Super-lens-based near-surface defect super-resolution imaging system and imaging method

Abstract

The invention discloses a near-surface defect super-resolution imaging system and method based on a super lens. The system comprises a scanning unit, a signal generation unit, a defect analysis unit and a super-lens structure, the signal generation unit is used for applying ultrasonic waves to a detected object, the super-lens structure is used for transmitting the ultrasonic waves from an object plane to an image plane, the scanning unit is used for collecting a scanning image transmitted by the super-lens structure, and the defect analysis unit is used for analyzing the defect of the detected object. And the defect analysis unit is used for analyzing the scanning image so as to determine defect information of the detected object. Wherein the super-lens structure comprises a substrate and a super-lens main body fixed on the substrate, the super-lens main body comprises a plurality of cylindrical objects which are periodically arranged, and each cylindrical object is used as a waveguide of elastic waves and is periodically arranged on the substrate by lattice constants. According to the invention, ultrahigh-resolution imaging can be realized, and the defect of the detected object can be accurately identified.

Description

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 diagnosis and non-destructive testing technology. In non-destructive testing applications, the detection reliability of tiny defects (such as sub-surface cracks and inclusions) is crucial to the structural safety of key components in high-value applications. Therefore, high-resolution ultrasonic imaging technology that can detect defects at an early stage is highly desired. However, the resolution of traditional ultrasonic testing is inherently limited by the diffraction limit, which is mainly determined by the wavelength. In general, high-resolution ultrasonic imaging can be obtained by increasing the detection frequency. However, as the frequency increases, the ultrasonic signal decays rapidly, resulting in a decrease in the signal-to-noise ratio and the detection range. Sub-wavelength 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] In the existing technology, defect detection imaging solutions mainly include signal post-processing technology and acoustic metamaterial technology. Signal post-processing technology achieves high-resolution imaging by post-processing the acquired signal. Acoustic metamaterial technology uses acoustic metamaterials to achieve high-resolution imaging, such as hyperbolic superlens, super-oscillation lens, resonant metamaterial, etc.

[0004] After analysis, it is found that the signal post-processing technology is limited to the processing of raw data, and the improvement of resolution is limited by the acquired raw signal, and deep subwavelength resolution (ultra-high resolution) cannot be achieved. For existing acoustic metamaterials, it is difficult for hyperbolic superlenses to perform acoustic imaging on a deep subwavelength scale. The design of superoscillation lenses relies on optimizing the mask structure to produce fine wave interference, and the energy focusing and super-resolution generated by the superoscillation phenomenon only stay in a very small area. A type of resonant superlens is a superlens composed of a periodic pore structure, which is mainly used in the frequency band below the sound wave and must work in water or air. It realizes the imaging of slits on thin plates, which is different from the non-destructive testing scenario. In addition, Rajagopal et al. proposed a series of porous structure metamaterials (plastic straws and porous media as non-periodic metamaterial lenses) based on Fabry–pérot resonance, and realized subwavelength imaging of subsurface defects of aluminum samples through liquid immersion detection. The above lenses all need to work in liquids as the medium for propagating sound waves. Under these conditions, the evanescent wave field enhancement occurs inside the superlens, not at the receiving end, which leads to poor resolution contrast and 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, the existing technology needs to be improved to break the diffraction limit and achieve ultra-high resolution imaging of near-surface defects in contact ultrasonic testing. Summary of the invention

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

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

[0008] 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.

[0009] According to a second aspect of the present invention, a method for super-resolution imaging of near-surface defects based on a superlens 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 superlens structure;

[0012] Acquiring 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, 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.

[0015] Compared with the prior art, the advantages of the present invention are that a metalens with a periodic columnar structure arrangement having a base is designed, which can be used flexibly according to the use requirements, has the advantages of being reusable and easy to process, and breaks the dependence of the metalens on fluid media (such as water and air), and can be applied to direct contact detection; it can meet the ultrasonic imaging detection requirements of the MHz frequency band and has a broader application prospect in non-destructive testing and biological diagnosis. In short, the present invention can break the diffraction limit and realize ultra-high resolution imaging of near-surface defects in contact ultrasonic detection.

