A terahertz array imaging device and method for online non-destructive testing

Abstract

The application provides a kind of terahertz array imaging device and method for online nondestructive testing, device includes microwave signal source, multi-channel spread spectrum device, multi-channel synchronous acquisition unit, terahertz transceiver array, one-dimensional motion device, main control computer;Real-time detection of industrial large-size material can be realized on-line, adopts multi-subarray offset combination mode, solves the problem that the volume of terahertz transmitting and receiving module is large, which leads to that array layout cannot meet the requirement of one wavelength interval;Air interface calibration test method based on metal plate is used instead of traditional metal ball calibration method, which effectively improves the imaging quality of plate material;Terahertz transmitting and receiving technology based on electronic scanning and multi-channel synchronous reception is used, linear frequency modulation signal system and coherent accumulation method are used to realize wideband signal high sensitivity reception, high-speed electronic switch is used with multi-channel synchronous reception to realize millisecond level high-speed data acquisition, and test efficiency is guaranteed.

Description

Technical Field

[0001] This invention relates to the field of terahertz imaging technology, and in particular to a terahertz array imaging device and method for online non-destructive testing. Background Technology

[0002] Terahertz waves typically refer to electromagnetic radiation with frequencies between 0.1 and 10 THz and wavelengths between 3 mm and 30 μm, falling between microwaves and infrared. Due to their non-ionizing radiation, high resolution, and strong penetrating power, terahertz technology is particularly suitable for non-destructive testing of non-polar molecular materials such as clothing, plastics, ceramics, and composite materials. For widely used materials such as polymer composites, foams, ceramics, and plastics, visible light, infrared radiation, and even ultrasound cannot penetrate them. Furthermore, conventional radiographic testing methods often render the materials themselves, as well as potential defects such as pores, misalignments, and cracks, nearly transparent, making it difficult to clearly image internal defects and thus limiting non-destructive testing of these materials. Terahertz waves, however, have good penetrating power in most non-metallic and non-polar materials, allowing for non-destructive testing of internal defects in these materials using a combination of terahertz waves and imaging techniques.

[0003] For terahertz imaging, the commonly used method is to use a single transceiver module, relying on mechanical scanning to image and detect the material under test. Testing of a sample only tens of centimeters in size requires tens of minutes or even hours, severely limiting the online detection of large-sized materials. Adopting a multi-transmitter, multi-receiver (MDR) system is an effective way to solve these problems. A typical example is the millimeter-wave imager developed by Rohde & Schwarz for security inspection, operating at 70GHz–80GHz, which falls within the quasi-terahertz band. It employs advanced millimeter-wave chip design technology, achieving a high degree of integration between transmitting and receiving antennas. The spacing between adjacent antennas in the array can reach the wavelength level, meeting the requirement that the transceiver antenna layout for array imaging meets a single wavelength requirement. However, with the increase in terahertz frequency, the integration difficulty increases. Individual terahertz transmitting or receiving units are on the centimeter scale, and the spacing between adjacent antennas cannot reach the operating frequency wavelength, affecting subsequent imaging performance. Furthermore, during imaging processing, the nonlinear error of the terahertz signal and the amplitude and phase errors between multiple channels must be calibrated. Currently, the conventional method uses a metal sphere as an ideal calibration body, but when dealing with planar materials, the calibrated imaging results are unsatisfactory. For multi-transmitter, multi-receiver systems, the commonly used method is step-frequency plus electronic scanning. When the number of required sweep points and array channels is small, it can reach tens of milliseconds. However, as the terahertz operating frequency increases, the imaging bandwidth increases, leading to an increase in the number of sweep points. In addition, the smaller the wavelength, the more terahertz transmission and reception channels are required, which will significantly reduce the testing efficiency and affect the online detection of large-size materials. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention provides a terahertz array imaging device and method for online non-destructive testing. This invention employs a multi-subarray offset combination method, solving the problem that the large size of the terahertz transmitting and receiving modules prevents the array layout from meeting wavelength spacing requirements. It utilizes an open-interface calibration test method with a metal plate, effectively addressing the issue of poor calibration performance with traditional metal spheres as calibration bodies. It employs a terahertz transceiver technology based on electronic scanning and multi-channel synchronous reception, achieving high-sensitivity reception of broadband signals through a linear frequency modulation signal system and coherent accumulation. High-speed electronic switches combined with multi-channel synchronous reception enable millisecond-level high-speed data acquisition, significantly improving testing efficiency and meeting the needs of industrial online non-destructive testing.

