CN111613203B - Phase regulation type far-field super-resolution focusing and imaging device - Google Patents
Phase regulation type far-field super-resolution focusing and imaging device Download PDFInfo
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- CN111613203B CN111613203B CN202010488670.8A CN202010488670A CN111613203B CN 111613203 B CN111613203 B CN 111613203B CN 202010488670 A CN202010488670 A CN 202010488670A CN 111613203 B CN111613203 B CN 111613203B
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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
- G10K11/30—Sound-focusing or directing, e.g. scanning using refraction, e.g. acoustic lenses
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01N—INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES
- G01N29/00—Investigating or analysing materials by the use of ultrasonic, sonic or infrasonic waves; Visualisation of the interior of objects by transmitting ultrasonic or sonic waves through the object
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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
- G10K11/34—Sound-focusing or directing, e.g. scanning using electrical steering of transducer arrays, e.g. beam steering
- G10K11/341—Circuits therefor
- G10K11/346—Circuits therefor using phase variation
Abstract
A phase regulation type far-field super-resolution focusing and imaging device relates to a super-resolution focusing and imaging device. The acoustic metamaterial unit comprises a cylindrical side shell, an inner thin cylinder and N continuous spiral blades; the inner thin cylinder is positioned at the axis of the cylinder side shell, and a plurality of continuous spiral blades are respectively connected with the inner thin cylinder and the cylinder side shell; the N continuous helical blades have the same helix angle and are arranged at equal intervals. The phase-control type far-field super-resolution focusing and imaging device comprises a plurality of the acoustic metamaterial units, and the acoustic metamaterial units are arranged into a one-dimensional array structure. The phase regulation type far-field super-resolution focusing and imaging device not only reduces the multivariable amplitude and phase regulation to univariate phase regulation, but also simplifies and lightens the structural design.
Description
Technical Field
The present invention relates to a super-resolution focusing and imaging device.
Background
The design structure of the acoustic metamaterial is rich and diversified, so that the sound wave regulation and control technology is also developed continuously. The metamaterial structure is reasonably designed, so that sound waves can be more conveniently controlled, and the method is beneficial to development of imaging technology. Particularly in the aspect of improving the focusing resolution, the structure of the metamaterial is reasonably designed, so that the amplitude and the phase of sound waves passing through the metamaterial are controlled, and the imaging resolution can be effectively improved. The design and research of the acoustic metamaterial has positive effects and profound effects on improving super-resolution focusing and super-resolution imaging.
In the well-known conventional imaging method, the resolution of the image is difficult to break through λ/2 because of the inherent limitations imposed by the diffraction limit. The main source of diffraction limit limitation is that evanescent waves carrying detailed basic information of the object to be measured decay exponentially and rapidly in free space. At present, the technical means for realizing the acoustic super-resolution focusing comprises a slit array with deep sub-wavelength intervals, wherein the slit is perforated on a thin plate, and the acoustic diffraction limit is successfully broken through by using a microcosmic coupled wave model, but the method sacrifices the integral phase regulation and control capability to a certain extent, and two parameters of amplitude and phase are required to be regulated at the same time, so that the control is not easy. There are also metamaterial structures that utilize some negative refractive index characteristics, but due to the need to construct resonant cells, their structure is often complex and cumbersome and also limited by the loss of the material itself.
Disclosure of Invention
In order to solve the defects in the prior art method, the invention provides a phase regulation type far-field super-resolution focusing and imaging device which not only reduces the multivariable amplitude and phase regulation to single-variable phase regulation, but also simplifies and lightens the structural design.
The acoustic metamaterial unit comprises a cylindrical side shell, an inner thin cylinder and N continuous spiral blades; the inner thin cylinder is positioned at the axis of the cylinder side shell, and a plurality of continuous spiral blades are respectively connected with the inner thin cylinder and the cylinder side shell; the N continuous helical blades have the same helix angle and are arranged at equal intervals.
The phase-control type far-field super-resolution focusing and imaging device comprises a plurality of the acoustic metamaterial units, and the acoustic metamaterial units are arranged into a one-dimensional array structure.
The phase regulation type far-field super-resolution focusing and imaging device is a far-field super-resolution focusing device based on phase modulation type acoustic metamaterial, and meanwhile, the device can be used for realizing the slow wave regulation function of sound waves and realizing the super-resolution focusing and imaging function by utilizing a one-dimensional array formed by the devices.