[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 attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0018] Figure 1 is a schematic diagram of a near-surface defect super-resolution imaging system based on a superlens according to an embodiment of the present invention;

[0019] Figure 2 is a schematic diagram of a metalens structure according to an embodiment of the present invention;

[0020] Figure 3 is a schematic diagram of sound field propagation when a lens is used according to an embodiment of the present invention;

[0021] Figure 4 is a schematic diagram of wave field simulation results under Fabry-Pérot resonance according to an embodiment of the present invention;

[0022] Figure 5 is a schematic diagram of processing a metalens according to an embodiment of the present invention;

[0023] Figure 6 A test block to be tested having a transverse through hole processed therein according to an embodiment of the present invention;

[0024] Figure 7 is a schematic diagram of a super-resolution imaging detection system according to an embodiment of the present invention;

[0025] Figure 8 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] Fig. 9 is a schematic diagram of experimental results of using a sine wave to detect a 0.4 mm side through hole according to an embodiment of the present invention;

[0027] Fig.10It is a schematic diagram of the experimental results of detecting a 0.4 mm transverse through hole using a pulse wave according to an embodiment of the present invention and the numerical simulation results of a 0.4 mm transverse through hole. DETAILED DESCRIPTION

[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 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 unless otherwise specifically stated.

[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 as 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 similar 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] See also Figure 1 As shown, in general, the present invention provides a near-surface defect super-resolution imaging system based on a super-lens, including: 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 detected. 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 detected. The present invention proposes a super-lens with practical value and a super-resolution imaging system based on the super-lens, which exceeds the traditional diffraction limit and lays a foundation for its application in biomedical diagnosis and non-destructive testing and evaluation.

[0034] Nondestructive testing has 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 subwavelength resolution ultrasonic imaging beyond the diffraction limit. Considering that existing research mainly focuses on superlenses that rely on fluid media, it is suitable for acoustic frequency bands with frequencies below 10KHz. The present invention proposes for the first time a periodic columnar structure superlens with a substrate for realizing subwavelength ultrasonic imaging of solid structures in the MHz domain. For example, 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.

[0035] Hereinafter, embodiments of a super-lens structure, resonance modes, super-lens processing, and a super-resolution imaging system for near-surface defects based on a super-lens will be described in detail.

[0036] 1. About the design of superlens structure

[0037] See also Figure 2 In order to design a superlens structure, a columnar structure superlens fixed on a thin plate substrate is designed. The size is in the order of microns. Each column acts as a waveguide for elastic waves and is periodically arranged on the thin plate with a lattice constant A. The thin plate is used as a substrate to fix 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 flexibly moved. Therefore, the designed superlens is reusable and practical. Figure 1 In , 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 to 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 replace other forms of periodically arranged columnar structures, such as round 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 detecting in transmission mode, the ultrasonic wave scattered by the defect passes through the superlens, and the maximum displacement of the lens receiving end is extracted to obtain Figure 3 Line scan image shown. The ultrasonic field inside the superlens can be expressed as:

[0041] U(x)=C1sink mx x+C2cosk mx x, 0<x<L (1)

[0042] Among them, C2 and C1 are constants, x represents the coordinate position of the sound propagation direction, k mx is the wave vector in the metalens. Under the Fabry–Pérot resonance condition, the transmission coefficient becomes 1, so the metalens transmits all waves (including evanescent waves) from the object plane to the image plane without any loss, thus achieving subwavelength imaging. The resonance 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 metalens. Consider Figure 3 The wave propagation path shown in the figure is that 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 k mx Satisfy the condition k mx Fabry–pérot resonance occurs when L = (2n-1)π / 2, where n is an integer. Correspondingly, the resonant frequency is:

[0043]

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

[0045] In order to verify the applicability of the above theory to the proposed superlens, a finite element analysis was performed, through which the wave field of the superlens under Fabry–Pérot resonance was displayed. Figure 4 Indicated when k mx The steady-state acoustic field in the resonant mode when L = π / 2, 3π / 2 and 5π / 2 corresponds to the first, second and third order Fabry–pérot resonances, respectively. Figure 4 (a) Figure 4 (b) and Figure 4 (c). The acoustic field with and without the base at the first-order resonance frequency is compared, see Figure 4 (d) and Figure 4 (f). It can be seen that the thin-plate substrate has little effect on the Fabry–Pérot resonance modes. At these resonance frequencies, standing waves are formed and the output surface of the metalens has a maximum displacement, which makes the measurement highly robust and has a high resolution contrast.

