CN108062948B - A method for regulating sound waves based on pattern cutting technology - Google Patents

Abstract

The invention discloses a method for regulating sound waves based on patterned cutting technology, comprising: determining a phase regulating film, the phase regulating film can change the phase of the transmitted sound waves by 180 degrees; and cutting the phase regulating film so that The distribution of the transmitted acoustic wave field of the trimmed phase control film changes. By controlling the trimming pattern, the transmitted acoustic wave plane can be focused on the focal point or spatially focused on the focal point, resulting in a stable propagating acoustic vortex or super-oscillation phenomenon. A subwavelength focal spot is generated, and the present invention realizes the regulation of different effects of transmitted acoustic waves by controlling the cutting pattern. The present invention is a passive device and has great advantages in energy consumption, volume and portability, and has broad application prospects.

Description

A method for regulating sound waves based on pattern cutting technology

technical field

The invention belongs to the technical field of sound wave regulation, and more particularly, relates to a method for regulating sound waves based on pattern cutting technology.

Background technique

The regulation of sound waves is of great significance for noise isolation and absorption, acoustic communication, acoustic stealth, acoustic imaging, and acoustic energy weapons. In the existing literature, the methods of regulating acoustic waves to achieve the above-mentioned functions include stacking of waveguide cavities and etching of metal plates.

By designing the structure of the waveguide cavity to change the transmitted acoustic phase, the distribution of the acoustic field can be adjusted by designing different phase changes at different positions in the plane perpendicular to the incident direction. In addition, subwavelength imaging can be achieved through a series of Helmholtz resonators. The sound field distribution can also be regulated by etching (or cutting) the metal plate into a specific pattern. The thick metal plate acts as a hard boundary to reflect the sound back, while the etched part contributes to the transmitted sound field as a sub-sound source, thereby modulating the sound waves. These are passive devices and are planar adjustment devices. For example, in the prior art, the stacking of waveguide cavities and the etching of metal plates are used to modulate the acoustic waves, so as to realize acoustic focusing and acoustic vortexing.

Both of the above two methods require thick steel plates as waveguides or hard boundaries to isolate sound waves, which makes the entire device bulky, difficult to process, and high in cost, which limits its application range. And the method of stacking phase units has limited precision of its specific effect due to its volume cannot be ignored. The metal plate etching method has limited freedom in design because only the etched part is transmissive.

SUMMARY OF THE INVENTION

Aiming at the defects of the prior art, the purpose of the present invention is to solve the problem that the existing acoustic wave regulation requires a thick steel plate as a waveguide or a hard boundary to isolate the acoustic wave, which makes the whole device bulky and difficult to process, and the cost is also high, which limits its application range. . In addition, the method of stacking phase units has technical problems such as its volume cannot be ignored and the accuracy of its specific effect is limited.

In order to achieve the above object, the present invention provides a method for regulating sound waves based on pattern cutting technology, comprising:

Determine the phase control film, the phase control film can change the phase of the transmitted acoustic wave by 180 degrees; cut the phase control film, so that the distribution of the acoustic wave field transmitted by the cut phase control film is changed, and by controlling The tailoring pattern can make the transmitted acoustic wave plane focus on the focal point or spatially focus on the focal point, generate a stably propagating acoustic vortex or form a super-oscillation phenomenon, thereby generating a sub-wavelength focal spot.

Optionally, by controlling the size of the cut, the path difference between the acoustic wave after passing through the cut area and the adjacent acoustic wave after passing through the non-cut area to reach the focus is half of the wavelength of the acoustic wave, so that the cut phase control film transmits The rear acoustic wave plane is focused on the focal point or spatially focused on the focal point.

Optionally, the phase control film is cut into a Fermat spiral pattern, so that the acoustic wave transmitted through the cut phase control film generates a stably propagated acoustic vortex.

Optionally, the phase control film is cut into a quasi-periodic pattern of a Penrose lattice, so that the acoustic wave passing through the cut phase control film forms a super-oscillation phenomenon, thereby generating a subwavelength focal spot.

Optionally, when the acoustic wave plane transmitted by the trimmed phase control film is focused on the focal point, trimming the phase control film includes:

The phase control film is cut into a symmetrically distributed strip structure, and the width l _n of the nth line to the symmetry center from the symmetry center satisfies:

Wherein, f _c is the designed focal length, λ is the wavelength of the acoustic wave, and N is the number of bus bars on one side of the strip structure.

Optionally, when the acoustic wave transmitted by the trimmed phase control film is spatially focused on the focal point, trimming the phase control film includes:

The phase control film is cut into a symmetrically distributed ring structure, and the ring radius rn of the _nth ring line satisfies:

Wherein, f _c is the designed focal length, λ is the wavelength of the acoustic wave, and N is the total number of loop lines of the annular structure.

Optionally, the Fermat spiral pattern includes two spirals, and the expressions of the two spirals respectively satisfy:

Among them, m is the linear coefficient, r ₁ and r ₂ are the polar diameters of the two spirals, respectively, and θ ₁ and θ ₂ are the polar angles of the two spirals, respectively.

Optionally, by selecting an appropriate m, a stable acoustic vortex can be generated after the sound waves of different wavelengths are transmitted through the tailored phase control film.

Optionally, when m=9.1, stable acoustic vortices can be generated after the acoustic waves of 11 mm to 17 mm are transmitted through the tailored phase control film.

