Long distance foot metal detecting device and method

Abstract

The application discloses a long-distance foot sole metal detection device and method, and relates to the technical field of nondestructive testing. In view of the problem that the foot area detection capability of a security door system is insufficient, the application redesigns a metal detection probe component, a detection signal acquisition circuit and a detection signal processing method, and develops a detection system based on the methods, which comprises a detection probe, a system control circuit and upper computer software. The system can realize detection of prohibited articles within a range of 200 mm above the foot sole of the foot, and improves the detection probability of the existing security door system.

Description

Technical Field

[0001] This invention patent relates to the field of non-destructive testing technology, specifically to a long-distance foot metal detection device and method. Background Technology

[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 for detecting metallic minerals. In the 1970s, the growth of the air transport industry created a significant demand for security checks, leading to the application of metal detection technology and the creation of the first metal detector gates. These early gates could only detect larger metal objects, such as firearms or knives, but had a high false alarm rate and could not identify non-metallic dangerous items. In the 1990s, with the introduction of digital signal processing and microprocessor technology, the sensitivity and accuracy of security gates improved dramatically, enabling zoned alarms and widespread application in critical locations such as airports, subways, and prisons. In the 21st century, security technology further broke through the limitations of single technologies, with new methods such as millimeter-wave and terahertz technologies being applied to the field, significantly enhancing the comprehensiveness of security checks.

[0003] However, security gates have historically had low sensitivity in detecting the soles of the feet. Traditional security gates primarily concentrate their electromagnetic fields vertically (between the two sides of the gate frame), with lower magnetic field strength in the sole area (closer to the ground), potentially leading to missed detection of small metal objects. For millimeter-wave security gates, because the soles of the feet are in close contact with the ground, the signal coverage of millimeter waves in this area is low, and signal penetration and reflection at the shoe-ground interface are interfered with, further affecting imaging quality and increasing the risk of missed detection compared to other parts of the body. In many scenarios, foot metal detectors are installed, specifically scanning an area 200mm above the feet, working in conjunction with the security gate to achieve more accurate detection.

[0004] Beijing Kuai'an Technology Co., Ltd. et al. (CN110850487A) designed a metal detector gate with enhanced foot detection. Based on a traditional metal detector gate, they added detection coils for both feet. Each foot detection coil has an even number of coil groups, including an external transmitting coil, an internal transmitting coil, and a receiving coil. An anti-vibration base and a footplate were also added, integrating the design with the original detector gate. The purpose of this method is to supplement the detection effect in the sole area; however, the coverage distance in the sole area is relatively small, only enabling detection of the ankle area.

[0005] Datong Kuai'an Technology Co., Ltd. (CN113466949A) has proposed a detection device and method for detecting prohibited metal items on the feet. Based on electromagnetic detection, a large coil group and two small coil groups are designed on a detection substrate. The large coil group includes 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 respectively, and include transmitting coils and detection coils. When metal is present within the detection range, the detection coil in the small coil group generates a signal, thus detecting the target. This method can roughly determine the location and type of the object being detected, but it is 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-area signal transmitting coils is 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 at a certain angle. When metal is present in the detection area, the two sets of detection coils generate signal changes, thereby detecting the target. This solution only adjusts the coil layout to achieve the detection of distant targets, but it does not incorporate methods for improving detection accuracy, such as optimizing coil design parameters and signal acquisition and processing methods.

[0007] Shandong Leicheng Electronic Technology Co., Ltd. (CN201910178026) has proposed a foot metal detection device for millimeter-wave security inspection equipment. This device is installed at the bottom of the millimeter-wave security inspection equipment and includes a foot support pedal, a detector protective shell, and a foot shape detection area. Multiple metal detectors are arranged along the foot shape detection area, and each metal detector has a pressure sensing coil on its surface. When a person passes through, it detects metal on the sole of the foot, supplementing the detection function of the millimeter-wave security inspection equipment. However, the detection method and detection capabilities of the device are not clearly described.

[0008] The methods described above are all based on electromagnetic detection technology to detect metal in the foot area, and they employ different coil layout designs. However, for long-distance applications, relevant designs are scarce, and the methods are incomplete. When using electromagnetic methods for detection, the structural parameters of the transmitting and excitation coils, as well as the excitation signal parameters, significantly influence the results, potentially improving detection distance and accuracy. However, the methods described above do not address the calculation of these parameters. Furthermore, when the target is at a distance, the detection signal is weak and difficult to identify, and the aforementioned detection methods lack corresponding signal processing techniques.