The acoustic metamaterial unit can be manufactured through a 3D printing technology. The acoustic metamaterial unit is cylindrical and consists of a plurality of continuous spiral blades which are uniformly distributed and have the same screw pitch, an inner thin cylinder and a cylinder side shell.
The time required for the sound wave to pass through the acoustic metamaterial unit with the length L is longer than the time required for the sound wave to pass through the matrix air with the length L, so that the sound wave can be considered to have a slower sound velocity inside the acoustic metamaterial unit with the length L, namely a slow wave effect is generated. Therefore, it can be equivalent to a cylindrical uniform medium with a sound velocity lower than that of the matrix air. First, assuming that the equivalent diameter of the acoustic metamaterial unit is De, the pitch length P of the continuous helical blade in the acoustic metamaterial unit is far smaller than the wavelength lambda of sound waves 0 The equivalent refractive index n of an acoustic metamaterial unit can be defined as the ratio of the path length to its projection in the propagation direction:
then, solving the acoustic equivalent parameters described by the formula by utilizing the equivalent medium theory, and treating the acoustic metamaterial unit as uniform cylindrical medium, wherein two physical parameters n eff And ρ eff The equivalent refractive index and dynamic mass density of the acoustic metamaterial unit respectively, when the acoustic wave passes through the equivalent medium with the length of L, the acoustic wave transmission coefficient T can be expressed as:
wherein k is 0 Is the sound wave vector in the air, ρ 0 Is the air mass density. The equivalent refractive index and dynamic mass density of the acoustic metamaterial unit can be obtained according to the formula. The effective refractive index of the acoustic metamaterial unit can be further deduced according to the occurrence position of the formants
Λ in the above formula represents the resonant mode frequency value, where the parameter c 0 Is the propagation velocity of sound waves in the air; when the working frequency corresponds to the transmission spectrumAt the minimum point, the transmittance is the lowest, and the transmission coefficient is expressed as:
from the resulting minimum transmission coefficient, the dynamic mass density of the acoustic metamaterial unit can be further deduced:
in order to realize the requirements of far-field super-resolution focusing and imaging, the acoustic transmission and phase regulation of the acoustic metamaterial unit are also required to be designed. The two physical parameters are respectively equivalent refractive index and equivalent dynamic mass density through the derived formulas, and the equivalent sound velocity inside the two physical parameters can be obtained through the formulas according to the equivalent refractive index. By adjusting parameters of the acoustic metamaterial unit: the relative changes of the equivalent refractive index and the equivalent dynamic mass density in the structure are realized by the length of the acoustic metamaterial unit and the pitch of the continuous helical blade, and finally the regulation and control effect on the phase can be realized.
In the conventional acoustic focusing principle, at a specific wavelength, there is a high frequency cutoff for the spatial frequency of the focused sound field, which makes finer high frequency information unable to penetrate the focusing device, and limits further reduction of the diffraction focus. Therefore, the super diffraction limit implementation thought is that in a limited interval, in addition to the traditional focusing phase, additional multi-ring band 0-pi phase modulation is added, and higher acoustic space frequency components are modulated in a limited area, so that far-field super-resolution focusing can be realized. The phase modulation function of the super-resolution focusing system designed by the method should be divided into two parts, and the traditional focusing phase function phi lens (r) and the super diffraction phase modulation function phi so (r). According to the principle of acoustic focusing, the first part should belong to a hyperbolic phase function, which can be written as:
the super-resolution focusing is realized by modulating the high-frequency and low-frequency spatial phases in a limited space based on the traditional focusing. At the acoustic wavelength lambda 0 Here, the sound field distribution in the focal plane can be expressed as:
the above formula gives the theoretical formula for super-resolution focusing. According to the formula, the function of super-resolution focusing modulation can be obtained by a reverse design method. For super-resolution high-frequency phase modulation function phi so (r) obtaining the distribution of the modulation function by linear programming theory by adopting 0-pi binary phase function. And then searching the device units (acoustic metamaterial units) with phase delays matched with each position one by one through the obtained total phase distribution diagram, and finally arranging the device unit (acoustic metamaterial unit) array into a one-dimensional array structure according to the required phase distribution situation, thereby realizing the super-resolution focusing and subsequent imaging functions of a far field through the array structure.
Drawings
Fig. 1 is a schematic structural diagram of an acoustic metamaterial unit according to embodiment 1.
Fig. 2 is an equivalent media diagram of an acoustic metamaterial unit of example 1.
