Coplanar capacitive sensor and method for optimizing the same

Abstract

The application relates to a coplanar capacitive sensor and an optimization method thereof, and belongs to the technical field of capacitive sensing, and solves the technical problem of poor imaging effect of a single-pair-electrode coplanar capacitive sensor in the prior art. The optimization method of the coplanar capacitive sensor comprises the following steps: changing the shape of adjacent edges of two electrodes, increasing the spacing of a part of positions of the adjacent edges of the two electrodes, and keeping the spacing of another part of positions of the adjacent edges of the two electrodes unchanged, so that an optimized coplanar capacitive sensor is obtained. In the application, by changing the shape of the adjacent edges of the two electrodes, the sensitivity distribution and the detection performance indexes such as the detection depth of the coplanar capacitive sensor are optimized, so that the imaging effect of the coplanar capacitive sensor is improved.

Description

Technical Field

[0001] This invention relates to the field of capacitive sensing technology, and in particular to a coplanar capacitive sensor and its optimization method. Background Technology

[0002] In capacitive sensing technology, the most common electrode structures are parallel plate electrodes and coplanar electrodes. Coplanar capacitive sensors operate based on the edge effect of an electric field. Compared to traditional parallel plate capacitive sensors, coplanar capacitive sensors offer advantages such as an open measurement space, easy control of signal strength by changing electrode dimensions, and the ability to exhibit multiple physical effects (electric, magnetic, and acoustic) within a single structure. Therefore, they are widely used in material performance monitoring, humidity sensing, electrical insulation performance sensing, chemical sensing, and biosensing. As an open sensor, coplanar capacitive sensors can measure various non-metallic objects under non-enclosed conditions, greatly expanding the application range of capacitive sensors.

[0003] Among them, the single-pair coplanar capacitance sensor uses moving scan imaging. Currently, in existing single-pair coplanar capacitance sensors, the electrodes are generally rectangular in shape. However, the moving scan imaging of this type of single-pair coplanar capacitance sensor is limited by the sensor's sensitive field distribution characteristics, resulting in large imaging artifacts, severe stretching problems, and low resolution. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide a coplanar capacitance sensor to solve the technical problem of poor imaging performance of existing single-pair electrode coplanar capacitance sensors.

[0005] On one hand, embodiments of the present invention provide an optimization method for a coplanar capacitance sensor, wherein the coplanar capacitance sensor to be optimized includes two electrodes symmetrically arranged, and the initial shape of the two electrodes is rectangular;

[0006] The optimization method includes:

[0007] By changing the shape of the adjacent sides of the two electrodes, the distance between a portion of the adjacent sides of the two electrodes is increased, while the distance between another portion of the adjacent sides of the two electrodes remains unchanged, thereby obtaining an optimized coplanar capacitance sensor.

[0008] A further improvement to the above method involves changing the shape of adjacent sides of the two electrodes, including the following steps:

[0009] The chamfer length is selected based on the electrode dimensions and the performance specifications of the coplanar capacitance sensor.

[0010] Based on the selected chamfer length, chamfer the corners at both ends of the adjacent sides of the two electrodes.

[0011] Based on a further improvement to the above method, the chamfer length is selected according to the electrode size and the performance indicators of the coplanar capacitance sensor, including:

[0012] The range of values ​​for the chamfer length is determined based on the dimensions of the electrode;

[0013] The chamfer length is selected within the range specified based on the performance parameters of the coplanar capacitance sensor.

[0014] A further improvement to the above method, wherein determining the range of values ​​for the chamfer length based on the dimensions of the electrode includes:

[0015] If L≥2W, then 0<R≤2W;

[0016] If L < 2W, then 0 < R ≤ 0.5L;

[0017] Where R is the chamfer length, L is the electrode length, and W is the electrode width.

[0018] Based on further improvements to the above method, the performance indicators include: measurement sensitivity, detection depth, and signal strength.

[0019] A further improvement to the above method, wherein selecting the chamfer length within the range based on the performance indicators of the coplanar capacitance sensor includes:

[0020] If the signal strength of the coplanar capacitance sensor optimized using the maximum value in the range as the chamfer length is greater than or equal to a preset threshold, then the maximum value in the range is selected as the chamfer length, or the chamfer length is selected from the range based on the measurement sensitivity and / or the detection depth.