[0009] This method proposes a novel coil scheme. By calculating various coil parameters, the technical parameters of the coil are determined, improving the strength and resolution of the detection signal and enhancing the detection effect. Simultaneously, a signal processing method is proposed, enabling the system to possess better anti-interference capabilities during long-term operation. Summary of the Invention

[0010] This method proposes a novel coil scheme. By calculating various coil parameters, the technical parameters of the coil are determined, improving the strength and resolution of the detection signal and enhancing the detection effect. Simultaneously, a signal processing method is proposed, enabling the system to possess better anti-interference capabilities during long-term operation.

[0011] The technical solution of this invention is a long-range foot metal detection device. The device includes: a host computer, a controller, an excitation signal generation 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 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 host computer is data-connected to the controller. The operator sends an operation signal to the controller via the host computer, the controller returns an interactive signal to the host computer, and the controller sends control signals to... The excitation signal generation module sends excitation signals to the left and right foot excitation coils. The left and right foot detection coils receive the signals, pass them through their respective low-pass filter modules, and then input them together into the differential amplifier module. After differential amplification, the signals are input into the signal acquisition module. The signal acquisition module converts the acquired signals and transmits them to the controller, which then sends the acquired signals to the host computer. The structure and parameters of the left foot excitation coil, left foot detection coil, and left foot low-pass filter module are completely identical to those of the corresponding right foot excitation coil, right foot detection coil, and right foot low-pass filter module.

[0012] A long-range metal detection method for the soles of feet, 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 foot sensor and calculate the signal excitation frequency f under this condition;

[0015] S21. Using a sine wave as the excitation signal, the fundamental signal frequency is f0, and the frequency change step size is... Set the excitation frequency , 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 resolve. min ;

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

[0018] S24, if Then i = i + 1, and recalculate. ,like Then determine the excitation frequency. ;

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

[0020] S4, the left and right feet are respectively connected to V through power amplifiers. seed Two-stage amplification is performed to obtain the excitation signals V for the left and right feet. inleft and V inright The two excitation signals have the same phase and equal amplitude.

[0021] S5, V inleft and V inright The excitation coils for the left and right feet are respectively connected;

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

[0023] S7, V outleft and V outright The two signals are then subjected to low-pass filtering and differential amplification to obtain the following result:

[0024] ;

[0025] Where k is the signal amplification factor;

[0026] S8. Through the signal acquisition module, V diff Collect data and obtain T. i Output signal V at time oi , i = 1, 2, 3…n;

[0027] S9. The host computer software performs dynamic cyclic processing on the collected data to obtain the detection results.

[0028] Furthermore, the specific method for step 7 is as follows:

[0029] S91, Set dynamic storage identifier Set the detection signal judgment threshold V threshold ;

[0030] S92. Store the data collected by the embedded controller. When T i = At 1000ms, all collected V values ​​will be... oi Stored in array middle;

[0031] S93, Apply Gaussian filtering and median filtering to... Preprocessing is performed to obtain the sequence. ;

[0032] S94, Obtain The peak values ​​within the first 20 periods are summed to obtain V. n ;

[0033] S95, if If n decreases by 1, proceed to step S92; Calculate the final characterization parameters ,when If metal is present, it is determined that metal is not present. Then, the value of V2 is assigned to V3 and the value of V1 is assigned to V2, and the process proceeds to step S92.

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

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

[0036] This invention presents a detection method for long-distance foot metal detection. The method designs a set of detection-excitation coil parameters, builds a foot detection system based on these parameters, and proposes a dynamic signal processing method suitable for long-distance foot detection. This effectively improves system resolution and detection probability, and eliminates the impact of environmental interference on system stability. The system can detect prohibited small items such as knives and lighters within a 20cm range, with a detection probability greater than 90% and a false alarm rate less than 5%. Attached Figure Description

[0037] Figure 1 This is a schematic diagram of the spatial distribution of the detection coil group.

[0038] Figure 2 This is a diagram showing the cross-sectional dimensions of the coil assembly structure.

