CN108062948B - Method for regulating and controlling sound wave based on patterned cutting technology - Google Patents
Method for regulating and controlling sound wave based on patterned cutting technology Download PDFInfo
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- CN108062948B CN108062948B CN201711210888.1A CN201711210888A CN108062948B CN 108062948 B CN108062948 B CN 108062948B CN 201711210888 A CN201711210888 A CN 201711210888A CN 108062948 B CN108062948 B CN 108062948B
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- G—PHYSICS
- G10—MUSICAL INSTRUMENTS; ACOUSTICS
- G10K—SOUND-PRODUCING DEVICES; METHODS OR DEVICES FOR PROTECTING AGAINST, OR FOR DAMPING, NOISE OR OTHER ACOUSTIC WAVES IN GENERAL; ACOUSTICS NOT OTHERWISE PROVIDED FOR
- G10K11/00—Methods or devices for transmitting, conducting or directing sound in general; Methods or devices for protecting against, or for damping, noise or other acoustic waves in general
- G10K11/18—Methods or devices for transmitting, conducting or directing sound
- G10K11/26—Sound-focusing or directing, e.g. scanning
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- D—TEXTILES; PAPER
- D04—BRAIDING; LACE-MAKING; KNITTING; TRIMMINGS; NON-WOVEN FABRICS
- D04H—MAKING TEXTILE FABRICS, e.g. FROM FIBRES OR FILAMENTARY MATERIAL; FABRICS MADE BY SUCH PROCESSES OR APPARATUS, e.g. FELTS, NON-WOVEN FABRICS; COTTON-WOOL; WADDING ; NON-WOVEN FABRICS FROM STAPLE FIBRES, FILAMENTS OR YARNS, BONDED WITH AT LEAST ONE WEB-LIKE MATERIAL DURING THEIR CONSOLIDATION
- D04H1/00—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres
- D04H1/70—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres
- D04H1/72—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres the fibres being randomly arranged
- D04H1/728—Non-woven fabrics formed wholly or mainly of staple fibres or like relatively short fibres characterised by the method of forming fleeces or layers, e.g. reorientation of fibres the fibres being randomly arranged by electro-spinning
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- D—TEXTILES; PAPER
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- D06H—MARKING, INSPECTING, SEAMING OR SEVERING TEXTILE MATERIALS
- D06H7/00—Apparatus or processes for cutting, or otherwise severing, specially adapted for the cutting, or otherwise severing, of textile materials
Abstract
The invention discloses a method for regulating and controlling sound waves based on a patterned cutting technology, which comprises 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; the phase control film is cut, so that the distribution of the sound wave field transmitted by the cut phase control film is changed, the transmitted sound wave plane can be focused on a focus or a space can be focused on the focus by controlling the cutting pattern, and a stably-propagated sound vortex or a super-oscillation phenomenon is generated, so that a sub-wavelength focal spot is generated.
Description
Technical Field
The invention belongs to the technical field of sound wave regulation and control, and particularly relates to a method for regulating and controlling sound waves based on a patterned cutting technology.
Background
The regulation and control of the sound waves have important significance for noise isolation and absorption, sound communication, sound stealth, sound imaging, sound energy weapons and the like. In the existing literature, methods for regulating and controlling the sound wave to achieve the above-mentioned various functions include stacking of waveguide cavities, etching of metal plates, and the like.
The phase of the transmitted sound is changed by designing the structure of the waveguide cavity, and different phase changes at different positions in a plane perpendicular to the incident direction can be designed to regulate the distribution of the sound field. In addition, sub-wavelength imaging can be realized 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 sound back, while the etched-out part acts as a sub-source to contribute to the transmitted sound field, thereby modulating the sound wave. These are passive components and belong to planar regulating devices. For example, in the prior art, the method of stacking the waveguide cavity and etching the metal plate is respectively used to regulate and control the sound wave, so as to realize acoustic focusing, acoustic vortex and the like.
In the two modes, the thick steel plate is used as a waveguide or a hard boundary to isolate sound waves, so that the whole device is heavy and large, is difficult to process, has high cost and limits the application range of the device. And the method of stacking phase units has limited accuracy of specific effects because the volume thereof cannot be ignored. However, the method of etching a metal plate has a limited degree of freedom in design because only the etched portion is transmissive.
Disclosure of Invention
Aiming at the defects of the prior art, the invention aims to solve the problems that the conventional sound wave regulation needs a thick steel plate as a waveguide or a hard boundary to isolate sound waves, so that the whole device is heavy and large, is difficult to process and has higher cost, and the application range of the device is limited. And the method for stacking the phase units has the technical problems that the volume of the method cannot be ignored, the precision of the specific effect is limited, and the like.
In order to achieve the above object, the present invention provides a method for regulating and controlling sound waves based on a patterned clipping technique, comprising:
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; the phase control film is cut, so that the distribution of the sound wave field transmitted by the cut phase control film is changed, the transmitted sound wave plane can be focused on a focal point or a space to be focused on the focal point by controlling the cutting pattern, and a stably-propagated sound vortex or a super-oscillation phenomenon is generated, so that a sub-wavelength focal spot is generated.