Fig. 3 is a schematic diagram of the slow acoustic modulation phase of the acoustic metamaterial unit of example 1.
Fig. 4 is a physical picture of the acoustic metamaterial unit of example 1.
Fig. 5 is a phase distribution diagram of a phase-modulated far-field super-resolution focusing and imaging device of example 2.
Fig. 6 is a sound field distribution diagram at a focal plane of far-field super-resolution focusing of the phase-modulated far-field super-resolution focusing and imaging device of example 2.
Fig. 7 is a super-resolution imaging diagram of the phase-modulated far-field super-resolution focusing and imaging device of example 2.
Detailed Description
The technical scheme of the invention is not limited to the specific embodiments listed below, and also includes any combination of the specific embodiments.
The first embodiment is as follows: the acoustic metamaterial unit comprises a cylindrical side shell, an inner thin cylinder and N continuous spiral blades;
the inner thin cylinder is positioned at the axis of the cylinder side shell, and a plurality of continuous spiral blades are respectively connected with the inner thin cylinder and the cylinder side shell; the N continuous helical blades have the same helix angle and are arranged at equal intervals.
The N continuous helical blades arranged at equal intervals in the embodiment divide the matrix (such as air) in the cylindrical acoustic metamaterial unit into N equal parts, and finally N helical channels are formed.
The second embodiment is as follows: the present embodiment differs from the first embodiment in that: n=4. Other steps and parameters are the same as in the first embodiment.
And a third specific embodiment: the present embodiment differs from the first or second embodiment in that: the pitch length of the continuous helical blade is P, the diameter of the inner thin cylinder is D, the outer diameter of the shell of the side surface of the cylinder is D, the length of the acoustic metamaterial unit is L, and L is a sub-wavelength size; and the pitch P of the continuous helical blade is much smaller than the acoustic wavelength lambda 0 . The other is the same as the first or second embodiment.
The present embodiment adjusts the parameter value of the structure: the equivalent refractive index n inside the structure is realized by means of the length L of the acoustic metamaterial unit and the pitch P of the continuous helical blade eff Equivalent density ρ eff And finally, the regulation and control action on the phase can be realized to obtain the required phase delay value.
The acoustic metamaterial unit is of a sub-wavelength size, and flexible control of the sound wave phase can be achieved through the specific and flexible sound field control method provided by the acoustic metamaterial unit.
The specific embodiment IV is as follows: the present embodiment differs from one or more of the embodiments in that: the acoustic metamaterial unit is made of a resin material. The other is the same as in one of the first to third embodiments.
Fifth embodiment: the phase-control type far-field super-resolution focusing and imaging device of the embodiment comprises a plurality of acoustic metamaterial units in the embodiment, wherein the acoustic metamaterial units are arranged in a one-dimensional array structure.
In the embodiment, each unit (acoustic metamaterial unit) of the one-dimensional array structure of the phase-control far-field super-resolution focusing and imaging device is of sub-wavelength magnitude, so that the device has the advantages of small volume, light weight, high flexibility and the like, and can replace a focusing lens in a traditional imaging system to realize the function of beam focusing. According to classical diffraction theory, a theoretical model and an optimization algorithm are provided for acoustic far-field super-resolution focusing, and the change of the mass density rho and the volume modulus k of two physical parameters in the acoustic metamaterial unit is realized by changing the pitch P of a continuous helical blade of the acoustic metamaterial unit and the length L of the acoustic metamaterial unit, so that the propagation speed of sound waves in the acoustic metamaterial unit (metamaterial) can be changed, the delay effect on the sound waves is realized, the super-resolution effect is generated on sound wave modulation according to the method, the super-resolution focusing is realized in a far field through a one-dimensional array formed by acoustic metamaterial units based on different phase delays, and further the far-field super-resolution and super-resolution imaging capabilities are verified through experiments.
Specific embodiment six: the present embodiment differs from the fifth embodiment in that: the phase modulation function of the phase-control far-field super-resolution focusing and imaging device is divided into a traditional focusing phase function phi lens (r) and super-resolution phase modulation function phi so (r) two parts; wherein the phase modulation function phi is high frequency for super resolution so (r) obtaining the distribution of the modulation function by linear programming theory by adopting 0-pi binary phase function. Other steps and parameters are the same as those of the fifth embodiment.
