CN108037508B - A method of realizing that sub-wavelength is differentiated based on patterning tailoring technique - Google Patents
A method of realizing that sub-wavelength is differentiated based on patterning tailoring technique Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
- G01S15/88—Sonar systems specially adapted for specific applications
- G01S15/89—Sonar systems specially adapted for specific applications for mapping or imaging
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
- G01S7/52003—Techniques for enhancing spatial resolution of targets
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- Engineering & Computer Science (AREA)
- Radar, Positioning & Navigation (AREA)
- Remote Sensing (AREA)
- Physics & Mathematics (AREA)
- Computer Networks & Wireless Communication (AREA)
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- Acoustics & Sound (AREA)
- Investigating Or Analyzing Materials By The Use Of Ultrasonic Waves (AREA)
Abstract
The invention discloses a kind of methods for realizing sub-wavelength resolution based on patterning tailoring technique, comprising: determines that phase regulates and controls film, the phase change 180 degree for the sound wave that the phase regulation film can be transmitted；Phase regulation film is cut, phase regulation film is cut into the quasi-periodic pattern of Pan Luosi lattice, so that the sound wave after the phase regulation film by the cutting forms hyperoscillating phenomenon, to generate the focal spot of sub-wavelength.The sound wave sub-wavelength that the present invention realizes far field is differentiated, and acquired sub-wavelength focal spot full width at half maximum is about 0.25 times of wavelength, it is meant that it is doubled in length resolution, and from entire area, the imaging precision limit can be 4 times of conventional means.
Description
Technical Field
The invention belongs to the technical field of sound waves, and particularly relates to a method for realizing sub-wavelength resolution based on a patterned cutting technology.
Background
Achieving sub-wavelength resolution of sound waves is of great significance to improving the resolution of sound-based imaging and detection modes (such as B-ultrasound, sonar detection, etc.). The resolution of the image is closely related to the wavelength used. Typical device imaging is limited by the rayleigh limit. The rayleigh limit is 0.5 wavelengths long (based on full width at half maximum), meaning that the minimum length that can be resolved by the prior art is 0.5 wavelengths long.
The prior art in practical application can hardly realize sub-wavelength resolution, and accordingly, the acoustic imaging quality is relatively low by using the prior art. In the existing literature, however, the way to achieve sub-wavelength resolution, i.e. break the diffraction limit, is mainly based on recovery of evanescent waves. Particularly, negative refraction materials or extremely anisotropic materials are mainly used for recovering high-frequency evanescent wave information. However, this approach is only proven in the near field and it is difficult to achieve a similar effect in the far field. Moreover, the devices involved in the literature are very bulky, heavy, difficult to machine, costly and not practical.
Disclosure of Invention
In view of the above defects or improvement requirements of the prior art, the present invention provides a method for achieving sub-wavelength resolution based on a patterned clipping technique, thereby solving the technical problems that the prior art can hardly achieve sub-wavelength resolution, the quality of the prior acoustic imaging is relatively low, and the prior art can not achieve sub-wavelength resolution within a wide range of distance in a far field.
In order to achieve the above object, the present invention provides a method for achieving sub-wavelength resolution 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; and cutting the phase control film into a quasi-periodic pattern of a Panlos lattice, so that the sound wave passing through the cut phase control film forms a super-oscillation phenomenon, and a sub-wavelength focal spot is generated.
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, 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.
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, the metal or non-metal particles of any density greater than the fibrous material are copper, iron, gold, silver, platinum, cobalt, nickel, lead, and their corresponding oxides.
Generally, compared with the prior art, the above technical solution conceived by the present invention has the following beneficial effects:
1. the acoustic sub-wavelength resolution of a far field is realized, and the full width at half maximum 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.
2. 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).
