Metalens-based near-surface defect super-resolution imaging system and imaging method

Abstract

Disclosed in the present invention are a metalens-based near-surface defect super-resolution imaging system and imaging method. The system comprises: a scanning unit, a signal generation unit, a defect analysis unit and a metalens structure, wherein the signal generation unit is used for applying an ultrasonic wave to an object to be subjected to detection; the metalens structure is used for transmitting the ultrasonic wave from an object plane to an image plane; the scanning unit is used for collecting a scanned image transmitted by means of the metalens structure; and the defect analysis unit is used for analyzing the scanned image, so as to determine defect information of the object to be subjected to detection. The metalens structure includes a substrate and a metalens main body fixed on the substrate, wherein the metalens main body includes a plurality of columnar bodies which are periodically arranged, each columnar body serves as a waveguide for an elastic wave, and the plurality of columnar bodies are periodically arranged on the substrate on the basis of a lattice constant. By means of the present invention, ultrahigh-resolution imaging can be realized, and a defect in an object to be subjected to detection can be accurately identified.

Description

Near-surface defect super-resolution imaging system and imaging method based on superlens Technical Field

[0001] The present invention relates to the field of ultrasonic testing technology, and more specifically, to a near-surface defect super-resolution imaging system and imaging method based on a superlens. Background Art

[0002] Ultrasonic imaging technology has been widely used in biomedical diagnostics and nondestructive testing. In nondestructive testing applications, the reliable detection of tiny defects, such as subsurface cracks and inclusions, is crucial to the structural safety of critical components in high-value applications. Therefore, high-resolution ultrasonic imaging technology capable of early defect detection is highly desirable. However, the resolution of traditional ultrasonic testing is inherently limited by the diffraction limit, which is primarily determined by the wavelength. Generally speaking, increasing the detection frequency can achieve high-resolution ultrasonic imaging. However, as the frequency increases, the ultrasonic signal attenuates rapidly, resulting in a decrease in the signal-to-noise ratio and detection range. Subwavelength ultrasonic imaging (super-resolution imaging) can achieve high detection resolution without sacrificing penetration depth. Therefore, breaking the diffraction limit and achieving ultra-high-resolution imaging of near-surface defects is widely needed and of great significance.

[0003] Existing defect detection imaging solutions primarily include signal post-processing and acoustic metamaterials. Signal post-processing achieves high-resolution imaging by post-processing acquired signals. Acoustic metamaterials utilize acoustic metamaterials, such as hyperbolic superlenses, super-oscillating lenses, and resonant metamaterials, to achieve high-resolution imaging.

[0004] Analysis shows that signal post-processing techniques are limited to processing raw data, and resolution improvements are limited by the acquired raw signal, making deep subwavelength resolution (ultra-high resolution) impossible to achieve. Existing acoustic metamaterials, such as hyperbolic superlenses, struggle to achieve acoustic imaging at deep subwavelength scales. The design of superoscillatory lenses relies on optimizing mask structures to produce fine wave interference. The energy focusing and super-resolution generated by the superoscillation phenomenon are limited to a very small region. A type of resonant superlens, consisting of a periodic pore structure, is primarily used below the acoustic frequency band and must operate in water or air. It achieves imaging of narrow slits in thin plates, which differs from non-destructive testing scenarios. Furthermore, Rajagopal et al. proposed a series of porous metamaterials based on Fabry–Pérot resonance (plastic straws and porous media as non-periodic metamaterial lenses) to achieve subwavelength imaging of subsurface defects in aluminum samples using liquid immersion testing. All of these lenses require operation in liquid, the medium through which the acoustic waves propagate. Under these conditions, the evanescent wave field enhancement occurs within the superlens rather than at the receiving end, resulting in poor resolution contrast and a low signal-to-noise ratio. Furthermore, in most cases of nondestructive testing and biomedical diagnosis, the object being tested is not allowed to be immersed in liquid.