[0005] In a first aspect, this disclosure provides a terahertz array imaging device for online non-destructive testing, comprising: a microwave signal source, a multi-channel spread spectrum device, a multi-channel synchronous acquisition unit, a terahertz transceiver array, a one-dimensional motion device, and a main control computer;

[0006] After the one-dimensional motion device reaches a certain position, it sends a hardware trigger pulse signal 1 to the multi-channel spread spectrum device. The multi-channel spread spectrum device, after detecting the hardware trigger pulse signal from the one-dimensional motion device via its internal FPGA, controls a 1-to-N electronic switch to switch the test channel and sends a hardware pulse trigger signal 2 to the microwave signal source. Upon receiving the hardware pulse trigger signal 2 from the multi-channel spread spectrum device, the microwave signal source generates broadband radio frequency and local oscillator microwave signals, and simultaneously generates a hardware pulse trigger signal 3 to the multi-channel synchronous acquisition unit. Upon receiving the hardware pulse trigger signal 3 from the microwave signal source, the multi-channel synchronous acquisition unit performs synchronous acquisition across all connected receiving channels and buffers the acquired data in the multi-channel synchronous acquisition unit.

[0007] The multi-channel spread spectrum device is used to spread the radio frequency microwave signal and the local oscillator microwave signal generated by the microwave signal source into N channels and M channels, respectively.

[0008] The terahertz transceiver array is designed to have N terahertz transmitting channels and M terahertz receiving channels. The N terahertz transmitting channels generate N terahertz signals by frequency multiplication of the broadband radio frequency microwave signal. The M terahertz receiving channels generate M test intermediate frequency signals by mixing the received signal reflected from the material under test with the terahertz local oscillator signal generated by frequency multiplication of the broadband local oscillator microwave signal.

[0009] In a further technical solution, the main control computer is used to realize the measurement control and data acquisition of the device, as well as the post-processing of the data.

[0010] A further technical solution is that the microwave signal source is used to generate broadband radio frequency microwave signals and broadband local oscillator microwave signals, and also has trigger input, trigger output and clock synchronization interface.

[0011] The microwave signal source typically generates broadband microwave sweep signals using two methods: step frequency and linear frequency modulation. By combining FPGA and direct digital frequency synthesis technology, dynamic reconfigurability of the two signal modes can be achieved. When the step frequency cannot meet the test efficiency, it can be dynamically switched to the linear frequency modulation mode.

[0012] A further technical solution is that the multi-channel spread spectrum device includes a 1-to-N electronic switch, a 1-to-M power divider, a power amplifier, a low-noise amplifier, and a timing control board;

[0013] The 1-to-N electronic switch is used to expand the broadband radio frequency microwave signal generated by the microwave signal source into N broadband radio frequency microwave signals, with the switching time between channels reaching the order of hundreds of nanoseconds.

[0014] The 1-to-M power divider is used to expand the broadband local oscillator microwave signal generated by the microwave signal source into M broadband local oscillator microwave signals for synchronous output.

[0015] In a further technical solution, the power amplifier and the low-noise amplifier are used to amplify the broadband radio frequency microwave signal and the broadband local oscillator microwave signal, ensuring that the output power of each signal output from the 1-to-N electronic switch and the 1-to-M power divider can meet the power requirements of the terahertz transmitting module and the terahertz receiving module.

[0016] The timing control board is used to realize the logic control of the microwave signal source, the one-dimensional motion device and the 1-to-N electronic switch; in order to improve the testing efficiency, the execution response between the devices is realized by hardware pulse triggering.

[0017] A further technical solution is that the one-dimensional motion device is used to realize the one-dimensional translation of the material under test along the vertical direction of the array;

[0018] During the one-dimensional motion carrying the test material, when the optical sensor senses the test material, the device starts to collect data; when the optical sensor senses that the test material is moving away, it sends a command to the device to stop the data collection operation.

[0019] In a further technical solution, the multi-channel synchronous acquisition unit includes a multi-channel synchronous acquisition card and a signal processing board.

[0020] In a further technical solution, the multi-channel synchronous acquisition card is used to acquire M-channel test intermediate frequency signals, and the signal processing board is used for down-conversion, filtering, and decimation operations of the acquired data.

