Electrical capacitance tomography system based on two-stage control 64 pole plate intensive planar array

Abstract

The invention relates to an electrical capacitance tomography system based on a two-stage control 64 polar plate intensive planar array, which comprises a planar array sensor, a data acquisition unit and an upper computer, and is characterized in that the planar array sensor is composed of 8 * 8 uniformly distributed polar plates; the data acquisition unit comprises a main control chip, a capacitance measurement chip and a multiplexing module, the multiplexing module comprises four 8 * 16 matrix analog switch chips CH446Q and two single-pole four-throw switches CH444G, 16 analog signal input and output X ends of each CH446Q are connected with 16 paths of the planar array sensor, the Y end of each CH446Q is connected with the S ends of the two single-pole four-throw switches CH444G, and each single-pole four-throw switch CH444G is connected with the main control chip. The Y end of the single-pole four-throw switch CH444G is connected with the measuring port of the capacitance measuring chip PCAP02; a sensitive electrode measurement method is adopted for capacitance measurement, and a dielectric constant distribution matrix of the reconstructed image is obtained by combining the measured capacitance value with the sensitivity matrix through an LBP algorithm. The system solves the problems that an existing planar array sensor imaging system is low in detection precision and low in detection speed.

Description

Technical Field

[0001] The invention relates to the technical field of electrical capacitance tomography, in particular to an electrical capacitance tomography system based on a secondary control 64-electrode plate dense planar array. Background Art

[0002] Since the 1970s, composite materials have become an indispensable material in the modern aviation industry due to their excellent physical properties and economy, such as corrosion resistance, fatigue resistance, light weight and high strength. Composite structures for aviation are usually called "fiber reinforced plastics", such as plastics, metals and ceramic materials reinforced by high-performance glass fibers and carbon fibers. However, the structure and properties of composite materials will change during production and service, and defects and damage will inevitably occur. In order to improve the safety and reliability of aircraft, an efficient and accurate defect detection technology is urgently needed to ensure the normal operation of composite materials. Electrical Capacitance Tomography (ECT), as one of the non-destructive testing technologies, has the advantages of high speed, non-invasiveness, low cost and simple operation. It is widely used in the field of composite material flaw detection for aviation. One of the key factors for its detection speed and sensitivity is a sufficient number of multi-electrode planar array capacitance sensors with optimized scale.

[0003] In the capacitance tomography system, the planar array sensor with 16 or less electrodes has little measurement data and relatively low detection accuracy. The 64-electrode planar array sensor with three-level multiplexer reported so far has the problem of multiple levels of circuit gating control, large noise, and exponential increase of measurement data affecting image reconstruction speed. For example, Pang Yu et al. (Pang Yu, Dong Ensheng, Wu Yunjing, et al. Research on damage detection of composite material components based on same-plane multi-electrode array sensor [J]. Nondestructive Detection, 2010, 34(06): 30-3.) constructed a 64-electrode planar array capacitance sensor and verified the feasibility of planar multi-electrode array sensor in composite material damage detection. However, using two 8-to-1 multiplexers ADG408 to implement circuit selection requires 0.8 seconds of stabilization time after switching channels, which limits the measurement speed. Taylor et al. (TAYLOR SH, GARIMELLA S V. An explicit conditioning method for image reconstruction in electrical capacitancetomography [J]. Flow Measurement and Instrumentation, 2015, 46: 155-62.) built a planar array sensor system containing 50 plates. The bottom substrate was equipped with 81 square array electrodes, of which 7x7 electrodes were set inside for tomography, the outer electrodes were used for ground shielding, and the top was the 50th electrode, covering the entire measurement area. The experiment verified that the sensor and its algorithm can effectively detect the void structure in the 1.27mm material layer. The electrode selection circuit used up to 12 chips, including 2 CD4053 chips, 8 HCT4514 chips and 2 CD4556 chips.

