Long-distance sole metal detection device and method

Abstract

The invention discloses a long-distance sole metal detection device and method, and relates to the technical field of nondestructive testing. In order to solve the problem that a security check door system is insufficient in foot area detection capability, the invention redesigns a metal detection probe part, a detection signal acquisition circuit and a detection signal processing method, and develops a set of detection system based on the methods, and the detection system comprises a detection probe, a system control circuit and upper computer software. According to the system, detection of forbidden articles within a range of 200mm above the soles of the feet can be realized, and the detection probability of an existing security door system is improved.

Description

Technical Field

[0001] The patent of this invention relates to the field of non-destructive testing technology, specifically to a long-distance sole metal detection device and method. Technical Background

[0002] The development of security gates has evolved from simple metal detection to intelligent, comprehensive security screening. Early metal detectors, developed in the 1960s, were based on electromagnetic induction and primarily used to detect metal minerals. In the 1970s, with the growth of the air transportation industry, a significant demand for security checks arose, and metal detection technology began to be applied to security inspections, leading to the creation of the first metal security gates. These gates could only detect larger metal objects, such as guns or knives, but suffered from a high false alarm rate and were unable to identify non-metallic dangerous goods. By the 1990s, with the introduction of digital signal processing and microprocessor technology, the sensitivity and accuracy of security gates had been significantly improved, enabling zoned alarms and widespread use in critical locations such as airports, subways, and prisons. Since the 21st century, security inspection technology has further transcended the limitations of single technologies. New technologies such as millimeter wave and terahertz technology have been applied to security inspections, significantly enhancing the comprehensiveness of security screening.

[0003] However, security gates have always had low detection sensitivity for the soles of the feet. The electromagnetic field of traditional security gates is mainly concentrated in the vertical direction (between the two sides of the door frame), and the magnetic field strength in the soles of the feet (close to the ground) is low, which may cause small metal objects to be missed. For millimeter-wave security gates, since the soles of the feet are close to the ground, the millimeter-wave signal coverage in this area is low, and the signal penetration and reflection at the junction of the shoes and the ground will be interfered, which will further affect its imaging effect. The risk of missed detection is higher than other parts of the body. In many scenarios, sole metal detectors are set up to specifically scan the range of 200mm above the soles of the feet, and together with the security gates, more accurate detection is achieved.

[0004] Beijing Kuaian Technology Co., Ltd. et al. (CN110850487A) designed a metal detection gate with enhanced foot detection. Based on a traditional metal security gate, they added detection coils for both feet. Each foot detection coil consists of an even number of foot coil groups, including an outer transmitting coil, an inner transmitting coil, and a receiving coil. A seismic-resistant base and pedals were also added, integrating the design with the original security gate. This method aims to enhance detection in the sole area, but the sole area covers a relatively small distance, and can only detect the ankle.

[0005] Datong Kuaian Technology Co., Ltd. (CN113466949A) has proposed a device and method for detecting prohibited metal items on the feet. Based on electromagnetic detection methods, a large coil group and two small coil groups are designed on the detection substrate. The large coil group contains a transmitting coil and a calibration coil. The two small coil groups are located inside the large coil group, corresponding to the left and right feet, and contain a transmitting coil and a detection coil. When metal is present within the detection range, the detection coil in the small coil group generates a signal, realizing the detection of the target. This method makes a rough judgment on the location and type of the detection object, but the detection object is also limited to the foot area.

[0006] Hangzhou Ruiying Technology Co., Ltd. (CN118732056A) has proposed a metal detection device, a human body detection device, and a metal detection method. Based on electromagnetic detection, a set of large-scale signal transmission coils are designed on the detection substrate. Two sets of detection coils are set at the left and right foot detection positions, respectively. These two sets of coils are arranged at a certain angle. When metal is present in the detection area, the two sets of detection coils generate signal changes, realizing the detection of the target. This solution only adjusts the coil layout to achieve detection of distant targets. For the detection system, methods for improving detection accuracy, such as optimizing coil design parameters, signal acquisition and processing methods, are not reflected in it.