3. 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 achieving sub-wavelength resolution based on a patterned clipping technique according to the present invention;
FIG. 2 is a diagram of a quasi-periodic pattern for cutting a phase-adjusting thin film into a Panos lattice according to the present invention;
FIG. 3 is a schematic diagram illustrating the calculation of the transmission integration field according to the present invention;
FIG. 4 is a transmission field pattern (xz plane) simulated by a Panos lattice structure provided by the present invention;
FIG. 5 is a detailed view of the simulated transmission field center of the Panlos lattice structure and a corresponding experimental test chart (xz plane) provided by the invention;
FIG. 6 is a graph of intensity distribution over the central section of the field of FIG. 5;
FIG. 7 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. 8 is a graph of focal spot intensity and full width at half maximum as a function of distance provided by the present invention;
FIG. 9 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. 10 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: 4;
FIG. 11 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: 2;
FIG. 12 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. 13 is a graph showing the results of the sound wave transmission test performed on the fiber film obtained when the mass ratio of the copper particles to the polyvinyl alcohol provided by the present invention is 1: 8;
FIG. 14 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. 15 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. 16 is a graph showing the results of the sound wave transmission test performed on the fiber film obtained when the mass of the copper particles and the 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 thin films and specific patterning design rules that can change the transmission phase by 180 degrees to achieve sub-wavelength resolution. The film is cut into designed patterns by laser cutting or other cutting means, and the subwavelength resolution can be carried out on sound waves with different frequencies. The resolved sub-wavelength focal spots can be used for sub-wavelength acoustic scanning imaging, and the imaging resolution can be greatly improved. 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 achieving sub-wavelength resolution based on a patterned clipping technique according to the present invention, 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, cutting the phase control film into a quasi-periodic pattern of a Panlos lattice, so that sound waves passing through the cut phase control film form a super-oscillation phenomenon, and focal spots of sub-wavelengths are generated.
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. 2 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. 2, according to the embodiment of the present invention, a 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. 2, and calculating the corresponding transmission field distribution according to a Rayleigh-Sophia diffraction formula when the planar sound wave is normally incident to the surface of the cut film. The hatched portion in fig. 2 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. 2, 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 be such that the final superposition results in a higher frequency (faster vibration) component. 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.
Specifically, the corresponding transmission field distribution can be calculated according to the Rayleigh-Sophia diffraction formula. The formation of the transmission field is specifically shown in fig. 3: fig. 3, 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,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,is a source point (r) in a cylindrical coordinate systemS,θS,zS) And a target point (r, theta, z)And (5) separating.
Fig. 4 is a simulated intensity diagram of a specifically generated super-oscillating acoustic field distribution, wherein the plane is shown as an xy plane, a planar acoustic wave is normally incident on the patterned device surface, the acoustic wave incident on a shadow portion (uncut portion) of the device undergoes a phase change of 180 degrees, and the acoustic wave incident on a blank portion (cut portion) does not undergo a phase change. 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. 4 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 subwavelength focal spot that is formed.
Fig. 5 is a simulated intensity plot of the central portion and the corresponding area of the experimental test intensity plot taken from fig. 4. 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. 6 is a graph of two intensity profiles through the center of a circle, taken from the simulated and experimental profiles of fig. 5, 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. 6, the half-height and half-width experiment results of the small peak formed at the center of the transmission region by the superoscillation are 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. 7 is a simulated intensity diagram of the sound field distribution with distance variation, wherein the plane shown is an xy plane, and 4 distances z (z) are simulated respectively1＝28mm，z2＝31mm,z3＝32mm，z4＝40mAnd m is selected. ) 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 shown in fig. 2 have such a super-oscillation phenomenon in a certain range, which indicates 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. 8 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 the sub-wavelength focal spot can be formed at a distance of 24 to 40 mm, and the full width at half maximum of the focal spot is smaller than the rayleigh criterion, i.e. the super resolution of the sub-wavelength in a wide range of distance in the far field is realized. 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. The invention utilizes the combined action of two partial areas with the initial phase difference of 180 degrees, and can 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 is, the larger the number of particles contained in the electrospun film is.
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.