[0004] The present invention realizes a capacitance tomography system based on a two-level controlled 64-plate dense planar array. Without changing the sensitive area, the plate area is reduced and the number of detected capacitance values ​​is increased, thereby improving the accuracy of reconstructed images. At the same time, the detection speed is improved through the sensitive electrode measurement method, so that both the measurement accuracy and speed meet the requirements of non-destructive testing. Summary of the invention

[0005] In view of the deficiencies in the prior art, the technical problem to be solved by the present invention is to provide a capacitance tomography system based on a two-level controlled 64-plate dense planar array, which solves the problem of low detection accuracy and slow detection speed of the existing planar array sensor imaging system.

[0006] The technical solution of the present invention to solve the technical problem is: A capacitance tomography system based on a two-level controlled 64-electrode dense planar array includes a planar array sensor, a data acquisition unit and a host computer. The planar array sensor is composed of 8x8 evenly distributed electrodes and is used to detect the capacitance value of a composite material. The data acquisition unit is mainly used to process the detection data of the planar array sensor and transmit it to the host computer through a serial port or Bluetooth. The host computer receives the collected data and restores the true value of the dielectric constant distribution in combination with an image reconstruction algorithm to achieve visual detection of the composite material. The data acquisition unit includes a main control chip, a capacitance measurement chip and a multiplexing module, wherein the multiplexing module includes four 8x16 matrix analog switch chips CH446Q and two single-pole four-throw switches CH444G, wherein the 16 analog signal input and output X ends of each CH446Q are connected to the 16 channels of the planar array sensor, the Y end of CH446Q is connected to the S ends of the two single-pole four-throw switches CH444G, and the Y end of the single-pole four-throw switch CH444G is connected to the measurement port of the capacitance measurement chip PCAP02; the single-pole four-throw switch CH444G is responsible for the circuit selection between the analog switch chip CH446Q and the capacitance measurement chip PCAP02 as a secondary switch, so as to select any two plates from 64 plates to measure the capacitance value; The main control chip realizes register configuration and data communication with the capacitance measurement chip PCAP02 through SPI communication. The capacitance measurement chip converts the capacitance value collected by the sensor into 24-bit data and stores it in the internal register. The main control chip reads the data from the register and converts it into decimal. The result is sent to the host computer in binary form through the serial port. The host computer converts it into the corresponding value according to the UART protocol. After the data is processed, it is combined with the image reconstruction algorithm to generate an image; at the same time, the capacitance data is directly displayed on the OLED screen for real-time monitoring; In the host computer, the finite element analysis software is used to simulate and analyze the 64-electrode planar array sensor, the electrode side length is set to 10mm, the electrode spacing is 1mm, the sensor sensitive area is 87mmx87mm, the substrate material and relative dielectric constant of the planar array sensor are set to 4.5, copper is applied on the substrate surface to realize the multi-electrode array, the relative dielectric constant of the object to be measured of the planar array sensor is set, and the sensitivity matrix S of the planar array sensor is determined by simulation analysis; The sensitive electrode measurement method is used to measure capacitance. The sensitive electrode measurement method only measures the capacitance values ​​of all side adjacent electrode pairs and corner adjacent electrode pairs of the excitation plate. For an 8x8 array sensor, the sensitive electrode measurement method only needs to detect 210 sets of data. The capacitance values ​​measured by the sensitive electrode measurement method are combined with the sensitivity matrix using the LBP algorithm to obtain the dielectric constant distribution matrix of the reconstructed image.

[0007] Furthermore, the system also includes a power supply module, which adopts a two-stage voltage reduction process, including an LM2596-5.0 chip and an AMS1117-3.3 chip. The LM2596-5.0 chip is used to convert the input 12V voltage into a 5V voltage for powering the analog switch chip CH446Q and the single-pole four-throw switch CH444G, and the AMS1117-3.3 chip is used to convert the 5V voltage into a 3.3V voltage for powering the main control chip and the capacitance measurement chip PCAP02.

[0008] Furthermore, the system also includes a backup battery circuit for coping with data loss caused by sudden power outages.

[0009] Furthermore, the system is used for damage detection of composite materials including crack defects and hole defects with length and width on the centimeter scale.

[0010] Furthermore, the length of the crack defect is 4-10 cm, the width is 1-3 cm, and the height is 0.1-0.6 cm; the length of the hole defect is 1-3 cm, the width is 1-3 cm, and the height is 0.4-0.6 cm.