[0021] Secondly, this disclosure provides a terahertz array imaging method for online nondestructive testing, implemented based on the terahertz array imaging device for online nondestructive testing described in the first aspect, including:

[0022] Step 1: The main control computer sets the parameters, including the operating frequency, the number of frequency points, the number of channels switched by the 1-to-N electronic switch in the multi-channel spread spectrum device, the number of intermediate frequency acquisition channels in the multi-channel synchronous acquisition unit, and the scanning range, scanning speed, and scanning step of the one-dimensional motion device.

[0023] Step 2: After the parameters are set, start data acquisition. After the one-dimensional motion device reaches a certain position, it sends a hardware trigger pulse signal 1 to the timing control board of the multi-channel spread spectrum device.

[0024] Step 3: After the timing control board of the multi-channel spread spectrum device detects the hardware trigger pulse signal 1 emitted from the one-dimensional motion device through the internal FPGA, it controls the 1-to-N electronic switch to complete the switching of the test channel and sends a hardware pulse trigger signal 2 to the microwave signal source.

[0025] Step 4: After receiving the hardware pulse trigger signal 2 from the timing control board of the multi-channel spread spectrum device, the microwave signal source generates broadband radio frequency and local oscillator microwave signals. At the same time, the microwave signal source generates a hardware pulse trigger signal 3 to the multi-channel synchronous acquisition unit.

[0026] Step 5: After receiving the hardware pulse trigger signal 3 from the microwave signal source, the multi-channel synchronous acquisition unit performs synchronous acquisition of each connected receiving channel and buffers the acquired signal into the multi-channel synchronous acquisition unit.

[0027] Step 6: Repeat steps 2 to 5 to complete the acquisition of data for all terahertz transmission channels and corresponding receiving channels under the control of the 1-to-N electronic switch, and buffer the acquired signals into the multi-channel synchronous acquisition unit.

[0028] Step 7: Repeat steps 2 to 6 to complete the signal acquisition at each motion position of the one-dimensional motion device, buffer the acquired signals in the multi-channel synchronous acquisition unit, and transmit all buffered data to the main control computer;

[0029] Step 8: Error calibration and 3D imaging are performed by the main control computer;

[0030] The multi-channel spread spectrum device is used to spread the radio frequency microwave signal and the local oscillator microwave signal generated by the microwave signal source into N channels and M channels, respectively.

[0031] The terahertz transceiver array is designed to have N terahertz transmitting channels and M terahertz receiving channels. The N terahertz transmitting channels generate N terahertz signals by frequency multiplication of the broadband radio frequency microwave signal. The M terahertz receiving channels generate M test intermediate frequency signals by mixing the received signal reflected from the material under test with the terahertz local oscillator signal generated by frequency multiplication of the broadband local oscillator microwave signal.

[0032] A further technical solution is that the combination method of the terahertz transmitting and receiving arrays is based on the principle of equivalent phase center, and adopts the method of multiple subarray offsets to increase the number of equivalent center sampling points, so as to achieve the terahertz array layout spacing that meets one wavelength.

[0033] A further technical solution involves the main control computer performing error calibration using an air interface calibration method based on a metal plate, defining the original echo signal of the m-th transmitting and n-th receiving modules as... The calibrated signal is S m,n for:

[0034]

[0035] T m,n =exp(-j2πf(TR) m +RR n ) / c)

[0036] SB m,n This is a background measurement without the material being measured, SP m,n For calibration

[0037] in,

[0038] Metal plate test data, TR m RRn is the distance from the m-th transmitting module to the center of the imaging projection plane, and RRn is the distance from the n-th receiving module to the center of the imaging projection plane.

[0039] The above one or more technical solutions have the following beneficial effects:

[0040] 1. This invention provides a terahertz array imaging device and method for online non-destructive testing, which can realize online real-time detection of large-size materials on industrial production lines. It adopts a multi-subarray offset combination method to solve the problem that the large size of the terahertz transmitting and receiving modules makes it impossible for the array layout to meet the wavelength interval requirement.

[0041] 2. The use of an air-to-ground calibration test method based on a metal plate instead of the traditional metal ball calibration method effectively improves the imaging quality of the plate material;

[0042] 3. This invention employs a terahertz transceiver technology based on electronic scanning and multi-channel synchronous reception, and achieves high-sensitivity reception of broadband signals by using a linear frequency modulation signal system and coherent accumulation method.