Optionally, the quasi-periodic pattern of the Penrose lattice is composed of two kinds of rhombus, and the acute angles of the two kinds of rhombus are 36 degrees and 72 degrees respectively, and the two kinds of rhombus are assembled into a quasi-like pentagon. The periodic pattern covers the plane of the phase control film, and the cut-out circular holes are located on the vertices of the two kinds of rhombus.

Optionally, determining the phase control film includes: uniformly mixing any metal particles or non-metallic particles with a density greater than that of the fiber material and any polymer material or soft material solution with a modulus smaller than the particles to obtain a mixed solution; using the mixed solution as a raw material, The electrospinning technology is used to obtain electrospinning fibers with particles, and then the electrospinning fibers are stacked to form an electrospinning film, and the electrospinning film is the phase regulating film.

In general, compared with the prior art, the above technical solutions conceived by the present invention have the following beneficial effects:

1. The present invention can achieve high-efficiency acoustic focusing of the sound wave after transmitting the thin film by cutting the film into a strip or ring pattern, and can be used for medical ultrasonic lithotripsy, acoustic positioning heating, acoustic weapons and other acoustic weapons that require precise control of high energy concentration. application.

2. The present invention cuts the film into a Fermat spiral pattern, so that the transmitted acoustic wave can generate a stable acoustic vortex, the acoustic vortex can stably propagate within a certain distance of the transmission field, and the vortex center intensity is zero. The invention can realize multi-functional and customized regulation of sound waves. The acoustic vortex obtained based on the film material of the invention can be used for noise isolation, acoustic communication, particle manipulation, etc. Therefore, the film provided by the invention can be cut by control The method of obtaining acoustic vortices from patterns has broad application prospects.

3. The present invention realizes far-field acoustic wave sub-wavelength resolution by cutting the film into a quasi-periodic pattern of Penrose lattice, and the obtained sub-wavelength focal spot full width at half maximum is about 0.25 times the wavelength. It means that the length resolution is doubled, and from the perspective of the entire area, the imaging accuracy limit can be 4 times that of the conventional method. In one direction, the wavelength used for imaging is reduced by half, and the imaging accuracy is doubled. It is said that the accuracy of subwavelength imaging in both directions is doubled, so the imaging accuracy is increased by 4 times.

4. The size is reduced. Compared with any previous designs with similar functions, the present invention utilizes the joint action of two regions with an initial phase difference of 180 degrees, which can reduce the device area by half in both x and y directions, so that the total film area can be reduced by 3/4 (The z direction is the direction of the incident wave, and the xy direction is perpendicular to the z direction).

5. Higher energy utilization. The present invention is based on the full transmission structure, utilizes the energy of the entire plane, and has a higher energy utilization rate. Moreover, the present invention is a passive device, and has great advantages in energy consumption, volume and portability.

Description of drawings

Fig. 1 is the schematic flow chart of the method for regulating acoustic wave based on pattern cutting technology provided by the present invention;

Fig. 2 is the transmission integrated field calculation schematic diagram provided by the present invention;

FIG. 3 is a schematic diagram of cropping a strip-shaped structure focusing pattern provided by the present invention;

4 is a schematic diagram of a sound wave focusing path provided by the present invention;

Fig. 5 is the simulation transmission field diagram (xz plane) of the strip structure provided by the present invention;

6 is a transmission field diagram (xz plane) of the experimental test of the strip structure provided by the present invention;

FIG. 7 is a schematic diagram of cropping a ring structure focusing pattern provided by the present invention;

8 is a simulated transmission field diagram (xy plane) of the annular structure provided by the present invention;

9 is a simulated transmission field diagram (yz plane) of the annular structure provided by the present invention;

Fig. 10 is the simulation relation diagram that the focus energy enhancement multiple provided by the present invention changes with the increase of the number of stripes and the number of rings N;

11 is a schematic diagram of the Fermat spiral pattern adopted in the present invention;

Fig. 12 is the schematic diagram of the sonic vortex formed by the present invention;

13 is a simulation and experimental test phase diagram of a specifically generated vortex field provided by the present invention;

14 is a simulation and experimental test intensity diagram of the vortex field specifically generated by the present invention;

15 is a simulated phase diagram of the vortex field specifically generated by the present invention as a function of distance;

Figure 16 is a simulation intensity diagram of the vortex field specifically generated by the present invention as a function of distance;

17 is a schematic diagram of a quasi-periodic pattern of cutting a phase control film into a Penrose lattice provided by the present invention;

18 is a simulated transmission field diagram (xz plane) of the Penrose lattice structure provided by the present invention;

FIG. 19 is a detailed diagram of the center of the simulated transmission field of the Penrose lattice structure provided by the present invention and a corresponding experimental test diagram (xz plane);

Fig. 20 is an intensity distribution diagram on the center section of the field in Fig. 19;

Fig. 21 is the simulation intensity diagram that the sound field distribution of the specific generation provided by the present invention varies with distance;

Figure 22 is a graph of the relationship between focal spot intensity and full width at half maximum provided by the present invention as a function of distance;

Figure 23 is the scanning electron microscope image of the fiber film obtained according to the method of the present invention when the quality of copper particles and polyvinyl alcohol provided by the present invention is 1:8;

Figure 24 is the scanning electron microscope image of the fiber film obtained according to the method of the present invention when the mass of copper particles and polyvinyl alcohol provided by the present invention is 1:4;

Figure 25 is the scanning electron microscope image of the fiber film obtained according to the method of the present invention when the mass of copper particles provided by the present invention and polyvinyl alcohol is 1:2;

Figure 26 is the scanning electron microscope image of the fiber film obtained according to the method of the present invention when the mass of copper particles and polyvinyl alcohol provided by the present invention is 1:1;

Figure 27 is a result diagram of the sound wave transmission test of the fiber film obtained when the mass of the copper particles provided by the present invention and polyvinyl alcohol is 1:8;

Figure 28 is a result diagram of the sound wave transmission test of the fiber film obtained when the mass of the copper particles and polyvinyl alcohol provided by the present invention is 1:4;

Figure 29 is a result diagram of the sound wave transmission test of the fiber film obtained when the mass of copper particles and polyvinyl alcohol provided by the present invention is 1:2;

FIG. 30 is a result diagram of the sound wave transmission test of the fiber film obtained when the mass of copper particles and polyvinyl alcohol provided by the present invention is 1:1.