[0007] Shandong Leicheng Electronic Technology Co., Ltd. (CN201910178026) has proposed a foot metal detection device for millimeter wave security inspection equipment. The device, installed at the base of the millimeter wave security inspection equipment, includes a foot-supporting pedal, a detector protective housing, and a foot-shaped detection area. Multiple metal detectors are positioned along the foot-shaped detection area. Each metal detector is equipped with a pressure-sensing coil. This detector detects metal on the soles of the feet when a person passes through, complementing the detection function of the millimeter wave security inspection equipment. However, the device's detection methods and capabilities are not clearly described.

[0008] The above methods are all based on electromagnetic detection technology to detect metal in the sole area of ​​the foot, and different designs are made for the layout of the coils. However, for long-distance application requirements, there are fewer related designs and the methods are incomplete. When detecting using electromagnetic methods, the structural parameters of the transmitting coil and the excitation coil, as well as the excitation signal parameters, have a significant impact on the results and can improve the detection distance and accuracy. However, the above methods do not study the calculation of these parameters. At the same time, when the detection target is far away, the detection signal is relatively weak and difficult to identify, and the above detection methods do not have relevant signal processing methods.

[0009] This method proposes a new coil solution. By calculating the coil's various parameters and determining its technical specifications, it improves the detection signal strength and resolution, enhancing the detection effect. It also proposes a signal processing method that gives the system better anti-interference capabilities during long-term operation. Summary of the Invention

[0010] This method proposes a new coil solution. By calculating the coil's various parameters and determining its technical specifications, it improves the detection signal strength and resolution, enhancing the detection effect. It also proposes a signal processing method that gives the system better anti-interference capabilities during long-term operation.

[0011] The technical solution of the present invention is a long-distance sole metal detection device, which includes: a host computer, a controller, an excitation signal generating module, a left foot excitation coil, a left foot detection coil, a right foot excitation coil, a right foot detection coil, a left foot low-pass filter module, a right foot low-pass filter module, a differential amplifier, and a signal acquisition module. The left foot excitation coil and the left foot detection coil are located at the bottom of the left foot, and the right foot excitation coil and the right foot detection coil are located at the bottom of the right foot; the host computer is data-connected to the controller, the operator sends an operation signal to the controller through the host computer, the controller returns an interactive signal to the host computer, and the controller sends a control signal to Excitation signal generating module, the excitation signal generating module sends an excitation signal to the left foot excitation coil and the right foot excitation coil, the left foot detection coil and the right foot detection coil receive the signal, pass the received signal through the corresponding low-pass filter module, and then input the differential amplifier module together. After differential amplification, the signal acquisition module converts the collected signal and transmits it to the controller, and the controller sends the collected signal to the host computer; the left foot excitation coil, left foot detection coil, left foot low-pass filter module and the corresponding right foot excitation coil, right foot detection coil, right foot low-pass filter module have exactly the same structure and parameters.

[0012] A long-distance sole metal detection method, the method comprising:

[0013] S1. Determine the structural parameters of the excitation coil and the detection coil;

[0014] S2. Determine the detection range h of the sole detector and calculate the signal excitation frequency f under this condition;

[0015] S21, use sine wave as the excitation signal, the basic signal frequency is f0, the frequency change step is Δf, set the excitation frequency f i =f0+iΔf, i=1,2,3…n; n is the maximum number of transformations set;

[0016] S22, determine the minimum output signal V that the system can distinguish min ;

[0017] S23, calculate the frequency excitation f i Under the condition, the output signals of the left and right foot detection coils in S1 are differentially measured to obtain the signal V i ;

[0018] S24, if V i <V min , then i=i+1, and recalculate V i , if V i >V min , then determine the excitation frequency f = f i ;

[0019] S3, the controller controls the direct digital synthesis method to generate a sinusoidal signal source V with a frequency of f seed ;

[0020] S4, left and right feet are respectively connected to V seed Perform two-stage amplification to obtain the excitation signal V for the left and right feet inleft and V inright , the two excitation signals have the same phase and amplitude;

[0021] S5, V inleft and V inright They are respectively fed into the excitation coils of the left and right feet;

[0022] S6. Measure the detection coil signal V of the left and right feet respectively outleft and V outright ;;

[0023] S7, V outleft and V outright Perform low-pass filtering respectively and perform differential amplification on the two signals to obtain:

[0024] V diff =k×|V outleft -V outright |;

[0025] Where k is the signal amplification factor;

[0026] S8, through the signal acquisition module, V diff Collect and obtain T i The output signal V at the moment oi , i=1,2,3…n;

[0027] S9. The host computer software processes the collected data in a dynamic cycle to obtain the test results.