[0011] Furthermore, the dielectric constant of the object to be measured is 3-5.

[0012] Furthermore, the system completes the detection within 2 seconds, meeting the requirements of fast and high-precision non-destructive testing of composite materials.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The invention is based on a capacitance tomography system of a two-level controlled 64-electrode dense planar array, and significantly improves the speed and accuracy of capacitance tomography through hardware two-level line selection control and software sensitive electrode measurement method.

[0014] Theoretical calculation and actual measurement results of the present invention show that the accuracy of the capacitance tomography system of the two-level controlled 64-plate dense planar array reaches more than 95%, and the speed reaches about 2S. Compared with the 16 or less plate planar array sensor system in the traditional capacitance tomography system, the imaging accuracy is significantly improved. Compared with the currently reported 64-plate planar array sensor using a three-level multiplexer, the detection speed is significantly improved. The system of the present invention is feasible and effective in the practical application of the non-destructive testing field of composite materials.

[0015] Since the capacitance data collected by this system is very small, and the capacitance difference between the sensor empty and full fields is at the fF level, the PCAP02 chip is selected for micro-capacitance detection, which achieves high-resolution detection with high detection accuracy, fast measurement speed, low power consumption and low price. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 This is the physical picture of the ECT system experimental platform hardware; Figure 2 It is a schematic diagram of the signal transmission structure of the ECT system; Figure 3 It is a connection diagram of various parts of the multiplexing module; Figure 4 A schematic diagram of the overall structure of a system according to an embodiment of the present invention; Figure 5 These are the planar array sensor models with different numbers of plates, where A: 16 plates; B: 64 plates; Figure 6 Schematic diagram of a 64-electrode planar array sensor according to an embodiment of the present invention; Figure 7 Comparison of the reconstruction effects of the LBP algorithm using different crack defect measurement methods; Figure 8 This is a comparison chart of the reconstruction effects of the LBP algorithm using different measurement methods for hole defects; Fig. 9 The upper computer interface displays the status diagram when the wood block is detected; Fig.10 A comparison of the imaging effects of using different sensors to detect damage to different defects in wood blocks. DETAILED DESCRIPTION

[0017] The specific embodiments of the present invention are given below. The specific embodiments are only used to further illustrate the present invention in detail and do not limit the protection scope of the present application.

[0018] The present invention is based on a two-stage controlled 64-electrode dense planar array electrical capacitance tomography (ECT) system (see Figure 1 and Figure 2 ) includes three parts: a planar array sensor, a data acquisition unit and a host computer. The planar array sensor is composed of a plurality of evenly distributed planar electrodes and is used to detect the capacitance value of the composite material. The data acquisition unit is mainly used to process the detection data of the planar array sensor and transmit it to the host computer through a serial port or Bluetooth. The host computer receives the collected data and combines the image reconstruction algorithm to restore the true value of the dielectric constant distribution, thereby realizing the visual detection of the composite material.

[0019] The data acquisition unit in the capacitance tomography system of the present invention comprises a main control chip, a capacitance measurement chip and a multiplexing module. The multiplexing module (see Figure 3) includes four 8x16 matrix analog switch chips CH446Q and two single-pole four-throw switches CH444G. The 16 analog signal input and output X ends of each CH446Q are connected to the 16 channels of the planar array sensor, and the Y end of CH446Q is connected to the S ends of the two single-pole four-throw switches CH444G. The Y end of the single-pole four-throw switch CH444G is connected to the measurement port of the capacitance measurement chip PCAP02. This is because the capacitance measurement chip PCAP02 can connect to three capacitance measurements at most at the same time, which cannot meet the detection requirements of 4 CH446Q chips. Therefore, the single-pole four-throw switch CH444G is used as a secondary switch to be responsible for the circuit selection between the analog switch chip CH446Q and the capacitance measurement chip PCAP02, so as to select any two plates from 64 plates to measure the capacitance value; In this application, an 8x16 matrix analog switch chip CH446Q is used as the first-stage analog switch to replace the 1x8 analog switch HCT4514 in the Taylor solution. The 16 analog signal input and output X ends of each CH446Q chip are connected to the 16 paths of the planar array sensor electrodes. A total of 4 CH446Q chips are required, and the Y end of the CH446Q chip is connected to the subsequent measurement circuit; a single-pole four-throw switch CH444G is selected as the secondary switch, which is responsible for the circuit selection between CH446Q and the capacitance measurement chip PCAP02. A total of two CH444G chips are required. The S end of the single-pole four-throw switch CH444G is respectively connected to the Y end of CH446Q, and the Y end of the single-pole four-throw switch CH444G is connected to the measurement port of PCAP02. The measurement of 64 plates can be achieved through two-stage control.