[0021] A further improvement to the above method, wherein selecting the chamfer length within the range based on the performance indicators of the coplanar capacitance sensor includes:

[0022] If the signal strength of the coplanar capacitance sensor optimized using the maximum value in the range as the chamfer length is less than a preset threshold, then the chamfer length is selected from the range based on the signal strength.

[0023] A further improvement to the above method, where the signal strength of the coplanar capacitance sensor optimized using the maximum value in the range as the chamfer length is less than a preset threshold, involves selecting the chamfer length from the range based on the signal strength, including the following steps:

[0024] Step 100: Set the current chamfer length R t =R max -λ;

[0025] Step 200: Determine whether to use the current chamfer length R t If the signal strength of the optimized coplanar capacitance sensor is less than a preset threshold, then select the current chamfer length R. t Perform a chamfering operation on the electrodes; if so, proceed to step 300.

[0026] Step 300: Make R t =R t -λ, if R t If R = 0, the process ends; if R = 0, the process ends. t If R is not equal to 0, then return to step 200; where R max λ represents the maximum value within the range of values, and λ is the step size for taking values.

[0027] Based on a further improvement of the above method, after optimizing the performance of the coplanar capacitance sensor, the optimization method also includes a verification step for the imaging effect of the optimized coplanar capacitance sensor:

[0028] The imaging performance of the optimized coplanar capacitance sensor was verified by scanning the defective test object with the optimized coplanar capacitance sensor to obtain reconstructed images.

[0029] On the other hand, embodiments of the present invention provide a coplanar capacitance sensor obtained using the above-described optimization method. The coplanar capacitance sensor includes two electrodes arranged symmetrically, wherein the distance between a portion of the adjacent sides of the two electrodes is greater than the distance between the other portion.

[0030] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0031] 1. In this invention, by changing the shape of the adjacent sides of the two electrodes, the detection performance indicators such as the sensitivity distribution and detection depth of the coplanar capacitance sensor are optimized, thereby improving the imaging effect of the coplanar capacitance sensor.

[0032] 2. In this invention, by changing the shape of the adjacent sides of two adjacent electrodes by means of chamfering, the distance between a part of the adjacent sides of the two electrodes can be increased, while the distance between another part of the adjacent sides of the two electrodes remains unchanged. This is easy to implement and easy to control.

[0033] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0034] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0035] Figure 1 This is a flowchart of an optimization method for a coplanar capacitance sensor in an embodiment of the present invention;

[0036] Figure 2 This is a schematic diagram of the coplanar capacitance sensor (sensor I) to be optimized in an embodiment of the invention;

[0037] Figures 3a to 3e The following are schematic diagrams of sensors II, III, IV, V, and VI in the embodiments of the present invention, in sequence.

[0038] Figures 4a to 4f The following are schematic diagrams of the sensitive field distribution of sensors 1 to VI in the embodiments of the present invention;

[0039] Figure 5 This is a schematic diagram illustrating the changes in measurement sensitivity of sensors 1 to VI in an embodiment of the present invention;

[0040] Figure 6 This is a schematic diagram illustrating the changes in detection depth from sensor 1 to sensor VI in an embodiment of the present invention;

[0041] Figure 7 This is a schematic diagram of the signal strength changes from sensor 1 to sensor VI in an embodiment of the present invention;

[0042] Figures 8a to 8f The images shown are, in sequence, reconstructed images of the object being measured obtained by sensors 1 to VI in Embodiment 2 of the present invention.

[0043] Figure 9 This shows the dielectric constant distribution of the test object in Embodiment 2 of the present invention;

[0044] Figure 10 This is a schematic diagram of the root mean square error variation of the reconstructed images acquired by sensors 1 to VI in Embodiment 2 of the present invention;

[0045] Figure 11 This is a schematic diagram showing the changes in the correlation coefficients of the reconstructed images acquired by sensors 1 to VI in Embodiment 2 of the present invention;

[0046] Figures 12a to 12f The images shown are, in sequence, the reconstructed images acquired by sensors 1 to 6 in Embodiment 3 of the present invention;

[0047] Figure 13a and Figure 13b The image reconstruction result of sensor I in Embodiment 4 of the present invention;

[0048] Figure 14a and Figure 14b The image reconstruction result of sensor V in Embodiment 4 of the present invention;

[0049] Figure 15 This is a graph showing the change in detection depth of five different sensor sizes according to embodiments of the present invention;

[0050] Figure 16 This is a graph showing the signal strength variation of sensors of five different sizes according to embodiments of the present invention;

[0051] Figures 17a to 17e The images shown are, in sequence, reconstructed images acquired by unoptimized sensors of five different sizes according to embodiments of the present invention;

[0052] Figures 18a to 18e The images shown are, in sequence, reconstructed images acquired by sensors of five different sizes optimized using the maximum chamfer length, according to embodiments of the present invention.

