Sound stealth device supporting pseudo surface wave double-sided transmission and design method thereof

Abstract

The invention discloses an acoustic stealth device supporting pseudo surface wave double-sided transmission and a design method thereof, and belongs to the technical field of acoustic communication. The sound stealth device comprises a plurality of Helmholtz resonators which are arranged in a periodic array mode, and the side walls of the adjacent Helmholtz resonators are connected to form a continuous metasurface. The metasurface is sequentially set as a first metasurface unit, a second metasurface unit and a third metasurface unit along the propagation direction of The second metasurface unit is used for placing an obstacle; a first sound wave inlet and a first sound wave outlet are respectively formed in the upper side surface and the lower side surface of the Helmholtz resonator in the first metasurface unit close to one side of the second metasurface; a second sound wave outlet and a second sound wave inlet are formed in the upper side surface and the lower side surface of the Helmholtz resonator in the third metasurface unit close to the other side of the second metasurface respectively; in a propagation state, the pseudo surface wave sequentially passes through the first sound wave inlet and outlet, the lower part of the second metasurface unit and the second sound wave inlet and outlet. According to the invention, the pseudo surface wave is bypassed through a specific path, so that effective hiding of the obstacle is realized.

Description

Technical Field

[0001] The invention relates to an acoustic stealth device supporting pseudo surface wave double-sided transmission and a design method thereof, belonging to the technical field of acoustic communication. Background Art

[0002] In the booming wave of modern information industry, acoustic communication has been widely used in many fields such as medical imaging and geological exploration due to its efficient signal transmission capability. Surface acoustic wave (SAW), as a sound wave mode that can propagate along the solid-liquid interface, plays a key role as a delay line in the field of on-chip acoustic communication because it can effectively slow down the propagation speed of electrical signals. In recent years, the rise of the concept of acoustic metamaterials has made the regulation of novel physical states and the development of devices based on acoustic artificial materials a research focus. Among them, pseudo-surface waves, as a special surface state, can achieve localized sound transmission along the surface of artificial structures, which is clearly different from common surface wave modes, thus triggering a widespread research boom.

[0003] The on-chip acoustic communication technology based on pseudo surface waves is fundamentally different from traditional surface waves. The properties of pseudo surface waves are closely related to the structure of acoustic metamaterials, which means that by structurally designing acoustic metamaterials, the propagation path of sound waves can be artificially controlled, thereby achieving more complex signal transmission functions. Compared with traditional metamaterials, acoustic metamaterials have significant advantages such as simple structure, high efficiency, and easy processing, and show great application potential in sound focusing and acoustic stealth.

[0004] However, the current research and application of acoustic metamaterials still have obvious shortcomings. Most of the structural designs proposed so far only use one side of the acoustic metasurface for acoustic manipulation. This single-dimensional manipulation method limits the freedom and flexibility of acoustic wave control. In practical applications, unilateral acoustic manipulation is often difficult to meet the needs of complex scenarios. For example, when it is necessary to realize multiple acoustic wave functions at the same time or deal with complex environmental interference, unilateral acoustic manipulation seems to be unable to cope with it. Moreover, with the continuous improvement of the requirements for acoustic communication performance, the existing unilateral acoustic manipulation structure design has gradually exposed its limitations in terms of space utilization, and cannot give full play to the advantages of acoustic metamaterials.

[0005] Therefore, it is urgent to strengthen the research on double-sided acoustic metasurfaces and, based on this, provide a new acoustic stealth structure for double-sided transmission of pseudo-surface waves in order to break through the existing technical bottleneck and promote the field of acoustic communications to a higher level. Summary of the invention

[0006] The object of the present invention is to provide an acoustic cloaking device supporting two-sided transmission of pseudo surface waves and a design method thereof, so as to realize effective obstacle-avoiding transmission of pseudo surface waves when encountering obstacles.

[0007] To achieve the above object / To solve the above technical problems, the present invention is implemented by the following technical solutions.

[0008] On the one hand, the present invention provides an acoustic stealth device supporting double-sided transmission of pseudo-surface waves, which includes: a plurality of Helmholtz resonators arranged in a periodic array, and the side walls of adjacent Helmholtz resonators are connected to form a continuous metasurface; The metasurface is sequentially set as a first metasurface unit, a second metasurface unit, and a third metasurface unit along the propagation direction of the pseudo-surface wave; the second metasurface unit is used to place an obstacle; the upper and lower sides of the Helmholtz resonators in the first metasurface unit close to the second metasurface are opened, corresponding to the first acoustic wave inlet and the first acoustic wave outlet respectively; the upper and lower sides of the Helmholtz resonators in the third metasurface unit close to the other side of the second metasurface are also opened, corresponding to the second acoustic wave outlet and the second acoustic wave inlet respectively; In the propagation state, the pseudo-surface wave sequentially bypasses the first acoustic wave inlet, the first acoustic wave outlet, below the second metasurface unit, the second acoustic wave inlet, and the second acoustic wave outlet to achieve obstacle stealth.

[0009] Optionally, each of the Helmholtz resonators is arranged in a square grid array.

[0010] Optionally, the central part of the Helmholtz resonator is set as a rectangular cavity, and the openings on the upper and lower sides of the Helmholtz resonator are set as cylindrical openings with the same aperture.

[0011] Optionally, the center line of the rectangular cavity coincides with the central axis of the cylindrical opening.

[0012] Optionally, the metasurface is a gradient refractive index metasurface that satisfies the gradient refractive index distribution.

