. Since this scheme regards each primitive as an independent functional unit and ignores the coupling effect between primitives, when sound waves pass through the sample, the coupling between them will destroy the preset phase and reduce the quality of the holographic pattern. At the same time, for a fine holographic pattern, functional units with a size of dozens of micrometers and metasurfaces with an array of tens of thousands or even hundreds of thousands of pixel points will also pose challenges to manufacturing. Amplitude regulation generates binary pixel points at different positions, and a patterned sound field is formed by the interference of in-phase sound waves at different positions. Currently, it can be generated by iterative angular spectrum and Rayleigh-Sommerfeld integral methods. The simultaneous amplitude and phase regulation scheme requires a complex spatial coiling structure for decoupling amplitude and phase. This scheme is not suitable for underwater high-frequency sound field regulation because the current processing accuracy is difficult to meet the spatial coiling structure with sub-wavelength dimensions, and the viscous loss will further affect the quality of the preset holographic pattern. Therefore, the schemes suitable for underwater high-frequency holographic reconstruction are mainly phase regulation and amplitude regulation.

[0003] Phase modulation requires high-precision 3D printing hardware support. At the same time, since the coupling effect between the primitive elements is ignored during the design, the preset phase will be damaged, affecting the quality of the holographic pattern. Currently, there are mainly two amplitude modulation schemes. One is to restore the phase of the source plane based on the iterative angular spectrum and further map it to the amplitude distribution according to the constraint conditions. The other scheme is to obtain the far-field sound field distribution based on the Rayleigh-Sommerfeld integral. The first scheme requires setting constraint conditions and it is difficult to obtain a uniformly distributed holographic sound field. Solving the far-field distribution based on the integral method involves a complex solution process and it is difficult to implement complex acoustic holographic patterns containing high pixel arrays.

[0004] The proposal of acoustic metasurfaces provides a feasible strategy for arbitrarily and efficiently manipulating the sound field. Acoustic metamaterials can arbitrarily control the amplitude and phase of sound waves. However, as the incident frequency increases, the available options for realizing a customized sound field underwater are mainly phase-type and amplitude-type metasurfaces. Realizing sound field patterning based on amplitude modulation is mainly to generate the required 0 and 1 distributions in specific regions, where 0 represents total reflection and 1 represents the sound wave passing freely. Currently, there is a scheme to generate bubbles in specific regions by electrolyzing water. In the regions where bubbles exist, due to the impedance difference, the sound wave will be completely reflected and transmitted in specific regions, realizing the 0 and 1 distributions. It is also possible to control the sound wave transmission by cutting a superhydrophobic film. The superhydrophobic film will form an air film underwater, and the required amplitude distribution can be generated by mechanical cutting. Since electrolyzing water requires a complex drive circuit and it is difficult to control the size of the bubbles, this will significantly affect the quality of the holographic pattern. At the same time, for holographic patterns with high pixel arrays, it is difficult to independently control each pixel point. The superhydrophobic film is prone to deformation underwater and often needs to be evenly extended with the help of a support. However, after being placed in water, it will still cause surface unevenness and damage the quality of the holographic pattern. At the same time, there is currently no complete scheme for realizing underwater holography based on amplitude modulation. Based on the improved iterative angular spectrum scheme or based on the Rayleigh-Sommerfeld integral, neither of these two schemes can realize a complex and fine acoustic holographic sound field with a uniform distribution underwater. Summary of the Invention

[0005] Aiming at the defects of the prior art, the purpose of the present invention is to provide a holographic sound field reconstruction method based on amplitude modulation and forward optimization, aiming to solve the problems of uneven patterns and low efficiency existing in the prior holographic sound field reconstruction.

[0006] To achieve the above purpose, the present invention provides a holographic sound field reconstruction method based on amplitude modulation and forward optimization, including the following steps:

[0007] Build a binary matrix network and randomly generate the initial value of the binary matrix network;

[0008] Based on the binary matrix network, the acoustic wave is transmitted by the angular spectrum method, and the intensity difference between the amplitude of the image plane and the amplitude of the target plane is calculated. When the intensity difference does not reach the preset value or does not meet the iteration termination condition, the genetic algorithm is used to regenerate the value of the binary matrix network, update the binary matrix network, and perform the next iteration until the optimal value of the binary matrix network is found;

[0009] Use the metal cutting process to fabricate the metasurface corresponding to the optimal value of the binary matrix network, and perform acoustic holographic reconstruction on the acoustic hologram to be measured.

[0010] Furthermore, the process of transmitting the acoustic wave by the angular spectrum method is expressed as follows:

[0011]

[0012] where P(x, y, 0) and P(x, y, z) represent the sound field of the source plane and the sound field of the image plane respectively, represents the Fourier transform, and H(k x , k x , z) represents the angular spectrum transfer function.