[0020] The overall structure of the system of the present invention is as follows: Figure 4 As shown, it includes a main control chip, a capacitance measurement chip, an analog switch, a planar array sensor, a host computer, an OLED screen and a power supply module. The STM32F103ZET6 chip is used as the main control chip. The register configuration and data communication between the capacitance measurement chip PCAP02 are realized through SPI communication. The capacitance value between two pairs of electrodes of 64 plates is measured through the analog switch unit. The channel gating of this part is also controlled by the main control chip. The capacitance measurement chip converts the capacitance value collected by the sensor into 24-bit data and stores it in the internal register. The main control chip reads the data from the register and converts it into a decimal result. The result is sent to the host computer in binary form through the serial port. The host computer converts it into the corresponding value according to the UART protocol. After the data is processed, it is combined with the image reconstruction algorithm to generate an image. At the same time, the capacitance data can also be directly displayed on the OLED screen for real-time monitoring.

[0021] The power supply module mainly includes two-stage step-down processing. The power supplies involved are 5V and 3.3V. The LM2596-5.0 chip is used to convert the input 12V voltage into 5V voltage, which is used to power the analog switch chip CH446Q and the single-pole four-throw switch CH444G. The AMS1117-3.3 chip is used to convert the 5V voltage into 3.3V voltage, which is used to power the main control chip and the capacitance measurement chip PCAP02.

[0022] The present invention also includes a backup battery circuit for dealing with data loss caused by sudden power failure. Two IN4148 diodes D1 and D2 are used (the positive pole of D1 is connected to a 3.3V power supply, the negative pole is connected to VBAT, and the positive pole of D2 is connected to a battery, and the negative pole is connected to VBAT). When the external power supply is working, the diode D1 is turned on and supplies power to the device connected to VBAT. When the external power supply is disconnected, the diode D2 is turned on, and D1 is turned off at the same time, and the battery continues to supply power to the device. For circuit protection, a Schottky diode is reversely connected to prevent current from passing when the power supply is reversely connected, so as to prevent damage to other components in the circuit.

[0023] The software preprocessing process of the present invention is as follows: using finite element analysis software to simulate and analyze the 64-electrode planar array sensor, setting the electrode plate side length to 10 mm, the electrode plate spacing to 1 mm, the sensor sensitive area to 87 mm x 87 mm, setting the substrate material and relative dielectric constant of the planar array sensor, copper coating on the substrate surface to realize a multi-electrode array, setting the relative dielectric constant of the measured object of the planar array sensor, and determining the sensitivity matrix S of the planar array sensor through simulation analysis; The sensitive electrode measurement method is used to measure capacitance. The sensitive electrode measurement method only measures the capacitance values ​​of all side adjacent electrode pairs and corner adjacent electrode pairs of the excitation plate. For an 8x8 array sensor, the sensitive electrode measurement method only needs to detect 210 sets of data. The capacitance values ​​measured by the sensitive electrode measurement method are combined with the sensitivity matrix obtained in the preprocessing process using the LBP algorithm to obtain the dielectric constant distribution matrix of the reconstructed image.