[0043] 4. The use of high-speed electronic switches in conjunction with multi-channel synchronous receivers enables high-speed data acquisition at the millisecond level, significantly improving testing efficiency and thus meeting the needs of industrial online non-destructive testing. Attached Figure Description

[0044] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0045] Figure 1 This is a structural block diagram of a terahertz array imaging device for online non-destructive testing as described in Embodiment 1 of the present invention;

[0046] Figure 2 The diagram shows the equivalent center of an embodiment of the present invention; wherein, (a) is an equivalent center diagram of a 2-transmit 2-receive configuration; (b) is an equivalent center diagram of an configuration achieved by adding a transmit array and left and right offset; and (c) is an equivalent center diagram of an configuration achieved by adding a receive array and flipping and left and right offset.

[0047] Figure 3 This is a schematic diagram of the imaging projection plane distribution according to Embodiment 1 of the present invention;

[0048] The components include: 1. Microwave signal source, 2. Multi-channel spread spectrum device, 3. Multi-channel synchronous acquisition unit, 4. Terahertz transceiver array, 5. One-dimensional motion device, and 6. Main control computer. Detailed Implementation

[0049] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0050] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0051] To address the shortcomings of existing technologies, this invention provides a terahertz array imaging device and method for online non-destructive testing. This invention employs a multi-subarray offset combination method, solving the problem that the large size of the terahertz transmitting and receiving modules prevents the array layout from meeting wavelength spacing requirements. It utilizes an open-interface calibration test method with a metal plate, effectively addressing the issue of poor calibration performance with traditional metal spheres as calibration bodies. It employs a terahertz transceiver technology based on electronic scanning and multi-channel synchronous reception, achieving high-sensitivity reception of broadband signals through a linear frequency modulation signal system and coherent accumulation. High-speed electronic switches combined with multi-channel synchronous reception enable millisecond-level high-speed data acquisition, significantly improving testing efficiency and meeting the needs of industrial online non-destructive testing.

[0052] Example 1

[0053] To address the problems existing in the background art, the present invention provides a terahertz array imaging device for online non-destructive testing, the device comprising: a microwave signal source, a multi-channel spread spectrum device, a terahertz transceiver array, a multi-channel synchronous acquisition unit, and a main control computer;

[0054] After the one-dimensional motion device reaches a certain position, it sends a hardware trigger pulse signal 1 to the multi-channel spread spectrum device. The multi-channel spread spectrum device, after detecting the hardware trigger pulse signal from the one-dimensional motion device via its internal FPGA, controls a 1-to-N electronic switch to switch the test channel and sends a hardware pulse trigger signal 2 to the microwave signal source. Upon receiving the hardware pulse trigger signal 2 from the multi-channel spread spectrum device, the microwave signal source generates broadband radio frequency and local oscillator microwave signals, and simultaneously generates a hardware pulse trigger signal 3 to the multi-channel synchronous acquisition unit. Upon receiving the hardware pulse trigger signal 3 from the microwave signal source, the multi-channel synchronous acquisition unit performs synchronous acquisition of the connected receiving channels and buffers the acquired data in the multi-channel synchronous acquisition unit.

[0055] Among them, the microwave signal source is used to generate broadband radio frequency microwave signals and broadband local oscillator microwave signals, and also has trigger input, trigger output and clock synchronization interface;

[0056] A multi-channel spread spectrum device is used to spread the radio frequency microwave signal and the local oscillator microwave signal generated by the microwave signal source into N channels and M channels, respectively.

[0057] The terahertz transceiver array is designed with N terahertz transmitting channels and M terahertz receiving channels. The N terahertz transmitting channels multiply the broadband radio frequency microwave signal to generate N terahertz signals. The M terahertz receiving channels receive the reflected signal from the material under test by mixing it with the terahertz local oscillator signal generated by multiplying the broadband local oscillator microwave signal, thus generating M intermediate frequency signals for testing. The terahertz transceiver array uses a multi-subarray offset method to increase the equivalent sampling center point, ensuring that the terahertz transmission and reception interval meets the requirement of one wavelength.

[0058] A multi-channel synchronous acquisition unit is used to synchronously acquire and digitally preprocess M-channel test intermediate frequency signals;

[0059] The one-dimensional motion device is used to realize the one-dimensional translation of the material under test along the vertical direction of the array. It can be equivalent to the industrial online conveyor belt transmission mode. During the movement of the material under test in one-dimensional motion, when the optical sensor senses the material under test, the device is started to collect data. When the optical sensor senses that the material under test is moving away, it sends a command to the device to stop the data collection operation.

[0060] The main control computer is used to implement the device's measurement control and data acquisition, as well as data post-processing.