Detailed ways

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, but not 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.

In view of the above defects or improvement requirements of the prior art, the present invention is based on a thin film capable of changing the transmission phase by 180 degrees and a specific patterning design rule to achieve sound wave regulation. Using laser cutting or other cutting methods to cut the film into a designed pattern can realize the sound field regulation of the different effects of the film after transmission and cutting. The shearing on this flexible film is very convenient, and the overall device is also very light and low in cost, which is favorable for mass production. This approach is also passive and has advantages in power consumption and portability.

FIG. 1 is a schematic flowchart of a method for regulating sound waves based on a patterned cutting technology provided by the present invention, as shown in FIG. 1 , including steps S101 to S102.

S101, determining a phase control film, the phase control film can change the phase of the transmitted acoustic wave by 180 degrees.

S102, cutting the phase control film, so that the distribution of the acoustic wave field after the transmission of the cut phase control film changes, and by controlling the cutting pattern, the transmitted acoustic wave plane can be focused on the focal point or spatially focused on the focal point, resulting in a stable The propagating acoustic vortices may form superoscillating phenomena, resulting in subwavelength focal spots.

Specifically, when the plane acoustic wave is incident on the surface of the cut film, the corresponding transmission field distribution can be calculated according to the Rayleigh-Sommerfeld diffraction formula. The formation of the transmission field is specifically shown in Figure 2: Figures a and b in Figure 2 are the cases discussed in the Cartesian coordinate system and the cylindrical coordinate system, respectively. The two situations are similar, and the Cartesian coordinate system is mainly introduced here. The plane where XOY is located represents the sub-sound source surface, and the plane where the point S is located is any target transmission plane parallel to the sound source surface that we are concerned about, and P represents the sound pressure. The sound pressure at any point on the target plane (including the amplitude and phase of the sound pressure) is the result of the superposition of the sub-sound waves emitted by all the source points on the sound source plane at the target point. From the Rayleigh-Sommerfeld diffraction integral formula, the sound pressure at a point on the target surface can be expressed as (the contribution of the part without film to the transmission field):

ω为入射波的角频率，k为入射波的波矢。ρ_air为空气的密度，

是直角坐标系下源点(x_S,y_S,z_S)和目标点(x,y,z)之间的距离，Ω₁表示无薄膜部分(被裁剪部分)的积分区间。in,

ω is the angular frequency of the incident wave, and k is the wave vector of the incident wave. ρ _air is the density of air,

is the distance between the source point (x _S , y _S , z _S ) and the target point (x, y, z) in the Cartesian coordinate system, Ω ₁ represents the integral interval of the film-free part (the clipped part).

For the part with the thin film, since the thin film has a 180-degree phase change to the incident sound wave, which is equivalent to an increase of 180 degrees in the initial phase of this part, it is expressed in the formula as:

Among them, Ω ₂ represents the integral interval with the thin film portion.

In the cylindrical coordinate system, the following are similar:

是柱坐标系下源点(r_S,θ_S,z_S)和目标点(r,θ,z)之间的距离。in,

is the distance between the source point (r _S , θ _S , z _S ) and the target point (r, θ, z) in the cylindrical coordinate system.

Optionally, when the acoustic wave plane transmitted by the trimmed phase modulation film is focused on the focal point, trimming the phase modulation film includes:

The phase control film is cut into a symmetrically distributed strip structure, as shown in Figure 2, the width l _n of the nth line to the symmetry center from the symmetry center satisfies:

Among them, f _c is the designed focal length, λ is the wavelength of the sound wave, and N is the number of bus bars on one side of the strip structure.

As shown in FIG. 2 , according to the embodiment of the present invention, the main body is composed of a film to be cut 1 and a cutting manner 2 . Cut the film according to the method shown in FIG. 2 . Further, for the strip structure, the specific integral interval of the transmission field is substituted into the formula, and after simplification, we can obtain the following expression of the sound pressure distribution after transmission:

式中等号左边的π表示有膜和没膜部分相差180度的初相位，所以令等号左边整体等于π的话，那么相邻源点到焦点的相位差就刚好为2π，这样的场就完全叠加而没有抵消的部分。4 is a schematic diagram of the acoustic wave focusing path provided by the present invention, as shown in FIG. 4 , the black part (uncropped part) in the figure represents an initial phase of 180 degrees, and the blank part (cropped part) represents an initial phase of 0. According to the principle of phase constructiveness, the path difference between two adjacent source points to the focal point should be half the wavelength, that is,

The π on the left side of the equal sign in the formula represents the initial phase difference of 180 degrees between the part with and without the film, so if the whole left side of the equal sign is equal to π, then the phase difference between the adjacent source point and the focal point is exactly 2π, and such a field is completely The parts that are superimposed without offsetting.