[0024] The present invention adopts the sensitive electrode measurement method to measure capacitance, taking into full consideration the large number of capacitances measured by dense planar array sensors. By deleting redundant capacitance data and retaining the capacitance values ​​that have a significant impact in the imaging process, the amount of data can be reduced while reducing noise superposition. The sensitive electrode measurement method only measures the capacitance values ​​of the side-adjacent electrode pairs and the corner-adjacent electrode pairs with higher sensitivity. Figure 6As shown in the figure, when plate 1 is used as the excitation plate, only three sets of capacitance values ​​between plates 1-2, 1-9, and 1-10 need to be detected, while the traditional method needs to detect 63 capacitance values ​​between plates 1-2, 1-3, 1-4, ..., 1-64. For an 8x8 array sensor, the sensitive electrode measurement method only needs to detect 210 sets of data, which greatly improves the measurement speed compared to the 2016 sets of data required by the traditional measurement method.

[0025] After the measured data is obtained, the measured capacitance data needs to be normalized using formula (1): (1) In the formula, To measure the capacitance value under full field condition, It is the capacitance value of the object field measurement when there are defects in the object being measured. is the capacitance value in the empty field state.

[0026] Then, the medium reconstructed image is obtained through ECT forward and inverse problem operations.

[0027] ECT forward problem operation refers to the process of obtaining the capacitance value between each pair of electrodes under given medium distribution conditions in the measured domain.

[0028] Capacitance between two plates: (3) In the formula, i and j represent the numbers of the excitation electrode and the detection electrode respectively, and D represents the cross-sectional area of ​​the object to be measured. Represents coordinates (x, y) and medium distribution A function that represents the capacitance at coordinate (x, y) Sensitivity to dielectric constant. Among them, It is not only affected by the coordinate position, but also by the dielectric constant of that position. Usually, for the convenience of solving, this phenomenon can be ignored, so the above formula can be simplified to: (4) In the formula, Capacitor By using the sensitivity function of the capacitance component and the dielectric constant distribution vector discretized and normalized, the direct problem model of ECT can be obtained: (5) Where C represents the normalized capacitance matrix, , N represents the number of independent capacitance measurements (N=nx(n-1) / 2, n is the number of electrodes), S represents the normalized sensitivity matrix, and G represents the normalized dielectric constant distribution matrix, which corresponds to the gray value matrix of the reconstructed image.

[0029] The inverse operation of ECT, namely image reconstruction, refers to the process of inverting the distribution G of the medium in the measured domain based on the measured capacitance data C and the obtained sensitivity matrix S. Its linear model is as follows: (6); The LBP (Linear backprojection) algorithm is used for image reconstruction. It does not exist, so the transpose of the sensitivity matrix S is used instead of its inverse for calculation: (7).

[0030] Correlation coefficient between the medium reconstruction image and the medium image Its definition formula is as follows: (8) Where G represents the dielectric constant distribution set by the model, represents the dielectric constant distribution of the reconstructed image; and Represents G and The average value of .

[0031] The working principle and workflow of the system of the present invention are: First, the host computer sends instructions to the slave computer to initialize the system and the capacitance measurement chip. When receiving the capacitance measurement instruction, the multiplexing module starts channel switching and cyclically stimulates the measurement of each capacitance data. When a set of data (when using the sensitive electrode measurement method, it is 210 sets of data for 64 plates) is measured, it is transmitted to the host computer through the serial port for real-time storage and imaging.

[0032] During the test, a test object of the same size as the sensor, such as a wooden block, can be placed above the sensor, and then a defect of corresponding size can be made at a certain position of the wooden block for detection.

[0033] In order to further illustrate the advantages of the system of the present invention, the following comparative analysis is performed: Example 1 Finite element analysis software was used to simulate and analyze the planar array sensor, and 16-electrode and 64-electrode planar array sensors were built. The initial electrode side length was 10 mm, and the electrode spacing was 1 mm. Figure 5As shown in the figure, the two planar array sensors have the same sensitive area, which is 87mmx87mm. The sensor model is divided into four parts: substrate, electrode plate, air domain and object to be measured. The substrate material is FR4 with a relative dielectric constant of 4.5; copper is applied on the surface of the substrate to realize the multi-electrode array; the relative dielectric constant of the object to be measured is set to 3. In the simulation analysis, the image correlation coefficient (CORR) is used as the optimization index, and the capacitance detection range, sensitivity and dielectric constant variation range of the composite material 3-5 of the PCAP02 chip are used for optimization design. The optimal electrode side length of the 64-electrode planar sensor is 10mm and the electrode spacing is 1mm. At the same time, the sensitivity matrix under this condition is obtained.