Optionally, by controlling the size of the cutting, the wave path difference between the sound wave after passing through the cutting region and the sound wave after passing through the non-cutting region and being adjacent to the sound wave after passing through the cutting region to the focal point is half of the wavelength of the sound wave, so that the sound wave after passing through the cutting phase control film is focused on the focal point in a plane or in a space.
Optionally, the phase modulating film is cut into a fermat spiral pattern such that the acoustic waves transmitted through the cut phase modulating film create a stably propagating acoustic vortex.
Optionally, the phase-control film is cut into a quasi-periodic pattern of a ploris lattice, so that a super-oscillation phenomenon is formed by sound waves passing through the cut phase-control film, and a sub-wavelength focal spot is generated.
Optionally, when the acoustic wave plane transmitted by the cut phase control film is focused on a focal point, cutting the phase control film includes:
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 centernSatisfies the following conditions:
wherein f iscFor the designed focal length, lambda is the acoustic wavelength, and N is the number of bus bars on one side of the bar structure.
Optionally, when the sound wave transmitted by the cut phase control film is focused on a focal point in space, cutting the phase control film includes:
cutting the phase control film into a symmetrically distributed annular structure, wherein the ring radius r of the nth loop linenSatisfies the following conditions:
wherein f iscFor the designed focal length, λ is the acoustic wavelength, and N is the total number of loops of the annular structure.
Optionally, the fermat spiral pattern comprises two spirals, the expressions of the two spirals satisfying:
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.
Optionally, a suitable m is selected so that sound waves with different wavelengths can generate stable acoustic vortex after being transmitted by the tailored phase control film.
Alternatively, when m is 9.1, the sound wave of 11 mm-17 mm can generate stable acoustic vortex after being transmitted by the cut phase control film.
Optionally, the quasi-periodic pattern of the blosson lattice is formed by splicing two diamonds, acute angles of the two diamonds are 36 degrees and 72 degrees respectively, the quasi-periodic pattern similar to a pentagon formed by splicing the two diamonds is paved on the plane of the phase control film, and the cut round holes are located at vertexes of the two diamonds.
Optionally, determining a phase modulating film comprises: 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; and (3) taking the mixed solution as a raw material, obtaining electrostatic spinning fibers with particles by utilizing 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.
Generally, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:
1. the invention can realize the high-efficiency acoustic focusing of the sound wave after the film is transmitted by cutting the film into strip-shaped or annular patterns, and can be used for medical ultrasonic lithotripsy, acoustic positioning heating, acoustic weapons and other acoustic application occasions requiring precise control of high energy concentration.
2. According to the invention, the film is cut into the Fermat spiral pattern, so that the transmitted sound wave can generate stable sound vortex, the sound vortex can be stably transmitted within a certain distance of a transmission field, and the central intensity of the vortex is 0. The invention can realize multifunctional and self-defined regulation and control of sound waves, and the acoustic vortex obtained based on the film material can be used for noise isolation, acoustic communication, particle control and the like, so that the film and the method for obtaining the acoustic vortex by controlling the cutting pattern provided by the invention have wide application prospect.
3. According to the invention, the film is cut into the quasi-periodic pattern of the Panlos lattice, so that the sub-wavelength resolution of the sound wave of a far field is realized, and the half-maximum width of the obtained sub-wavelength focal spot is about 0.25 times of the wavelength. The method means that the length resolution is doubled, the imaging precision limit can be 4 times that of the conventional method in terms of the whole area, the wavelength used for imaging is reduced by half in one direction, and the imaging precision is doubled, namely, the precision of the imaging is doubled by using sub-wavelength imaging in two directions for a film plane, so that the imaging precision is doubled to be 4 times of the original imaging precision.
4. The size is reduced. Compared with the design of any similar function, the invention utilizes the combined action of two partial areas with 180-degree difference of initial phases, and can reduce the area of the device by half in both the x direction and the y direction, so that the total area of the film can be reduced by 3/4 (the z direction is the incident wave direction, and the xy direction is vertical to the z direction).
5. The energy utilization rate is higher. The invention is based on a full transmission structure, utilizes the energy of the whole plane and has higher energy utilization rate. The invention is a passive device, and has great advantages in energy consumption, volume and portability.