[0061] In the above scheme, the microwave signal source generally realizes broadband microwave sweep signal through two methods: step frequency and linear frequency modulation. By using a combination of FPGA and direct digital frequency synthesis technology, dynamic reconfigurability of the two signal modes, step frequency and linear frequency modulation, is realized. When the step frequency cannot meet the test efficiency, it dynamically switches to the linear frequency modulation mode.

[0062] In the above scheme, the multi-channel spread spectrum device includes a 1-to-N electronic switch, a 1-to-M power divider, a power amplifier, a low-noise amplifier, and a timing control board; among which...

[0063] A 1-to-N electronic switch is used to expand a broadband radio frequency microwave signal generated by a microwave signal source into N broadband radio frequency microwave signals, with the switching time between channels reaching the order of hundreds of nanoseconds.

[0064] A 1-to-M power divider is used to expand the broadband local oscillator microwave signal generated by the microwave signal source into M broadband local oscillator microwave signals for synchronous output.

[0065] Power amplifiers and low-noise amplifiers are used to amplify broadband radio frequency microwave signals and broadband local oscillator microwave signals, ensuring that the output power of each signal output from the 1-to-N electronic switch and the 1-to-M power divider can meet the power requirements of the terahertz transmitting module and the terahertz receiving module.

[0066] The timing control board is used to implement the logic control of the microwave signal source, the one-dimensional motion device, and the 1-to-N electronic switch; in order to improve the testing efficiency, hardware pulse triggering is used to realize the execution response between the devices.

[0067] The terahertz transceiver array comprises N terahertz transmitting channels and M terahertz receiving channels. The N terahertz transmitting channels are used to generate terahertz transmitting signals by frequency multiplication and amplification of N broadband radio frequency microwave signals, which are then radiated by a terahertz antenna. The M terahertz receiving channels are used to generate terahertz local oscillator signals by frequency multiplication and amplification of M broadband local oscillator microwave signals, which are then mixed with the received reflected signals from the material under test through a terahertz mixer to obtain M test intermediate frequency signals. To meet imaging requirements, the N terahertz transmitting channels and M terahertz receiving channels are combined to form a terahertz transmitting array and a terahertz receiving array, respectively.

[0068] The terahertz transceiver array uses a multi-subarray offset method to increase the equivalent sampling center point, thus satisfying the requirement that the terahertz transceiver interval meets one wavelength.

[0069] The multi-channel synchronous acquisition unit includes a multi-channel synchronous acquisition card and a signal processing board. The multi-channel synchronous acquisition card is used to acquire M channels of intermediate frequency signals for testing. The signal processing board is used for down-conversion, filtering, decimation and other operations on the acquired data.

[0070] The one-dimensional motion device is used to realize the one-dimensional translation of the material under test along the vertical direction of the array. In order to improve the testing efficiency, the one-dimensional motion device adopts a continuous scanning mode, that is, non-stop scanning. After reaching each position, a hardware pulse trigger signal is generated to the timing control board, which controls the data acquisition process.

[0071] The main control computer includes measurement and control software and data analysis software. The measurement and control software is used to acquire data, and the data analysis software is used to process the acquired data, including error calibration algorithms and 3D imaging algorithms.

[0072] When the microwave signal source adopts a linear frequency modulation (LFM) operating mode, the signal-to-noise ratio is improved through coherent accumulation. To ensure the effectiveness of coherent accumulation, it is necessary to ensure that each group of acquired data has strong coherence. Therefore, the following methods are adopted: First, clock synchronization is performed in the microwave signal source, the multi-channel synchronous acquisition unit, and the multi-channel synchronous acquisition module; Second, after the FPGA detects the arrival trigger pulse of the one-dimensional motion device, it controls the 1-to-N electronic switch to switch channels according to a strict timing relationship, and at the same time generates a pulse trigger signal for the microwave signal source signal generation. Simultaneously, the microwave signal source generates a synchronous pulse trigger signal to the multi-channel synchronous acquisition unit.

[0073] The combination method of terahertz transmitting and receiving arrays is based on the principle of equivalent phase center, that is, the center of a pair of terahertz transmitting and receiving channels is the equivalent center point, and the spacing needs to be half a wavelength according to imaging requirements. Figure 2 (a) is a schematic diagram of the equivalent center of a 2-transmit, 2-receive array, obtaining a total of 2*2=4 equivalent center sampling points. For the terahertz band, due to hardware size limitations, it is impossible to guarantee a small spacing between each transmitting module or each receiving module. To solve this problem, the following two solutions are adopted. One is to further increase the number of transmitting or receiving channels in the transmitter or receiver array with a larger spacing to meet the requirement of a smaller equivalent center sampling point, such as... Figure 2 (b) This is achieved by increasing the number of transmission channels to the same number as the original terahertz transmission array, and then shifting the equivalent center sampling point left or right; the second method is to add transmission or reception arrays of the same specifications, and then flip and shift their placement, such as... Figure 2 (c) is achieved by adding a terahertz receiving array with the same specifications as the original terahertz receiving array and rotating it around the terahertz transmitting array, while increasing the equivalent center sampling point by shifting it left and right.