[0013] Optionally, the design process of the gradient refractive index metasurface includes: Setting the equivalent refractive index of the gradient refractive index metasurface in space; By deriving the dispersion curve of the pseudo-surface wave mode, obtaining the relationship between the structural parameters of the Helmholtz resonator and the equivalent refractive index of the gradient refractive index metasurface; Based on the equivalent refractive index and the relationship between the structural parameters of the Helmholtz resonator and the equivalent refractive index of the gradient refractive index metasurface, using the genetic algorithm optimization method to solve for the structural parameters of the Helmholtz resonator that satisfy the gradient refractive index distribution along the direction; According to the optimized structural parameters of the Helmholtz resonator, manufacturing the Helmholtz resonator and arranging it in a periodic array to obtain the gradient refractive index metasurface required by the target.

[0014] Optionally, the equivalent refractive index of the gradient refractive index metasurface is spatially set to: ; wherein, represents the equivalent refractive index at different positions of the metasurface, and respectively represent coordinate variables, represents the maximum refractive index at the midline of the metasurface, represents the hyperbolic secant function, represents the refractive index modulation factor.

[0015] Optionally, the relationship between the structural parameters of the Helmholtz resonator and the equivalent refractive index of the gradient refractive index metasurface is expressed as: ; wherein, represents the imaginary unit, represents the angular frequency, represents the mass density of the background medium, represents the propagation wave vector of the pseudo surface wave along the direction, represents the top surface acoustic impedance at the opening on the upper side of the Helmholtz resonator, represents the lattice parameter, represents the aperture at the opening on the upper side of the Helmholtz resonator, represents the aperture at the opening on the lower side of the Helmholtz resonator, represents the side length of the rectangular cavity, represents the height of the Helmholtz resonator, represents the depth of the rectangular cavity, represents the wall thickness of the Helmholtz resonator.

[0016] Optionally, the top surface acoustic impedance at the opening on the upper side of the Helmholtz resonator is expressed as: ; ; wherein, represents the acoustic pressure of the pseudo surface wave, represents the volume flow of the pseudo surface wave, represents the normal vibration velocity of the pseudo surface wave, represents the propagation wave vector of the pseudo surface wave along the direction.

[0017] Optionally, the acoustic pressure of the pseudo surface wave and the normal vibration velocity of the pseudo surface wave are respectively expressed as: ; ; In the formula, represents the sound pressure amplitude, represents time.

[0018] Optionally, the top surface acoustic impedance at the opening on the upper side of the Helmholtz resonator is obtained by solving using the impedance transfer method. The corresponding solution process includes: Set the aperture diameter at the opening on the upper side of the Helmholtz resonator to be the same as that at the opening on the lower side, and calculate the bottom surface acoustic impedance at the opening on the lower side of the Helmholtz resonator; According to the bottom surface acoustic impedance at the opening on the lower side of the Helmholtz resonator, use the impedance transfer formula to calculate the bottom surface acoustic impedance of the rectangular cavity; According to the bottom surface acoustic impedance of the rectangular cavity, repeatedly use the impedance transfer formula to calculate the top surface acoustic impedance of the rectangular cavity; According to the top surface acoustic impedance of the rectangular cavity, repeatedly use the impedance transfer formula to calculate the top surface acoustic impedance at the opening on the upper side of the Helmholtz resonator.

[0019] Optionally, the bottom surface acoustic impedance at the opening on the lower side of the Helmholtz resonator is expressed as: ; ; ; In the formula, represents the bottom surface acoustic impedance at the opening on the lower side of the Helmholtz resonator, represents the equivalent acoustic impedance in the lower short tube of the Helmholtz resonator, represents the speed of sound.

[0020] Optionally, the bottom surface acoustic impedance of the rectangular cavity is calculated by the following impedance transfer formula: ; In the formula, represents the bottom surface acoustic impedance of the rectangular cavity.

[0021] Optionally, the thickness of the metasurface is set to 1 / 20 of the working wavelength.

[0022] On the other hand, the present invention also provides a design method for an acoustic stealth device applicable to the pseudo-surface wave double-sided transmission as described in the first aspect, which includes: Set the equivalent refractive index of the gradient refractive index metasurface in space; By deriving the dispersion curve of the pseudo-surface wave mode, the relationship between the structural parameters of the Helmholtz resonator and the equivalent refractive index of the gradient refractive index metasurface is obtained; Based on the equivalent refractive index and the relationship between the structural parameters of the Helmholtz resonator and the equivalent refractive index of the gradient refractive index metasurface, using the genetic algorithm optimization method, solve for the structural parameters of the Helmholtz resonator that satisfy the gradient refractive index distribution along the According to the optimized structural parameters of the Helmholtz resonator, fabricate the Helmholtz resonator and arrange it in a periodic array to obtain the gradient refractive index metasurface required by the target, and then design an acoustic stealth device based on the gradient refractive index metasurface.

[0023] Compared with the prior art, the beneficial effects achieved by the present invention are as follows: The acoustic stealth device designed by the present invention is composed of a continuous metasurface formed by periodically arranging double-sided perforated Helmholtz resonators, enabling the pseudo-surface wave to bypass obstacles and continue to propagate when encountering obstacles, thus realizing the effective obstacle avoidance transmission of the pseudo-surface wave; secondly, the present invention further designs a double-sided metasurface that satisfies the gradient refractive index distribution. This design not only enhances the transmission efficiency of the pseudo-surface wave but also verifies the acoustic focusing and self-imaging effects of the pseudo-surface wave during the interface conduction process through numerical simulation, providing more possibilities for acoustic wave manipulation; thirdly, the acoustic stealth device designed by the present invention exhibits extremely strong robustness and compatibility. In the case of different geometric shapes of obstacles, the device can still maintain the obstacle avoidance transmission performance of the pseudo-surface wave, which greatly improves the reliability and adaptability of the device in practical applications; in addition, the present invention also constructs a rapid prediction model of the double-sided metasurface by combining parameter optimization methods such as the genetic algorithm. This method can efficiently solve the structural parameters of the Helmholtz resonator that satisfy a specific refractive index distribution, thus realizing the efficient and flexible regulation of the pseudo-surface wave. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The figure shows a schematic structural diagram of the structural unit of the Helmholtz resonator of the present invention; Figure 2 The figure shows a schematic diagram of the working principle of the acoustic stealth device of the present invention; Figure 3 The figure shows a schematic diagram of the dispersion curve of the pseudo-surface wave mode; Figure 4 The figure shows a schematic diagram of the comparison of the acoustic pressure fields with and without the laying of the acoustic stealth device; Figure 5 The figure shows a schematic diagram of the comparison of the pseudo-surface wave transmittance with and without the laying of the acoustic stealth device; Figure 6 The figure shows a schematic diagram of the pseudo-surface wave transmission in the presence of obstacles with different shapes; Figure 7 The figure shows a schematic diagram of acoustic focusing simulation of the acoustic stealth device of the present invention based on a double-sided metasurface; Figure 8 The figure shows a schematic diagram of acoustic self-imaging effect simulation of the acoustic stealth device of the present invention based on a double-sided metasurface; Figure 9 The figure shows a schematic diagram of the double-sided metasurface structure with a gradient refractive index distribution of the present invention. Detailed implementation manners