所以条纹宽度可以表示为：The width l _n of the bar pattern has been marked in the figure, n represents the number of lines to the center, f _c is the designed focal length, and λ is the wavelength of the sound wave that needs to be adjusted. Since l ₀ =0, we can get

So the stripe width can be expressed as:

Specifically, the larger the maximum value N of n, the stronger the focus intensity and the larger the corresponding entire image area. The N designed in FIG. 2 is illustrated by taking 6 as an example. f _c is the designed focal length, which can be specified according to requirements, then l _n will also change accordingly.

Figure 5 and Figure 6 are the simulation and experimental test results of the specific focusing effect respectively. The plane acoustic wave is incident on the surface of the patterned device, and the acoustic wave incident on the shadow part (uncropped part) of the device undergoes a 180-degree phase change. The phase change of the blank portion (cropped portion) does not occur. Each point in the plane interferes and superimposes each other as sub sound sources, and finally gathers at the focal point of the design. From the intensity distributions in Figures 5 and 6, we can see that there is an obvious bright spot in the middle, which is the designed focus, so the experimental and simulation results are in good agreement.

5 and 6, it can be seen that after the phase control film is cut into a strip structure, the transmitted acoustic wave will focus the plane on the focal point, which shows that the film-based cutting method provided by the present invention can make the acoustic wave plane focus.

Optionally, when the acoustic wave transmitted by the trimmed phase control film is spatially focused on the focal point, trimming the phase control film includes:

The phase control film is cut into a symmetrically distributed ring structure, and the ring radius rn of the _nth ring line satisfies:

Among them, f _c is the designed focal length, λ is the wavelength of the acoustic wave, and N is the total number of loop lines of the annular structure.

相对于条形只在一个方向上聚焦，该环形结构在两个维度都有聚焦的效果。Fig. 7 is a schematic diagram of the design of the annular focusing pattern, which is similar to the principle of the strip structure. Correspondingly, in Fig. 7, 1 represents the film to be cut, and 2 represents the cutting method. Referring to the above theoretical analysis of the strip structure, in the annular structure, the nth The ring radius r _n of the ring bar satisfies

In contrast to bars that focus only in one direction, the ring structure has a focusing effect in both dimensions.

It should be noted that, since the principle of focusing sound waves is the same between the strip structure and the ring structure provided by the present invention, the same symbol n can be used to refer to the line number of the strip structure or the ring line number of the ring structure, and N refers to the strip. The total number of lines in the shape structure or the total number of loops in the loop structure.

Fig. 8 and Fig. 9 are simulation diagrams of the focusing effect corresponding to the annular structure, Fig. 8 is the intensity distribution of the xy section, and Fig. 9 is the intensity distribution of the xz plane. It can be seen that most of the energy is concentrated at the central focal point, and is focused on both the xy and xz planes.

8 and 9, it can be seen that after the phase control film is cut into a ring structure, the transmitted acoustic waves are spatially focused to the focal point, indicating that the film-based cutting method provided by the present invention can make the acoustic waves spatially focused.

Figure 10 is the simulated focus center energy enhancement factor (represented in dB). The legend in Figure 10 shows that the triangle and square represent the case where the cropping pattern is a strip and ring structure, respectively. It can be seen from Figure 10 that the energy at the focus center varies with the number of stripes ( or the number of loops) increases. Their laws are similar, and the energy enhancement multiples are all positively correlated with the number of stripes, but the enhancement multiples of the ring structure are larger.

The invention realizes the passive regulation of sound waves by cutting the film that can change the transmission phase by 180 degrees into a specific pattern. For example, the film is cut into a stripe pattern (Figure 3), which can be used to focus sound waves perpendicular to the stripe direction. If the film is cut into a ring pattern (Figure 7), which can be used to focus in-plane perpendicular to the direction of sound propagation, the corresponding focus intensity will be stronger.

Optionally, the phase control film can be cut into a Fermat spiral pattern, so that the acoustic wave transmitted through the cut phase control film generates a stably propagated acoustic vortex.

Specifically, as shown in FIG. 11 , according to the embodiment of the present invention, the main body is composed of a film 1 to be cut and a cutting method 2 . The film is cut according to the pattern shown in Figure 11 to obtain a Fermat spiral pattern. According to the principle that the phase superposition is a sharp change in the phase of the center superposition field from 0 to 360 degrees, the Fermat spiral pattern is selected. The Fermat spiral pattern includes two spirals, and the expressions of the two spirals satisfy:

Among them, the above formula is a polar coordinate representation method, m is a linear coefficient, which determines the size of the pattern, and this parameter can be changed according to the wavelength that needs to be adjusted to suit the wavelength. r ₁ and r ₂ are the polar diameters of the two spirals, respectively, and θ ₁ and θ ₂ are the polar angles of the two spirals, respectively.

Optionally, when m=9.1, stable acoustic vortices can be generated after the acoustic waves of 11 mm to 17 mm are transmitted through the tailored phase control film. When m is other values, there will be similar effects, and m mainly affects the size of the entire pattern and the corresponding wavelength. The modulation wavelength and pattern thread pitch are usually in the same order of magnitude.

As shown in FIG. 12 , the shaded part (uncropped part) in the figure represents that the initial phase is 180 degrees, and the blank part (cropped part) represents that the initial phase is 0. Specifically, a 180-degree phase change occurs for the sound wave incident on the shadow portion, and no phase change occurs for the sound wave incident on the blank portion. Each point in the plane interferes and superimposes each other as sub sound sources, and finally forms a stable propagating vortex in the transmission field.