[0074] Example 2

[0075] Based on the above embodiments, this embodiment provides a terahertz array imaging method for online nondestructive testing, including the following steps:

[0076] Step 1: The main control computer 6 sets the parameters, including the operating frequency, the number of frequency points, the number of channels switched by the 1-to-N electronic switch in the multi-channel spread spectrum device 2, the number of intermediate frequency acquisition channels in the multi-channel synchronous acquisition unit 3, and the scanning range, scanning speed, and scanning step of the one-dimensional motion device 5.

[0077] Step 2: After the parameters are set, start data acquisition. After the one-dimensional motion device 5 reaches a certain position, it sends a hardware trigger pulse signal to the timing control board of the multi-channel spread spectrum device 2.

[0078] Step 3: After the timing control board of the multi-channel spread spectrum device 2 detects the hardware trigger pulse signal from the one-dimensional motion device 5 through its internal FPGA, it controls the 1-to-N electronic switch to complete the switching of the test channel and sends a hardware pulse trigger signal to the microwave signal source 1.

[0079] Step 4: After receiving the hardware pulse trigger signal from the timing control board of the multi-channel spread spectrum device 2, the microwave signal source 1 generates broadband radio frequency and local oscillator microwave signals. At the same time, the microwave signal source 1 generates a hardware pulse trigger signal to the multi-channel synchronous acquisition unit 3.

[0080] Step 5: After receiving the hardware pulse trigger signal from the microwave signal source 1, the multi-channel synchronous acquisition unit 3 performs synchronous acquisition of each connected receiving channel and caches the acquired data in the multi-channel synchronous acquisition unit 3.

[0081] Step 6: Repeat steps 2 to 5 to complete the acquisition of data for all terahertz transmission channels and corresponding receiving channels under the control of the 1-to-N electronic switch, and cache the acquired data in the multi-channel synchronous acquisition unit 3;

[0082] Step 7: Repeat steps 2 to 6 to complete the signal acquisition at each motion position of the one-dimensional motion device 5, buffer the acquired signals in the multi-channel synchronous acquisition unit 3, and transmit all buffered data to the main control computer 6.

[0083] Step 8: Error calibration and 3D imaging are performed by the main control computer 6;

[0084] In the above scheme, error calibration and 3D imaging algorithms are the core components for displaying the results of nondestructive testing of materials. The error calibration algorithm is mainly used to compensate for the nonlinear amplitude and phase errors of the terahertz signal introduced by the nonlinearity of the terahertz active device, as well as the inter-channel amplitude and phase inconsistencies introduced by the use of a multi-transmitter multi-receiver array. The 3D imaging algorithm can employ frequency domain and time domain algorithms. Frequency domain algorithms include the commonly used range migration algorithm (RMA), while time domain algorithms can employ the 3D filtered back projection algorithm (BP).

[0085] The error calibration algorithm employs an air interface calibration method based on a metal plate, defining the original echo signal of the m-th transmitting module and the n-th receiving module as... The calibrated signal is S m,n for

[0086]

[0087] T m,n =exp(-j2πf(TR) m +RR n ) / c)

[0088] SB m,n This is a background measurement without the material being measured, SP m,n Metal for calibration

[0089] in,

[0090] Tablet test data, TR m Let RR be the distance from the m-th transmitting module to the center of the imaging projection plane. nLet be the distance from the nth receiving module to the center of the imaging projection surface. (Imaging projection surface distribution) Figure 3 As shown.

[0091] This embodiment enables real-time online detection of large-size materials on industrial production lines through the above-described scheme. The use of a multi-subarray offset combination method solves the problem that the large size of the terahertz transmitting and receiving modules prevents the array layout from meeting the wavelength spacing requirements. The use of an air-to-ground calibration test method based on a metal plate replaces the traditional metal ball calibration method, effectively improving the imaging quality of the plate material. To ensure testing efficiency, a terahertz transceiver technology based on electronic scanning and multi-channel synchronous reception is employed. High-sensitivity reception of broadband signals is achieved through a linear frequency modulation signal system and coherent accumulation. High-speed data acquisition at the millisecond level is achieved using a high-speed electronic switch in conjunction with multi-channel synchronous reception.