Drawings
FIG. 1 is a schematic flow chart of a method for regulating and controlling sound waves based on a patterned cutting technique according to the present invention;
FIG. 2 is a schematic diagram illustrating the calculation of the transmission integration field according to the present invention;
FIG. 3 is a schematic diagram illustrating the cutting of a focusing pattern of a stripe structure according to the present invention;
FIG. 4 is a schematic diagram of the focusing path of the acoustic wave provided by the present invention;
FIG. 5 is a simulated transmission field pattern (xz plane) for a bar structure provided by the present invention;
FIG. 6 is a transmission field diagram (xz plane) for experimental test of a stripe structure provided by the present invention;
FIG. 7 is a schematic diagram of the ring-shaped focus pattern clipping provided by the present invention;
FIG. 8 is a simulated transmission field pattern (xy plane) for a ring structure provided by the present invention;
FIG. 9 is a simulated transmission field pattern (yz plane) for a toroidal structure provided by the present invention;
FIG. 10 is a graph showing a simulation relationship of the focal point energy enhancement factor according to the present invention with the number of fringes and the number of rings N increased;
FIG. 11 is a schematic representation of a Fermat spiral pattern used in the present invention;
FIG. 12 is a schematic illustration of the acoustic vortices formed by the present invention;
FIG. 13 is a phase diagram of simulation and experimental testing of a specifically generated vortex field provided by the present invention;
FIG. 14 is a graph of simulated and experimental test intensities of a vortex field generated in accordance with embodiments of the present invention;
FIG. 15 is a simulated phase plot of the vortex field as a function of distance generated by embodiments of the present invention;
FIG. 16 is a graph of simulated intensity of a vortex field as a function of distance generated in accordance with embodiments of the present invention;
FIG. 17 is a diagram illustrating a quasi-periodic pattern for cutting a phase-adjusting film into a Panos lattice according to the present invention;
FIG. 18 is a simulated transmission field pattern (xz plane) for the Panos lattice structure provided by the present invention;
FIG. 19 is a detailed view of the simulated transmission field center of the Panlos lattice structure and the corresponding experimental test chart (xz plane) provided by the present invention;
FIG. 20 is a graph of intensity distribution over the field center sectional line of FIG. 19;
FIG. 21 is a graph of simulated intensity of a specifically generated sound field distribution as a function of distance as provided by the present invention;
FIG. 22 is a graph of focal spot intensity and full width at half maximum as a function of distance provided by the present invention;
FIG. 23 is a scanning electron micrograph of a fiber film obtained according to the method of the present invention, wherein the mass ratio of copper particles to polyvinyl alcohol provided by the present invention is 1: 8;
FIG. 24 is a scanning electron micrograph of a fibrous film according to the method of the present invention, wherein the mass ratio of copper particles to polyvinyl alcohol provided by the present invention is 1: 4;
FIG. 25 is a scanning electron micrograph of a fibrous film according to the method of the present invention, wherein the mass ratio of copper particles to polyvinyl alcohol provided by the present invention is 1: 2;
FIG. 26 is a scanning electron micrograph of a fiber film obtained according to the method of the present invention, wherein the mass ratio of copper particles to polyvinyl alcohol provided by the present invention is 1: 1;
FIG. 27 is a graph showing the results of a sound wave transmission test performed on a fiber film obtained when the mass ratio of copper particles to polyvinyl alcohol provided by the present invention is 1: 8;
FIG. 28 is a graph showing the results of a sound wave transmission test performed on a fiber film obtained when the mass ratio of copper particles to polyvinyl alcohol provided by the present invention is 1: 4;
FIG. 29 is a graph showing the results of a sound wave transmission test performed on a fiber film obtained when the mass ratio of copper particles to polyvinyl alcohol provided by the present invention is 1: 2;
fig. 30 is a graph showing the results of a sound wave transmission test performed on a fiber film obtained when the mass of copper particles and polyvinyl alcohol provided by the present invention is 1: 1.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
In response to the above deficiencies or needs in the 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 acoustic wave modulation. The film is cut into designed patterns by laser cutting or other cutting means, and sound field regulation and control of different effects of the film after transmission cutting can be realized. The flexible film is very convenient to cut, the whole device is light, the cost is low, and the flexible film is beneficial to large-scale production and manufacturing. This approach is also passive, with advantages in power consumption and portability.
Fig. 1 is a schematic flow chart of a method for regulating and controlling sound waves based on a patterned cutting technique, as shown in fig. 1, including steps S101 to S102.
S101, determining a phase control film, wherein the phase control film can change the phase of the transmitted sound wave by 180 degrees.
S102, the phase control film is cut, so that the distribution of the acoustic wave field transmitted by the cut phase control film is changed, the transmitted acoustic wave plane can be focused on a focal point or a space to be focused on the focal point by controlling the cutting pattern, and a stably-propagated acoustic vortex or a super-oscillation phenomenon is generated, so that a sub-wavelength focal spot is generated.
Specifically, when the planar acoustic wave is normally incident on the surface of the cut film, the corresponding transmission field distribution can be calculated according to the Rayleigh-Sofmeiffel diffraction formula. The formation of the transmission field is illustrated in particular by fig. 2: fig. 2, a and b, are discussed in terms of a rectangular coordinate system and a cylindrical coordinate system, respectively, and the two cases are similar, and are mainly described herein as a rectangular coordinate system. The plane where XOY is located represents a sub sound source plane, the plane where the point S is located is any one of the target transmission planes that we are interested in being parallel to the sound source plane, and P represents sound pressure. The sound pressure (including the amplitude and phase of the sound pressure) at any point of the target plane is the result of the superposition of the sub-sound waves emitted from all the source points on the sound source plane at the target point. From the rayleigh-solifife diffraction integral equation, the sound pressure at a point on the target surface can be expressed as (the portion without the thin film contributes to the transmission field):
wherein the content of the first and second substances,
ω is the angular frequency of the incident wave and k is the wavevector of the incident wave. RhoairIs the density of the air and is,
is a source point (x) under a rectangular coordinate systemS,yS,zS) And the distance, Ω, between the target point (x, y, z)1The integration interval without the thin film portion (cut portion) is shown.