[0005] In summary, it is necessary to improve the existing technology to break the diffraction limit and achieve ultra-high resolution imaging of near-surface defects in contact ultrasonic testing. Technical issues

[0006] The purpose of the present invention is to overcome the above-mentioned defects of the prior art and provide a near-surface defect super-resolution imaging system and imaging method based on a super-lens. Technical Solutions

[0007] According to a first aspect of the present invention, a near-surface defect super-resolution imaging system based on a metalens is provided. The system comprises: a scanning unit, a signal generating unit, a defect analysis unit, and a metalens structure. The signal generating unit is configured to apply ultrasonic waves to an object under test; the metalens structure is configured to transmit the ultrasonic waves from an object plane to an image plane; the scanning unit is configured to capture a scanned image transmitted via the metalens structure; and the defect analysis unit is configured to analyze the scanned image to determine defect information of the object under test.

[0008] The superlens structure includes a substrate and a superlens body fixed on the substrate. The superlens body includes a plurality of periodically arranged columns, and each column serves as a waveguide for elastic waves and is periodically arranged on the substrate with a lattice constant.

[0009] According to a second aspect of the present invention, a method for super-resolution imaging of near-surface defects based on a metalens is provided. The method comprises the following steps:

[0010] Applying ultrasonic waves to the object to be measured;

[0011] The ultrasonic wave is transmitted from the object plane to the image plane using a super lens structure;

[0012] collecting a scanned image transmitted through the superlens structure;

[0013] Analyzing the scanned image to determine defect information of the object being measured;

[0014] The superlens structure includes a substrate and a superlens body fixed on the substrate. The superlens body includes a plurality of periodically arranged columns, and each column serves as a waveguide for elastic waves and is periodically arranged on the substrate with a lattice constant. Beneficial effects

[0015] Compared with existing technologies, the advantages of this invention lie in its design of a metalens with a periodic columnar structure arranged on a base. This allows for flexible use according to specific requirements, is reusable, and is easy to process. Furthermore, it overcomes the metalens' dependence on fluid media (such as water and air), making it suitable for direct contact testing. It can also meet the requirements of ultrasonic imaging in the MHz frequency band, offering broader application prospects in nondestructive testing and biodiagnosis. In short, this invention can break the diffraction limit and achieve ultra-high-resolution imaging of near-surface defects in contact ultrasonic testing.

[0016] Further features and advantages of the present invention will become apparent from the following detailed description of exemplary embodiments of the present invention with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

[0018] FIG1 is a schematic diagram of a near-surface defect super-resolution imaging system based on a metalens according to one embodiment of the present invention;

[0019] FIG2 is a schematic diagram of a metalens structure according to an embodiment of the present invention;

[0020] FIG3 is a schematic diagram of sound field propagation when a lens is used according to one embodiment of the present invention;

[0021] FIG4 is a schematic diagram of wave field simulation results under Fabry–pérot resonance according to an embodiment of the present invention;

[0022] FIG5 is a schematic diagram of processing a metalens according to one embodiment of the present invention;

[0023] FIG6 is a diagram of a test block with a transverse through hole machined therein according to an embodiment of the present invention;

[0024] FIG7 is a schematic diagram of a super-resolution imaging detection system according to an embodiment of the present invention;

[0025] FIG8 is a schematic diagram of numerical simulation results of a 0.4 mm transverse through hole according to an embodiment of the present invention;

[0026] FIG9 is a schematic diagram of experimental results of detecting a 0.4 mm SDH using a sine wave according to an embodiment of the present invention;

[0027] FIG10 is a schematic diagram showing experimental results of detecting a 0.4 mm SDH using a pulse wave according to an embodiment of the present invention and numerical simulation results of a 0.4 mm SDH. Best Mode for Carrying Out the Invention

[0028] Various exemplary embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It should be noted that unless otherwise specifically stated, the relative arrangement of components and steps, numerical expressions and numerical values ​​set forth in these embodiments do not limit the scope of the present invention.

[0029] The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses.

[0030] Technologies, methods, and equipment known to ordinary technicians in the relevant art may not be discussed in detail, but where appropriate, the technologies, methods, and equipment should be considered part of the specification.

[0031] In all examples shown and discussed herein, any specific values ​​should be interpreted as merely exemplary and not limiting. Therefore, other examples of the exemplary embodiments may have different values.

[0032] It should be noted that like reference numerals and letters refer to like items in the following figures, and therefore, once an item is defined in one figure, it need not be further discussed in subsequent figures.