[0034] Figure 7 Table 1 shows the theoretical reconstruction images and objective evaluation indicators of the composite material with a crack defect of 9 cm in length, 1 cm in width and 0.5 cm in height using the 4x4 sensor and the 8x8 sensor, where the 4x4 sensor is recorded as sensor A and the 8x8 sensor is recorded as sensor B. It can be seen from the reconstructed images and correlation coefficients that the theoretical reconstructed image obtained by the dense sensor and sensitive electrode measurement method is significantly better than the relatively sparse 4x4 sensor, while the number of measurements only increases from 120 times in the 4x4 sensor single excitation measurement method to 210 times in the dense sensor sensitive electrode measurement method.

[0035]

[0036] Figure 8 Table 2 shows the reconstruction images and objective evaluation indicators of composite materials with 2 cm, 2 cm wide, and 0.5 cm high hole defects using 4x4 sensors and 8x8 sensors. From the imaging results and correlation coefficients, sensor B is closer to the standard image, and the imaging effect of the data measured by the sensitive electrode measurement method is better.

[0037]

[0038] In summary, when other conditions remain unchanged, the detection effect of sensor B is significantly better than that of sensor A. At the same time, the results show that the sensitive electrode measurement method that deletes redundant data not only reduces the number of measured capacitances, but also improves the quality of reconstructed images.

[0039] The constructed ECT system was used to conduct a physical experiment. The object to be tested was a small wooden block with a length of 2 cm, a width of 1 cm, and a height of 1 cm. Its dielectric constant was 3, which is similar to that of common composite materials used in aviation. The object to be tested was placed at different positions above the planar array sensor, and the capacitance data was measured using the sensitive electrode measurement method to observe the imaging effects of different defect positions. Fig.10In the figure, 1 refers to a defect at the lower left corner of the sensor, and 2 refers to a defect at the center of the sensor. The difference is that the positions are different, but the defect sizes are the same. In this embodiment, a small wooden block is directly used as a defect, and the surrounding air is used as a non-defective one, and imaging is performed using the difference in detection capacitance data.

[0040]

[0041] Depend on Fig.10 As can be seen from Table 3, for different defect distribution types, the image reconstruction effect of sensor B is better than that of sensor A. Under the same defect conditions, the reconstructed image of sensor B is less affected by noise and has a larger CORR value, that is, the detection accuracy is higher and it can resist 40dB noise interference. In terms of system detection speed, sensor B only takes 2 seconds to measure 210 sets of data, which fully meets the requirements of fast and high-precision non-destructive testing of composite materials. In summary, the overall effect of the dense planar array is far better than that of sensor A, proving its feasibility in the field of non-destructive testing of composite materials.

[0042] Example 2 The parameters of the planar array sensor in this embodiment are: 8*8 array, substrate size is 89mm*89mm, material is FR4, plate size is 10mm*10mm, material is copper, and plate spacing is 1mm.

[0043] The main control chip is STM32F103ZET6, which communicates with the capacitance measurement chip PCAP02 through SPI. The communication modes with the host computer include wired and wireless. The wired transmission uses CH340 to communicate with the host computer through the serial port, and the wireless transmission uses the ESP8266 module to realize communication.

[0044] The capacitance measurement chip PCAP02 is connected to the planar array sensor in a normal drift mode, a 1PF ceramic capacitor is used as a reference capacitor, and PC6 and PC7 are selected as power detection ports.

[0045] Analog switch chip CH446Q: Since CH446Q is an 8*16 matrix analog switch, 4 chips are selected to realize the gate measurement of 64 signals. The 16 X ports are connected to the plates of the planar array sensor, and the Y port is connected to the subsequent CH444G.

[0046] Single-pole four-throw switch CH444G: Two pieces of CH444G are used to realize the circuit selection between CH446Q and PCAP02. The S end of CH444G is connected to the Y end of CH446Q respectively, and the Y end of CH444G is connected to the two measurement ports of PCAP02 respectively.

