A method and system for detecting ferromagnetic materials in a local area

Abstract

This invention discloses a method and system for detecting ferromagnetic materials in a localized area, belonging to the field of magnetic detection technology. The method generates a quasi-static low-frequency bias magnetic field covering the detection area by rotating a permanent magnet at a constant frequency. A magnetic sensor detects changes in this magnetic field within the detection area and outputs a sensing signal. Based on this sensing signal, it is determined whether the low-frequency bias magnetic field is distorted within the detection area, thereby determining the presence of ferromagnetic materials. The ferromagnetic material detection scheme provided in this application can be applied in controllable / controlled scenarios such as door frames and passageways. It accurately extracts phase difference-related voltage signals using phase-sensitive detection technology, improving detection accuracy and sensitivity. This effectively solves the problems of low detection accuracy and susceptibility to interference in localized areas inherent in traditional ferromagnetic material detection schemes, and can be widely applied in security, industrial inspection, and other fields.

Description

Technical Field

[0001] This application relates to the field of ferromagnetic material detection technology, specifically to a method and system for detecting ferromagnetic materials in a local area. Background Technology

[0002] The detection of ferromagnetic materials is of paramount importance in numerous fields, including medical treatment, security inspection, industrial component testing, and cultural relic preservation. For example, in densely populated security scenarios such as airports and train stations, it is necessary to detect whether people entering specific areas are carrying prohibited ferromagnetic items; in hospital radiology departments (MRI: magnetic resonance imaging) examinations, demagnetization confirmation is required, necessitating the screening for ferromagnetic materials; and on industrial production lines, it is essential to ensure that components are free of excess ferromagnetic impurities to avoid affecting product quality and equipment operational safety.

[0003] Traditional manual inspection (handheld metal detectors) has limitations in sensitivity, anti-interference ability, and system integration, making it difficult to detect small ferromagnetic materials (such as paperclips, which are easily missed). Existing ferromagnetic detection systems are mostly passive detection schemes based on low-noise, high-sensitivity magnetic sensors, relying on capturing information about the disturbance of the Earth's magnetic field caused by ferromagnetic materials as the basis for interpretation. However, the Earth's magnetic field, as a static magnetic field, is highly susceptible to environmental disturbances; detection systems cannot distinguish between magnetic interference from distant sources and detection signals. Furthermore, existing ferromagnetic material detection systems require magnetic sensors with low noise levels to handle the subtle geomagnetic disturbances caused by ferromagnetic materials.

[0004] Furthermore, existing ferromagnetic material detection equipment is often bulky and unsuitable for limited spaces such as door frames and passageways. In these limited areas, a precise, sensitive detection method that is largely unaffected by environmental interference is needed to effectively detect ferromagnetic materials. Currently, technical solutions for detecting ferromagnetic materials in limited areas are scarce; existing methods either lack sufficient accuracy or are prohibitively expensive, hindering large-scale application. Summary of the Invention

[0005] To address the aforementioned shortcomings of existing ferromagnetic material detection methods, this application provides a high-precision, high-sensitivity, and highly interference-resistant ferromagnetic material detection method suitable for localized areas. This method utilizes a rotating permanent magnet to generate a low-frequency bias magnetic field, combined with phase-sensitive detection technology, to achieve accurate and reliable detection of small ferromagnetic materials, meeting the practical needs of various fields for detecting ferromagnetic materials in localized areas.

[0006] A first aspect of this application provides a method for detecting ferromagnetic material within a localized region. The method includes: rotating a permanent magnet at a constant frequency to generate a quasi-static low-frequency bias magnetic field covering the detection region; using a first magnetic sensor to detect changes in the low-frequency bias magnetic field within the detection region and outputting a sensing signal; and based on the sensing signal and a reference signal, determining whether the low-frequency bias magnetic field is distorted within the detection region, thereby determining whether ferromagnetic material exists in the detection region. The reference signal and the sensing signal output by the first magnetic sensor when not interfered with by ferromagnetic material have the same waveform, frequency, and constant phase difference.

[0007] In some embodiments, the detection area includes a door frame and a passageway. Preferably, the permanent magnet is a bar magnet or a circular magnet that is partially magnetized.