[0039] Figure 3 A block diagram of a foot metal detection system.

[0040] Figure 4This is a photo of a metal detection system on the soles of the feet.

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

[0042] Figure 6 The image shows the results of the left foot detection experiment.

[0043] Figure 7 The image shows the results of the right foot detection experiment.

[0044] Figure 8 This is a schematic diagram illustrating the placement of the test specimens. Detailed Implementation

[0045] This invention proposes a method and 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 subject's feet are located, and their distribution is as follows: Figure 1 As shown.

[0047] Each coil set includes an excitation coil and a detection coil. When an excitation signal is applied to the excitation coil, it generates an induced magnetic field in the detection area, resulting in an induced current in the detection coil. When metal is present in the area, the original magnetic field changes, causing a change in the signal in the detection coil. The metal in the area can be detected by observing the change in the detection signal.

[0048] To achieve the detection of distant targets, this invention establishes a model and conducts simulation calculations for the detection objects specified in the GB15120-2018 General Technical Specification for Walk-Through Metal Detectors. The results show that the inner diameter r1, outer diameter R1, height H1, and number of turns n1 of the excitation coil, as well as the inner diameter r2, outer diameter R2, height H2, and number of turns n2 of the detection coil, all affect the results. Figure 2 As shown. To achieve the best detection results, this invention optimizes the design of the above parameters to obtain the optimal coil group structure.

[0049] Based on the optimized coil, this invention designs a metal detection system for the sole of the foot, 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 host computer software, such as... Figure 3 As shown.

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

[0051] When the metal is far from the coil group, the signal change of the detection coil is very weak. To improve the detection effect, this invention incorporates three targeted designs. First, increasing the excitation signal strength 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 identical 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 coils, the difference between the two signals will be amplified separately to increase the sensitivity. Finally, after the signal acquisition is completed, the host computer software accumulates nearly 20 sets of data per second to improve the resolution of the detection criteria and suppress random errors in the system. At the same time, due to differences in coil processing and other factors, there may be differences between the two signals, causing static detection errors. This invention dynamically stores the accumulated data within 3 seconds during the detection process, subtracts the sum of the first second from the sum of the third second, and uses the difference as the final judgment criterion.

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

[0053] Implementation steps of long-range foot metal detection method

[0054] S1, Embedded controller controls DDS signal source V seed ;

[0055] S2, the left and right feet are respectively connected to V through power amplifiers. seed Amplify the signal to 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 equal amplitude.

[0056] S3, V inleft and V inright The excitation coils for the left and right feet are respectively connected;

[0057] S4. Measure the detection coil signals V for the left and right feet respectively. outleft and V outright ;

[0058] S5, V outleft and V outright After filtering, differential amplification is performed to obtain the output signal V. o ;

[0059] S6. Obtain T through the signal acquisition module iThe output signal V at time (i = 1, 2, 3…n) oi (i = 1, 2, 3…n);

[0060] S7, the host computer software performs dynamic cyclic processing on the collected data.

[0061] S71, Set dynamic storage identifier Set the detection signal judgment threshold V threshold ;

[0062] S72. Store the data collected by the embedded controller. When T i = At 1000ms, all collected V values ​​will be... oi Stored in array middle;

[0063] S73, Apply Gaussian filtering and median filtering to... Preprocessing is performed to obtain the sequence. ;

[0064] S74, Obtain The peak values ​​within the first 20 periods are summed to obtain V. n ;

[0065] S75, if If n decreases by 1, proceed to step S72; Calculate the final characterization parameters ,when If metal is present, it is determined that metal is not present. Then, the value of V2 is assigned to V3, and the value of V1 is assigned to V2. Then, proceed to step S72.

[0066] Example

[0067] Based on the methods described above, a foot metal detection system can be built as follows: Figure 4 As shown.

[0068] During testing, the prosthesis is divided into four areas: the sole of the foot, the instep, the ankle, and the calf. Figure 5 As shown. The detection limit is the upper part of the lower leg area, up to 20cm from the sole of the foot.

[0069] Metal targets were placed at different locations on the prosthesis. Three detectors were used: a small knife with a wooden handle (No. 1), a brass bullet (No. 2), and a lighter (No. 3). The three detectors were used to probe from three different directions to determine the detection range of the testing device for each of the three targets. The placement method was as follows: Figure 8 As shown.