[0033] As shown in FIG1 , in general, the present invention provides a near-surface defect super-resolution imaging system based on a super-lens, comprising: a signal generating unit 110, a super-lens structure 120, a scanning unit 130, and a defect analysis unit 140. The signal generating unit 110 is used to apply ultrasonic waves to the object to be inspected. The super-lens structure 120 is used to transmit ultrasonic waves from the object plane to the image plane. The scanning unit 130 is used to collect the scanned image transmitted via the super-lens structure 120. The defect analysis unit 140 is used to analyze the scanned image to determine the defect information of the object to be inspected. The present invention proposes a super-lens with practical value and a super-resolution imaging system based thereon, which surpasses the traditional diffraction limit and lays the foundation for its application in biomedical diagnosis and non-destructive testing and evaluation.

[0034] Non-destructive testing has very high requirements for high-resolution ultrasonic imaging, but it is limited by the detection wavelength. Metamaterials have unprecedented acoustic properties and are a promising technology for achieving sub-wavelength resolution ultrasonic imaging beyond the diffraction limit. Considering that existing research mainly focuses on super lenses that rely on fluid media, they are suitable for acoustic frequency bands with frequencies below 10 kHz. The present invention proposes for the first time a periodic columnar structure super lens with a substrate for realizing sub-wavelength ultrasonic imaging of solid structures in the MHz domain. For example, the super lens structure includes a substrate and a super lens body fixed on the substrate. The super lens body includes a plurality of periodically arranged columns, and each column acts as a waveguide for elastic waves and is periodically arranged on the substrate with a lattice constant.

[0035] Hereinafter, embodiments of the metalens structure, resonant modes, metalens processing, and a near-surface defect super-resolution imaging system based on a metalens will be described in detail.

[0036] 1. About the design of superlens structure

[0037] Referring to the superlens structure in Figure 2, a columnar superlens fixed on a thin plate substrate is designed. The size is on the order of microns, and each column serves as a waveguide for elastic waves and is periodically arranged on the thin plate with a lattice constant A. The thin plate serves as a substrate for fixing the columnar structure. At the same time, the thin plate enables the superlens to be tightly coupled to the detection surface as a whole and can be moved flexibly. Therefore, the designed superlens is reusable and practical. In Figure 1, the period of the array is A, the side length of the column is a, the thickness of the substrate is T, and the thickness of the superlens is L. The thickness of the substrate T is much smaller than the wavelength to reduce the attenuation of the evanescent wave and also ensure that the impact on the resonant mode is minimized.

[0038] It should be understood that the square columnar structure in the super lens structure can also be replaced by other forms of periodically arranged columnar structures, such as circular columns, one-dimensionally arranged strip structures, etc. The columnar structure can be made of ceramic, organic glass or metal materials.

[0039] 2. Resonance modal analysis

[0040] When testing in transmission mode, the ultrasonic wave scattered by the defect passes through the metalens, and the maximum displacement of the lens receiving end is extracted to obtain the line scan image shown in Figure 3. The ultrasonic field inside the metalens can be expressed as:

[0041] , (1)

[0042] Where C2 and C1 are constants, The coordinate position of the sound propagation direction, is the wave vector in the superlens. Under the Fabry–pérot resonance condition, the transmission coefficient becomes 1, so the superlens transmits all waves (including evanescent waves) from the object plane to the image plane without any loss, thereby realizing subwavelength imaging. The resonant mode is mainly determined by the height of the columnar structure (for example, an integer multiple of 1 / 4 of the wavelength), which is considered to be the most important parameter in the design of the Fabry–pérot superlens. Considering the wave propagation path shown in Figure 3, one end of the lens is tightly coupled to the surface to be detected through a coupling agent, and the other end is a freely moving surface. Therefore, the boundary conditions are different from those of the superlens in fluid acoustics. Under the boundary conditions where one end is fixed and the other end is free, when the parallel momentum Meet the conditions Fabry–pérot resonance occurs when n is an integer. Correspondingly, the resonant frequency is:

[0043] (2)

[0044] in is the longitudinal wave velocity in the slender rod-shaped structure, E is the Young's modulus of the metal material, It's the density.

[0045] In order to verify the applicability of the above theory to the proposed superlens, a finite element analysis was performed, which showed the wave field of the superlens under Fabry–Pérot resonance. = 、 and The steady-state acoustic field at the resonant modes corresponds to the first, second, and third-order Fabry–Pérot resonances, respectively, as shown in Figures 4(a), 4(b), and 4(c). The acoustic field at the first-order resonant frequency with and without the base is compared in Figures 4(d) and 4(f). It can be seen that the thin plate substrate has little effect on the Fabry–Pérot resonance mode. At these resonant frequencies, standing waves form and the output surface of the metalens experiences maximum displacement, resulting in highly robust measurements with high resolution contrast.