[0053] Figure 19 This is a graph showing the correlation coefficient changes of reconstructed images acquired by sensors of five different sizes in Embodiment 5 of the present invention;

[0054] Figure 20 This is a graph showing the variation of root mean square error in reconstructed images acquired by sensors of five different sizes in Embodiment 5 of the present invention.

[0055] Figure label:

[0056] 1-Electrode. Detailed Implementation

[0057] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0058] One specific embodiment of the present invention discloses an optimization method for a coplanar capacitive sensor. The coplanar capacitive sensor to be optimized includes two symmetrically arranged electrodes 1, the initial shape of which is rectangular.

[0059] The optimization method includes: changing the shape of the adjacent sides of the two electrodes 1, increasing the distance between the two ends of the adjacent sides of the two electrodes, while keeping the distance between the central parts of the adjacent sides of the two electrodes unchanged, thereby obtaining an optimized coplanar capacitance sensor.

[0060] Among them, the shape of electrode 1 of the coplanar capacitance sensor has a great influence on its imaging effect.

[0061] Compared with the prior art, the optimization method in this embodiment of the invention improves the imaging effect of the coplanar capacitance sensor by changing the shape of the adjacent sides of the two electrodes 1 and optimizing the detection performance indicators such as the sensitivity distribution and detection depth of the coplanar capacitance sensor.

[0062] At the same time, when changing the shape of the adjacent sides of the two electrodes 1, the distance between the two ends of the adjacent sides of the two electrodes 1 is increased, while the distance between the middle parts of the adjacent sides of the two electrodes 1 remains unchanged, so that the relative position of the two electrodes 1 does not change, thus avoiding the occurrence of multiple variables.

[0063] In the coplanar capacitive sensor to be optimized, the long sides of the two electrodes 1 are adjacent.

[0064] like Figure 1 As shown, in one embodiment, changing the shape of adjacent sides of the two electrodes 1 includes the following steps:

[0065] Step 1: Select the chamfer length based on the size of electrode 1 and the performance indicators of the coplanar capacitance sensor.

[0066] Step 2: According to the selected chamfer length, perform chamfering operation on the corners at both ends of the adjacent sides of the two electrodes 1.

[0067] In this invention, by chamfering the shape of the adjacent sides of the two electrodes 1, the distance between the two ends of the adjacent sides of the two electrodes 1 can be increased, while the distance between the central parts of the adjacent sides of the two electrodes 1 remains unchanged. This is easy to implement and control. Furthermore, chamfering the corners at both ends of the adjacent sides of the electrodes 1 ensures that the position of the center of the sensitive field at the top of the sensor does not change.

[0068] Preferably, the chamfering angle of the above-mentioned chamfering operation is 45°.

[0069] It should be noted that in the above chamfering operation, chamfering refers to connecting two objects with a diagonal line. The chamfer length mentioned above refers to the amount of the long and wide sides of electrode 1 removed after the chamfering operation.

[0070] Specifically, step 1: Selecting the chamfer length based on the dimensions of electrode 1 and the performance specifications of the coplanar capacitive sensor includes:

[0071] Step 10: Determine the range of values ​​for the chamfer length based on the dimensions of the electrode 1;

[0072] Step 11: Select the chamfer length within the specified range based on the performance indicators of the coplanar capacitance sensor.

[0073] In this embodiment, the chamfer length is determined based on the size of electrode 1. This ensures that when the adjacent sides of the two electrodes 1 are changed by chamfering, the overall spacing between the two electrodes 1 will not change. Then, the chamfer length is selected within the range of values ​​based on the performance indicators of the coplanar capacitance sensor, thereby determining the chamfer length that meets the detection requirements.

[0074] More specifically, determining the range of values ​​for the chamfer length based on the dimensions of the electrode 1 includes:

[0075] If L≥2W, then 0<R≤2W;

[0076] If L < 2W, then 0 < R ≤ 0.5L;

[0077] Where R is the chamfer length, L is the length of electrode 1, and W is the width of electrode 1.

[0078] Specifically, in step 11, the performance indicators of the coplanar capacitance sensor include: measurement sensitivity, detection depth, and signal strength.