[0070] A total of 100 scans were performed, with 48 scans placing metal objects (3 objects x 2 (left and right feet x 8 (position + arrangement)) and 52 scans without placing any objects. The detection results for the left and right feet are as follows. Figure 6 , Figure 7 As shown.

[0071] Simultaneously, in 240 unloaded (without the object being tested) tests, only 3 false alarms occurred.

[0072] Based on the results of metal detection experiments and unloaded detection experiments, it can be calculated that:

[0073] Its overall metal target detection probability is

[0074]

[0075] Its false alarm rate is

[0076] Experimental results demonstrate that the system effectively detects metal targets at a distance of 20cm.

Claims

1. A long-range foot metal detection device, the device comprising: The system comprises a host computer, a controller, an excitation signal generation 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 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 host computer and controller are connected via data connection. The operator sends operation signals to the controller via the host computer, and the controller returns interactive signals to the host computer. The controller sends control signals to the excitation signal generation module, which then sends excitation signals to the left and right-foot excitation coils. The left and right-foot detection coils receive the signals, pass them through their respective low-pass filter modules, and then input them together into the differential amplifier module. After differential amplification, the signals are input into the signal acquisition module, which converts the acquired signals and transmits them to the controller. The controller then sends the acquired signals to the host computer. The structure and parameters of the left-foot excitation coil, left-foot detection coil, and left-foot low-pass filter module are identical to those of the corresponding right-foot excitation coil, right-foot detection coil, and right-foot low-pass filter module. The metal detection method of the long-range foot metal detection device is as follows: S1. Determine the structural parameters of the excitation coil and the detection coil; S2. Determine the detection range h of the foot sensor and calculate the signal excitation frequency f under this condition; S21. Using a sine wave as the excitation signal, the fundamental signal frequency is f0, and the frequency change step size is... Set the excitation frequency , i = 1, 2, 3…n; n is the maximum number of transformations set; S22. Determine the minimum output signal V that the system can resolve. min ; S23, Calculate frequency excitation Under the condition, the output signals of the left and right detection coils in S1 are differentially divided to obtain signal V. i ; S24, if Then i = i + 1, and recalculate. ,like Then determine the excitation frequency. ; S3. The controller controls the direct digital synthesis method to generate a sinusoidal signal source V with frequency f. seed ; S4, the left and right feet are respectively connected to V through power amplifiers. seed Two-stage amplification is performed to obtain the excitation signals V for the left and right feet. inleft and V inright The two excitation signals have the same phase and equal amplitude. S5, V inleft and V inright The excitation coils for the left and right feet are respectively connected; S6. Measure the detection coil signals V for the left and right feet respectively. outleft and V outright ; S7, V outleft and V outright The two signals are then subjected to low-pass filtering and differential amplification to obtain the following result: ； Where k is the signal amplification factor; S8. Through the signal acquisition module, V diff Collect data and obtain T. i Output signal V at time oi , i = 1, 2, 3…n; S9. The host computer software performs dynamic cyclic processing on the collected data to obtain the detection results.

2. The long-range foot metal detection device as described in claim 1, characterized in that, The specific method for step 7 is as follows: S91, Set dynamic storage identifier Set the detection signal judgment threshold V threshold ; S92. Store the data collected by the embedded controller. When T i = At 1000ms, all collected V values ​​will be... oi Stored in array middle; S93, Apply Gaussian filtering and median filtering to... Preprocessing is performed to obtain the sequence. ; S94, Obtain The peak values ​​within the first 20 periods are summed to obtain V. n ; S95, if If n decreases by 1, proceed to step S92; Calculate the final characterization parameters ,when If metal is present, it is determined that metal is not present. Then, the value of V2 is assigned to V3 and the value of V1 is assigned to V2, and the process proceeds to step S92.

3. The long-range foot metal detection device as described in claim 1, characterized in that, The specific parameters in step S1 are as follows: The inner diameter of the excitation coil for the left and right feet is r1=40mm, the outer diameter is R1=70mm, the height is H1=40mm, and the number of coil turns is n1=1200. The inner diameter of the detection coil for the left and right feet is r2=140mm, the outer diameter is R2=146mm, the height is H2=8mm, and the number of coil turns is n2=2400.

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