Specifically, referring to the transmission field sound pressure calculation formula given in Fig. 2, the Fermat spiral pattern of the present application, by substituting the integral interval, can obtain the sound pressure of the point on the transmitted acoustic wave target surface as:

Among them, R represents the maximum radius of the Fermat spiral pattern (the maximum radius of the pattern shown in Figure 2 or Figure 3), and _PF represents the contribution of the clipped part to the sound pressure. In one example, R may be set to 5 cm.

Figure 13 is the phase diagram of the simulation and experimental test of the vortex field generated specifically, the plane shown is the xy plane, the plane acoustic wave is normally incident on the surface of the patterned device, and the acoustic wave incident on the shadow part (uncropped part) of the device occurs 180 The phase change of degrees, the incident to the blank part (the clipped part) does not change the phase. Each point in the plane interferes with each other as sub-sources, and finally forms a vortex behind the device. From the phase field in Figure 13, we can see that the phase distribution of the entire plane varies from -180 degrees to 180 degrees at the center, and the experimental results are in good agreement with the simulation results.

Fig. 14 is the simulation and experimental test intensity map of the vortex field generated specifically, the plane shown is the xy plane, the plane acoustic wave is normally incident on the surface of the patterned device, and the acoustic wave incident on the shadow part (uncropped part) of the device occurs 180 The phase change of degrees, the incident to the blank part (the clipped part) does not change the phase. Each point in the plane interferes with each other as sub-sources, and finally forms a vortex behind the device. From the intensity field in Figure 14, we can see that the intensity at the center of the entire plane is extremely weak, almost zero, which proves the existence of a phase singularity point. Strength does not exist. At the same time, such an intensity distribution field can be used for particle rotation, manipulation, etc.

Figure 15 is the simulated phase diagram of the generated vortex field as a function of distance. The plane shown is the xy plane, and the situation at 4 distances z is simulated respectively. At these distances, a perfect vortex is formed, and the entire plane is The phase distribution varies from -180 degrees to 180 degrees at the center. From the phase field in Figure 15, we can see that as the distance z increases, the entire phase field begins to rotate counterclockwise (at a very small distance, the vortex is still unstable), which proves such a vortex field. Acoustic vortices can be generated by sound waves transmitted through the tailoring pattern within a certain distance.

Figure 16 is a graph of the simulated intensity of the generated vortex field as a function of distance. The displayed plane is the xy plane. The situations at four distances z are simulated respectively, and perfect vortices are formed at these distances. From the phase field in Figure 15, we can see that with the increase of the distance z, the entire intensity field remains almost unchanged (the vortex is not stable at a very small distance), and the central field intensity is all 0, which proves that the transmitted Sound waves form such a vortex field within a certain distance.

It can be seen from Fig. 13-Fig. 16 that a stable acoustic vortex can be formed based on the thin film and tailoring technology provided by the present invention, and an acoustic vortex can be formed within a certain distance of transmission, and the application range is wider; and the obtained acoustic vortex intensity efficiency high, the loss is small. Such acoustic vortices can be specifically used in noise isolation, acoustic communication, particle manipulation, and the like.

Optionally, the phase control film is cut into a quasi-periodic pattern of a Penrose lattice, so that the acoustic wave passing through the cut phase control film forms a super-oscillation phenomenon, thereby generating a subwavelength focal spot.

Among them, the length of the Rayleigh limit is 0.5 times the wavelength (based on the full width at half maximum), which means that the minimum length that can be resolved by the prior art is 0.5 times the wavelength. The goal of subwavelength resolution is to generate a focal spot whose full width at half maximum is lower than the Rayleigh limit length.

Optionally, the quasi-periodic pattern of the Penrose lattice is composed of two kinds of rhombus, and the acute angles of the two kinds of rhombus are 36 degrees and 72 degrees respectively, and the two kinds of rhombus are assembled into a quasi-periodic pattern similar to a pentagon. On the plane of the phase control film, the cut-out circular holes are located on the vertices of the two types of rhombus.

Optionally, the radius of the circular holes is determined according to the size of the pattern, so that the circular holes are as large as possible without interfering with each other, and the diameter of the circular holes and the average spacing of the circular holes are in an order of magnitude with the regulated sound wave wavelength.

17 is a schematic diagram of a quasi-periodic pattern of cutting the phase control film into a Penrose lattice provided by the present invention. As shown in FIG. 17 , according to the embodiment of the present invention, the main body is composed of a film 1 to be cut and a cutting method 2 . The film is cut according to the method shown in Fig. 17. When the plane acoustic wave is incident on the surface of the cut film, the corresponding transmission field distribution can be calculated according to the Rayleigh-Sommerfeld diffraction formula. The shaded part in Figure 17 represents that the initial phase of the transmitted acoustic wave is 180 degrees, and the blank part represents that the initial phase of the acoustic wave is 0.

As shown in FIG. 17 , the pattern outlined by the dotted line in the figure is a quasi-periodic pattern similar to the Penrose lattice. The pattern is made up of two kinds of rhombus (acute angles are 36 degrees and 72 degrees respectively), and a plane is covered with this quasi-periodic pattern similar to a pentagon (the specific size depends on the period), and the cut circular hole is located in the on the vertices of the rhombus. The radius of the round hole is determined according to the size of the pattern, so that the round hole is as large as possible without interfering with each other. The hole diameter and the average spacing of the holes are also in an order of magnitude with the regulated wavelength.