[0008] The principle behind this method for detecting ferromagnetic materials is as follows: when ferromagnetic materials are present in the detection area, the magnetic field near them will be distorted or twisted due to the magnetic focusing effect of the materials. Therefore, by detecting whether such distortion exists, the presence of ferromagnetic materials in the detection area can be determined.

[0009] Furthermore, a plurality of the first magnetic sensors are disposed at at least one edge of the detection area to detect changes in the low-frequency bias magnetic field in the detection area.

[0010] In some embodiments, the reference signal is generated by sensing the low-frequency bias magnetic field signal using a second magnetic sensor. The second magnetic sensor is positioned at a location where the low-frequency bias magnetic field can be effectively sensed and where there is no interference from ferromagnetic materials. Alternatively, a circuit / electrical signal processing method can be used to directly generate an electrical signal with the same frequency and waveform as the low-frequency magnetic field bias signal (under conditions without ferromagnetic interference), and a constant phase difference, as the reference signal. Preferably, the reference signal and the sensed signal are 90 degrees out of phase.

[0011] Furthermore, the method further includes: extracting a voltage signal (i.e., a target signal) that is only related to the phase difference between the reference signal and the target signal using phase-sensitive detection technology; determining, based on the voltage signal, whether the low-frequency bias magnetic field is distorted in the detection area; if distortion is determined to have occurred, then ferromagnetic material is present in the detection area. When ferromagnetic material is present in the detection area, the target signal will no longer be a constant DC voltage signal, but will exhibit local fluctuations.

[0012] Corresponding to the above method, a second aspect of this application also provides a system for detecting ferromagnetic materials in a local area. The system includes: a permanent magnet, a drive motor, several first magnetic sensors, a reference signal source, and a data processing module.

[0013] The permanent magnet is driven by the output shaft of the drive motor and rotates at a constant frequency to generate a quasi-static low-frequency bias magnetic field covering the detection area. Each of the first magnetic sensors detects changes in the low-frequency bias magnetic field within the detection area and outputs a corresponding sensing signal. The reference signal source generates a reference signal that has the same waveform, frequency, and constant phase difference as the sensing signal output by the first magnetic sensor when it is not disturbed by ferromagnetic material. The data processing module determines the presence of ferromagnetic material in the detection area based on each sensing signal and the reference signal.

[0014] Furthermore, the data processing module extracts a voltage signal that is only related to the phase difference between each of the sensing signals and the reference signal using phase-sensitive detection technology. Based on the voltage signal, it determines whether the low-frequency bias magnetic field is distorted in the detection area. If distortion is determined, then ferromagnetic material is present in the detection area. The implementation details of the above system correspond to the method for detecting ferromagnetic material in a local area provided in the first aspect of this application, and will not be repeated here.

[0015] The technical solution for detecting ferromagnetic materials provided in this application replaces the Earth's magnetic field with a low-frequency magnetic field generated by a mechanically rotating permanent magnet as the background / bias magnetic field. Combined with phase-sensitive detection technology, it analyzes whether this low-frequency background magnetic field is distorted in the detection area, thereby determining the presence of ferromagnetic materials. Compared to existing ferromagnetic material detection solutions, the technical solution provided in this application significantly improves sensitivity, accuracy, and anti-interference capabilities, meeting the stringent requirements for detecting ferromagnetic materials in scenarios with electromagnetic interference. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 A schematic diagram of a system for localized detection of iron provided in this application in one embodiment.

[0018] Explanation of reference numerals in the attached diagram: 1-Permanent magnet, 2-Drive motor, 31-Magnetic sensor, 32-Magnetic sensor, 4-Security gate. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0020] In one embodiment, the method for detecting ferromagnetic materials in a localized area provided in this application requires the use of... Figure 1 The system shown is used to implement this. Figure 1 As shown, the system includes: a permanent magnet 1, a drive motor 2, a magnetic sensor 31, a magnetic sensor 32, and a data processing module (…). Figure 1 (Not shown in the text).

[0021] The permanent magnet 1 is mechanically connected to the output shaft of the drive motor 2, enabling the drive motor 2 to drive the permanent magnet 1 to rotate at a constant speed in the plane. In this way, the permanent magnet 1 can rotate within the detection area (…). Figure 1 The security gate 4 generates a low-frequency bias magnetic field. A magnetic sensor 31 is installed on the edge of the gate frame of the security gate 4 to detect changes in the low-frequency bias magnetic field inside the gate. Obviously, when a security object carrying ferromagnetic material passes through the security gate, the low-frequency bias magnetic field is distorted or concentrated by the ferromagnetic material, causing a distortion in the magnetic field at the location of the magnetic sensor 31. Clearly, whether or not this distortion is detected determines whether the security object inside the security gate 4 carries ferromagnetic material.