[0028] Furthermore, the specific method of step 7 is:

[0029] S91, set the dynamic storage flag n=3, set the detection signal determination threshold V threshold ;

[0030] S92, store the data collected by the embedded controller, when T i = 1000ms, all the collected V oi Store in array middle;

[0031] S93, through Gaussian filtering, median filtering Perform preprocessing to obtain the series

[0032] S94, Acquisition The peak values ​​in the first 20 cycles are accumulated to get V n ;

[0033] S95, if n≠1, then the value of n is decremented by 1 and the process goes to step S92; if n=1, calculate the final characterization parameter V out =V3-V1, when V out >V threshold If yes, it is determined that there is metal; otherwise, it is determined that there is no metal, and the value of V2 is assigned to V3, and the value of V1 is assigned to V2, and the process goes to step S92.

[0034] Furthermore, the specific parameters in step S1 are:

[0035] The inner diameter of the left and right foot excitation coils is r1 = 40 mm, the outer diameter is R1 = 70 mm, the height is H1 = 40 mm, and the number of coil turns is n1 = 1200. The inner diameter of the left and right foot detection coils is r2 = 140 mm, the outer diameter is R2 = 146 mm, the height is H2 = 8 mm, and the number of coil turns is n2 = 2400.

[0036] This paper presents a method for long-range sole metal detection. This method employs a set of detection and excitation coil parameters, based on which a sole detection system is constructed. Furthermore, a dynamic signal processing method suitable for long-range sole detection is proposed, effectively improving the system's resolution and detection probability while eliminating the effects of environmental interference on system stability. The system can detect small prohibited items such as knives and lighters within a range of 20 cm, with a detection probability greater than 90% and a false alarm rate less than 5%. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 Schematic diagram of the spatial distribution of the detection coil group.

[0038] Figure 2 This is a cross-sectional dimensioning drawing of the coil group structure.

[0039] Figure 3This is a block diagram of the foot metal detection system.

[0040] Figure 4 This is a photo of the sole metal detection system.

[0041] Figure 5 This is a schematic diagram of the placement of the detector.

[0042] Figure 6 This is the result of the left foot detection experiment.

[0043] Figure 7 This is the result of the right foot detection experiment.

[0044] Figure 8 Schematic diagram of the placement of the probe test pieces. DETAILED DESCRIPTION

[0045] The present invention provides a method and a detection system for detecting metal in the sole area of ​​the foot.

[0046] The detection method is based on the principle of electromagnetic induction. Two sets of coils are designed in the area where the soles of the feet of the person being tested are located. The distribution is as follows: Figure 1 shown.

[0047] Each coil set consists of an excitation coil and a detection coil. When an excitation signal is applied to the excitation coil, an induced magnetic field is generated within the detection area, which then induces a current in the detection coil. When metal appears within the area, the magnetic field changes, causing the signal in the detection coil to change. This change in the detection signal allows metal detection within the area.

[0048] In order to realize the detection of long-distance targets, the present invention establishes a model and carries out simulation calculations for the detection objects in the general technical specifications of GB15120-2018 walk-through metal detection doors. The results show that the inner diameter r1, outer diameter R1, height H1 of the excitation coil, and the number of coil turns n1, the inner diameter r2, outer diameter R2, height H2, and number of coil turns n2 of the detection coil will affect the results. Figure 2 In order to obtain the best detection effect, the present invention optimizes the above parameters to obtain the best coil group structure.

[0049] Based on the optimized coil, the present invention designs a set of sole metal detection system, which includes an excitation signal generation module, a detection coil group, a low-pass filter module, a differential amplifier module, a signal acquisition module, an embedded controller and a host computer software. Figure 3 shown.

[0050] When the system starts working, the excitation signals are applied to both foot excitation coils. Due to the principle of electromagnetic induction, the corresponding signals are detected in the detection coils. When the person being inspected enters the detection area, if there is metal in the area under the feet, it will interfere with the magnetic field in the detection area, causing the signal in the detection coil to change.

