Search

CN-121978053-A - Heterogeneous fusion nondestructive testing imaging system based on dual-frequency terahertz solid-state source

CN121978053ACN 121978053 ACN121978053 ACN 121978053ACN-121978053-A

Abstract

The application discloses a heterogeneous fusion nondestructive testing imaging system based on a dual-frequency terahertz solid-state source, which is used for solving the problems that the prior art still has obvious defects in the aspects of cooperative optimization of penetration capability and resolution, imaging speed improvement, efficient utilization of light energy, multi-frequency signal separation and the like, and relates to the technical fields of terahertz nondestructive testing and optical imaging, wherein the heterogeneous fusion nondestructive testing imaging system comprises a 110 GHz and 340 GHz orthogonal polarization terahertz source, a wire grid polarization beam combiner, a beam expanding optical assembly, a 64 multiplied by 64 element terahertz area array detector, a piezoelectric ceramic micro-displacement platform, an electrically-controlled adjustable attenuator, an electronic control and synchronization unit and an image fusion processing unit. The application realizes coaxial illumination by combining orthogonal polarization beams, combines time division multiplexing acquisition to avoid signal aliasing, overcomes high-frequency undersampling by utilizing sub-pixel micro-scanning and super-resolution reconstruction, and finally fuses a low-frequency penetration image and a high-frequency detail image to realize rapid full-field imaging with high penetration depth and high spatial resolution.

Inventors

  • Sun Shuoshi
  • LIU HAIQING
  • LI GEN
  • WANG GANG

Assignees

  • 安徽中科太赫兹科技有限公司

Dates

Publication Date
20260505
Application Date
20260403

Claims (9)

  1. 1. The heterogeneous fusion nondestructive testing imaging system based on the dual-frequency terahertz solid-state source is characterized by comprising a first terahertz solid-state source (1 a), a second terahertz solid-state source (1 b), a wire grid polarizer (2), a beam expanding optical assembly (3), a sample stage (4) to be tested, a terahertz imaging lens (5), a terahertz area array detector (6), a piezoelectric ceramic micro-displacement platform (7), an electrically-controlled adjustable attenuator (8), an electronic control and synchronization unit (9) and an image processing and fusion unit (10); The first terahertz solid-state source (1 a) outputs 110 GHz terahertz waves with horizontal polarization, and the second terahertz solid-state source (1 b) outputs 340 GHz terahertz waves with vertical polarization, wherein the two terahertz waves are respectively formed into parallel light beams by a collimating lens and then are incident to a wire grid polarizer (2) arranged on a main optical axis at an angle of 45 DEG, and the wire grid polarizer (2) has high transmission to the horizontal polarized light and high reflection to the vertical polarized light so that the two light beams are synthesized into a composite light beam with coaxial propagation; The composite beam irradiates a sample placed on a sample stage (4) to be detected after being expanded by a beam expansion optical assembly (3), and a transmission or reflection signal is focused to a terahertz area array detector (6) by a terahertz imaging lens (5), wherein an electronic control and synchronization unit (9) controls a first terahertz solid-state source (1 a) and a second terahertz solid-state source (1 b) to be alternately started and synchronously triggers the terahertz area array detector (6) to collect image data with corresponding frequency frame by frame; The electronic control adjustable attenuator (8) is arranged in the light path of the first terahertz solid-state source (1 a), and the image processing and fusing unit (10) is used for registering and fusing images of different frequency channels.
  2. 2. The heterogeneous fusion nondestructive testing imaging system based on the dual-frequency terahertz solid source as claimed in claim 1, wherein the electronic control and synchronization unit (9) turns on the first terahertz solid source (1 a) and turns off the second terahertz solid source (1 b) in odd frames, turns on the second terahertz solid source (1 b) and turns off the first terahertz solid source (1 a) in even frames, and synchronously triggers the terahertz area array detector (6) to acquire images frame by frame.
  3. 3. The dual-frequency terahertz solid-state source-based heterogeneous fusion nondestructive inspection imaging system of claim 2, wherein the piezoceramic micro-displacement platform (7) performs 2 x 2 or 3 x 3 sub-pixel micro-scanning within each frequency channel with a micro-displacement step size of 0.75 mm corresponding to half of the terahertz area array detector (6) pixel pitch of 1.5 mm.
  4. 4. The heterogeneous fusion nondestructive testing imaging system based on the dual-frequency terahertz solid source as set forth in claim 3, wherein the image processing and fusion unit (10) inputs a multi-frame image acquired by the piezoelectric ceramic micro-displacement platform (7) in the same frequency channel into a super-resolution reconstruction algorithm module to generate a high-resolution image with an equivalent pixel spacing of 0.75 mm or less.
  5. 5. The heterogeneous fusion nondestructive testing imaging system based on the dual-frequency terahertz solid source as claimed in claim 1, wherein the electronically controlled adjustable attenuator (8) dynamically adjusts attenuation by the electronic control and synchronization unit (9) according to preset parameters or sample information fed back in real time so as to control the power of the first terahertz solid source (1 a) incident to the sample.
  6. 6. The heterogeneous fusion nondestructive testing imaging system based on the dual-frequency terahertz solid source as claimed in claim 1, wherein the terahertz area array detector (6) is a 64×64-element micro-bolometer array, and the noise equivalent power is 1 The pixel pitch is 1.5 mm.
  7. 7. The dual-frequency terahertz solid-state source-based heterogeneous fusion nondestructive inspection imaging system of claim 1, wherein the beam expansion optical assembly (3) is composed of a pair of aspherical terahertz lenses for expanding the composite beam into a uniform illumination area with a diameter of 100 mm.
  8. 8. The heterogeneous fusion nondestructive testing imaging system based on the dual-frequency terahertz solid-state source according to claim 1, wherein the image processing and fusion unit (10) adopts wavelet transformation or a multi-scale Laplacian pyramid algorithm to fuse the 110 GHz image and the 340 GHz image which are reconstructed by super resolution, so as to generate a comprehensive image containing deep structure information and surface layer detail information.
  9. 9. The heterogeneous fusion nondestructive testing imaging system based on the dual-frequency terahertz solid source as claimed in claim 8, wherein the image processing and fusion unit (10) uses a 110 GHz image as a base layer, uses a 340 GHz image as an enhancement layer in the fusion process, and performs superposition according to the energy matching principle.