[0079] It should be noted that, in this embodiment of the invention, the measurement sensitivity is defined as the ratio between the change in capacitance value measured by the coplanar capacitance sensor and the change in dielectric constant of the measured object that caused the change in capacitance value. That is, the definition of the measurement sensitivity S is as follows:

[0080]

[0081] In the formula, ΔC is the change in capacitance, and Δε is the change in dielectric constant.

[0082] Detection depth refers to the maximum detection distance of a coplanar capacitive sensor. It is defined as the capacitance C(d = γ) at which the object being measured is located at that distance above the coplanar capacitive sensor. 3％ The difference between the capacitance value C(d=∞) when the measured object is at infinity above the sensor and the capacitance value C(d=∞) when the measured object is just on the sensor is exactly 3% of the difference between the capacitance value C(d=0) when the measured object is at infinity above the sensor and the capacitance value C(d=∞) when the measured object is at infinity above the sensor. Its mathematical description is as follows:

[0083]

[0084] In a specific embodiment, step 2: selecting the chamfer length within the range of values ​​based on the performance indicators of the coplanar capacitance sensor includes:

[0085] (1) If the signal strength of the coplanar capacitance sensor optimized by using the maximum value in the range as the chamfer length is greater than or equal to a preset threshold, then the maximum value in the range is selected as the chamfer length, or the chamfer length is selected from the range according to the measurement sensitivity and / or the detection depth.

[0086] (2) If the signal strength of the coplanar capacitance sensor optimized by using the maximum value in the range as the chamfer length is less than a preset threshold, then the chamfer length is selected from the range based on the signal strength.

[0087] Studies have found that when optimizing electrode 1 through chamfering, better measurement sensitivity and detection depth can be obtained as the chamfer length increases. However, the signal strength of the coplanar capacitance sensor will decrease. Therefore, in this invention, it is first necessary to verify whether the signal strength requirement (i.e., signal strength greater than or equal to a preset threshold) is met when the maximum value in the range is used as the chamfer length. If the signal strength requirement is met, the maximum value in the range can be selected as the chamfer length to obtain the optimal measurement sensitivity or detection depth, or the chamfer length can be selected according to actual needs. If the signal strength requirement is not met, the corresponding chamfer length needs to be selected according to the signal strength requirement.

[0088] Furthermore, if the signal strength of the coplanar capacitance sensor optimized using the maximum value in the range as the chamfer length is less than a preset threshold, then selecting the chamfer length from the range based on the signal strength includes the following steps:

[0089] Step 100: Set the current chamfer length R t =R max -λ;

[0090] Step 200: Determine whether to use the current chamfer length R t If the signal strength of the optimized coplanar capacitance sensor is lower than a preset threshold, then select the current chamfer length R. t Perform a chamfering operation on electrode 1; if so, proceed to step 300.

[0091] Step 300: Make R t =R t -λ, if R t If R = 0, the process ends; if R = 0, the process ends. t If R is not equal to 0, then return to step 200; where R max λ represents the maximum value within the range of values, and λ is the step size for taking values.

[0092] In this embodiment, the maximum value R in the range is thus determined. max Starting the judgment process helps reduce the number of calculations and quickly select the chamfer length.

[0093] It should be noted that the signal strength of the coplanar capacitance sensor to be optimized generally meets the requirements. Therefore, in step 300, R is generally not considered. t =0. If in step 300, R is reached. t When the value is 0, it may be because the value step size λ is set too large. The value step size λ can be reduced and the operation of selecting the chamfer length from the value range according to the signal strength can be performed again.

[0094] Furthermore, steps 100 to 300 in this embodiment are performed in simulation software.

[0095] In another embodiment, if the signal strength of the coplanar capacitance sensor optimized using the maximum value in the range as the chamfer length is less than a preset threshold, then selecting the chamfer length from the range based on the signal strength includes the following steps: starting from the minimum value in the range, gradually increasing the chamfer length with a preset step size, performing chamfering operations on the two corners at both ends of the adjacent sides of electrode 1 until the signal strength of the coplanar capacitance sensor is the preset threshold.

[0096] In one embodiment, after optimizing the performance of the coplanar capacitance sensor, the optimization method further includes a verification step for the imaging effect of the optimized coplanar capacitance sensor:

[0097] Step 3: Scan the defective test object with the optimized coplanar capacitance sensor to obtain a reconstructed image, in order to verify the imaging effect of the optimized coplanar capacitance sensor.