[0013] Furthermore, the binary matrix network includes a series of 0s and 1s, where 0 represents total reflection of the acoustic wave and 1 represents free passage of the acoustic wave; in the metasurface, the area corresponding to 1 is removed by laser cutting to allow the acoustic wave to pass freely. The amplitude modulation proposed by the present invention only needs to use laser cutting of metal to achieve fine control of the sound field, greatly reducing the manufacturing time and simultaneously reducing the manufacturing cost.

[0014] Furthermore, the thickness range of the metasurface is 50 microns to 200 microns.

[0015] The present invention also provides an electronic device, including: a computer-readable storage medium and a processor;

[0016] The computer-readable storage medium is used to store executable instructions;

[0017] The processor is used to read the executable instructions stored in the computer-readable storage medium and execute the above method.

[0018] The present invention also provides a computer-readable storage medium, which stores computer instructions for causing a processor to execute the above method.

[0019] The present invention also provides a computer program product, including a computer program or instruction, which when executed by a processor implements the above method.

[0020] Through the above technical solution conceived by the present invention, compared with the prior art, the following can be achieved

[0021] Beneficial effects:

[0022] 1. First, in terms of method, the present invention provides a more direct and efficient hologram generation scheme. Compared with the iterative angular spectrum for generating underwater holograms, the present invention more directly generates a series of 0 and 1 elements, avoiding mapping phase to amplitude, so the obtained holographic pattern will be more uniform. Compared with obtaining acoustic holograms based on the Rayleigh-Sommerfeld integral, the present invention only involves matrix operations, avoiding the use of complex integral solutions, so the efficiency will be higher. At the same time, the method provided by the present invention can realize an underwater multi-functional sound field, for example, multi-depth, multi-frequency, etc. In terms of the implementation scheme, the present invention does not require a complex driving circuit, greatly reducing the implementation cost. At the same time, since the holographic metasurface is generated based on the metal cutting process, there are no problems such as deformation of the superhydrophobic film underwater.

[0023] 2. To achieve a high-fidelity underwater holographic sound field based on amplitude modulation, it is necessary to carefully design the on or off state of each pixel point on the source plane. The present invention proposes a forward optimization scheme using a genetic algorithm combined with the angular spectrum transmission theory. By controlling the pixel point state with the genetic algorithm, the sound field on the image plane can be quickly obtained using the angular spectrum transmission theory, and the obtained sound field is compared with the target pattern until the algorithm converges. Further, according to the 0 and 1 distributions, they are mapped into the material, and the material in the 1 distribution area is removed by laser cutting to allow sound waves to pass through. Since the source plane is regarded as a series of binary elements from the beginning, the mapping of phase to amplitude again is avoided, improving the fidelity of the holographic pattern. At the same time, this scheme uses the metal cutting process, there are no problems such as underwater deformation, and the processing is simple. The precise laser cutting process makes it possible to generate any complex sound field. Description of the Drawings

[0024] Figure 1 It is a schematic diagram of multi-functional holography realized based on an amplitude metasurface.

[0025] Figure 2 It is a schematic diagram of the holographic sound field reconstruction method of amplitude modulation and forward optimization provided in Embodiment 1 of the present invention.

[0026] Figure 3 It is a result diagram of the holographic sound field reconstruction method of amplitude modulation and forward optimization provided in Embodiment 1 of the present invention.

[0027] Figure 4 It is a schematic diagram of the holographic sound field reconstruction method of amplitude modulation and forward optimization provided in Embodiment 2 of the present invention.

[0028] Figure 5 It is a schematic diagram of the holographic sound field reconstruction method of amplitude modulation and forward optimization provided in Embodiment 3 of the present invention. Detailed implementation manners

[0029] In order to make the objectives, technical solutions and advantages of the present invention clearer, the present 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 only used to explain the present invention and are not used to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0030] The present invention provides a holographic sound field reconstruction method for amplitude modulation and forward optimization, including the following steps:

[0031] Build a binary matrix network and randomly generate the initial value of the binary matrix network;

[0032] Based on the binary matrix network, transmit the sound wave through the angular spectrum method, calculate the intensity difference between the amplitude of the image plane and the amplitude of the target plane. When the intensity difference does not reach the preset value or does not meet the iteration termination condition, use the genetic algorithm to regenerate the value of the binary matrix network, update the binary matrix network, and perform the next iteration until the optimal value of the binary matrix network is found;

[0033] Use the metal cutting process to manufacture a metasurface corresponding to the optimal value of the binary matrix network, and perform acoustic holographic reconstruction on the acoustic hologram to be measured.