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

[0047] Figure 5 is a schematic diagram of processing a superlens. Figure 6 It is a schematic diagram of the test block under test with a transverse through hole.

[0048] For example, the main material of the metalens is single-crystal silicon, which is easily available and made with high precision. Moreover, the surface of single-crystal silicon is a mirror surface, which has good optical backscattering performance, which is helpful for the next step of laser vibration measurement. Single-crystal silicon is cut using a precision dicing machine (ADT 7122, Advanced Dicing Technologies, Israel) with a diamond cutting blade of 0.08 mm thickness, and a manufacturing error of 0.01 mm. Two side-drilled holes (SDH) with a diameter of 0.4 mm, a spacing of 0.4 mm (about λ / 30), and a distance of 0.1 mm from the top surface are manufactured in a 100 mm × 100 mm × 10 mm 304 stainless steel block by wire electrospark cutting as the near-surface defects to be detected.

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

[0050] Figure 7 It is a specific embodiment of a super-resolution imaging system based on transmission ultrasonic detection. It includes a super lens structure, a laser vibrometer, a PC, an arbitrary function generator and a power amplifier. Figure 7 In the present work, longitudinal waves were used to perform transmission detection of subsurface defects in a stainless steel block. A superlens was coupled to the detection surface to extract the time domain signal containing the defect information, and finally achieve subwavelength imaging. During the detection process, an optical table and a custom fixture were used to ensure good coupling and horizontality. A piezoelectric transducer (OLYMPUS V101-RB) with a center frequency of 0.50MHz and a chip size of 25.4mm was used to excite the longitudinal plane wave through an arbitrary function generator (Tektronix AFG 31152), and the voltage was amplified 200 times by a power amplifier (Ciprian HVA-400-A). A laser vibrometer (Polytec PSV-500HV) was used to detect the displacement field on the lens surface, and a raster scan with a spatial resolution of 0.2mm was performed, and the signal was averaged 200 times in the time domain to improve the signal-to-noise ratio. The maximum normalized amplitude change from each time domain signal was plotted relative to the measurement position on the sample position to obtain A-scan and C-scan images.

[0051] To further verify the effect of the present invention, numerical simulation and experimental verification were carried out. Specifically, two 304 stainless steel specimens with SDHs spaced 0.4 mm (λ / 30) apart were designed and manufactured. A sine wave with a center frequency of 0.50 MHz, the first-order resonant frequency, was used for detection. A-scan and C-scan imaging were performed on the test block using sine wave signals and pulse signals, respectively. The results of the SDHs detection with a spacing of 0.4 mm are shown in Figure 2. Figure 8-10 As shown, Figure 8 This is the numerical simulation result of a 0.4 mm horizontal through hole. Figure 8 (a) is the wave field distribution diagram, Figure 8 (b) is the A-scan result. Fig. 9 This is the experimental result of using sine wave to detect 0.4mm horizontal through hole. Fig. 9 (a) is the result of scan A, Fig. 9 (b) is the C scan result. Fig.10 This is the experimental result of using pulse wave to detect 0.4mm horizontal through hole. Fig.10 (a) is the result of scan A, Fig.10 (b) is the C-scan result. It can be seen from the experimental results that when the metalens is used to image the internal defects, the signal amplitude drops sharply at the defect location, the defects can be effectively identified, and the detection contrast is high.