[0098] Specifically, in step 3, the Landweber algorithm can be used for image reconstruction. The Landweber iterative algorithm is a widely used method in the field of coplanar capacitance imaging technology, and it is developed from the gradient descent method. Based on the least squares criterion, it corrects the solution in the negative gradient direction of the data residuals, transforming the solution of the inverse problem of coplanar capacitance imaging technology into the solution of the extremum problem of the objective function functional. Its objective function is as follows:

[0099]

[0100] To find the minimum value of equation (3-1), we expand it, and the function is as follows:

[0101]

[0102] Taking the derivative of f(G) in equation (3-2), we can obtain the formula for calculating the gradient residual:

[0103]

[0104] Using the LBP algorithm results as the initial values ​​for the iterative process, and combining them with the gradient descent method, the iterative formula for the Landweber iterative image reconstruction algorithm can be obtained:

[0105]

[0106] In the formula, α is the iteration factor; k is the number of iterations;

[0107] By continuously iterating using the Landweber iterative algorithm, a reconstructed image with high quality and clear edges can be obtained.

[0108] To evaluate the feasibility of the designed coplanar capacitance acquisition system, the root mean square error (RMSE) of the reconstructed image is used to assess its quality. The definition of the RMSE E of the reconstructed image is:

[0109]

[0110] In the formula, G R G represents the actual relative permittivity distribution inside the test object. F R represents the reconstructed relative permittivity distribution inside the analyte; R is the number of rows in the relative permittivity distribution matrix; and C is the number of columns in the relative permittivity distribution matrix.

[0111] The correlation coefficient Ic of the reconstructed image refers to the linear correlation between the vectors before and after image reconstruction, and its calculation formula is as follows:

[0112]

[0113] In the formula, and These are the average values ​​of G' and G, respectively.

[0114] A second aspect of the present invention provides a coplanar capacitance sensor obtained using the above-described optimization method, such as... Figures 3a to 3e As shown in the figure. The coplanar capacitive sensor includes two electrodes 1 arranged symmetrically, wherein the distance between a portion of the adjacent sides of the two electrodes 1 is greater than the distance between the other portion.

[0115] Preferably, the distance between the two ends of the adjacent sides of the two electrodes 1 is greater than the distance between their central parts.

[0116] The coplanar capacitance sensor obtained by the optimization method in this embodiment of the invention improves the imaging effect of the coplanar capacitance sensor by changing the shape of the adjacent sides of the two electrodes 1 and optimizing the detection performance indicators such as the sensitivity distribution and detection depth of the coplanar capacitance sensor.

[0117] The following describes in detail the detection performance indicators and imaging effects of the coplanar capacitance sensor obtained through the optimization method of this embodiment of the invention.

[0118] Example 1

[0119] In this embodiment, Figure 2 A coplanar capacitive sensor to be optimized, designated Sensor I, is shown, with a rectangular electrode 1. Electrode 1 of the sensor to be optimized is a rectangular plate with a length of 20 mm and a width of 60 mm. Electrode 1 of Sensor I was optimized using chamfer lengths of 5 mm, 10 mm, 15 mm, and 20 mm, respectively, yielding the following results. Figure 3a , Figure 3b , Figure 3c and Figure 3d The coplanar capacitive sensors with optimized electrode 1 shown in sequence are numbered Sensor II, Sensor III, Sensor IV, and Sensor V. For comparison, a coplanar capacitive sensor with adjacent sides of electrode 1 of Sensor I shortened to a single point (i.e., triangular electrode 1) was also added for comparison. Figure 3e As shown, its number is sensor VI.

[0120] Among them, such as Figure 7 As shown, although the signal strength of sensors 1 to 6 gradually decreases, the signal strength of all sensors 1 to 6 still meets the signal strength requirements.

[0121] I. Regarding Measurement Sensitivity

[0122] Figures 4a to 4f The sensitive field distributions of sensors I through VI are shown respectively. Figures 4a to 4f It can be seen that as the adjacent sides of electrode 1 gradually change, the sensitivity distribution also changes accordingly. In single-sensor scanning imaging, the more concentrated the sensor sensitivity distribution is within the test area, the better the imaging effect. Figures 4a to 4f The sensitivity distribution in the three-dimensional view is regarded as a "brush". As the adjacent sides become shorter, the "brush" becomes thinner, which means that the sensitivity distribution of the sensitive field has been optimized.