[0046] 3. Processing of the metalens structure and the test block

[0047] Figure 5 is a schematic diagram of a metalens being processed. Figure 6 is a schematic diagram of a test block being processed with a transverse through hole.

[0048] For example, the main material of the super lens is single-crystal silicon, which is easy to obtain and can be manufactured with high precision. Moreover, the surface of the single-crystal silicon is mirror-like, with good optical backscattering performance, which is helpful for the next step of laser vibration measurement. The single-crystal silicon is cut using a precision dicing machine (ADT 7122, Advanced Dicing Technologies, Israel) with a 0.08 mm thick diamond cutting blade, with a manufacturing error of 0.01 mm. The single-crystal silicon is cut into a 100 mm × 100 mm × 10 mm 304 stainless steel block by wire electrospark cutting with a diameter of 0.4 mm and a spacing of 0.4 mm (approximately ) and two side drilled holes (SDHs) 0.1 mm away from the top surface were used as near-surface defects to be detected.

[0049] 4. Super-resolution imaging system based on super-lens structure.

[0050] Figure 7 shows a specific embodiment of a super-resolution imaging system based on transmission ultrasonic testing. The system includes a metalens structure, a laser vibrometer, a PC, an arbitrary function generator, and a power amplifier. In Figure 7, longitudinal waves are used for transmission testing of subsurface defects in a stainless steel block. The metalens is coupled to the test surface, and time-domain signals containing defect information are extracted, ultimately achieving subwavelength imaging. During the testing process, an optical platform and custom fixtures are used to ensure good coupling and levelness. A piezoelectric transducer (OLYMPUS V101-RB) with a center frequency of 0.50 MHz and a chip size of 25.4 mm is used to excite longitudinal plane waves via an arbitrary function generator (Tektronix AFG 31152). The voltage is amplified 200 times by a power amplifier (Ciprian HVA-400-A). A laser vibrometer (Polytec PSV-500HV) is used to detect the displacement field on the lens surface, performing raster scanning with a spatial resolution of 0.2 mm. The signal is averaged 200 times in the time domain to improve the signal-to-noise ratio. The maximum normalized amplitude change from each time domain signal is plotted against the measurement position on the sample position to obtain A-scan and C-scan images. Modes for Carrying Out the Invention

[0051] To further verify the effect of the present invention, numerical simulation and experimental verification were carried out. Specifically, two 0.4 mm ( ) 304 stainless steel specimens with SDHs spaced 0.4 mm apart were inspected using a sine wave with a center frequency of 0.50 MHz at the first-order resonant frequency. A-scan and C-scan imaging were performed on the specimens under inspection using sine wave signals and pulse signals, respectively. The inspection results for SDHs with a spacing of 0.4 mm are shown in Figures 8-10. Figure 8 shows the numerical simulation results for a 0.4 mm SDH, Figure 8(a) shows the wavefield distribution, and Figure 8(b) shows the A-scan results. Figure 9 shows the experimental results for inspecting a 0.4 mm SDH using a sine wave, with Figure 9(a) showing the A-scan results and Figure 9(b) showing the C-scan results. Figure 10 shows the experimental results for inspecting a 0.4 mm SDH using a pulse wave, with Figure 10(a) showing the A-scan results and Figure 10(b) showing the C-scan results. The experimental results show that when imaging internal defects using a metalens, the signal amplitude drops sharply at the defect location, allowing for effective defect identification with high detection contrast.

[0052] In summary, this paper designs a silicon-based metalens with a base based on the Fabry–Pérot resonance theory. The columnar structure is periodically arranged on a thin substrate. The frequency of Fabry–Pérot resonance is theoretically analyzed, and the wave field of the metalens in the resonant mode is numerically verified. Experimental results show that the designed 0.50 MHz columnar structure metalens achieves super-resolution ultrasound imaging with high resolution contrast ( ), which can accurately identify two sub-surface defects in stainless steel structures.