In a specific example, the diameter of the circular hole can be set to be 4 mm, the side length of the rhombus can be set to be 16 mm, and the wavelength of the adjusted sound wave can be set to be 11 mm to 17 mm.

A simple example of a superoscillating function is shown below:

f(x)= _∑an cos(2πnx)

The formula represents the superposition of cosine functions of some different spatial frequency components, f(x) represents the superoscillation function, x represents the position in one direction, and an represents the strength of the _nth component in the function, or the contribution to the total function. By selecting the value of an appropriately, a higher frequency (faster vibration) component can _be obtained by the final superposition. The value of a _n corresponds to the contribution of each part, and the contribution of points at different positions on the cut film pattern to the target focal spot is determined by their distance and direction to the focal spot, so adjusting the distribution of the film pattern can form a specific a _n Distribution. The diffraction superposition of the Penrose lattice on the transmission field just satisfies a similar relationship, which can be superimposed to generate higher frequency components. By generating higher frequency components, the minimum full width at half maximum of the focal spot can be limited by this high frequency component, so that the full width at half maximum of the focal spot is smaller than the Rayleigh criterion based on the incident frequency.

Fig. 18 is the simulation intensity diagram of the superoscillating sound field distribution generated specifically, the plane shown is the xy plane, the plane acoustic wave is normally incident on the surface of the patterned device, and the acoustic wave incident on the shadow part (uncropped part) of the device occurs 180 degrees The phase changes, and the incident to the blank portion (the clipped portion) does not change the phase. Each point in the plane interferes with each other as sub-sources, and finally forms a vortex behind the device. From the phase field in Figure 18, we can see that the entire plane forms a five-axis symmetric pattern, and at the very center, there is a focal spot with a weaker intensity, which is the super-oscillation subwavelength focal spot formed here.

FIG. 19 is a simulated intensity map of the central portion taken from FIG. 18 and an experimental test intensity map of the corresponding region. The plane shown is the xy plane. From this figure, we can see that the experimental results are in good agreement with the simulation, and there is a weak focal spot in the center, which is the super-oscillation subwavelength focal spot, that is, the transmitted The subwavelength focal spot is located at the very center of the flat acoustic field.

Further, Fig. 20 shows two intensity distribution diagrams passing through the center of the circle taken from the simulation and experimental distributions of Fig. 18. From the intensity distribution curve, we can more clearly see that there is a small peak between the two intensity peaks, and this The small peaks represent the focal spots formed by the superoscillation. It can be seen from Fig. 20 that the experimental result of the half-height half-width of the small peak formed by the superoscillation in the center of the transmission area is: 4.8mm, and the simulation result is: 3.5mm, which shows that the focal spot in the center of the transmitted acoustic wave obtained by the cutting pattern of the present invention is different. The full width at half maximum is less than the Rayleigh criterion (7.3mm, which is half of the wavelength of the regulated acoustic wave), so a focal spot with a subwavelength width is formed, which is used for subwavelength acoustic scanning imaging, which can greatly improve the imaging resolution.

Figure 21 is the simulation intensity diagram of the generated sound field distribution with distance, the plane shown is the xy plane, and four distances z (z ₁ =28mm, z ₂ =31mm, z ₃ =32mm, z ₄ = 40mm.), ideal superoscillations are formed at these distances. We can see that as the distance increases, the intensity of the central focal spot first weakens and then increases, and the width of the focal spot also decreases first and then increases. It can be seen that within a certain range, the sound waves of the trimmed phase control film shown in Figure 17 have the same The super-oscillation phenomenon is shown, indicating that the cutting technology provided by the present invention can achieve sub-wavelength resolution in a large range of far-field distances, and can generate focal spots with sub-wavelength widths.

Figure 22 more clearly shows the relationship between focal spot intensity and full width at half maximum with distance. We can see that subwavelength focal spots can be formed between 24 and 40 mm, and the full width at half maximum of the focal spot is smaller than Rayleigh. Criterion, that is, the realization of subwavelength super-resolution in the far-field and a large range of distances. Correspondingly, the time when the focal spot is the smallest is also the time when the intensity is the smallest, which is also in line with the principle of super-oscillation. In practical applications, it is necessary to increase the power of the sound source accordingly to increase the intensity of the focal spot.

The invention realizes sub-wavelength resolution of far field and can be used for acoustic scanning imaging. The resulting subwavelength focal spot full width at half maximum is about 0.25 times the wavelength. It means that the length resolution is doubled, and from the perspective of the entire area, the imaging accuracy limit can be 4 times that of conventional methods.

To sum up, the present invention utilizes the joint action of two regions with an initial phase difference of 180 degrees, so that the area of the film can be reduced. The invention is based on the full transmission structure, utilizes the energy of the entire plane, and has a higher energy utilization rate. Moreover, the present invention is a passive device, and has great advantages in energy consumption, volume and portability.

Optionally, determining the phase control film includes: uniformly mixing any metal particles or non-metallic particles with a density greater than that of the fiber material and any polymer material or soft material solution with a modulus smaller than the particles to obtain a mixed solution; using the mixed solution as a raw material, The electrospinning technology is used to obtain electrospinning fibers with particles, and then the electrospinning fibers are stacked to form an electrospinning film, and the electrospinning film is the phase regulating film.

The present invention can prepare electrospinning films with different diameters and distributions through the mixed solution obtained by mixing different particles with different polymer materials or soft material solutions. Due to the vibration of the particles in the film, there is a 180-degree phase for sound waves in different frequency ranges. Change, among them, the more particles, the lower the response frequency; the thicker the film (in the case of less than 1 mm), the lower the response frequency.