[0123] Figure 5 The measurement sensitivity of sensors I to VI is shown in the figure. It can be seen that as the chamfer length increases, the measurement sensitivity of sensors I to VI gradually decreases (becomes better), while the measurement sensitivity of sensor V is better than that of sensor VI.

[0124] II. Regarding the depth of detection

[0125] In this embodiment, a 1mm thick epoxy resin plate is placed in the measurement domain of sensors 1 to 6, and lifted out in 0.2mm increments. The detection depth of each sensor is obtained by measuring the capacitance value. The detection depth variation curves of each sensor are shown below. Figure 6 As shown in the image.

[0126] Depend on Figure 6 It can be seen that as the chamfer length increases, the detection depth of sensors I to VI gradually increases (becomes better), while the detection depth of sensor V is better than that of sensor VI.

[0127] Example 2

[0128] In this embodiment, the improvement effect of the coplanar capacitive sensor optimization method of the present invention on the reconstructed image quality is verified by simulation.

[0129] In this embodiment, sensors 1 through VI are used to perform scanning imaging simulation experiments on the same defective object. The object is 150mm × 150mm in size, the defect is 30mm × 30mm in size, and the material of the object is an epoxy resin board with a dielectric constant of 4.5. Under the same scanning step size and scanning mode, the Landweber algorithm is used for image reconstruction.

[0130] By iteratively applying the Landweber algorithm, a reconstructed image with high quality and clear edges can be obtained, as shown in the image below. Figures 8a to 8f As shown in the image.

[0131] To evaluate the feasibility of the designed coplanar capacitance acquisition system, the root mean square error (RMSE) and correlation coefficient of the reconstructed images are used to assess the image quality. Since calculating the RMSE requires knowledge of the actual dielectric constant distribution within the object under test, the dielectric constant distribution from the simulation experiment is calculated based on the relative positions of the defects and the object under test. Figure 9 As shown.

[0132] Based on the calculated dielectric constant distribution matrix, the root mean square error E, the quality evaluation index of the reconstructed image of the internal defects of the test object, is obtained using equation (3-5). Figure 10 The figure shows the root mean square error of the reconstructed images obtained by sensors 1 to VI through simulation in this embodiment. Simultaneously, the correlation coefficient of the reconstructed image quality evaluation index for internal defects of the tested object is calculated using equation (3-6). Figure 11 The figure shows the root mean square error of the reconstructed images obtained by sensors I to VI through simulation in this embodiment.

[0133] It can be seen that as the chamfer radius increases, the "brush" of the sensitivity distribution from sensor I to sensor V narrows, improving the resolution of the scanning image and reducing the root mean square error of the image, thus achieving image optimization. In other words, optimizing the sensitivity distribution can significantly improve the scanning imaging results. Furthermore, compared to sensor VI, sensor V has a narrower "brush" of sensitivity distribution, resulting in higher scanning image resolution, lower root mean square error of the reconstructed image, and a higher correlation coefficient. Therefore, the imaging results of sensor V are superior to those of sensor VI.

[0134] Example 3

[0135] In this embodiment, the effect of the optimization method of the coplanar capacitance sensor of the present invention on improving the quality of reconstructed images is verified through measurement experiments.

[0136] In this embodiment, sensors 1 through VI are used to perform scanning imaging experiments on the same defective test object. The test object is 150mm × 150mm in size, the defect is 30mm × 30mm in size, and the material of the test object is an epoxy resin board with a dielectric constant of 4.5.

[0137] The operation steps of the measurement experiment in this embodiment are the same as those of the simulation experiment in Embodiment 2. Due to the influence of the experimental environment and instrument errors, the experimental data are greatly affected by the environment; therefore, a wavelet filtering algorithm is used to process the experimental data. Specifically, the images obtained by sensors 1 to VI scanning the object being measured are shown below. Figures 12a to 12f As shown in the image.

[0138] Figure 10 The figure shows the root mean square error of the reconstructed images obtained by scanning and imaging sensors 1 to VI in this embodiment through experiments. Figure 11 The figure shows the root mean square error of the reconstructed images obtained by sensors I to VI through experiments in this embodiment.