According to the phase regulation type far-field super-resolution focusing and imaging device, device units (acoustic metamaterial units) with phase delays matched with each position are searched one by one according to the obtained total phase distribution diagram, and finally, according to the required phase distribution situation, an acoustic metamaterial unit array is arranged into a one-dimensional array structure, and far-field super-resolution focusing is achieved through the array structure.
The acoustic metamaterial units are arranged into a one-dimensional array structure, the phase of the acoustic metamaterial units is modulated when the plane wave source sound waves pass through the phase-regulation type far-field super-resolution focusing and imaging device of the embodiment mode, and the output sound waves form focuses beyond diffraction limit. When the sound wave output by the phase-control type far-field super-resolution focusing and imaging device in the embodiment enters along the direction perpendicular to the surface of the metal template used in the experiment, the BK probe fixed in advance behind the metal template is utilized to collect the sound wave of the transmitted sound wave behind the phase-control type far-field super-resolution focusing and imaging device, and finally all collected sound signals are demodulated and finally the imaging effect is displayed through software.
Seventh embodiment: the difference between this embodiment and the fifth or sixth embodiment is that: the phase-control far-field super-resolution focusing and imaging device comprises 64 acoustic metamaterial units in one specific embodiment. Other steps and parameters are the same as those of the fifth or sixth embodiment.
Example 1
This embodiment will be described with reference to fig. 1 to 4. The acoustic metamaterial unit comprises a cylindrical side shell, an inner thin cylinder and 4 continuous spiral blades;
the inner thin cylinder is positioned at the axis of the cylinder side shell, and 4 continuous helical blades are respectively connected with the inner thin cylinder and the cylinder side shell; the 4 continuous helical blades have the same helix angle and are arranged at equal intervals between the 4 continuous helical blades.
In this embodiment, 4 continuous spiral blades are arranged at equal intervals to divide the matrix in the cylindrical acoustic metamaterial unit into 4 equal parts, and finally form 4 spiral channels for transmitting sound waves.
The acoustic metamaterial unit in the embodiment is a spiral acoustic metamaterial with the same pitch of 4 continuous spiral blades. The internal structure of the acoustic metamaterial unit can be clearly seen by means of fig. 1.
Wherein the pitch length of the continuous helical blade is P, the diameter of the inner thin cylinder is D, the outer diameter of the side shell of the cylinder is D, and the length of the acoustic metamaterial unit is L. In the simulation and experiment of the implementation, two parameters of the diameter d=4mm of the inner thin cylinder and the outer diameter d=17mm of the shell of the side surface of the cylinder are determined. The next effort is to use finite element simulation software COMSOL Multiphysics to make specific phase measurements on the acoustic metamaterial units, where the finite element simulation software tests the results of the phase delays by adjusting two parameters, namely the pitch P of the continuous helical blade and the length L of the acoustic metamaterial unit. And a phase delay library of 0-2 pi is built through a large number of simulation results. And then measuring the sample structure by using a four-microphone method, and placing the acoustic metamaterial unit into a long-wave catheter for measurement so as to test whether the acoustic metamaterial unit is matched with the simulated phase delay result or not by using an experimental method.
The result obtained after experimental verification in this embodiment is consistent with the simulation result.
First, assume that the equivalent diameter of the acoustic metamaterial unit of the present embodiment is De, and that the pitch length P of the continuous helical blade in the acoustic metamaterial unit is much smaller than the acoustic wave wavelength lambda 0 The equivalent refractive index n of an acoustic metamaterial unit can be defined as the ratio of the path length to its projection in the propagation direction:
then, solving the acoustic equivalent parameters described by the formula by utilizing the equivalent medium theory, and treating the acoustic metamaterial unit as uniform cylindrical medium, wherein two physical parameters n eff And ρ eff The equivalent refractive index and dynamic mass density of the acoustic metamaterial unit respectively, when the acoustic wave passes through the equivalent medium with the length of L, the acoustic wave transmission coefficient T can be expressed as:
wherein k is 0 Is the sound wave vector in the air, ρ 0 Is the air mass density. The equivalent refractive index and dynamic mass density of the acoustic metamaterial unit can be obtained according to the formula. The effective refractive index of the acoustic metamaterial unit can be further deduced according to the occurrence position of the formants