[0025] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the embodiments of the present invention and the specific features in the embodiments are detailed descriptions of the technical solution of the present invention, rather than limitations on the technical solution of the present invention. Without conflict, the embodiments of the present invention and the technical features in the embodiments can be combined with each other.

[0026] Embodiment 1 Considering that when the pseudo surface wave encounters an obstacle, the transmission efficiency will be greatly reduced due to the significant acoustic scattering effect, which seriously restricts the further application of the pseudo surface wave in the field of on-chip acoustic communication. To address this technical bottleneck, this embodiment innovatively proposes a design concept of a double-sided metasurface, which can effectively achieve the obstacle avoidance transmission function of the pseudo surface wave, thereby improving its transmission efficiency and application potential. Specifically, this embodiment introduces an acoustic stealth device that supports the double-sided transmission of pseudo surface waves, which includes: a plurality of Helmholtz resonators arranged in a periodic array, and the side walls of adjacent Helmholtz resonators are connected to form a continuous metasurface, and the operating frequency is set to 3900 Hz.

[0027] The metasurface is sequentially set as a first metasurface unit, a second metasurface unit, and a third metasurface unit along the propagation direction of the pseudo surface wave. The second metasurface unit is used to place an obstacle. The upper and lower sides of the Helmholtz resonators in the first metasurface unit close to the second metasurface are opened, corresponding to the first acoustic wave inlet and the first acoustic wave outlet respectively. The upper and lower sides of the Helmholtz resonators in the third metasurface unit close to the other side of the second metasurface are also opened, corresponding to the second acoustic wave outlet and the second acoustic wave inlet respectively.

[0028] In the propagation state, the pseudo surface wave sequentially bypasses the first acoustic wave inlet, the first acoustic wave outlet, below the second metasurface unit, the second acoustic wave inlet, and the second acoustic wave outlet to achieve obstacle stealth.

[0029] In practical applications of this embodiment, first, according to the actual application scenarios and requirements, a number of Helmholtz resonators are arranged in a periodic array, and the adjacent side walls are connected to form a continuous metasurface. Then, the obstacle to be hidden is placed inside the second metasurface unit. When the pseudo surface wave encounters the obstacle, the sound wave enters the device through the first sound wave inlet in the first metasurface unit and is conducted to the lower part of the second metasurface unit through the first sound wave outlet. Then, the sound wave enters the device through the second sound wave inlet in the third metasurface unit and is conducted back to the upper surface through the second sound wave outlet. During the whole process, the sound wave can bypass the obstacle and continue to propagate forward, thus constructing an "acoustic transparent full-transmission channel" on the transmission path of the pseudo surface wave to achieve the stealth effect of the obstacle.

[0030] Embodiment 2 On the basis of Embodiment 1, this embodiment also has the following design: Each of the Helmholtz resonators is arranged in a square grid array. This arrangement helps to form a continuous and ordered metasurface structure, enabling the pseudo surface wave to effectively propagate and interact between these resonators.

[0031] The central part of the Helmholtz resonator is set as a rectangular cavity. The rectangular cavity can provide a stable sound field environment, enabling the sound wave to resonate inside the cavity, thereby enhancing the transmission efficiency of the sound wave. Secondly, the design of the rectangular cavity also facilitates coupling with other structures (such as adjacent resonators or external sound fields) to achieve effective conduction and conversion of sound waves.

[0032] The upper and lower sides of the Helmholtz resonator are provided with cylindrical openings of the same aperture. The design of the cylindrical openings enables the sound wave to smoothly enter and leave the resonator, while maintaining the consistency of the phase and amplitude of the sound wave. The openings with the same aperture also ensure that the sound wave transmission characteristics between the resonators are similar, which is beneficial to forming a uniform sound field distribution. The cylindrical openings also help to reduce the scattering and reflection of the sound wave at the openings, improving the transmission efficiency of the sound wave.

[0033] The center line of the rectangular cavity coincides with the central axis of the cylindrical opening. This design ensures that the propagation path of the sound wave inside the resonator is consistent with the opening direction, enabling the sound wave to be conducted along a predetermined path.

[0034] In this embodiment, the structural parameters of the Helmholtz resonator satisfy: the lattice constant is 2 cm, the height is 0.55 cm, the wall thickness is 0.1 cm, the diameters of the upper and lower openings are respectively and the side length of the rectangular cavity is and the depth of the rectangular cavity is 0.35 cm, specifically as Figure 1 shown.

[0035] Refer to Figure 2 , the single-sided structure (purple part) can enable sound waves to propagate along one side of the structure, and the acoustic stealth device is composed of double-sided perforated Helmholtz resonators (orange part), which can enable sound waves to flexibly conduct between the upper and lower surfaces of the structure. When the pseudo surface wave propagates along the upper surface of the structure and encounters an obstacle, the device can use the double-sided perforated structure to cleverly conduct the pseudo surface wave propagating along the upper surface to the lower surface. During this process, the sound wave can bypass the obstacle. After bypassing, the double-sided perforated structure is used to return the sound wave to the upper surface and make it continue to propagate along the initial direction. This design actually constructs a "sound transparent channel" for the pseudo surface wave, thereby realizing the function of obstacle avoidance transmission.