For the part with the film, since the film has a 180-degree phase change to the incident sound wave, which is equivalent to the initial phase of the part is increased by 180 degrees, the expression in the formula is:
wherein omega2The integration interval with the thin film portion is shown.
In a cylindrical coordinate system, the following are similar:
wherein the content of the first and second substances,
is a source point (r) in a cylindrical coordinate systemS,θS,zS) And a target point (r, θ, z).
Optionally, when the acoustic wave plane transmitted by the cut phase control film is focused on a focal point, cutting the phase control film includes:
cutting the phase control film intoSymmetrically distributed strip-shaped structures, as shown in FIG. 2, the nth line to the centre of symmetry has a width l from the centre of symmetrynSatisfies the following conditions:
wherein f iscFor the designed focal length, λ is the acoustic wavelength, and N is the number of bus bars on one side of the bar structure.
As shown in fig. 2, according to an embodiment of the present invention, a body is composed of a film 1 to be cut and a cutting pattern 2. The film was cut according to the method of fig. 2. Further, for the strip structure, the specific integral interval of the transmission field is substituted into a formula, and the following expression of the sound pressure distribution after transmission can be obtained through simplification:
fig. 4 is a schematic diagram of the focusing path of the sound wave provided by the present invention, and is shown in fig. 4, in which the black portion (uncut portion) represents that the initial phase is 180 degrees, and the blank portion (cut portion) represents that the initial phase is 0. According to the principle of phase length, the difference of the wave path from two adjacent source points to the focal point should be half of the wavelength, i.e. the phase length
Where pi to the left of the equal sign indicates the initial phase where there is a 180 degree difference between the film and film-free parts, so if the left of the equal sign is made equal to pi as a whole, then the phase difference from the adjacent source to the focus is exactly 2 pi, and the fields overlap completely without cancellation.
Width l of the stripe patternnHas been marked in the figure, n denotes the number of lines to the centre, fcIs the designed focal length, and λ is the acoustic wavelength that needs to be adjusted and controlled correspondingly. Due to l0When the value is 0, we can obtain
The stripe width can be expressed as:
specifically, the larger the maximum value N of N is, the stronger the focusing intensity is, and the larger the corresponding entire image area is, and N designed in fig. 2 is described as an example of 6. f. ofcIs the designed focal length, which can be specified according to the requirements, then lnAnd will vary accordingly.
Fig. 5 and 6 are graphs of simulation and experimental test effects of a specific focusing effect, respectively, in which a plane acoustic wave is normally incident on a patterned device surface, a 180-degree phase change occurs in an acoustic wave incident on a shadow portion (uncut portion) of the device, and no phase change occurs in an acoustic wave incident on a blank portion (cut portion). Each point in the plane is used as a sub sound source to be mutually interfered and superposed, and finally, the point is gathered at the designed focus. From the intensity distributions of fig. 5 and 6, we can see that there is a clear bright spot in the middle, which is the focus of the design, thus showing that the experimental and simulation results are well matched.
As can be seen from fig. 5 and 6, after the phase control film is cut into the strip-shaped structure, the transmitted sound wave focuses the sound wave on the focal point, which illustrates that the sound wave can be focused on the plane by using the cutting method based on the film provided by the present invention.
Optionally, when the sound wave transmitted by the cut phase control film is focused on a focal point in space, cutting the phase control film includes:
cutting the phase control film into a symmetrically distributed annular structure, wherein the ring radius r of the nth loop linenSatisfies the following conditions:
wherein f iscFor the designed focal length, λ is the acoustic wavelength, and N is the total number of loops of the ring structure.
Fig. 7 is a schematic view of an annular focusing pattern design, similar to the principle of the bar structure, and accordingly, fig. 7 shows 1 a film to be cut, 2 a cutting manner,referring to the above-mentioned focusing theory analysis of the strip structure, in the annular structure, the ring radius r of the nth ring stripnSatisfy the requirement of
The ring structure has a focusing effect in both dimensions, as opposed to a focusing in only one direction for the strips.
It should be noted that, because the strip-shaped structure and the ring-shaped structure provided by the present invention make the principle of focusing sound waves consistent, the same symbol N may be used to refer to the serial number of the strip-shaped structure lines or the serial number of the ring-shaped structure rings, and N refers to the total number of the strip-shaped structure lines or the total number of the ring-shaped structure rings.
Fig. 8 and 9 are simulation diagrams of focusing effect of the corresponding ring structure, fig. 8 is an xy-section intensity distribution, and fig. 9 is an xz-plane intensity distribution. It can be seen that the energy is mostly concentrated at the central focus and there is focus in both the xy, xz planes.
As can be seen from fig. 8 and 9, after the phase control film is cut into the annular structure, the transmitted sound wave focuses the space on the focal point, which illustrates that the sound wave can be focused by using the cutting method based on the film provided by the present invention.