[0022] The magnetic sensor 32 is positioned at a location where it can effectively sense the low-frequency bias magnetic field and is free from interference by ferromagnetic materials (i.e., unaffected by ferromagnetic materials in the detection area). Figure 1 As shown, the magnetic sensor 32 is positioned near the permanent magnet 1, but at a distance from the security gate 4 (small ferromagnetic materials can only locally distort the magnetic field). The magnetic sensor 32 and the magnetic sensor 31 sense the same magnetic field / magnetic field component in the same direction. Therefore, the sensing signal output by the magnetic sensor 32 has the same waveform and frequency as the sensing signal output by the magnetic sensor 31 when there is no ferromagnetic material in the detection area, but differs by a constant phase. In this embodiment, the sensing signal output by the magnetic sensor 32 is used as a reference signal for subsequent demodulation.

[0023] Of course, besides using a magnetic sensor positioned at a location capable of effectively sensing the low-frequency bias magnetic field and free from ferromagnetic interference to generate the reference signal, a circuit / electrical signal processing method can also be used to directly generate an electrical signal with the same frequency, waveform, and constant phase difference as the low-frequency magnetic field bias signal (under conditions free from ferromagnetic interference). Preferably, the reference signal is 90 degrees out of phase with the sensing signal.

[0024] The sensing signals from magnetic sensors 31 and 32 are both input to the data processing module for processing. The data processing module uses the sensing signal from the second magnetic sensor 32 as a reference signal and determines whether the low-frequency bias magnetic field is distorted within the security gate 4 through phase detection.

[0025] for Figure 1 In the illustrated embodiment, the method for detecting ferromagnetic materials in a small area provided in this application is implemented as follows: the output shaft of the drive motor 1 is controlled to rotate at a constant frequency to generate a quasi-static low-frequency bias magnetic field covering the security gate 4. The data processing module simultaneously acquires the sensing signal output by the first magnetic sensor 31 and the reference signal output by the sensor 32. Based on the sensing signal and the reference signal, phase-sensitive detection technology is used to extract a voltage signal that is only related to the phase difference between the sensing signal and the reference signal as a target signal. Based on the target signal, it is determined whether ferromagnetic materials exist in the detection area.

[0026] Furthermore, to comprehensively detect whether various parts of the object being inspected carry ferromagnetic materials, multiple magnetic sensors 31 can be installed at corresponding locations along the edge of the security gate 4 frame. Based on a reference signal, the local distortion of the low-frequency bias magnetic field can be determined. For example, a row of magnetic sensors 31 can be installed on each side of the security gate 4 frame. Alternatively, several magnetic sensors can be installed on the ground directly opposite the security gate 4 frame to detect whether the object's feet carry small ferromagnetic materials. Clearly, based on the sensing signal of each magnetic sensor 31 and the aforementioned reference signal, the corresponding target signal can be determined through phase-sensitive detection. This determines whether ferromagnetic materials exist in each detection area and further identifies the specific location of the ferromagnetic materials (near the magnetic field sensor 31 corresponding to the target signal with the most severe distortion after normalization of the target signals).

[0027] Obviously, for those skilled in the art, the above method is not limited to the detection of ferromagnetic materials in security gate scenarios; the corresponding detection area can also include local areas such as passageways where ferromagnetic scanning of objects is performed. Preferably, the permanent magnet is a bar magnet or a circular magnet that is partially magnetized.

[0028] Furthermore, determining whether ferromagnetic material exists in the detection region based on the voltage component (target signal) includes: determining whether the low-frequency bias magnetic field is distorted in the detection region based on the voltage component (target signal); if distortion is determined to occur, then ferromagnetic material exists in the detection region. When ferromagnetic material exists in the detection region, the target signal will no longer be a constant DC voltage signal, but will exhibit local fluctuations.

[0029] Corresponding to the above method, a second aspect of this application also provides a system for detecting ferromagnetic materials in a local area. The system includes: a permanent magnet, a drive motor, several first magnetic sensors, a reference signal source, and a data processing module.