[0051] When the metal is far away from the coil group, the signal change of the detection coil is very weak. In order to improve the detection effect, the present invention has made three targeted designs. First, increasing the intensity of the excitation signal can effectively increase the rate of change of the detection signal. Therefore, a DDS plus power amplification scheme is adopted to obtain a high-power excitation signal. Second, the parameters of the left and right coil groups are completely consistent and can be used as a reference for each other. Therefore, the two detection signals are filtered and differentially amplified. When metal is detected in the area of ​​one of the feet, the difference between the two signals will amplify the change in the signal alone, improving its sensitivity. Finally, after completing the signal acquisition, the host computer software will accumulate nearly 20 groups of data per second, improve the resolution of the detection criterion, and suppress the random error of the system. At the same time, due to reasons such as coil processing, there will be differences between the two signals, causing static detection errors. During the detection process, the present invention dynamically stores the accumulated data within 3 seconds, subtracts the summed signal of the 1st second from the summed signal of the 3rd second, and uses this difference as the final judgment standard.

[0052] Finally, the parameters processed by the host computer serve as the basis for determining whether metal is present. When the value exceeds a certain threshold, metal is determined to be present in the detection area. The host computer software also features a threshold adjustment function, allowing system users to set different thresholds according to scenario requirements to adjust detection sensitivity.

[0053] Steps to implement long-distance foot metal detection method

[0054] According to the above-mentioned method for detecting the wall thickness of a pipe with an insulation layer, the specific implementation steps are as follows:

[0055] S1, embedded controller controls DDS to generate signal source V seed ;

[0056] S2, the left and right feet are respectively connected to V seed Amplify and obtain the high-power excitation signal V for the left and right feet inleft and V inright , the two excitation signals have the same phase and amplitude;

[0057] S3, V inleft and V inright They are respectively fed into the excitation coils of the left and right feet;

[0058] S4, measure the detection coil signal V of the left and right feet respectively outleft and Voutright ;

[0059] S5, V outleft and V outright After filtering respectively, differential amplification operation is performed to obtain the output signal V o ;

[0060] S6. Obtain T through the signal acquisition module i Output signal V at time (i=1,2,3…n) oi (i=1,2,3…n);

[0061] S7, host computer software performs dynamic cycle processing on the collected data

[0062] S71, set the dynamic storage flag n=3, set the detection signal determination threshold V threshold ;

[0063] S72, store the data collected by the embedded controller, when T i = 1000ms, all the collected V oi Store in array middle;

[0064] S73, through Gaussian filtering, median filtering Perform preprocessing to obtain the series

[0065] S74, Acquisition The peak values ​​in the first 20 cycles are accumulated to get V n ;

[0066] S75, if n≠1, then the value of n is reduced by 1, and the process goes to step S72; if n=1, calculate the final characterization parameter V out =V3-V1, when V out >V threshold When it is determined that there is metal, otherwise it is determined that there is no metal, the value of V2 is assigned to V3, the value of V1 is assigned to V2, and the process goes to step S72.

[0067] Example

[0068] According to the above method, build a metal detection system for the soles of the feet. Figure 4 shown.

[0069] When conducting test experiments, the prosthesis will be divided into four areas: sole, instep, ankle, and calf. Figure 5 The detection limit is the upper end of the calf area, 20 cm away from the sole of the foot.

[0070] Metal targets are set at different positions of the prosthesis. Three detection objects are used: a wooden-handled knife (No. 1), a brass bullet (No. 2), and a lighter (No. 3). The three detection objects are detected in three directions to obtain the detection range of the test device for the three objects. The placement is as follows: Figure 8 shown.

[0071] A total of 100 scans were performed, of which 48 were with metal objects placed (3 objects × 2 (left and right feet) × 8 (positions + placement)), and 52 were without objects placed. The detection results for the left and right feet are as follows Figure 6 、 Figure 7 shown.

[0072] At the same time, 240 detections were performed under no-load conditions (without the object to be tested), and only 3 false alarms occurred.