[0092] Those skilled in the art will understand that the modules or steps of the present invention described above can be implemented using general-purpose computer devices. Optionally, they can be implemented using computer-executable program code, thereby allowing them to be stored in a storage device for execution by a computer device, or they can be fabricated as separate integrated circuit modules, or multiple modules or steps can be fabricated as a single integrated circuit module. The present invention is not limited to any particular combination of hardware and software.

[0093] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

[0094] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A terahertz array imaging device for online nondestructive testing, characterized in that, include: The device includes: a multi-channel spread spectrum device, a multi-channel synchronous acquisition unit, a terahertz transceiver array, a one-dimensional motion device, and a main control computer; After the one-dimensional motion device reaches a certain position, it sends a hardware trigger pulse signal 1 to the multi-channel spread spectrum device. The multi-channel spread spectrum device, after detecting the hardware trigger pulse signal from the one-dimensional motion device via its internal FPGA, controls a 1-to-N electronic switch to switch the test channel and sends a hardware pulse trigger signal 2 to the microwave signal source. Upon receiving the hardware pulse trigger signal 2 from the multi-channel spread spectrum device, the microwave signal source generates broadband radio frequency and local oscillator microwave signals, and simultaneously generates a hardware pulse trigger signal 3 to the multi-channel synchronous acquisition unit. Upon receiving the hardware pulse trigger signal 3 from the microwave signal source, the multi-channel synchronous acquisition unit performs synchronous acquisition of the connected receiving channels and buffers the acquired data in the multi-channel synchronous acquisition unit. The main control computer is used to implement the device's measurement control and data acquisition, as well as data post-processing, including error calibration algorithms and three-dimensional imaging algorithms. When performing error calibration, the main control computer adopts an air interface calibration method based on a metal plate, defining the original echo signal of the m-th transmitting and n-th receiving modules as... The calibrated signal is for: in, This is a background measurement without the material being tested being placed on it. For calibration of metal plate test data, Let m be the distance from the m-th transmitting module to the center of the imaging projection plane. Let be the distance from the nth receiving module to the center of the imaging projection surface; The multi-channel spread spectrum device is used to spread the radio frequency microwave signal and the local oscillator microwave signal generated by the microwave signal source into N channels and M channels, respectively. The terahertz transceiver array is designed with N terahertz transmitting channels and M terahertz receiving channels. The N terahertz transmitting channels multiply the broadband radio frequency microwave signal to generate N terahertz signals. The M terahertz receiving channels receive the reflected signal from the material under test by mixing it with the terahertz local oscillator signal generated by multiplying the broadband local oscillator microwave signal, thus generating M intermediate frequency signals for testing. The combination method of the terahertz transmitting and receiving arrays is based on the principle of equivalent phase center, using multiple subarray offsets to increase the number of equivalent center sampling points and ensure that the terahertz array layout spacing meets a wavelength requirement. The multiple subarray offset methods include: further increasing the number of transmitting or receiving channels in the transmitting or receiving array with a large spacing; or adding transmitting or receiving arrays of the same specifications, flipping and offsetting their placement.

2. The terahertz array imaging device for online nondestructive testing as described in claim 1, characterized in that, Also includes: A microwave signal source, which generates broadband radio frequency microwave signals and broadband local oscillator microwave signals, and also has trigger input, trigger output and clock synchronization interface.

3. The terahertz array imaging device for online nondestructive testing as described in claim 1, characterized in that, The one-dimensional motion device is used to realize the one-dimensional translation of the material under test along the vertical direction of the array; During the one-dimensional motion carrying the material under test, when the optical sensor senses the material under test, the device is activated to collect data. When the optical sensor detects that the material being measured is moving away, it sends a command to the device to stop data acquisition.

4. A terahertz array imaging device for online nondestructive testing as described in claim 1, characterized in that, The multi-channel spread spectrum device includes a 1-to-N electronic switch, a 1-to-M power divider, a power amplifier, a low-noise amplifier, and a timing control board; The 1-to-N electronic switch is used to expand the broadband radio frequency microwave signal generated by the microwave signal source into N broadband radio frequency microwave signals, with the switching time between channels reaching the order of hundreds of nanoseconds. The 1-to-M power divider is used to expand the broadband local oscillator microwave signal generated by the microwave signal source into M broadband local oscillator microwave signals for synchronous output.