Λ in the above formula represents the resonant mode frequency value, where the parameter c 0 Is the propagation velocity of sound waves in the air; when the working frequency corresponds to the minimum value point of the transmission spectrum, the transmittance is the lowest, and the transmission coefficient is expressed as:
from the resulting minimum transmission coefficient, the dynamic mass density of the acoustic metamaterial unit can be further deduced:
in order to realize far-field super-resolution focusing and imaging, the acoustic transmission and phase regulation of the acoustic metamaterial unit are also required to be designed. The two physical parameters are respectively equivalent refractive index n can be obtained by the above derived formulas eff And equivalent dynamic mass density ρ eff The equivalent sound velocity c in the lens can be obtained by a formula according to the equivalent refractive index eff . If the value of the physical parameter is actually changed, the equivalent refractive index n in the structure is realized by adjusting the parameter value of the acoustic metamaterial unit structure, namely the length L of the acoustic metamaterial unit and the pitch P of the continuous helical blade eff Equivalent dynamic mass density ρ eff Can finally realize the regulation and control action on the phase to obtain the required phase delay value。
The acoustic metamaterial unit is made of a three-dimensional photo-curing resin material. The resin has white appearance and the viscosity at 25 ℃ is 280cps to 420cps; critical exposure 9mJ/cm 2 ～9.5mJ/cm 2 The method comprises the steps of carrying out a first treatment on the surface of the The tensile modulus is 2589-2695 MPa; the tensile strength is 38-56 MPa; the elongation at break is 8-12%; the notch impact strength is 32-38J/m; the heat distortion temperature is 38-50 ℃. The left side in fig. 4 shows a cross-sectional picture of the acoustic metamaterial unit after being cut, so that the internal spiral channel can be clearly seen, no impurity exists in the acoustic metamaterial unit, the structure surface is smooth, and the influence of acoustic loss is reduced. The right side in fig. 4 shows the complete acoustic metamaterial unit.
Example 2
The phase-control type far-field super-resolution focusing and imaging device comprises a plurality of acoustic metamaterial units which are arranged into a one-dimensional array structure.
The phase modulation function of the super-resolution focusing system of the present embodiment should be divided into two parts, the conventional focusing phase function phi lens (r) and super-resolution phase modulation function phi so (r). Wherein the phase modulation function phi is high frequency for super resolution so (r) obtaining the distribution of the modulation function by linear programming theory by adopting 0-pi binary phase function. The feasibility of the scheme is verified, and a traditional focusing phase function phi is designed on the assumption that the working wavelength of sound waves is 4.3kHz lens (r) as shown in FIG. 5 (a), wherein the lens radius is 500mm. Designing a group of super-resolution binary phase modulation functions phi of high-frequency phases 0-pi so (r) as shown in fig. 5 (b). The total phase distribution of the super-resolution modulation phase can be obtained by superimposing the phase values of fig. 5 (a) and 5 (b), as shown in fig. 5 (c); the total phase distribution is then discretized as shown in fig. 5 (d). The distribution condition of the phase value of each discrete position is subjected to corresponding phase modulation value by using the phase regulation type far-field super-resolution focusing and imaging device designed by the embodiment, and finally, the subsequent super-resolution focusing is realized through a one-dimensional array formed by phase regulation type far-field super-resolution focusing and imaging device units (acoustic metamaterial units)And imaging functions.
The phase delay value corresponding to the discrete phase distribution in the phase control type far-field super-resolution focusing and imaging device designed in the implementation is found according to the discrete phase distribution by using the total discrete phase distribution in fig. 5 (d). The phase regulation type far-field super-resolution focusing and imaging device matched with the total phase distribution after the dispersion is achieved by adjusting the structural parameters (P and L) of the acoustic metamaterial unit. And arranging the acoustic metamaterial units meeting the phase requirements into a one-dimensional array, scanning a field at a focal plane of the one-dimensional array through an acoustic probe to acquire data, and analyzing the acquired data through an acoustic demodulation system. The three lines shown in fig. 6 represent the sound field distribution at the focal plane under the conventional focusing simulation, the sound field distribution at the focal plane under the super-resolution focusing simulation, and the sound field distribution at the focal plane under the super-resolution focusing experiment of the present embodiment, respectively. The focusing phenomenon of the sound field is achieved by both conventional focusing and super-resolution focusing in fig. 6, except that the focal size at the focal plane is greatly different. Fwhm=0.5λ at its focal point in conventional focus; fwhm=0.326 λ at its focus under super-resolution focusing.