[0036] From the dispersion curves of the pseudo surface wave modes carried by the double-layer metasurface, this embodiment can deeply insight into its acoustic characteristics. Refer to Figure 3 , the symbol line, blue line and red line respectively represent the simulation results, theoretical results and air solution. At low frequencies, the pseudo surface mode is close to the air line (represented by the red solid line), but deviates from the air line near the resonance frequency. This deviation indicates that the pseudo surface wave excites a larger transmission wave vector in the propagation direction, and the wave number perpendicular to the artificial surface is imaginary. This means that the acoustic energy is mainly concentrated near the ultra-thin artificial surface and decays in the direction perpendicular to the surface. This characteristic makes the acoustic stealth device have unique advantages in regulating the propagation of sound waves.

[0037] By comparing the acoustic pressure fields with and without the laying of the stealth device, this embodiment can also intuitively see the excellent performance of the acoustic stealth device. Refer to Figure 4 , under the condition that the working frequency is 3900 Hz, the structure array is arranged in turn with three five-column single-sided perforations and two seven-column double-sided perforations, and the obstacle is placed at a specific position. In this embodiment, it is specifically placed above the thirteenth column from the left. Among them, the density and sound velocity of the metasurface are 1190 kg / m³ and 2730 m / s respectively, and the material density and sound velocity of the obstacle are 2000 kg / m³ and 4000 m / s respectively. It is not difficult to see from the comparison diagram that when the double-sided metasurface is not laid, the sound wave produces obvious scattering after encountering the obstacle, resulting in an obvious shadow area of the sound wave energy behind the obstacle. However, after applying the acoustic metasurface, the sound wave can be conducted to the lower side of the metasurface and then bypass the obstacle and continue to propagate forward, significantly reducing the scattering of the sound wave, thereby forming an acoustic transparent area. This comparison fully demonstrates the effectiveness of the acoustic stealth device in reducing sound wave scattering and realizing sound wave obstacle avoidance transmission.

[0038] The transmittance is also one of the important indicators to measure the performance of the acoustic stealth device. As Figure 5As shown, within the target frequency band of 3900 - 4100 Hz, the double-sided metasurface structure designed based on this embodiment can achieve a transmittance greater than 0.5. In sharp contrast, the acoustic wave transmittance without laying the double-sided metasurface is nearly zero. This data indicates that the structure proposed based on this embodiment can effectively improve the obstacle avoidance transmission ability of the pseudo-surface wave, enabling the acoustic wave to maintain a high transmission efficiency when encountering obstacles.

[0039] In addition, this embodiment further verifies the robustness of the acoustic stealth device against obstacles of different shapes and sizes. Referring to Figure 6 , the acoustic stealth device in this embodiment not only has a stealth effect on obstacles of a specific shape but also performs excellently on obstacles of different shapes. In the presence of obstacles of different shapes, whether the shape of the obstacle is a rhombus or a square, obvious acoustic scattering phenomena will occur in front of the obstacle without laying the double-sided metasurface, resulting in the appearance of the obstacle. However, after applying the double-sided metasurface of this embodiment, the acoustic wave can continue to propagate forward along the bottom of the metasurface, significantly reducing the scattering of the acoustic wave, thereby achieving the stealth effect of the obstacle. By comparing the stealth effects of two obstacles with different shapes, it can be found that although the shapes of the obstacles are different, the metasurface structure can effectively regulate the propagation path of the pseudo-surface wave to achieve acoustic stealth. This characteristic makes the acoustic stealth device have broad application prospects in complex and changeable acoustic environments.

[0040] Embodiment 3 Based on the double-sided metasurface introduced in Embodiment 2, this embodiment will further introduce a gradient refractive index metasurface that can meet the gradient refractive index distribution, which can achieve two more complex acoustic regulation functions of acoustic focusing and self-imaging while ensuring the obstacle avoidance transmission of the pseudo-surface wave. The design process of the gradient refractive index metasurface includes: setting the equivalent refractive index of the gradient refractive index metasurface in space; by deriving the dispersion curve of the pseudo-surface wave mode, obtaining the relationship between the structural parameters of the Helmholtz resonator and the equivalent refractive index of the gradient refractive index metasurface; based on the equivalent refractive index and the relationship between the structural parameters of the Helmholtz resonator and the equivalent refractive index of the gradient refractive index metasurface, using the genetic algorithm optimization method to solve for the structural parameters of the Helmholtz resonator that satisfy the gradient refractive index distribution along the direction; according to the optimized structural parameters of the Helmholtz resonator, fabricating the Helmholtz resonator and arranging it in a periodic manner to obtain the gradient refractive index metasurface required by the target.

[0041] Specifically, to achieve the acoustic focusing effect, it is first necessary to construct a gradient refractive index metasurface, whose equivalent refractive index is set in space as: ; In the formula, represents the equivalent refractive index at different positions of the metasurface, represents the maximum refractive index at the midline of the metasurface, represents the hyperbolic secant function, represents the refractive index modulation factor, and the specific value in this embodiment is set to 1. When takes 1.5, the refractive index at the midline of the metasurface is the largest.