[0052] In summary, the present invention designs a silicon-based superlens with a base based on the Fabry–Pérot resonance theory, and the columnar structure is periodically arranged on the thin plate substrate. The frequency of Fabry–Pérot resonance is theoretically analyzed, and the wave field of the superlens in the resonant mode is numerically verified. The experimental results show that the designed 0.50MHz columnar structure superlens achieves super-resolution ultrasonic imaging (λ / 30) with high resolution contrast, which can accurately identify two sub-surface defects in the stainless steel structure.

[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 used flexibly according to the use requirements, has the advantages of being reusable and easy to process, and the significantly reduced feature size makes the manufacturing simple.

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

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

[0057] 4) This paper analyzes the Fabry–pérot resonance mode under elastic wave conditions for the first time, calculates the Fabry–pérot resonance frequency theoretically, and verifies the acoustic field distribution inside the superlens under the Fabry–pérot resonance mode using numerical simulation. The experimental results demonstrate the sub-wavelength ultrasonic imaging capability of the superlens, with a resolution of up to λ / 30.

[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] Computer readable storage medium can be a tangible device that can hold and store instructions used by an instruction execution device. Computer readable storage medium 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 (non-exhaustive list) of computer readable storage medium 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 disk read-only memory (CD-ROM), a digital versatile disk (DVD), a memory stick, a floppy disk, a mechanical encoding device, for example, a punch card or a convex structure in a groove on which instructions are stored, and any suitable combination thereof. The computer readable storage medium used here is not interpreted as a transient signal itself, such as a radio wave or other freely propagating electromagnetic wave, an electromagnetic wave propagated by a waveguide or other transmission medium (for example, a light pulse by an optical fiber cable), or an electrical signal transmitted by a 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, optical fiber transmissions, wireless transmissions, 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 for storage in the computer-readable storage medium in each computing / processing device.

[0061] The computer program instructions for performing the operation 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, etc., and conventional procedural programming languages, such as "C" language or similar programming languages. Computer-readable program instructions may be executed entirely on a user's computer, partially on a user's computer, as an independent software package, partially on a user's computer, 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., using an Internet service provider to connect via the Internet). In some embodiments, an electronic circuit, such as a programmable logic circuit, a field programmable gate array (FPGA), or a programmable logic array (PLA), may be personalized by utilizing the state information of the computer-readable program instructions, and the electronic circuit may execute the computer-readable program instructions, thereby realizing various aspects of the present invention.

[0062] Various aspects of the present invention are described herein with reference to the flow charts and / or block diagrams of the methods, devices (systems) and computer program products according to embodiments of the present invention. It should be understood that each box of the flow chart and / or block diagram and the combination of each box in the flow chart and / or block diagram 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 that implements the functions / actions specified in one or more boxes in the flowchart and / or block diagram is generated. These computer-readable program instructions can also be stored in a computer-readable storage medium, and these instructions cause the computer, programmable data processing device, and / or other equipment to work in a specific manner, so that the computer-readable medium storing the instructions includes a manufactured product, which includes instructions for implementing various aspects of the functions / actions specified in one or more boxes 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 operating 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 boxes in the flowchart and / or block diagram.

[0065] The flow charts and block diagrams in the accompanying drawings show the possible 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 flow chart or block diagram can represent a part of a module, a program segment or an instruction, and a part of the module, a program segment or an instruction contains one or more executable instructions for realizing the specified logical function. In some alternative implementations, the functions marked in the box can also occur in a different order from the order 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 flow chart, and the combination of the boxes in the block diagram and / or flow chart 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 it is equivalent to implement it by hardware, implement it by software, and implement it by combining software and hardware.

[0066] Embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the described embodiments. The selection of terms used herein is intended to best explain the principles of the embodiments, practical applications, or technical improvements in the marketplace, or to enable other persons of ordinary skill 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: U(x)=C1 sink mx x+C2 cosk mx x,0<x<L Among them, C2 and C1 are constants, x is the coordinate position of the sound propagation direction, k mx is the wave vector in the superlens. Under the boundary condition that one end is fixed and the other end is free, when the parallel momentum k mx Satisfy the condition k mx When L = (2n-1)π / 2, 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, ρ 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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