Fig. 10 is a simulated focal center energy enhancement factor (expressed in dB), and the legend in fig. 10 indicates that the triangle and the square represent the case where the cropping pattern is a stripe and a loop structure, respectively, and it can be seen from fig. 10 that the energy at the focal center increases as the number of stripes (or the number of loop stripes) increases. Their laws are similar, with the energy enhancement factor being positively correlated to the number of fringes, except that the enhancement factor is greater for the annular structure.
The film with the transmission phase changed by 180 degrees is cut into specific patterns, so that the passive regulation and control of the sound wave are realized. For example, cutting the film into a striped pattern (fig. 3) can be used to focus the acoustic waves perpendicular to the stripe direction. If the film is cut into a circular pattern (fig. 7), which can be used to focus in-plane perpendicular to the direction of sound propagation, the corresponding focal intensity will be stronger.
Alternatively, the phase modulating film may be cut into a fermat spiral pattern such that the acoustic waves transmitted through the cut phase modulating film create a stably propagating acoustic vortex.
Specifically, as shown in fig. 11, according to the embodiment of the present invention, the body is composed of a film 1 to be cut and a cutting pattern 2. And cutting the film according to the pattern of fig. 11 to obtain a fermat spiral pattern, wherein the fermat spiral pattern is selected according to the principle that the phase superposition is that the phase of the central superposition field is changed violently from 0 to 360 degrees. The fermat spiral pattern comprises two spirals, the expressions of which satisfy:
the above formula is a polar coordinate representation method, m is a linear coefficient, the size of the pattern is determined, and the parameter can be changed according to the wavelength required to be adjusted so as to adapt to the wavelength. r is1And r2The diameter of the poles, theta, of the two spirals, respectively1And theta2Respectively the polar angles of the two spirals.
Alternatively, when m is 9.1, the sound wave of 11 mm-17 mm can generate stable acoustic vortex after being transmitted by the cut phase control film. Similar effects can be obtained when m is other values, and m mainly affects the size of the whole pattern and the corresponding wavelength. The wavelength of the modulation and the pitch of the pattern threads are typically on the order of one.
As shown in fig. 12, the hatched portion (uncut portion) represents 180 degrees in the initial phase, and the blank portion (cut portion) represents 0 in the initial phase. Specifically, the phase of the acoustic wave incident on the hatched portion is changed by 180 degrees, and the phase of the acoustic wave incident on the blank portion is not changed. Each point in the plane is used as a sub sound source to be mutually interfered and superposed, and finally, a vortex which is stably transmitted is formed in a 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 integration interval, can obtain the sound pressure of the point on the transmitted sound wave target surface as:
wherein R represents the maximum radius of the Fermat spiral pattern (e.g., the maximum radius of the pattern shown in FIG. 2 or FIG. 3), PFRepresenting the contribution of the clipped part to the sound pressure. In one example, R may be set to 5 centimeters.
Fig. 13 is a phase diagram of simulation and experimental test of a specifically generated vortex field, the plane shown is an xy plane, a planar acoustic wave is normally incident on the patterned device surface, a 180-degree phase change occurs in an acoustic wave incident on a shadow portion (uncut portion) of the device, and no phase change occurs in an incident on a blank portion (cut portion). Each point in the plane is used as a sub-sound source to be mutually interfered and superposed, and finally, a vortex is formed behind the device. From the phase field of fig. 13 we can see that the whole plane phase distribution varies from-180 degrees to 180 degrees at the center, and the experimental results and the simulation results agree well.
Fig. 14 is a graph of simulated and experimentally tested intensity of a specifically generated vortex field, the plane shown being the xy plane, with a planar acoustic wave normally incident on the patterned device surface, with a 180 degree phase change of the acoustic wave incident on the shadow portion (uncut portion) of the device, and no phase change incident on the blank portion (cut portion). Each point in the plane is used as a sub-sound source to be mutually interfered and superposed, and finally, a vortex is formed behind the device. From the intensity field of fig. 14 we can see that the intensity is very weak, almost 0, at the center of the whole plane, and the side demonstrates the existence of a phase singularity, i.e. a point where the phase changes dramatically at the center, where the field intensity is absent. Meanwhile, the intensity distribution field can be used for particle rotation, manipulation and the like.
Fig. 15 is a simulated phase diagram of a specific generated vortex field as a function of distance, the plane shown is an xy plane, and the conditions at 4 distances z, at which perfect vortex is formed, are simulated, and the phase distribution of the whole plane is changed from-180 degrees to 180 degrees at the center. From the phase field of fig. 15, we can see that as the distance z increases, the whole phase field starts to rotate counterclockwise (at a very small distance, the vortex is not stable yet), which proves such a vortex field, and at the same time, it shows that the acoustic wave transmitted through the clipping pattern can generate acoustic vortex within a certain distance range.