[0053] In summary, compared with the prior art, the present invention has the following advantages:

[0054] 1) The present invention designs a metalens with a periodic columnar structure arrangement having a base, which can be flexibly used according to the use requirements, has the advantages of being reusable and easy to process, and the significantly reduced feature size makes manufacturing simple.

[0055] 2) The present invention adopts a new superlens structure, which breaks the superlens' dependence on fluid media (such as water and air), can be applied to direct contact detection, and has broader application prospects in non-destructive testing and biological diagnosis.

[0056] 3) The lens structure designed in the present invention is applicable to ultrasonic testing in the MHz frequency band and is practical in non-destructive testing and biological diagnosis.

[0057] 4) This paper first analyzed the Fabry–Pérot resonance mode under elastic wave conditions, calculated the Fabry–Pérot resonance frequency theoretically, and verified the acoustic field distribution inside the metalens under the Fabry–Pérot resonance mode using numerical simulation. The experimental results demonstrate the subwavelength ultrasonic imaging capability of the metalens with a resolution of up to .

[0058] The present invention may be a system, a method and / or a computer program product. The computer program product may include a computer-readable storage medium carrying computer-readable program instructions for causing a processor to implement various aspects of the present invention.

[0059] A computer-readable storage medium can be a tangible device that can hold and store instructions used by an instruction execution device. Computer-readable storage media can be, for example, but not limited to, an electrical storage device, a magnetic storage device, an optical storage device, an electromagnetic storage device, a semiconductor storage device, or any suitable combination thereof. More specific examples (a non-exhaustive list) of computer-readable storage media include: a portable computer disk, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or flash memory), a static random access memory (SRAM), a portable compact disc read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, such as a punch card or a raised structure within a groove on which instructions are stored, and any suitable combination thereof. As used herein, a computer-readable storage medium is not to be construed as a transient signal per se, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagating through a waveguide or other transmission medium (e.g., a light pulse passing through a fiber optic cable), or an electrical signal transmitted through an electrical wire.

[0060] The computer-readable program instructions described herein can be downloaded from a computer-readable storage medium to each computing / processing device, or downloaded to an external computer or external storage device via a network, such as the Internet, a local area network, a wide area network, and / or a wireless network. The network can include copper transmission cables, fiber optic transmission, wireless transmission, routers, firewalls, switches, gateway computers, and / or edge servers. The network adapter card or network interface in each computing / processing device receives the computer-readable program instructions from the network and forwards the computer-readable program instructions to be stored in the computer-readable storage medium in each computing / processing device.

[0061] The computer program instructions for performing the operations of the present invention may be assembly instructions, instruction set architecture (ISA) instructions, machine instructions, machine-dependent instructions, microcode, firmware instructions, state setting data, or source code or object code written in any combination of one or more programming languages, including object-oriented programming languages ​​such as Smalltalk, C++, Python, and conventional procedural programming languages ​​such as "C" or similar programming languages. The computer-readable program instructions may be executed entirely on the user's computer, partially on the user's computer, as a stand-alone software package, partially on the user's computer and partially on a remote computer, or entirely on a remote computer or server. In the case of a remote computer, the remote computer may be connected to the user's computer via any type of network, including a local area network (LAN) or a wide area network (WAN), or may be connected to an external computer (e.g., via the Internet using an Internet service provider). In some embodiments, the state information of the computer-readable program instructions is used to personalize an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), so that the electronic circuit can execute the computer-readable program instructions, thereby implementing various aspects of the present invention.

[0062] Various aspects of the present invention are described herein with reference to flowcharts and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the present invention. It should be understood that each block of the flowcharts and / or block diagrams, and combinations of blocks in the flowcharts and / or block diagrams, can be implemented by computer-readable program instructions.

[0063] These computer-readable program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, or other programmable data processing device, thereby producing a machine, so that when these instructions are executed by the processor of the computer or other programmable data processing device, a device is generated that implements the functions / actions specified in one or more blocks in the flowchart and / or block diagram. These computer-readable program instructions can also be stored in a computer-readable storage medium, where these instructions cause the computer, programmable data processing device, and / or other device to operate in a specific manner. Thus, the computer-readable medium storing the instructions comprises an article of manufacture that includes instructions for implementing various aspects of the functions / actions specified in one or more blocks in the flowchart and / or block diagram.