[0034] Further, the process of transmitting the sound wave through the angular spectrum method is expressed as follows:

[0035]

[0036] where P(x, y, 0) and P(x, y, z) respectively represent the sound field of the source plane and the sound field of the image plane, represents the Fourier transform, and H(k x , k x , z) represents the angular spectrum transfer function.

[0037] Further, the binary matrix network includes a series of 0s and 1s, where 0 represents total reflection of the sound wave and 1 represents free passage of the sound wave; in the metasurface, the area corresponding to 1 is removed by laser cutting to allow the sound wave to pass freely. Since it only contains two variables, 0 and 1, in the genetic algorithm, binary variables are processed faster than non-binary variables because binary coding can directly correspond to the bit operations of the computer, reducing the complexity of decoding and calculation, thereby improving the execution efficiency of the algorithm. In the genetic algorithm, a series of possible binary solutions form the individuals in the genetic algorithm, and the fitness function is defined as P i and U iThey respectively represent the sound field distributions of the source plane and the image plane. Since the genetic algorithm is used to solve the minimum value of a function, when the fitness function obtains the minimum value, it means that the pattern on the image plane is close to the preset pattern.

[0038] Furthermore, the thickness range of the metasurface is 50 microns to 200 microns.

[0039] The present invention also provides an electronic device, including: a computer-readable storage medium and a processor;

[0040] The computer-readable storage medium is used to store executable instructions;

[0041] The processor is used to read the executable instructions stored in the computer-readable storage medium and execute the above method.

[0042] The present invention also provides a computer-readable storage medium, which stores computer instructions for causing a processor to execute the above method.

[0043] The present invention also provides a computer program product, including a computer program or instructions, and when the computer program or instructions are executed by a processor, the above method is implemented.

[0044] Figure 1 It is a schematic diagram of multifunctional holography implemented based on an amplitude metasurface. I: Dual-depth holography. A single frequency is incident on the metasurface, and the numbers 1 and 2 are respectively observed at different depths. II: Dual-frequency holography. In the figure, red and blue respectively represent low-frequency and high-frequency incident sound waves. III: Complex holography. The metasurface is composed of binary amplitude modulation units. The yellow color block represents 0, and the sound wave is completely reflected in this area. The yellow wireframe represents 1, and the sound wave can transmit through this area.

[0045] Example 1

[0046] Figure 2It is a schematic diagram of the holographic sound field reconstruction method of amplitude modulation and forward optimization provided in this embodiment. Three sound waves of different frequencies are incident on the metasurface respectively, forming three different patterns at three different depths, namely "A", "B" and "C". The three letters of different colors correspond to three different incident frequencies. The lower left corner shows that the metasurface is composed of a series of 0s and 1s. The first iteration above is a strategy for generating holograms based on the iterative angular spectrum method, combining forward transmission and back transmission to obtain the required phase. Here, the present invention adopts a genetic algorithm forward optimization strategy, that is, back transmission is not considered, only forward transmission of sound waves is considered, that is, the iterative process below. The randomly generated initial solution is transmitted to the image plane using the angular spectrum, and the difference between the image plane amplitude and the target pattern intensity is compared. When the algorithm termination condition is not met, a new solution is regenerated and the next iteration is entered until the optimal solution is found. The metasurface is designed according to the optimized distribution of 0 and 1 elements.

[0047] exist Figure 3 In the figure, hollow numbers "1" and "2" are designed for two different image planes, and their distances are represented by z 1 and z 2 Indicates. 1 represents the distance between the sample and the first hologram, z 2 represents the distance between two holograms, such as Figure 3 As shown in (a), at a distance z from the sample surface 1 At a distance of z from the first hologram, the plane wave modulated by the metasurface forms the number "1". 2 At a distance of 25 mm, the number "2" can be observed. In the theoretical design, the two dimensions are 25 × 25 mm. 2 The target pattern is discretized into 90×90 binary pixels. The incident frequency is designed to be 2MHz. The size of each pixel is 0.37λ×0.37λ. According to the constraints, the farthest optimized distance can reach 27mm. This embodiment selects z 1 =5mm and z 2 =5mm two planes are used as image planes for generating digital "1" and "2" holographic patterns respectively. Figure 3 (b) in the figure shows the theoretical calculation results of the sound field distribution at different depths. It can be found that the hollow digital "1" and "2" patterns appear clearly on both target planes. As the calculation plane moves away from the target plane, the sound field will no longer maintain a regular pattern shape due to the diffraction of the sound waves. Figure 3 (c) shows the experimental sample that realizes double-depth holography. The sample size is the same as the pattern size, 25×25mm 2 The sample thickness is also 50 μm, which is only λ / 15. Figure 3 (d) shows the sound field obtained by theoretical calculation, simulation and experiment in 16×16mm2 The distribution of the three results is shown in Figure 2. The theoretical, simulation and experimental results are consistent. By controlling the “on” or “off” of the metal surface elements, high-fidelity holograms were achieved at two different depths, and the feasibility of the scheme was verified based on underwater experiments.