[0042] Furthermore, to obtain the structural parameters of the double-sided metasurface that satisfy the gradient refractive index distribution, the relationship between the structural parameters of the Helmholtz resonator and the equivalent refractive index of the gradient refractive index metasurface will be obtained by deriving the dispersion curve of the pseudo surface wave mode. The specific determination process is as follows: Assume that the propagation of the pseudo surface wave on the metasurface is lossless, and different from the surface wave, the pseudo surface wave is localized in the air domain, and the energy decays exponentially along the normal direction ( kg / m 3 , m / s). Based on the above assumptions, consider a pseudo surface wave propagating on the double-sided metasurface, and its sound pressure and normal vibration velocity are expressed as: ; In the formula, represents the sound pressure of the pseudo surface wave, represents the sound pressure amplitude, represents the transmission wave vector of the pseudo surface wave along direction, represents the transmission wave vector of the pseudo surface wave along direction, represents the angular frequency, represents the time; represents the normal vibration velocity of the pseudo surface wave perpendicular to the metasurface, represents the imaginary unit, represents the mass density of the background medium.

[0043] Considering that all geometric dimensions of the Helmholtz resonator structural unit are much smaller than the working wavelength, a lumped-parameter method calculation model is constructed in this embodiment. Specifically, the impedance transfer method is used to solve the top surface acoustic impedance at the opening on the upper side of the Helmholtz resonator. The corresponding solution process includes: setting the aperture at the opening on the upper side of the Helmholtz resonator to be the same as the aperture at the opening on the lower side, and calculating the bottom surface acoustic impedance at the opening on the lower side of the Helmholtz resonator; according to the bottom surface acoustic impedance at the opening on the lower side of the Helmholtz resonator, using the impedance transfer formula, calculating the bottom surface acoustic impedance of the rectangular cavity; according to the bottom surface acoustic impedance of the rectangular cavity, repeatedly using the impedance transfer formula, calculating the top surface acoustic impedance of the rectangular cavity; according to the top surface acoustic impedance of the rectangular cavity, repeatedly using the impedance transfer formula, calculating the top surface acoustic impedance at the opening on the upper side of the Helmholtz resonator.

[0044] Specifically, the double-sided metasurface structure designed in this embodiment can be approximately regarded as composed of two short tubes on both sides and a central cavity in cascade. To simplify the calculation, it is first assumed that the aperture diameters of the openings on the upper and lower sides of the Helmholtz resonator are the same ( ), and the bottom surface acoustic impedance at the opening on the lower side of the Helmholtz resonator can be approximately expressed as: ; ; ; In the formula, represents the bottom surface acoustic impedance at the opening on the lower side of the Helmholtz resonator, represents the equivalent acoustic impedance in the lower short tube of the Helmholtz resonator, represents the speed of sound.

[0045] Furthermore, using the impedance transfer formula, the bottom surface acoustic impedance of the rectangular cavity is obtained, expressed as: ; In the formula, represents the bottom surface acoustic impedance of the rectangular cavity.

[0046] On this basis, taking as the bottom surface acoustic impedance at the opening on the lower side of the Helmholtz resonator, repeating the calculation process of formula (5), the top surface acoustic impedance at the opening on the upper side of the Helmholtz resonator of the metasurface in formula (3) can be obtained through the impedance transfer method , expressed as: ; In the formula, represents the top surface acoustic impedance at the opening on the upper side of the Helmholtz resonator, represents the volume flow of the pseudo surface wave.

[0047] Since the metasurface only supports the transmission of pseudo-surface waves, that is, the normal wave vector satisfies the relationship , then the relationship between the structural parameters of the Helmholtz resonator and the equivalent refractive index of the gradient refractive index metasurface can be expressed as: ; In the formula, represents the lattice constant of the Helmholtz resonator, represents the aperture diameter at the upper side opening of the Helmholtz resonator, represents the aperture diameter at the lower side opening of the Helmholtz resonator, represents the side length of the rectangular cavity, represents the height of the Helmholtz resonator, represents the depth of the rectangular cavity, represents the wall thickness of the Helmholtz resonator. The above formula shows that the equivalent refractive index is determined by the 7 structural parameters of the Helmholtz resonator.

[0048] Finally, based on the genetic algorithm, the structural parameters of the Helmholtz resonator that satisfy the gradient refractive index distribution of Equation (1) along the direction can be quickly obtained, and then the design of the gradient refractive index metasurface required for the target can be completed.

[0049] For simple illustration, in this embodiment, the equivalent refractive index is discretized into 6 different values according to the refractive index curve. The specific structural parameters of the Helmholtz resonator structural unit are shown in Table 1. The side length of the cavity in the table is the side length of the rectangular cavity of the Helmholtz resonator, the aperture diameter of the opening is the aperture diameter at the upper and lower side openings of the Helmholtz resonator. Here, equal values are taken. The height is the height of the Helmholtz resonator, the lattice constant is the lattice constant of the Helmholtz resonator, the depth of the cavity is the depth of the rectangular cavity, and the depth of the opening is the depth of the cylindrical opening corresponding to the upper and lower side openings of the Helmholtz resonator.

[0050]

[0051] As Figure 9 shown, the gray area is the coverage area of the single-sided metasurface, and the blue area is the coverage area of the double-sided metasurface. A total of 11*21 structural units are laid. Along the direction, the Helmholtz resonator structural units corresponding to the refractive index distribution are laid in sequence. The pseudo-surface wave is incident from the boundary shown in the figure along the direction. The double-sided metasurface based on the gradient refractive index can respectively achieve the acoustic focusing effect as shown in Figure 7 and the acoustic self-imaging effect as shown in Figure 8 .

[0052] On the basis of completing the metasurface that satisfies the gradient refractive index distribution, this embodiment also verifies the acoustic focusing effect through numerical simulation. First, a test coordinate system is established with the center of the double-sided metasurface as the origin, and the refractive index corresponding structural units are arranged in sequence along the direction. A total of 19 units are arranged in each column. It is stipulated that the unit array direction is direction, and 23 units are arranged in each row. The acoustic wave propagation direction is set as direction, and the positive propagation direction is from left to right. A plane wave is incident on the upper surface on the left side, and the sound pressure distribution curve is scanned along the axis on the lower surface to verify the acoustic focusing effect. As can be seen from Figure 7 , when a plane wave is incident on the lower side of the upper surface, it is not difficult to observe that as the propagation distance increases, the acoustic wave gradually conducts from the upper surface to the lower surface for transmission, and at the same time, the acoustic focusing effect is achieved.