The experimental metal templates were engraved with the desired slit patterns (total engraving of three groups of samples, slit widths of 0.33λ,0.38λ,0.5λ, and duty cycle of 50%). The one-dimensional linearly arranged horn array is used as a plane wave source, and when the sound wave passes through the phase regulation type far-field super-resolution focusing and imaging device which is matched with the phase distribution after the adjustment of the embodiment, the phase of the sound wave is modulated by the phase regulation type far-field super-resolution focusing and imaging device, and the sound wave is output to form a focus exceeding the diffraction limit. When the sound wave output by the phase regulation type far-field super-resolution focusing and imaging device is incident along the direction vertical to the surface of a metal template used for experiments, the BK probe fixed at the rear of the metal template in advance is utilized to collect sound waves of transmission sound waves at the rear of the phase regulation type far-field super-resolution focusing and imaging device, and finally all collected sound signals are demodulated and finally the imaging effect is presented through software. Fig. 7 (a) to (c) show imaging effects of three groups of samples under conventional focusing and super-resolution focusing of the present embodiment, respectively. Each image is a physical image of the sample, an imaging image under the traditional focusing and an imaging image under the super-resolution focusing in the embodiment from left to right in sequence. From the imaging effect of the three groups of samples, it can be clearly seen that the super-resolution focusing (0.326 lambda) can clearly distinguish the distance between two adjacent slits in the three groups of samples, and the level is clear, while the slit with the slit of 0.5 lambda can only be barely distinguished under the conventional focusing (0.5 lambda), as shown in fig. 7 (c). However, since the slits in fig. 7 (a) and 7 (b) are both smaller than 0.5λ, the conventional focusing manner cannot be distinguished.
Claims (1)
1. The imaging method under the super-resolution focusing is characterized in that the imaging under the super-resolution focusing is carried out by utilizing a phase regulation type far-field super-resolution focusing and imaging device;
the phase regulation type far-field super-resolution focusing and imaging device comprises a plurality of acoustic metamaterial units which are arranged into a one-dimensional array structure;
the acoustic metamaterial unit comprises a cylindrical side shell, an inner thin cylinder and N continuous spiral blades; the inner thin cylinder is positioned at the axis of the cylinder side shell, and a plurality of continuous spiral blades are respectively connected with the inner thin cylinder and the cylinder side shell; the N continuous spiral blades have the same helix angle and are arranged at equal intervals;
the phase modulation function of the phase-control far-field super-resolution focusing and imaging device is divided into a traditional focusing phase function phi lens (r) and super-resolution phase modulation function phi so (r) two parts; wherein the phase modulation function phi is high frequency for super resolution so (r) obtaining the distribution of the modulation function by a linear programming theory by adopting a 0-pi binary phase function;
according to the working wavelength of sound wave, a traditional focusing phase function phi is designed lens (r) designing a group of binary phase modulation functions phi of super-resolution high-frequency phases 0-pi according to the radius of the lens so (r); will phi lens (r) and phi so Superposing the phase values of (r) to obtain the total phase distribution of the super-resolution modulation phase;
then discretizing the total phase distribution, carrying out corresponding phase modulation value taking on the distribution condition of the phase value of each position after discretization by using a designed phase regulation type far-field super-resolution focusing and imaging device, and finally realizing the subsequent super-resolution focusing and imaging functions by a one-dimensional array formed by phase regulation type far-field super-resolution focusing and imaging device units;
searching a phase delay value corresponding to the discrete total phase distribution in the phase regulation type far-field super-resolution focusing and imaging device according to the discrete phase distribution; the phase regulation type far-field super-resolution focusing and imaging device matched with the total phase distribution after the dispersion is achieved by adjusting the structural parameters P and L of the acoustic metamaterial unit; wherein P is the pitch of a continuous helical blade of the acoustic metamaterial unit, and L is the length of the acoustic metamaterial unit;
the method comprises the steps of arranging acoustic metamaterial units meeting phase requirements into a one-dimensional array, collecting data by sweeping a field at a focal plane of the one-dimensional array through an acoustic probe, and analyzing the collected data through an acoustic demodulation system;
carving a slit pattern by using a metal template, modulating an acoustic wave by using a phase regulation type far-field super-resolution focusing and imaging device, and outputting the acoustic wave to form a focus exceeding the diffraction limit; when the sound wave output by the phase regulation type far-field super-resolution focusing and imaging device is incident along the direction vertical to the surface of the metal template, the BK probe fixed at the rear of the metal template in advance is utilized to collect the sound wave of the transmission sound wave behind the phase regulation type far-field super-resolution focusing and imaging device, and then all the collected sound signals are demodulated and finally the imaging effect is presented through software.
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