According to the mixed liquid with different mass ratios of the copper particles and the polyvinyl alcohol, which is prepared by the invention, after the uniformly mixed copper particle/polyvinyl alcohol mixed liquid is obtained, the mixed liquid can be used as a raw material for electrostatic spinning. In the embodiment of the invention, the electrostatic spinning films with different diameters and distributions can be obtained by changing parameters such as receiving distance, spinning voltage, injection speed and the like. In a certain range, the larger the spinning voltage, the smaller the fiber diameter. The speed of the bolus injection needs to be coordinated with the speed of the spinning (mainly the speed of the filament after balancing the electric field force, the surface tension and the like). The recommended spinning conditions are: the environmental temperature is 25 ℃, the humidity is 30-45%, the spinning voltage is 9.7-11.7 kV, and the injection speed is 0.02-0.03 mL/s. Scanning electron micrographs of the surface of the prepared film are shown in fig. 9 to 12, and the mass ratios of the copper particles to the polyvinyl alcohol in the process of preparing the electrostatic spinning film are respectively 1:8, 1:4, 1:2 and 1: 1. It can be seen from the figure that the different concentrations are significantly different than the number of particles. Fig. 13 to 16 are results of the acoustic wave transmission test performed on the films of the above-described proportions, respectively. We can see that they are all able to have a 180 degree phase change at the corresponding frequency range (grey areas as shown in fig. 13-16) and maintain a high transmission (greater than 80%). And as the particle fraction increases, the frequency range gradually shifts to lower frequencies, so that these films cover the frequency range from 3.8kHz to 24 kHz.
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.
According to the mixed liquid with different mass ratios of the lead oxide particles and the polyacrylonitrile, the uniformly mixed lead oxide particle/polyacrylonitrile mixed liquid is obtained, and then the mixed liquid can be used as a raw material for electrostatic spinning. In the embodiment of the invention, the electrostatic spinning films with different diameters and distributions can be obtained by changing parameters such as receiving distance, spinning voltage, injection speed and the like. In a certain range, the larger the spinning voltage, the smaller the fiber diameter. The speed of the bolus injection needs to be coordinated with the speed of the spinning (mainly the speed of the filament after balancing the electric field force, the surface tension and the like). The recommended spinning conditions are: the environmental temperature is 25 ℃, the humidity is 30-45%, the spinning voltage is 8.7-10.7 kV, and the injection speed is 0.03-0.04 mL/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 scheme depicted in fig. 2, the scheme shown in fig. 2 is only representative of a sub-wavelength resolution method of sound waves, and the method of cutting the film provided by the present invention to obtain sub-wavelength sound waves is within the 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.
It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.
Claims (4)
1. A method for realizing sub-wavelength resolution based on a patterned clipping 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;
cutting the phase control film into a quasi-periodic pattern of a Panlos lattice, so that the sound wave passing through the cut phase control film forms a super-oscillation phenomenon, and a sub-wavelength focal spot is generated;
the quasi-periodic pattern of the Panlos 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 the vertexes of the two diamonds.
2. The method for achieving sub-wavelength resolution based on the patterned cropping technology as claimed in claim 1, wherein 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 aperture of the circular holes and the average distance between the circular holes are in an order of magnitude with the regulated acoustic wave wavelength.
3. The method for achieving sub-wavelength resolution based on the patterned cutting technology according to claim 1 or 2, wherein the determining of the phase control 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.
4. The method for achieving sub-wavelength resolution based on the patterned cutting technology according to claim 3, wherein the metal particles or non-metal particles with the arbitrary density larger than the fiber material are copper, iron, gold, silver, platinum, cobalt, nickel, lead and their corresponding oxides.
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| WO2012151472A2 (en) * | 2011-05-05 | 2012-11-08 | Massachusetts Institute Of Technology | Phononic metamaterials for vibration isolation and focusing of elastic waves |
| CN105158729A (en) * | 2015-09-25 | 2015-12-16 | 南京大学 | Sound source directional sensing device with deep sub-wavelength size |
| CN105895074A (en) * | 2016-04-11 | 2016-08-24 | 南京大学 | Acoustic unidirectional hyper surface |
| EP3239973A1 (en) * | 2016-04-28 | 2017-11-01 | Eidgenössische Materialprüfungs- und Forschungsanstalt EMPA | Phononic crystal vibration isolator with inertia amplification mechanism |
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