[0053] On the basis of completing the acoustic focusing based on the double-sided metasurface, this embodiment also verifies the acoustic wave self-imaging effect, that is, the acoustic Talbot effect, through numerical simulation. Referring to Figure 8 , the acoustic wave propagation direction is set as direction, and the positive propagation direction is from bottom to top. A periodic acoustic signal is incident on the upper surface on the left side, and its spatial distribution satisfies the data coding form of {1 0 1 0 1}. The sound pressure distribution curve is scanned along the right boundary of the structure on the lower surface. It can be seen from the simulation results that the received signal satisfies the amplitude distribution characteristics of {1 0 1 0 1}. As can be seen from Figure 8 , when the pseudo surface wave is incident in the form of {1 0 1 0 1}, it can achieve the self-imaging effect while transferring to the lower surface for transmission, indicating that even in the presence of obstacles, the structure designed by the present invention can not only achieve the stealth effect, but also be compatible with the relevant gradient metasurface to ensure the obstacle avoidance transmission function of more complex signals.

[0054] Embodiment 4 Referring to Figures 1 to 9 , based on the same technical concept, this embodiment will introduce a design method for an acoustic stealth device applicable to the double-sided transmission of pseudo surface waves as described in Embodiment 3. The design process is as follows: First, the equivalent refractive index of the gradient refractive index metasurface is set in space. Then, by deriving the dispersion curve of the pseudo surface wave mode, the relationship between the structural parameters of the Helmholtz resonator and the equivalent refractive index of the gradient refractive index metasurface is obtained. Then, based on the equivalent refractive index and the relationship between the structural parameters of the Helmholtz resonator and the equivalent refractive index of the gradient refractive index metasurface, using the genetic algorithm optimization method, the solution along The structural parameters of a Helmholtz resonator whose direction satisfies the gradient refractive index distribution. Finally, according to the optimized structural parameters of the Helmholtz resonator, the Helmholtz resonator is fabricated and arranged in a periodic manner to obtain the gradient refractive index metasurface required by the target.

[0055] Specifically, to achieve the acoustic focusing effect, first, a gradient refractive index metasurface needs to be constructed, and its equivalent refractive index is set in space as: ; In the formula, represents the equivalent refractive index at different positions of the metasurface, represents the maximum refractive index at the midline of the metasurface, represents the hyperbolic secant function, represents the refractive index modulation factor, and the specific value in this embodiment is set to 1. When takes 1.5, the refractive index at the midline of the metasurface is the largest.

[0056] Furthermore, to obtain the structural parameters of the double-sided metasurface that satisfies the gradient refractive index distribution, the relationship between the structural parameters of the Helmholtz resonator and the equivalent refractive index of the gradient refractive index metasurface will be obtained by deriving the dispersion curve of the pseudo surface wave mode. The specific determination process is as follows: Assume that the propagation of the pseudo surface wave on the metasurface is lossless, and different from the surface wave, the pseudo surface wave is localized in the air domain, and the energy decays exponentially along the normal direction ( kg / m 3 , m / s). Based on the above assumptions, considering a pseudo surface wave propagating on the double-sided metasurface, its sound pressure and normal particle velocity are expressed as: ; In the formula, represents the sound pressure of the pseudo surface wave, represents the sound pressure amplitude, represents the propagation wave vector of the pseudo surface wave along the direction, represents the propagation wave vector of the pseudo surface wave along the direction, represents the angular frequency, represents the time; represents the normal particle velocity of the pseudo surface wave perpendicular to the metasurface, represents the imaginary unit, represents the mass density of the background medium.

[0057] Considering that all geometric dimensions of the Helmholtz resonator structural unit are much smaller than the working wavelength, a lumped-parameter method calculation model is constructed in this embodiment. Specifically, the impedance transfer method is used to solve the top surface acoustic impedance at the opening on the upper side of the Helmholtz resonator. The corresponding solution process includes: setting the aperture at the opening on the upper side of the Helmholtz resonator to be the same as the aperture at the opening on the lower side, and calculating the bottom surface acoustic impedance at the opening on the lower side of the Helmholtz resonator; according to the bottom surface acoustic impedance at the opening on the lower side of the Helmholtz resonator, using the impedance transfer formula, calculating the bottom surface acoustic impedance of the rectangular cavity; according to the bottom surface acoustic impedance of the rectangular cavity, repeatedly using the impedance transfer formula, calculating the top surface acoustic impedance of the rectangular cavity; according to the top surface acoustic impedance of the rectangular cavity, repeatedly using the impedance transfer formula, calculating the top surface acoustic impedance at the opening on the upper side of the Helmholtz resonator.

[0058] Specifically, the double-sided metasurface structure designed in this embodiment can be approximately regarded as composed of two short tubes on both sides and a central cavity in cascade. To simplify the calculation, it is first assumed that the aperture diameters of the openings on the upper and lower sides of the Helmholtz resonator are the same ( ), and the bottom surface acoustic impedance at the opening on the lower side of the Helmholtz resonator can be approximately expressed as: ; ; ; In the formula, represents the bottom surface acoustic impedance at the opening on the lower side of the Helmholtz resonator, represents the equivalent acoustic impedance in the lower short tube of the Helmholtz resonator, represents the speed of sound.

[0059] Furthermore, using the impedance transfer formula, the bottom surface acoustic impedance of the rectangular cavity is obtained, expressed as: ; In the formula, represents the bottom surface acoustic impedance of the rectangular cavity.