[0073] Through the results of metal detection test and no-load detection test, it can be calculated:

[0074] The overall metal target detection probability is

[0075]

[0076] The false alarm rate is

[0077] The experimental results show that the system can effectively detect metal targets at a distance of 20 cm.

Claims

1. A long-distance foot metal detection device, comprising: The upper computer, controller, excitation signal generating module, left foot excitation coil, left foot detection coil, right foot excitation coil, right foot detection coil, left foot low-pass filter module, right foot low-pass filter module, differential amplifier, signal acquisition module, the left foot excitation coil and left foot detection coil are located at the bottom of the left foot, and the right foot excitation coil and right foot detection coil are located at the bottom of the right foot; the upper computer is data-connected to the controller, the operator sends an operation signal to the controller through the upper computer, the controller returns an interactive signal to the upper computer, the controller sends a control signal to the excitation signal generating module, the excitation signal generating module sends an excitation signal to the left foot excitation coil and the right foot excitation coil, the left foot detection coil and the right foot detection coil receive the signal, pass the received signal through the corresponding low-pass filter module, and then input it into the differential amplifier module together, after differential amplification, input it into the signal acquisition module, the signal acquisition module converts the collected signal and transmits it to the controller, and the controller sends the collected signal to the upper computer; the left foot excitation coil, left foot detection coil, left foot low-pass filter module have exactly the same structure and parameters as the corresponding right foot excitation coil, right foot detection coil, and right foot low-pass filter module.

2. A metal detection method using the long-distance foot metal detection device according to claim 1, characterized in that: The method includes: S1. Determine the structural parameters of the excitation coil and the detection coil; S2. Determine the detection range h of the sole detector and calculate the signal excitation frequency f under this condition; S21, use sine wave as the excitation signal, the basic signal frequency is f0, the frequency change step is Δf, set the excitation frequency f i =f0+iΔf, i=1,2,3…n; n is the maximum number of transformations set; S22, determine the minimum output signal V that the system can distinguish min ; S23, calculate the frequency excitation f i Under the condition, the output signals of the left and right foot detection coils in S1 are differentially measured to obtain the signal V i ; S24, if V i <V min , then i=i+1, and recalculate V i , if V i >V min , then determine the excitation frequency f = f i ; S3, the controller controls the direct digital synthesis method to generate a sinusoidal signal source V with a frequency of f seed ; S4, left and right feet are respectively connected to V seed Perform two-stage amplification to obtain the excitation signal V for the left and right feet inleft and V inright , the two excitation signals have the same phase and amplitude; S5, V inleft and V inright They are respectively fed into the excitation coils of the left and right feet; S6. Measure the detection coil signal V of the left and right feet respectively outleft and V outright ;; S7, V outleft and V outright Perform low-pass filtering respectively and perform differential amplification on the two signals to obtain: V diff =k×|V outleft -V outright |; Where k is the signal amplification factor; S8, through the signal acquisition module, V diff Collect and obtain T i The output signal V at the moment oi , i=1,2,3…n; S9. The host computer software processes the collected data in a dynamic cycle to obtain the test results.

3. The metal detection method according to claim 2, wherein: The specific method of step 7 is: S91, set the dynamic storage flag n=3, set the detection signal determination threshold V threshold ; S92, store the data collected by the embedded controller, when T i = 1000ms, all the collected V oi Store in array middle; S93, through Gaussian filtering, median filtering Perform preprocessing to obtain the series S94, Acquisition The peak values ​​in the first 20 cycles are accumulated to get V n ; S95, if n≠1, then the value of n is reduced by 1 and the process goes to step S92; if n=1, calculate the final characterization parameter V out =V3-V1, when V out >V threshold If yes, it is determined that there is metal; otherwise, it is determined that there is no metal, and the value of V2 is assigned to V3, and the value of V1 is assigned to V2, and the process goes to step S92.

4. The metal detection method according to claim 2, wherein: The specific parameters in step S1 are: The inner diameter of the left and right foot excitation coils is r1 = 40 mm, the outer diameter is R1 = 70 mm, the height is H1 = 40 mm, and the number of coil turns is n1 = 1200. The inner diameter of the left and right foot detection coils is r2 = 140 mm, the outer diameter is R2 = 146 mm, the height is H2 = 8 mm, and the number of coil turns is n2 = 2400.

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