[0139] from Figure 10 , Figure 11 as well as Figures 12a to 12f It can be seen that the measurement experiment results are consistent with the simulation experiment results, and the internal defects of the measured object can be identified well. The results show that as the chamfer length increases, the accuracy of sensor I to sensor VI in restoring the defect shape gradually improves, and the tensile deformation problem gradually decreases. Among these, observation... Figure 12b It can be observed that when the chamfer length is too small, it has no significant effect on the sensor's scanning imaging. (Comparison) Figure 12e and Figure 12f It can be observed that, compared to sensor VI, sensor V scanning imaging produces fewer artifacts and has better imaging results, which is caused by the insufficient signal strength.

[0140] Furthermore, in this embodiment of the invention, scanning imaging was also performed on test objects with circular and triangular defects. It was found that the optimized sensors could more realistically reproduce the shape and size of the defects, with fewer artifacts in the reconstructed images and a significant improvement in stretching deformation. Especially for scanning small defects, the difference in imaging performance between the various sensors was more pronounced.

[0141] Example 4

[0142] In this embodiment, by comparing the scanning imaging of sensor I (the coplanar capacitance sensor to be optimized) and sensor V (the optimized coplanar capacitance sensor), the improvement of the stretching and deformation problem of the reconstructed image by the optimization method of this embodiment is illustrated.

[0143] Due to the sensitivity distribution characteristics of a single pair of coplanar capacitive sensors, the scanned image is also stretched along the sensitivity distribution direction. Therefore, the stretching directions of the images obtained by horizontal scanning and vertical scanning are different.

[0144] In this embodiment, the measured area of ​​the object is 150mm × 150mm, and it has five defects (small defects) with sides of 10mm × 10mm. The object is scanned laterally and longitudinally using sensor I and sensor V respectively. The image reconstruction result of sensor I is as follows. Figure 13a and Figure 13b As shown, the image reconstruction results of sensor V are as follows: Figure 14a and Figure 14b As shown.

[0145] from Figure 13a and Figure 13b As can be seen, for the unoptimized sensor I, different scanning directions have a significant impact on the scanning results, resulting in severe defect deformation. For square defects, the scanned image is elliptical, exhibiting severe stretching issues, and adjacent defects show adhesion, indicating that the sensor has low resolution. When using this sensor to scan and reconstruct images, a combination of longitudinal and lateral scanning is required, which wastes more time.

[0146] from Figure 14a and Figure 14b As can be seen from the data, for the sensor V optimized using the optimization method of the present invention, different scanning directions have little impact on the scanning results, the defect deformation is significantly improved, the adhesion between adjacent defects is reduced, and for square defects, the scanned image is circular, which greatly reduces the stretching problem and the shape restoration is higher, indicating that the sensor has high resolution and good imaging effect.

[0147] Example 5

[0148] To verify the universality of the optimization method for the coplanar capacitive sensor in this embodiment of the invention, five coplanar capacitive sensors of different sizes were selected for optimization verification in this embodiment.

[0149] In this embodiment, the electrode 1 dimensions of the five coplanar capacitive sensors to be optimized are 10mm×30mm, 15mm×45mm, 20mm×60mm, 25mm×75mm, and 30mm×90mm, respectively. When performing chamfer optimization on these five coplanar capacitive sensors, the chamfer length values ​​are respectively 0-10mm, 0-15mm, 0-20mm, 0-25mm, and 0-30mm, with each chamfer length varying in 5mm increments to obtain the corresponding optimized sensors. Simultaneously, for comparison, a coplanar capacitive sensor with its adjacent sides of electrode 1 shortened to a single point (i.e., triangular electrode 1) is added for comparison. Therefore, for the five sensors to be optimized, 4, 5, 6, 7, and 8 sensors are obtained for comparison, respectively.

[0150] The performance parameters of the five sensors of different sizes are shown in Table 1. The detection depth variations of the sensors are as follows: Figure 15 As shown in the figure, the signal strength changes as follows Figure 16 As shown in the image.

[0151] Table 1

[0152]

[0153] Depend on Figure 15 and Figure 16 As can be seen from Table 1, the detection depth of the sensors of the above five sizes increases as the adjacent sides of electrode 1 become shorter, while the signal strength decreases as the adjacent sides of electrode 1 become shorter.

[0154] Under the same experimental conditions, an unoptimized sensor and a sensor optimized using the maximum chamfer length were selected from the five sensor sizes mentioned above. These were used to scan and image a defective test object to obtain reconstructed images. The test object was a 150mm × 150mm × 3mm epoxy resin board with a 30mm × 30mm × 3mm hole in its center. The reconstructed image acquired by the unoptimized sensor is shown below. Figures 17a to 17e As shown; the reconstructed image acquired by the sensor optimized using the maximum chamfer length is as follows. Figures 18a to 18e As shown in the image.