Fig. 16 is a simulated intensity plot of a specifically generated vortex field as a function of distance, the plane shown being the xy plane, simulating the case at 4 distances z, respectively, at which perfect vortices are formed. From the phase field of fig. 15, it can be seen that the whole intensity field is almost constant (at a very small distance, the vortex is not stable) with the increase of the distance z, and the central field intensity is 0, which proves that the transmitted sound wave forms such a vortex field in a certain distance range.
As can be seen from fig. 13-16, stable acoustic vortices can be formed based on the film and the cutting technique provided by the present invention, and acoustic vortices can be formed within a certain transmission distance, which has a wider application range; and the obtained acoustic vortex strength is high in efficiency and low in loss. Such acoustic vortices are particularly useful in noise isolation, acoustic communication, particle manipulation, and the like.
Optionally, the phase-adjusting film is cut into a quasi-periodic pattern of a pantoea lattice, so that the sound wave passing through the cut phase-adjusting film forms a super-oscillation phenomenon, thereby generating a sub-wavelength focal spot.
The rayleigh limit is 0.5 wavelength (based on full width at half maximum), which means that the minimum length that can be resolved by the prior art is 0.5 wavelength. The goal of sub-wavelength resolution is to produce a focal spot with a full width at half maximum below the rayleigh limit length.
Optionally, the quasi-periodic pattern of the pantoea lattice is formed by splicing two diamonds, acute angles of the two diamonds are 36 degrees and 72 degrees respectively, the quasi-periodic pattern similar to a pentagon formed by splicing the two diamonds is paved on the plane of the phase control film, and the cut round holes are positioned at vertexes of the two diamonds.
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 mutual interference, and the aperture of the circular holes, the average distance between the circular holes and the regulated acoustic wave wavelength are in an order of magnitude.
FIG. 17 is a diagram of a quasi-periodic pattern for cutting a phase-adjusting film into a Panos lattice according to the present invention. As shown in fig. 17, according to the embodiment of the present invention, the body is composed of a film 1 to be cut and a cutting pattern 2. And cutting the film according to the method of fig. 17, and calculating the corresponding transmission field distribution according to the rayleigh-soliofil diffraction formula when the planar sound wave is normally incident on the surface of the cut film. The hatched portion in fig. 17 represents that the initial phase of the transmitted sound wave is 180 degrees, and the blank portion represents that the initial phase of the sound wave is 0.
As shown in fig. 17, the pattern outlined by the dashed lines is a quasi-periodic pattern similar to a bloos lattice. The pattern is formed by splicing two rhombuses (the acute angles are respectively 36 degrees and 72 degrees), a plane is paved by the quasi-periodic pattern similar to a pentagon (the specific size is determined according to the period), and the cut round holes are positioned at the vertexes of the rhombuses. The radius of the round hole is determined according to the size of the pattern, so that the round holes are as large as possible and do not interfere with each other. The aperture and the average distance of the circular holes are also in an order of magnitude with the regulated wavelength.
In one specific example, a circular hole with a diameter of 4 mm, a diamond with a side length of 16 mm, and a wavelength of the adjusted sound wave of 11 mm to 17 mm can be set.
A simple example of a superoscillatory function is shown below:
f(x)＝∑ancos(2πnx)
the formula represents the superposition of cosine functions of several different spatial frequency components, f (x) represents the superoscillatory function, x represents the position in one direction, anRepresenting the intensity of the nth term component in the function, or the contribution to the overall function. By appropriate selection of anCan make the final superposition even moreHigh frequency (faster vibration) components. a isnThe value of (a) 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 the distance and the direction from the points to the focal spot, so that the specific a can be formed by adjusting the distribution of the film patternnDistribution of (2). And the diffraction superposition of the Panos lattice on the transmission field just meets the similar relation, and can superpose to generate a higher-frequency component. Generating a higher frequency component may cause the minimum full width at half maximum of the focal spot to be limited to this high frequency component, thereby causing the full width at half maximum of the focal spot to be smaller than the rayleigh criterion with respect to the incident frequency.
Fig. 18 is a simulated intensity diagram of a specifically generated super-oscillating acoustic field distribution, the plane shown is an xy plane, a planar acoustic wave is normally incident on the patterned device surface, a 180-degree phase change occurs in an acoustic wave incident on a shadow portion (uncut portion) of the device, and no phase change occurs in an incident on a blank portion (cut portion). Each point in the plane is used as a sub-sound source to be mutually interfered and superposed, and finally, a vortex is formed behind the device. From the phase field of fig. 18 we can see that the whole plane forms a five-axis symmetric pattern and that at the very center there is a weak focal spot where it is the superoscillatory sub-wavelength focal spot that is formed.
Fig. 19 is a simulated intensity plot of the central portion and the corresponding area of the experimental test intensity plot taken from fig. 18. The displayed plane is an xy plane, and from the figure, it can be seen that the experimental result is well consistent with the simulation, and the centers of the xy plane and the xy plane have a weaker focal spot, namely, a super-oscillation sub-wavelength focal spot, that is, the center of the transmitted acoustic flat field is the sub-wavelength focal spot.