5. A terahertz array imaging device for online nondestructive testing as described in claim 4, characterized in that, The power amplifier and low-noise amplifier are used to amplify broadband radio frequency microwave signals and broadband local oscillator microwave signals, ensuring that the output power of each signal output from the 1-to-N electronic switch and the 1-to-M power divider can meet the power requirements of the terahertz transmitting module and the terahertz receiving module. The timing control board is used to realize the logic control of the microwave signal source, the one-dimensional motion device and the 1-to-N electronic switch; in order to improve the testing efficiency, the execution response between the devices is realized by hardware pulse triggering.

6. A terahertz array imaging device for online nondestructive testing as described in claim 1, characterized in that, The multi-channel synchronous acquisition unit includes a multi-channel synchronous acquisition card and a signal processing board.

7. A terahertz array imaging device for online nondestructive testing as described in claim 6, characterized in that, The multi-channel synchronous acquisition card is used to acquire M-channel intermediate frequency signals for testing, and the signal processing board is used for down-conversion, filtering, and decimation operations of the acquired data.

8. A terahertz array imaging method for online nondestructive testing, implemented based on the terahertz array imaging device for online nondestructive testing as described in any one of claims 1-7, characterized in that, include: Step 1: The main control computer sets the parameters, including the operating frequency, the number of frequency points, the number of channels switched by the 1-to-N electronic switch in the multi-channel spread spectrum device, the number of intermediate frequency acquisition channels in the multi-channel synchronous acquisition unit, and the scanning range, scanning speed, and scanning step of the one-dimensional motion device. Step 2: After the parameters are set, start data acquisition. After the one-dimensional motion device reaches a certain position, it sends a hardware trigger pulse signal 1 to the timing control board of the multi-channel spread spectrum device. Step 3: After the timing control board of the multi-channel spread spectrum device detects the hardware trigger pulse signal 1 emitted from the one-dimensional motion device through the internal FPGA, it controls the 1-to-N electronic switch to complete the switching of the test channel and sends a hardware pulse trigger signal 2 to the microwave signal source. Step 4: After receiving the hardware pulse trigger signal 2 from the timing control board of the multi-channel spread spectrum device, the microwave signal source generates broadband radio frequency and local oscillator microwave signals. At the same time, the microwave signal source generates a hardware pulse trigger signal 3 to the multi-channel synchronous acquisition unit. Step 5: After receiving the hardware pulse trigger signal 3 from the microwave signal source, the multi-channel synchronous acquisition unit performs synchronous acquisition of each connected receiving channel and buffers the acquired signal into the multi-channel synchronous acquisition unit. Step 6: Repeat steps 2 to 5 to complete the acquisition of data for all terahertz transmission channels and corresponding receiving channels under the control of the 1-to-N electronic switch, and buffer the acquired signals into the multi-channel synchronous acquisition unit. Step 7: Repeat steps 2 to 6 to complete the signal acquisition at each motion position of the one-dimensional motion device, buffer the acquired signals in the multi-channel synchronous acquisition unit, and transmit all buffered data to the main control computer; Step 8: Error calibration and 3D imaging are performed by the main control computer; When performing error calibration, the main control computer adopts an air interface calibration method based on a metal plate, defining the original echo signal of the m-th transmitting and n-th receiving modules as... The calibrated signal is for: in, This is a background measurement without the material being tested being placed on it. For calibration of metal plate test data, Let m be the distance from the m-th transmitting module to the center of the imaging projection plane. Let be the distance from the nth receiving module to the center of the imaging projection surface; The multi-channel spread spectrum device is used to spread the radio frequency microwave signal and the local oscillator microwave signal generated by the microwave signal source into N channels and M channels, respectively. The terahertz transceiver array, through array design, determines N terahertz transmission channels and M terahertz reception channels. The N terahertz transmission channels generate N terahertz signals by frequency multiplication of broadband radio frequency microwave signals. The M terahertz reception channels generate M test intermediate frequency signals by mixing the received reflected signal from the test material with the terahertz local oscillator signal generated by frequency multiplication of the broadband local oscillator microwave signal. The terahertz transceiver array uses a multi-subarray offset method to increase the equivalent sampling center point, satisfying the requirement that the terahertz transmission interval meets one wavelength. The methods for offsetting multiple subarrays include: further increasing the transmission or reception channels in the transmission or reception array with a large interval; or adding transmission or reception arrays of the same specifications, flipping and offsetting them.

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