[0060] On this basis, taking as the bottom surface acoustic impedance at the opening on the lower side of the Helmholtz resonator and repeating the calculation process of formula (5), the top surface acoustic impedance at the opening on the upper side of the Helmholtz resonator of the metasurface in formula (3) can be obtained by the impedance transfer method , expressed as: ; In the formula, represents the top surface acoustic impedance at the opening on the upper side of the Helmholtz resonator, represents the volume flow of the pseudo surface wave.

[0061] Since the metasurface only supports the transmission of pseudo-surface waves, that is, the normal wave vector satisfies the relationship , the relationship between the structural parameters of the Helmholtz resonator and the equivalent refractive index of the gradient refractive index metasurface can be expressed as: ; In the formula, represents the lattice constant of the Helmholtz resonator, represents the aperture diameter at the upper side opening of the Helmholtz resonator, represents the aperture diameter at the lower side opening of the Helmholtz resonator, represents the side length of the rectangular cavity, represents the height of the Helmholtz resonator, represents the depth of the rectangular cavity, represents the wall thickness of the Helmholtz resonator. The above formula shows that the equivalent refractive index is determined by the 7 structural parameters of the Helmholtz resonator.

[0062] Finally, based on the genetic algorithm, the structural parameters of the Helmholtz resonator that satisfy the gradient refractive index distribution of Equation (1) along the direction can be quickly obtained, and then the design of the gradient refractive index metasurface required for the target can be completed.

[0063] For simplicity, in this embodiment, the equivalent refractive index is discretized into 6 different values according to the refractive index curve. The specific structural parameters of the Helmholtz resonator structural unit are shown in Table 1. The side length of the cavity in the table is the side length of the rectangular cavity of the Helmholtz resonator, the aperture diameter of the opening is the aperture diameter at the upper and lower side openings of the Helmholtz resonator, the same value is taken here, the height is the height of the Helmholtz resonator, the lattice constant is the lattice constant of the Helmholtz resonator, the depth of the cavity is the depth of the rectangular cavity, and the depth of the opening is the depth of the cylindrical opening corresponding to the upper and lower side openings of the Helmholtz resonator.

[0064]

[0065] As Figure 9 shown, the gray area is the coverage area of the single-sided metasurface, and the blue area is the coverage area of the double-sided metasurface. A total of 11*21 structural units are laid. Along the direction, the Helmholtz resonator structural units corresponding to the refractive index distribution are laid in sequence. The pseudo-surface wave is incident from the boundary shown in the figure along the direction. The double-sided metasurface based on the gradient refractive index can respectively achieve the acoustic focusing effect as shown in Figure 7 and the acoustic self-imaging effect as shown in Figure 8 .

[0066] On the basis of completing the metasurface that satisfies the gradient refractive index distribution, this embodiment also verifies the acoustic focusing effect through numerical simulation. First, a test coordinate system is established, with the center of the double-sided metasurface as the origin, and the refractive index corresponding structural units are arranged in sequence along the direction. A total of 19 units are arranged in each column. It is stipulated that the unit array direction is direction, and 23 units are arranged in each row. The acoustic wave propagation direction is set as direction, and the positive propagation direction is from left to right. A plane wave is incident on the left upper surface, and the sound pressure distribution curve is scanned along the axis on the lower surface to verify the acoustic focusing effect. From Figure 7 , it can be seen that when a plane wave is incident on the lower side of the upper surface, it is not difficult to observe that as the propagation distance increases, the acoustic wave gradually conducts from the upper surface to the lower surface for transmission, and at the same time, the acoustic focusing effect is achieved.

[0067] On the basis of completing the acoustic focusing based on the double-sided metasurface, this embodiment also verifies the acoustic wave self-imaging effect, that is, the acoustic Talbot effect, through numerical simulation. Referring to Figure 8 , the acoustic wave propagation direction is set as direction, and the positive propagation direction is from bottom to top. A periodic acoustic signal is incident on the left upper surface, and its spatial distribution satisfies the data coding form of {1 0 1 0 1}. The sound pressure distribution curve is scanned along the right boundary of the structure on the lower surface. It can be seen from the simulation results that the received signal satisfies the amplitude distribution characteristics of {1 0 1 0 1}. From Figure 8 , it can be seen that when the pseudo surface wave is incident in the form of {1 0 1 0 1}, it can achieve the self-imaging effect while transferring to the lower surface for transmission, indicating that even in the presence of obstacles, the structure designed by the present invention can not only achieve the stealth effect, but also be compatible with the relevant gradient metasurface to ensure the obstacle avoidance transmission function of more complex signals.

[0068] The above are only the preferred embodiments of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the technical principle of the present invention, several improvements and deformations can be made, and these improvements and deformations should also be regarded as the protection scope of the present invention.

Claims

1. An acoustic stealth device supporting double-sided transmission of pseudo-surface waves, characterized in that, Including: A plurality of Helmholtz resonators arranged in a periodic array, with the side walls of adjacent Helmholtz resonators connected to each other to form a continuous metasurface; The metasurface is sequentially set as a first metasurface unit, a second metasurface unit, and a third metasurface unit along the propagation direction of the pseudo surface wave; the second metasurface unit is used to place an obstacle; the upper and lower sides of the Helmholtz resonator in the first metasurface unit close to one side of the second metasurface are provided with openings, which respectively correspond to a first acoustic wave inlet and a first acoustic wave outlet; the upper and lower sides of the Helmholtz resonator in the third metasurface unit close to the other side of the second metasurface are also provided with openings, which respectively correspond to a second acoustic wave outlet and a second acoustic wave inlet; In the propagation state, the pseudo surface wave sequentially bypasses the first acoustic wave inlet, the first acoustic wave outlet, below the second metasurface unit, the second acoustic wave inlet, and the second acoustic wave outlet to achieve obstacle invisibility.