Further, fig. 20 is a graph of two through-center intensity profiles taken from the simulated and experimental profiles of fig. 18, from which we can more clearly see a small peak between the two intensity peaks, which represents the focal spot formed by the superoscillation. As can be seen from fig. 20, the half height and half width of the small peak formed at the center of the transmission region by the superoscillation was as follows: 4.8mm, the simulation result is: 3.5mm, which shows that the full width at half maximum of the focal spot at the center of the transmitted sound wave obtained by cutting the pattern of the invention is smaller than the Rayleigh criterion (7.3mm, which is half of the wavelength of the regulated sound wave), so that the focal spot with the sub-wavelength width is formed and is used for sub-wavelength acoustic scanning imaging, and the imaging resolution can be greatly improved.
FIG. 21 is a simulated intensity diagram of the distribution of a specifically generated sound field varying with distance, the plane shown is an xy plane, and 4 distances z (z) are simulated respectively1＝28mm，z2＝31mm,z3＝32mm，z440 mm. ) The ideal superoscillation phenomenon is formed at these distances. It can be seen that, as the distance increases, the central focal spot intensity decreases first and then increases, and the focal spot width also decreases first and then increases, so that the acoustic waves of the cut phase control film in a certain range have such a super-oscillation phenomenon, which shows that the cutting technology provided by the present invention can realize sub-wavelength resolution in a far field and a large range of distances, and can generate a focal spot with a sub-wavelength width.
Fig. 22 shows more clearly the relationship between the intensity of the focal spot and the variation of the full width at half maximum with distance, and we can see that a sub-wavelength focal spot can be formed at a distance of 24 to 40mm, and the full width at half maximum of the focal spot is smaller than the rayleigh criterion, i.e. a sub-wavelength super-resolution is achieved over a large distance in the far field. Correspondingly, when the focal spot is minimum, the focal spot is also minimum in intensity, which also conforms to the principle of superoscillation, and the practical application needs to correspondingly increase the power of the sound source so as to increase the intensity of the focal spot.
The invention realizes the sub-wavelength resolution of the far field and can be used for acoustic scanning imaging. The resulting sub-wavelength focal spot full width at half maximum is about 0.25 wavelengths. Meaning that the length resolution is doubled while the imaging accuracy limit can be 4 times that of conventional approaches, as seen over the whole area.
In conclusion, the invention utilizes the combined action of two partial areas with the initial phase difference of 180 degrees to reduce the area of the film. The invention is based on a full transmission structure, utilizes the energy of the whole plane and has higher energy utilization rate. The invention is a passive device, and has great advantages in energy consumption, volume and portability.
Optionally, determining a phase modulating film comprises: 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; and (3) taking the mixed solution as a raw material, obtaining electrostatic spinning fibers with particles by utilizing 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.
According to the invention, different particles and different high polymer materials or soft material solutions are mixed to obtain a mixed solution, so that electrostatic spinning films with different diameters and distribution can be prepared, and due to the vibration of the particles in the films, the phase of sound waves with different frequency ranges is changed by 180 degrees, wherein the more the particles are, the lower the response frequency is; the thicker the film (less than 1 mm), the lower the response frequency.
Optionally, any metallic or non-metallic particles having a density greater than the fibrous material are copper, iron, gold, silver, platinum, cobalt, nickel, lead, and their corresponding oxides.
Alternatively, the area of the electrospun film is related to the movement range of the injector for spinning in the plane perpendicular to the spinning direction, the larger the movement range, the larger the area of the electrospun film. The thickness of the electrospun film is related to the spinning time, the longer the spinning time, the thicker the thickness of the electrospun film. The diameter of the electrospun fiber is related to the spinning voltage, the larger the spinning voltage, the smaller the diameter of the electrospun fiber. The number of particles in the electrospun film is related to the mass ratio of the particles to the solution of the high molecular material or the soft material, and the larger the mass ratio, the larger the number of particles contained in the electrospun film.
The phase control film provided by the invention is described in detail by combining the following specific embodiments:
example 1:
copper particles with the diameter of 0.5 to 1.5 microns and polyvinyl alcohol (PVA 124) aqueous solution are uniformly mixed, the concentration of the adopted polyvinyl alcohol aqueous solution is 7 to 12 percent, and the mass ratio of the copper particles to the polyvinyl alcohol is specifically adjusted according to actual requirements.
The concentration of the polyvinyl alcohol solution in the embodiment of the present invention may be other concentrations with stable dissolution.
Copper particles are given in the examples of the invention: the polyvinyl alcohol is 1:1, 1:2, 1:4 and 1: 8. The mixed solution is used as a raw material, electrostatic spinning fibers with particles with the diameter of 0.5-1.5 microns can be obtained by using an electrostatic spinning technology, and electrostatic spinning films are formed by stacking the electrostatic spinning fibers.