[0155] Through comparison, it is evident that optimizing the coplanar capacitance sensor using the optimization method of this invention can improve image resolution, enhance the sensor's ability to identify the shape and size of defects, and reduce tensile deformation problems.

[0156] Furthermore, image evaluation is performed using image correlation coefficient and root mean square error. The variations in correlation coefficient and root mean square error of the reconstructed images acquired by the five sensor sizes mentioned above are as follows: Figure 19 and Figure 20 As shown in the image.

[0157] Depend on Figure 19 and Figure 20 As can be seen, the quality of the reconstructed images obtained by sensors of all sizes is improved after optimization. The correlation coefficients of the reconstructed images all increase, and the root mean square errors all decrease. This verifies the universality of the optimization method for the coplanar capacitance sensor in this embodiment of the invention.

[0158] Those skilled in the art will understand that all or part of the processes of the methods described in the above embodiments can be implemented by a computer program instructing related hardware, and the program can be stored in a computer-readable storage medium. The computer-readable storage medium may be a disk, optical disk, read-only memory, or random access memory, etc.

[0159] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. An optimization method for a coplanar capacitive sensor, characterized in that, The coplanar capacitive sensor to be optimized includes two symmetrically arranged electrodes, the initial shape of which is rectangular; The optimization method includes: The chamfer length is selected based on the size of the electrodes and the performance indicators of the coplanar capacitive sensor. The corners of the two adjacent sides of the two electrodes are symmetrically chamfered according to the selected chamfer length, so that the distance between a part of the adjacent sides of the two electrodes is increased, while the distance between the other part of the adjacent sides of the two electrodes remains unchanged, thereby obtaining an optimized coplanar capacitive sensor. The performance indicators include: measurement sensitivity, detection depth, and signal strength.

2. The optimization method according to claim 1, characterized in that, The chamfer length is selected based on the electrode dimensions and the performance specifications of the coplanar capacitive sensor, including: The range of values ​​for the chamfer length is determined based on the dimensions of the electrode; The chamfer length is selected within the range specified based on the performance parameters of the coplanar capacitance sensor.

3. The optimization method according to claim 2, characterized in that, Determining the range of values ​​for the chamfer length based on the dimensions of the electrode includes: like ,but ; like ,but ; Where R is the chamfer length, L is the electrode length, and W is the electrode width.

4. The optimization method according to claim 2, characterized in that, The step of selecting the chamfer length within the specified range based on the performance indicators of the coplanar capacitance sensor includes: If the signal strength of the coplanar capacitance sensor optimized using the maximum value in the range as the chamfer length is greater than or equal to a preset threshold, then the maximum value in the range is selected as the chamfer length, or the chamfer length is selected from the range based on the measurement sensitivity and / or the detection depth.

5. The optimization method according to claim 2, characterized in that, The step of selecting the chamfer length within the specified range based on the performance indicators of the coplanar capacitance sensor includes: If the signal strength of the coplanar capacitance sensor optimized using the maximum value in the range as the chamfer length is less than a preset threshold, then the chamfer length is selected from the range based on the signal strength.

6. The optimization method according to claim 5, characterized in that, If the signal strength of the coplanar capacitance sensor optimized using the maximum value in the range as the chamfer length is less than a preset threshold, then the chamfer length is selected from the range based on the signal strength, including the following steps: Step 100: Adjust the current chamfer length ; Step 200: Determine which chamfer length to use. If the signal strength of the optimized coplanar capacitance sensor is less than a preset threshold, then select the current chamfer length. Perform a chamfering operation on the electrodes; if so, proceed to step 300. Step 300: Make ,like Then it ends, if Then return to step 200; in, The maximum value within the range of values. This is the step size for obtaining the value.

7. The optimization method according to claim 1, characterized in that, After optimizing the performance of the coplanar capacitance sensor, the optimization method also includes a verification step for the imaging effect of the optimized coplanar capacitance sensor: The imaging performance of the optimized coplanar capacitance sensor was verified by scanning the defective test object with the optimized coplanar capacitance sensor to obtain reconstructed images.

8. A coplanar capacitance sensor obtained by the optimization method according to any one of claims 1-7, characterized in that, The coplanar capacitance sensor includes two electrodes arranged symmetrically. In this case, the distance between a portion of the adjacent sides of the two electrodes is greater than the distance between the other portions.

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