2. The acoustic stealth device supporting the double-sided transmission of pseudo surface waves according to claim 1, characterized in that Each of the Helmholtz resonators is arranged in a square grid array; wherein, the central part of the Helmholtz resonator is set as a rectangular cavity, the upper and lower sides of the Helmholtz resonator are provided with cylindrical openings with the same aperture, and the central axis of the rectangular cavity coincides with the central axis of the cylindrical opening.

3. The acoustic stealth device supporting the double-sided transmission of pseudo surface waves according to claim 2, wherein The metasurface is a gradient refractive index metasurface that satisfies the gradient refractive index distribution; wherein, the design process of the gradient refractive index metasurface includes: Setting the equivalent refractive index of the gradient refractive index metasurface in space; By deriving the dispersion curve of the pseudo surface wave mode, obtaining the relationship between the structural parameters of the Helmholtz resonator and the equivalent refractive index of the gradient refractive index metasurface; Based on the relationship between the equivalent refractive index and the structural parameters of the Helmholtz resonator and the equivalent refractive index of the gradient refractive index metasurface, using the genetic algorithm optimization method, solve for the structural parameters of the Helmholtz resonator that satisfy the gradient refractive index distribution along the direction; According to the optimized structural parameters of the Helmholtz resonator, manufacturing the Helmholtz resonator and arranging it in a periodic manner to obtain the gradient refractive index metasurface required by the target.

4. The acoustic stealth device supporting the double-sided transmission of pseudo surface waves according to claim 3, characterized in that, The equivalent refractive index of the gradient refractive index metasurface is set in space as: ； In the formula, represents the equivalent refractive index at different positions of the metasurface, respectively represent coordinate variables, represents the maximum refractive index at the midline of the metasurface, represents the hyperbolic secant function, represents the refractive index modulation factor.

5. The acoustic stealth device supporting the double-sided transmission of pseudo-surface waves according to claim 4, characterized in that The relationship between the structural parameters of the Helmholtz resonator and the equivalent refractive index of the gradient refractive index metasurface is expressed as: ； In the formula, represents the imaginary unit, represents the angular frequency, represents the mass density of the background medium, represents the transmission wave vector of the pseudo surface wave along the direction, represents the top surface acoustic impedance at the opening on the upper side of the Helmholtz resonator, represents the lattice parameter, represents the aperture diameter at the opening on the upper side of the Helmholtz resonator, represents the aperture diameter at the opening on the lower side of the Helmholtz resonator, represents the side length of the rectangular cavity, represents the height of the Helmholtz resonator, represents the depth of the rectangular cavity, represents the wall thickness of the Helmholtz resonator.

6. The acoustic stealth device supporting the double-sided transmission of pseudo-surface waves according to claim 5, characterized in that, The top surface acoustic impedance at the opening on the upper side of the Helmholtz resonator is expressed as: ； ； wherein, denotes the sound pressure of the pseudo surface wave, denotes the volume flow of the pseudo surface wave, denotes the normal vibration velocity of the pseudo surface wave, denotes that the pseudo surface wave is along the propagation wave vector in the direction; Wherein, the acoustic pressure of the pseudo surface wave and the normal vibration velocity of the pseudo surface wave are respectively expressed as: ； ； In the formula, represents the sound pressure amplitude, represents time.

7. The acoustic stealth device supporting double-sided transmission of pseudo surface waves according to claim 6, wherein The top surface acoustic impedance at the opening on the upper side of the Helmholtz resonator is obtained by solving through the impedance transfer method, and the corresponding solving process includes: Setting the aperture at the opening on the upper side of the Helmholtz resonator to be the same as the aperture at the opening on the lower side, and calculating the bottom surface acoustic impedance at the opening on the lower side of the Helmholtz resonator; According to the bottom surface acoustic impedance at the opening on the lower side of the Helmholtz resonator, using the impedance transfer formula, calculating the bottom surface acoustic impedance of the rectangular cavity; According to the bottom surface acoustic impedance of the rectangular cavity, repeatedly using the impedance transfer formula, calculating the top surface acoustic impedance of the rectangular cavity; According to the top surface acoustic impedance of the rectangular cavity, repeatedly using the impedance transfer formula, calculating the top surface acoustic impedance at the opening on the upper side of the Helmholtz resonator.

8. The acoustic stealth device supporting double-sided transmission of pseudo surface waves according to claim 7, characterized in that, The bottom surface acoustic impedance at the opening on the lower side of the Helmholtz resonator is expressed as: ； ； ； In the formula, represents the bottom surface acoustic impedance at the opening on the lower side of the Helmholtz resonator, represents the equivalent acoustic impedance in the short tube on the lower side of the Helmholtz resonator, represents the speed of sound; The acoustic impedance of the bottom surface of the rectangular cavity is calculated by the following impedance transfer formula: ； In the formula, represents the acoustic impedance of the bottom surface of the rectangular cavity.

9. The acoustic stealth device supporting double-sided transmission of pseudo surface waves according to claim 1, characterized in that, The thickness of the metasurface is set to 1 / 20 of the working wavelength.

10. A design method for an acoustic stealth device applicable to supporting double-sided transmission of pseudo-surface waves as described in any one of claims 3-9, characterized in that, Including: Spatially setting the equivalent refractive index of the gradient refractive index metasurface; By deriving the dispersion curve of the pseudo-surface wave mode, the relationship between the structural parameters of the Helmholtz resonator and the equivalent refractive index of the gradient refractive index metasurface is obtained; Based on the relationship between the equivalent refractive index and the structural parameters of the Helmholtz resonator and the equivalent refractive index of the gradient refractive index metasurface, using the genetic algorithm optimization method, solve for the structural parameters of the Helmholtz resonator that satisfy the gradient refractive index distribution along the direction; According to the optimized structural parameters of the Helmholtz resonator, the Helmholtz resonator is fabricated and arranged in a periodic manner to obtain the gradient refractive index metasurface required by the target, and then an acoustic stealth device is designed based on the gradient refractive index metasurface.

Images