[0047] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A capacitance tomography system based on a two-level controlled 64-plate dense planar array, comprising a planar array sensor, a data acquisition unit and a host computer, wherein the planar array sensor is composed of 8x8 evenly distributed plates and is used to detect the capacitance value of a composite material; the data acquisition unit is mainly used to process the detection data of the planar array sensor and transmit it to the host computer through a serial port or Bluetooth; the host computer receives the collected data and restores the true value of the dielectric constant distribution in combination with an image reconstruction algorithm to realize visual detection of the composite material; it is characterized in that: The data acquisition unit includes a main control chip, a capacitance measurement chip and a multiplexing module, wherein the multiplexing module includes four 8x16 matrix analog switch chips CH446Q and two single-pole four-throw switches CH444G, wherein the 16 analog signal input and output X ends of each CH446Q are connected to the 16 channels of the planar array sensor, the Y end of CH446Q is connected to the S ends of the two single-pole four-throw switches CH444G, and the Y end of the single-pole four-throw switch CH444G is connected to the measurement port of the capacitance measurement chip PCAP02; the single-pole four-throw switch CH444G is responsible for the circuit selection between the analog switch chip CH446Q and the capacitance measurement chip PCAP02 as a secondary switch, so as to select any two plates from 64 plates to measure the capacitance value; The main control chip realizes register configuration and data communication with the capacitance measurement chip PCAP02 through SPI communication. The capacitance measurement chip converts the capacitance value collected by the sensor into 24-bit data and stores it in the internal register. The main control chip reads the data from the register and converts it into decimal. The result is sent to the host computer in binary form through the serial port. The host computer converts it into the corresponding value according to the UART protocol. After the data is processed, it is combined with the image reconstruction algorithm to generate an image; at the same time, the capacitance data is directly displayed on the OLED screen for real-time monitoring; In the host computer, the finite element analysis software is used to simulate and analyze the 64-electrode planar array sensor, the electrode side length is set to 10mm, the electrode spacing is 1mm, the sensor sensitive area is 87mmx87mm, the substrate material and relative dielectric constant of the planar array sensor are set to 4.5, copper is applied on the substrate surface to realize the multi-electrode array, the relative dielectric constant of the object to be measured of the planar array sensor is set, and the sensitivity matrix S of the planar array sensor is determined by simulation analysis; The sensitive electrode measurement method is used to measure capacitance. The sensitive electrode measurement method only measures the capacitance values ​​of all side adjacent electrode pairs and corner adjacent electrode pairs of the excitation plate. For an 8x8 array sensor, the sensitive electrode measurement method only needs to detect 210 sets of data. The capacitance values ​​measured by the sensitive electrode measurement method are combined with the sensitivity matrix using the LBP algorithm to obtain the dielectric constant distribution matrix of the reconstructed image.

2. The system according to claim 1, characterized in that The system also includes a power supply module, which adopts a two-stage step-down process, including an LM2596-5.0 chip and an AMS1117-3.3 chip. The LM2596-5.0 chip is used to convert the input 12V voltage into a 5V voltage for powering the analog switch chip CH446Q and the single-pole four-throw switch CH444G. The AMS1117-3.3 chip is used to convert the 5V voltage into a 3.3V voltage for powering the main control chip and the capacitance measurement chip PCAP02.

3. The system according to claim 1, characterized in that The system also includes a backup battery circuit for coping with data loss caused by sudden power failure.

4. The system according to claim 1, characterized in that The system is used for damage detection of composite materials including crack defects and hole defects with length and width on the centimeter scale.

5. The system according to claim 1, characterized in that The crack defect has a length of 4-10 cm, a width of 1-3 cm, and a height of 0.1-0.6 cm; the hole defect has a length of 1-3 cm, a width of 1-3 cm, and a height of 0.4-0.6 cm.

6. The system according to claim 1, characterized in that The dielectric constant of the object to be measured is 3-5.

7. The system according to claim 1, characterized in that The system completes the test within 2 seconds, meeting the requirements of fast and high-precision non-destructive testing of composite materials.

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