Description

Heterogeneous fusion nondestructive testing imaging system based on dual-frequency terahertz solid-state source Technical Field The invention relates to the technical field of terahertz nondestructive testing and optical imaging, in particular to a heterogeneous fusion nondestructive testing imaging system based on a dual-frequency terahertz solid-state source. Background Terahertz waves are located in an electromagnetic spectrum region between microwaves and infrared light, have the unique advantages of non-ionization, strong penetrability, transparency to various nonpolar materials and the like, show wide application prospects in the fields of nondestructive testing, safety inspection, biomedical imaging, industrial quality control and the like in recent years, and particularly in the detection of internal defects of nonmetallic materials such as composite materials, layered structures, ceramics, foams and the like, terahertz imaging technology has become an important nondestructive testing means because the terahertz imaging technology can provide spatial resolution better than microwaves and penetrability better than infrared, however, the conventional terahertz imaging system still faces a plurality of key technical bottlenecks in practical application. The current mainstream terahertz imaging system mainly comprises a single-frequency continuous wave imaging system and a mechanical scanning type imaging system, wherein the single-frequency system usually adopts a solid-state source with fixed frequency (such as 100 GHz or 300 GHz) for illumination, and is simple in structure, but is limited by physical characteristics of terahertz waves, namely a low-frequency band (such as 100 GHz) has strong penetrating capacity and can penetrate thicker samples, but the wavelength of the low-frequency band is longer, so that the spatial resolution is lower, micron-sized cracks or layering is difficult to identify, and a high-frequency band (such as more than 300 GHz) can provide higher spatial resolution, but the penetration depth is obviously reduced due to material absorption enhancement, so that signal attenuation is easy to cause even complete loss. Therefore, the dual requirements of "high penetration depth" and "high spatial resolution" are difficult to be combined by the single-frequency system, and the applicability of the single-frequency system in the detection of complex multi-layer structures is limited. On the other hand, the traditional terahertz imaging is based on a mechanical raster scanning mode, namely, a point source and a point detector are matched with a two-dimensional displacement platform to acquire signals point by point and reconstruct images, the method can obtain a high signal to noise ratio, but the imaging speed is extremely low, an image can be completed usually in a few minutes to a few hours, the requirements of modern industrial on-line detection on instantaneity and high flux cannot be met, although a full-field imaging scheme based on a terahertz area array camera is generated in recent years, the space sampling rate is insufficient due to the fact that the pixel size of the terahertz detector is large (for example, the typical pixel interval is 1.5 mm), the undersampling problem is more easily generated due to the fact that the wavelength is short, the actual exertion of the resolution of a system is restricted, in addition, the area array imaging is often influenced by Gaussian beam energy distribution, the center of a field is bright, the edge is dark, and the image consistency and the detection reliability are further reduced. More critical is that the existing system often lacks effective common aperture optical design by introducing multi-frequency illumination to fuse different frequency band advantages, the traditional beam combination mode such as a semi-transparent semi-reflective beam splitter can cause at least 50% of energy loss and reduce the signal to noise ratio of the system, meanwhile, the main flow terahertz area array detector (such as a micro-bolometer) is broadband response type and cannot distinguish different frequency components at the physical level, if double-frequency simultaneous illumination is carried out, the output of the terahertz area array detector generates signal aliasing and cannot separate information of each frequency band, so that the multi-frequency fusion strategy is difficult to implement, and although the frequency selection can be realized through a narrow-band filter, the cost of the elements is high, the insertion loss is high, the elements are difficult to be integrated with a solid source efficiently, and the miniaturization and the engineering deployment of the system are not facilitated. In summary, the existing terahertz nondestructive testing imaging technology still has obvious defects in the aspects of cooperative optimization of penetration capability and resolution, imaging speed improvement, efficient utilization of lig