The preferred spinning conditions are that the ambient temperature is 25 ℃, the humidity is 30% -45%, the spinning voltage is 9.7-11.7 kV, and the injection speed is 0.02m L/s-0.03 m L/s, the prepared film surface micro-topography scanning electron microscope images are shown in fig. 23-26, the mass ratio of the copper particles to the polyvinyl alcohol during the electrospinning process is respectively 1:8, 1:4, 1:2, 1:1, the film is prepared, the mass ratio of the copper particles to the polyvinyl alcohol is obviously different from the number of the copper particles to the polyvinyl alcohol in the different concentration ratio, the different concentration ratio is obviously different from the number of the particles to the polyvinyl alcohol in the film preparation, the obtained film is more than the corresponding transmission frequency range of the obtained film, the obtained film is gradually increased from the low-frequency range of the film, the transmission ratio of the obtained film is 30-30% and the obtained by changing the parameters such as the receiving distance, the spinning voltage, the injection speed and the distribution are equal to the speed of the spinning filament after the balance of the electric field force and the surface tension, and the like, and the recommended spinning conditions are that the film preparation is 1:8, 1:4, 1:2, 1:1, the film is obviously, the film is obtained by the low-30% of the film, the film.
Example 2:
lead oxide particles with the diameter of 0.5-1.5 microns and Dimethylformamide (DMF) solution (PAN is insoluble in water and soluble in organic solvent such as DMF) of Polyacrylonitrile (PAN) are uniformly mixed, the concentration of the DMF solution of the adopted polyacrylonitrile is 8-12%, and the mass ratio of the lead oxide particles to the polyacrylonitrile is specifically adjusted according to actual requirements.
The concentration of the polyacrylonitrile solution in the embodiment of the present invention may also be other concentrations with stable dissolution.
Lead oxide particles are given in the examples of the invention: polyacrylonitrile is in four cases of 1:1, 1:4, 1:8 and 1: 16. The mixed solution is used as a raw material, electrostatic spinning fibers with particles with the diameter of 0.5-1.5 microns can be obtained by using an electrostatic spinning technology, and electrostatic spinning films are formed by stacking the electrostatic spinning fibers.
In the embodiment of the invention, parameters such as receiving distance, spinning voltage, injection speed and the like are changed to obtain electrostatic spinning films with different diameters and distribution, the larger the spinning voltage is, the smaller the fiber diameter is, the injection speed needs to be coordinated with the spinning speed (mainly the speed of the filament after balancing electric field force, surface tension and the like), and the recommended spinning conditions are that the ambient temperature is 25 ℃, the humidity is 30-45%, the spinning voltage is 8.7-10.7 kV, and the injection speed is 0.03m L/s-0.04 m L/s.
It is worth noting that the particles and soft materials used in example 2 can be interchanged with those of example 1, if it is desired that the final film be water insoluble, then a water insoluble polymer such as polyacrylonitrile; if the film is required to have magnetism, magnetic particles such as ferroferric oxide and the like are used.
The electrostatic spinning film based on the invention has controllable thickness, and the longer the spinning time is, the thicker the thickness is; the thickness of the stable film is only 20 microns at the thinnest, which is the controlled wavelength 1/650, which is much thinner than the current level (about 1/250), making it applicable in more scenes. The electrostatic spinning film prepared by the invention is very convenient to cut, the whole device is very light, the cost is lower, and the large-scale production and manufacturing are facilitated. The electrostatic spinning film is adopted to realize the regulation and control of the acoustic wave phase, is passive and has advantages in energy consumption and portability.
The invention is based on the electrostatic spinning technology to manufacture the phase control film. The phase of the transmission of the sound wave is changed by 180 degrees due to the vibration of the particles in the film. The acoustic response frequency of the film is mainly determined by the density of the spun fibers and particles, the modulus ratio, the mass ratio of the total particles to the fiber material, the thickness of the film and the like. And the parameters can be adjusted through the material proportion and the spinning parameters. The film can be continuously manufactured in a large area, and further, the film can be cut by combining with a corresponding cutting technology to manufacture a multifunctional device. The flexible film is very convenient to cut, the whole device is light, the cost is low, and the flexible film is beneficial to large-scale production and manufacturing. This approach is also passive, with advantages in power consumption and portability.
Alternatively, the film capable of changing the transmission phase by 180 degrees may be an electrospun film, or may be any other device or material capable of changing the transmission phase; the portion where no phase change occurs is a portion which is cut (cut), and may be any material which can transmit sound waves completely without changing the transmission phase.
Alternatively, the cutting pattern is not limited to the four schemes described in fig. 3, fig. 7, fig. 11 and fig. 17, the above 4 schemes are only representative of the cutting pattern, and the method for adjusting and controlling the distribution of the transmitted acoustic wave field by cutting the film provided by the present invention is within the protection scope of the present invention.
Alternatively, such a regulation method is applicable to fluid media, i.e. regulation in air or water or other fluids is applicable.
Optionally, besides the regulation of the acoustic wave, the method is also completely suitable for the regulation of the light wave or the electromagnetic wave, and only the film needs to be replaced by a material capable of changing the transmission phase of the light wave.
The above description is only for the preferred embodiment of the present application, but the scope of the present application is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present application should be covered within the scope of the present application. Therefore, the protection scope of the present application shall 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 centernSatisfies the following conditions:
wherein f iscFor 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 linenSatisfies the following conditions:
wherein f iscFor 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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