Optionally, any metallic particles or non-metallic particles having a density greater than that of the fiber material are copper, iron, gold, silver, platinum, cobalt, nickel, lead and their corresponding oxides.

Optionally, the area of the electrospinning film is related to the movement range of the injector used for spinning in a plane perpendicular to the spinning direction, and the larger the movement range, the larger the area of the electrospinning film. The thickness of the electrospinning film is related to the spinning time, and the longer the spinning time is, the thicker the electrospinning film is. The diameter of the electrospun fibers is related to the spinning voltage, and the larger the spinning voltage, the smaller the diameter of the electrospun fibers. The number of particles in the electrospinning film is related to the mass ratio of the particles to the polymer material or soft material solution. The larger the mass ratio, the more the number of particles contained in the electrospinning film.

The phase control film provided by the present invention is described in detail below in conjunction with specific embodiments:

Example 1:

The copper particles with a diameter of 0.5 microns to 1.5 microns are evenly mixed with the polyvinyl alcohol (model: PVA124) aqueous solution. The concentration of the polyvinyl alcohol aqueous solution used is 7% to 12%, and the mass ratio of copper particles and polyvinyl alcohol is based on actual Specific adjustments are required.

Wherein, the concentration of the polyvinyl alcohol solution in the embodiments of the present invention can also be other concentrations with relatively stable dissolution.

In the examples of the present invention, copper particles are given: polyvinyl alcohol is 1:1, 1:2, 1:4, 1:8 four cases. Using the mixed solution as a raw material, electrospinning technology can be used to obtain electrospinning fibers with particles having a diameter of 0.5-1.5 microns, and the electrospinning fibers are stacked to form an electrospinning film.

After the mixed liquid of different mass ratios of copper particles and polyvinyl alcohol is prepared according to the present invention, after obtaining a uniformly mixed mixed liquid of copper particles/polyvinyl alcohol, this can be used as a raw material for electrospinning. In the embodiment of the present invention, electrospinning films with different diameters and distributions can be obtained by changing parameters such as receiving distance, spinning voltage, and bolus injection speed. Within a certain range, the larger the spinning voltage, the smaller the fiber diameter. The speed of the bolus needs to be coordinated with the speed of the spinneret (mainly the speed of the filament after the electric field force and surface tension are balanced). The recommended spinning conditions are: ambient temperature of 25 degrees Celsius, humidity of 30% to 45%, spinning voltage of 9.7kV to 11.7kV, and bolus injection rate of 0.02mL/s to 0.03mL/s. The SEM images of the surface morphology of the prepared films are shown in Figures 23 to 26. The mass ratios of copper particles and polyvinyl alcohol during the production of electrospinning films are 1:8, 1:4, 1:2, 1, respectively. :1. It can be seen from the figure that the number of particles with different concentration ratios is significantly different. Figures 27 to 30 respectively show the results of the acoustic transmission test of the films of the above ratios. We can see that they can have a 180-degree phase change in the corresponding frequency range (gray area shown in Figure 27-Figure 30), and maintain a high transmittance (greater than 80%). And as the particle fraction increases, the frequency range gradually shifts to lower frequencies, so these films cover the frequency range from 3.8kHz to 24kHz.

Example 2:

Mix lead oxide particles with a diameter of 0.5 microns to 1.5 microns and polyacrylonitrile (PAN) dimethylformamide (DMF) solution (PAN is insoluble in water, soluble in organic solvents such as DMF, etc.) The concentration of the DMF solution is 8% to 12%, and the mass ratio of lead oxide particles and polyacrylonitrile is adjusted according to actual needs.

Wherein, the concentration of the polyacrylonitrile solution in the embodiments of the present invention may also be other concentrations with relatively stable dissolution.

In the examples of the present invention, lead oxide particles are given: polyacrylonitrile is 1:1, 1:4, 1:8, 1:16 four cases. Using the mixed solution as a raw material, electrospinning technology can be used to obtain electrospinning fibers with particles having a diameter of 0.5-1.5 microns, and the electrospinning fibers are stacked to form an electrospinning film.

According to the mixed liquid of different lead oxide particles and polyacrylonitrile mass ratios prepared according to the present invention, after obtaining a uniformly mixed mixed liquid of lead oxide particles/polyacrylonitrile, this can be used as a raw material for electrospinning. In the embodiment of the present invention, electrospinning films with different diameters and distributions can be obtained by changing parameters such as receiving distance, spinning voltage, and bolus injection speed. Within a certain range, the larger the spinning voltage, the smaller the fiber diameter. The speed of the bolus needs to be coordinated with the speed of the spinneret (mainly the speed of the filament after the electric field force and surface tension are balanced). The recommended spinning conditions are: ambient temperature of 25 degrees Celsius, humidity of 30% to 45%, spinning voltage of 8.7kV to 10.7kV, and bolus injection speed of 0.03mL/s to 0.04mL/s.

It is worth pointing out that the particles and soft materials used in Example 2 can be replaced with those in Example 1. If the final film is required to be water-insoluble, a water-insoluble polymer such as polyacrylonitrile is used; if the film is required to be magnetic, magnetic particles such as ferric oxide, etc.

The thickness of the electrospinning film based on the present invention is controllable, and the longer the spinning time, the thicker the thickness; the thinnest thickness of the stable film is only 20 microns, which is 1/650 of the regulated wavelength, which is far thinner than the current level (about 1/250), making it applicable to more scenes. The shearing on the electrospinning film prepared by the present invention is very convenient, and the whole device is also very light and low in cost, which is favorable for mass production. The realization method of adjusting the acoustic wave phase by using the electrospinning film of the present invention is passive, and has advantages in energy consumption and portability.