[0048] Embodiment 2

[0049] By encoding frequency information into the metasurface, different frequencies can be used to excite different patterns, such as Figure 4 (a) is a schematic diagram of dual-frequency single-depth holography. 1 At , two plane waves carrying the target frequency are modulated by the metasurface to form hollow numbers "1" and "2" respectively. The blue beam and the red beam represent two different frequencies. On the image plane, two patterns of different frequencies are represented by the same color as the beam. (b) is the multi-depth sound field distribution. The figure shows the distribution of the sound field on the plane before and after the target plane. The hollow numbers "1" and "2" can be clearly seen at the target position. (c) is a sample used to achieve dual-frequency single-depth holographic production. The sample size is 20×20mm 2 (d) The results of theoretical calculation, numerical simulation and experimental measurement at z 1 =12mm, the distribution of the sound field intensity. The first row shows the operating frequency f 1 =2MHz. The second row shows the operating frequency f 2 =3MHz case.

[0050] Embodiment 3

[0051] Figure 5 Schematic diagram of the holographic acoustic field reconstruction method of amplitude modulation and forward optimization provided in this embodiment. (a) is a schematic diagram of a complex pattern hologram. At a distance z from the sample surface 1 At 100°, a Chinese character “物” surrounded by petals appears on the image plane. (b) is the distribution of the sound field near the target plane. (c) is the sample used to produce complex holographic patterns. The sample size is 25×25mm 2 , the operating frequency is 3MHz, the figure shows the local enlargement of the sample, where each unit size is 83×83μm 2 (d) The results of theoretical calculation, numerical simulation and experimental measurement at z 1 =5mm, the distribution of field intensity. As an example of realizing complex pattern acoustic holographic design, this example selects a Chinese character "物" surrounded by petals as the target pattern. Since the pattern contains many details, it is necessary to make the discrete pixels as small as possible. In the theoretical design, the target pattern is discretized into 301×301 pixels, and the total number of pixels contained in the pattern exceeds 90,000.

[0052] Those skilled in the art can easily understand that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent replacements, and improvements made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A holographic sound field reconstruction method with amplitude modulation and forward optimization, characterized in that: The following steps are involved: Building a binary matrix network and randomly generating an initial value of the binary matrix network; Based on the binary matrix network, the sound wave is transmitted by the angular spectrum method, and the intensity difference between the image plane amplitude and the target pattern amplitude is calculated. When the intensity difference does not reach a preset value or does not meet the iteration termination condition, the value of the binary matrix network is regenerated by using a genetic algorithm, the binary matrix network is updated, and the next iteration is performed until the optimal value of the binary matrix network is found; The metal cutting process is used to produce a metasurface with the optimal value corresponding to the binary matrix network, and the acoustic holographic reconstruction of the sound waves to be measured is performed.

2. The holographic sound field reconstruction method according to claim 1, characterized in that: The process of sound wave transmission is expressed as follows by the angular spectrum method: Among them, P(x,y,0) and P(x,y,z) represent the source plane sound field and the image plane sound field respectively. represents Fourier transform, H(k x ,k x ,z) represents the angular spectrum transfer function.

3. The holographic sound field reconstruction method according to claim 1, characterized in that: The binary matrix network includes a series of 0s and 1s, where 0 represents total reflection of sound waves and 1 represents free passage of sound waves; in the metasurface, the area corresponding to 1 is removed by laser cutting to allow the sound waves to pass freely.

4. The holographic sound field reconstruction method according to claim 1, characterized in that: The thickness of the super surface ranges from 50 microns to 200 microns.

5. An electronic device, characterized in that: include: A computer readable storage medium and a processor; The computer-readable storage medium is used to store executable instructions; The processor is used to read the executable instructions stored in the computer-readable storage medium and execute the method according to any one of claims 1 to 4.

6. A computer-readable storage medium, characterized in that: The computer-readable storage medium stores computer instructions, and the computer instructions are used to enable a processor to execute the method according to any one of claims 1 to 4.

7. A computer program product comprising a computer program or instructions, characterized in that When the computer program or instruction is executed by a processor, the method according to any one of claims 1 to 4 is implemented.

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