[0064] Computer-readable program instructions may also be loaded onto a computer, other programmable data processing apparatus, or other device so that a series of operational steps are performed on the computer, other programmable data processing apparatus, or other device to produce a computer-implemented process, thereby causing the instructions executed on the computer, other programmable data processing apparatus, or other device to implement the functions / actions specified in one or more blocks in the flowchart and / or block diagram.

[0065] The flowcharts and block diagrams in the accompanying drawings show the possible implementation architecture, functions and operations of the systems, methods and computer program products according to multiple embodiments of the present invention. In this regard, each box in the flowchart or block diagram can represent a module, program segment or part of an instruction, and the module, program segment or part of the instruction contains one or more executable instructions for implementing the specified logical function. In some alternative implementations, the functions marked in the box can also occur in an order different from that marked in the accompanying drawings. For example, two consecutive boxes can actually be executed substantially in parallel, and they can sometimes be executed in the opposite order, depending on the functions involved. It should also be noted that each box in the block diagram and / or flowchart, and the combination of boxes in the block diagram and / or flowchart, can be implemented by a dedicated hardware-based system that performs the specified function or action, or can be implemented by a combination of dedicated hardware and computer instructions. It is well known to those skilled in the art that implementation by hardware, implementation by software, and implementation by a combination of software and hardware are all equivalent.

[0066] While various embodiments of the present invention have been described above, the foregoing description is intended to be illustrative, non-exhaustive, and not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is selected to best explain the principles of the embodiments, their practical applications, or technological improvements in the marketplace, or to enable others skilled in the art to understand the embodiments disclosed herein. The scope of the present invention is defined by the appended claims.

Claims

1. A near-surface defect super-resolution imaging system based on a superlens, comprising: A scanning unit, a signal generating unit, a defect analyzing unit and a super lens structure, wherein the signal generating unit is used to apply ultrasonic waves to the object to be measured, the super lens structure is used to transmit the ultrasonic waves from the object plane to the image plane, the scanning unit is used to collect the scanning image transmitted via the super lens structure, and the defect analyzing unit is used to analyze the scanning image to determine the defect information of the object to be measured; The superlens structure includes a substrate and a superlens body fixed on the substrate, and the superlens body includes a plurality of periodically arranged columns, and each column serves as a waveguide for elastic waves and is periodically arranged on the substrate with a lattice constant.

2. The system according to claim 1, characterized in that The superlens structure is a superlens based on Fabry–Pérot resonance and can be applied to contact ultrasonic detection.

3. The system according to claim 1, characterized in that The thickness of the substrate is smaller than the wavelength.

4. The system according to claim 1, characterized in that The columnar body is a square columnar body or a round columnar body, and the columnar body is made of ceramic, organic glass or metal material.

5. The system according to claim 1, characterized in that The columns are arranged on the substrate in a one-dimensional form or a two-dimensional form.

6. The system according to claim 1, characterized in that One end of the super lens structure is coupled to the surface of the object to be detected through a coupling agent, and the other end is a freely movable surface.

7. The system according to claim 6, characterized in that The ultrasonic field inside the superlens structure is expressed as: ， Where C2 and C1 are constants, is the coordinate position of the sound propagation direction, is the wave vector in the superlens. Under the boundary conditions that one end is fixed and the other end is free, when the parallel momentum Satisfy the conditions When , Fabry–pérot resonance occurs, and the resonant frequency is expressed as: in, is the longitudinal wave velocity in the columnar structure, E is the Young's modulus of the metal material, is the density, and n is an integer.

8. The system according to claim 1, characterized in that The ultrasonic wave is a continuous wave signal or a pulse signal.

9. An imaging method based on the system according to any one of claims 1 to 8, comprising the following steps: Applying ultrasonic waves to the object to be measured; The ultrasonic wave is transmitted from the object plane to the image plane using a superlens structure; Acquiring a scanned image transmitted through the superlens structure; Analyzing the scanned image to determine defect information of the object being measured; The superlens structure includes a substrate and a superlens body fixed on the substrate, and the superlens body includes a plurality of periodically arranged columns, and each column serves as a waveguide for elastic waves and is periodically arranged on the substrate with a lattice constant.

10. A computer-readable storage medium having a computer program stored thereon, wherein: When the computer program is executed by a processor, the steps of the method according to claim 9 are implemented.

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