The invention prepares the phase control film based on the electrospinning technology. The vibration of the particles in the film causes a 180-degree shift in the transmission phase of the sound wave. The acoustic response frequency of the film is mainly determined by the density and modulus ratio of spun fibers and particles, the mass ratio of total particles to fiber materials, and the thickness of the film. And these parameters can be adjusted by material ratio and spinning parameters. This thin film can be continuously manufactured in a large area, and further, this thin film can be cut into a multifunctional device by combining with the corresponding cutting technology. The shearing on this flexible film is very convenient, and the overall device is also very light and low in cost, which is favorable for mass production. This approach is also passive and has advantages in power consumption and portability.

Optionally, the film that can change the transmission phase by 180 degrees can be an electrospinning film, or any other device or material that can change the transmission phase; the part that does not change the phase is the part that is cut (cut out), It can also be any material that can completely transmit sound waves without changing the transmission phase.

Optionally, the pattern of cutting is not limited to the four schemes described in Fig. 3, Fig. 7, Fig. 11 and Fig. 17, and the above-mentioned four schemes are only the representative of the cutting pattern, and the film provided by the present invention is used for cutting and regulating transmission. The methods for distributing the sound wave field all fall within the protection scope of the present invention.

Optionally, this regulation method is applicable to fluid media, ie regulation in air or water or other fluids is applicable.

Optionally, in addition to the regulation of sound waves, this method is also fully applicable to the regulation of light waves or electromagnetic waves, and it is only necessary to replace the film with a material that can change the transmission phase of light waves.

The above are only the preferred embodiments of the present application, but the protection scope of the present application is not limited to this. Any person skilled in the art can easily think of changes or replacements within the technical scope disclosed in the present application, All should be covered within the scope of protection of this application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims (5)

1. A method for regulating and controlling sound waves based on a patterned cutting technology is characterized by comprising the following steps:

determining a phase control film, wherein the phase control film can change the phase of the sound wave transmitted by the phase control film by 180 degrees; determining a phase modulating film comprising: uniformly mixing metal particles or non-metal particles with any density larger than that of the fiber material and a high polymer material or soft material solution with any modulus smaller than that of the particles to obtain a mixed solution; taking the mixed solution as a raw material, obtaining electrostatic spinning fibers with particles by using an electrostatic spinning technology, and further forming an electrostatic spinning film by stacking the electrostatic spinning fibers, wherein the electrostatic spinning film is the phase control film;

cutting the phase control film to change the distribution of the sound wave field transmitted by the cut phase control film, and controlling the cutting pattern to focus the transmitted sound wave plane on a focal point or space on the focal point, generate stably-transmitted sound vortex or form a super-oscillation phenomenon so as to generate a sub-wavelength focal spot;

by controlling the cutting size, the wave path difference between the sound wave after passing through the cutting area and the sound wave after passing through the non-cutting area and being adjacent to the sound wave after passing through the cutting area and reaching the focus is half of the wave length of the sound wave, so that the sound wave plane after passing through the phase control film after being cut is focused on the focus or is spatially focused on the focus; the phase control film is cut into Fermat spiral patterns, so that sound waves transmitted by the cut phase control film generate stably-transmitted sound vortex, the phase control film is cut into quasi-periodic patterns of the Panos lattice, the quasi-periodic patterns of the Panos lattice are spliced by two diamonds, acute angles of the two diamonds are 36 degrees and 72 degrees respectively, the quasi-periodic patterns similar to pentagons are spliced by the two diamonds and are paved on the plane of the phase control film, and the cut round holes are positioned at the vertexes of the two diamonds, so that the sound waves passing through the cut phase control film form a super-oscillation phenomenon, and therefore, sub-wavelength focal spots are generated.

2. The method for regulating and controlling sound waves based on the patterned cutting technology, according to claim 1, wherein when the plane of the sound waves transmitted by the cut phase regulating film is focused on a focal point, the cutting of the phase regulating film comprises:

cutting the phase control film into strip-shaped structures which are symmetrically distributed, wherein the width l from the nth line of the symmetric center to the symmetric center is equal to the width l of the symmetric center_nSatisfies the following conditions:

wherein f is_cFor the designed focal length, lambda is the acoustic wavelength, and N is the number of bus bars on one side of the bar structure.

3. The method for regulating and controlling sound waves based on the patterned cutting technology, according to claim 1, wherein when the sound waves transmitted by the cut phase regulating film are focused on a focal point in space, the cutting of the phase regulating film comprises the following steps:

cutting the phase control film into a symmetrically distributed annular structure, wherein the ring radius r of the nth loop line_nSatisfies the following conditions:

wherein f is_cFor the designed focal length, λ is the acoustic wavelength, and N is the total number of loops of the annular structure.

4. The method for regulating and controlling sound waves based on the patterned cutting technology according to claim 1, wherein the Fermat spiral pattern comprises two spirals, and the expressions of the two spirals respectively satisfy:

wherein m is a linear coefficient, r₁And r₂The diameter of the poles, theta, of the two spirals, respectively₁And theta₂Respectively the polar angles of the two spirals.

5. The method for modulating sound waves based on the patterned cutting technology according to claim 4, wherein the proper m is selected so that sound waves with different wavelengths can generate stable acoustic vortex after being transmitted through the cut phase modulation film.

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