[0030] The permanent magnet is driven by the output shaft of the drive motor and rotates at a constant frequency to generate a quasi-static low-frequency bias magnetic field covering the detection area. Each of the first magnetic sensors detects changes in the low-frequency bias magnetic field within the detection area and outputs a corresponding sensing signal. The reference signal source generates a reference signal that has the same waveform, frequency, and constant phase difference as the sensing signal output by the first magnetic sensor when it is not disturbed by ferromagnetic material. The data processing module determines the presence of ferromagnetic material in the detection area based on each sensing signal and the reference signal.

[0031] Furthermore, the reference signal is generated by sensing the low-frequency bias magnetic field signal using a second magnetic sensor, which is positioned at a location where the low-frequency bias magnetic field can be effectively sensed and where there is no interference from ferromagnetic materials.

[0032] Clearly, the data processing module may include multiplier / correlator circuits and low-pass filter circuits for executing the phase detection algorithm. The implementation details of the above system correspond to the method for detecting ferromagnetic materials in a local region provided in the first aspect of this application, and will not be repeated here.

[0033] The technical solution for detecting ferromagnetic materials provided in this application utilizes a mechanically rotating permanent magnet to generate a stable low-frequency magnetic field, replacing the Earth's magnetic field as a bias / background magnetic field. Phase-sensitive detection technology is then used to analyze whether this low-frequency magnetic field is distorted due to ferromagnetic materials in the detection area. This determines the presence of ferromagnetic materials in the detection area. Compared to existing ferromagnetic material detection solutions, the technical solution provided in this application detects ferromagnetic materials through the phase parameters of the magnetic field signal, significantly improving sensitivity, accuracy, and anti-interference capabilities. It is suitable for scenarios requiring strict detection of ferromagnetic materials in environments with electromagnetic interference.

[0034] The above description is merely an embodiment of this application and is not intended to limit this application. For those skilled in the art, the technical solutions provided in this application can be modified and varied in various ways. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for detecting ferromagnetic materials in a localized area, characterized in that, The method includes: rotating a permanent magnet at a constant frequency to generate a quasi-static low-frequency bias magnetic field covering a detection area; using a first magnetic sensor to detect the change of the low-frequency bias magnetic field in the detection area to output a sensing signal; and based on the sensing signal and a reference signal, determining whether the low-frequency bias magnetic field is distorted in the detection area, thereby determining whether ferromagnetic material exists in the detection area.

2. The method as described in claim 1, characterized in that, The method includes: setting a first magnetic sensor at at least one edge of the detection area to detect changes in the low-frequency bias magnetic field in the detection area.

3. The method as described in claim 2, characterized in that, The detection area includes door frames and passageways.

4. The method as described in claim 1 or 2, characterized in that, The reference signal has the same waveform, frequency, and constant phase difference as the sensing signal output by the first magnetic sensor when it is not disturbed by ferromagnetic materials.

5. The method as described in claim 4, characterized in that, The permanent magnet is a bar magnet or a circular magnet that is partially magnetized.

6. The method as described in claim 4, characterized in that, The reference signal is generated by sensing the low-frequency bias magnetic field signal using a second magnetic sensor. The second magnetic sensor is positioned at a location where the low-frequency bias magnetic field can be effectively sensed and where there is no interference from ferromagnetic materials.

7. The method as described in claim 4, characterized in that, The method further includes: extracting a voltage component that is only related to the phase difference between the sensing signal and the reference signal using phase-sensitive detection technology; determining whether the low-frequency bias magnetic field is distorted in the detection area based on the voltage component; if distortion is determined to occur, then ferromagnetic material exists in the detection area.

8. A system for detecting ferromagnetic materials in a localized area, characterized in that, The system includes: a permanent magnet, a drive motor, several first magnetic sensors, a reference signal source, and a data processing module. The permanent magnet is driven by the output shaft of the drive motor and rotates at a constant frequency to generate a quasi-static low-frequency bias magnetic field covering the detection area. Each of the first magnetic sensors is used to detect the change of the low-frequency bias magnetic field in the detection area to output a corresponding sensing signal; the reference signal source is used to generate a reference signal, which has the same waveform, frequency, and constant phase difference as the sensing signal output by the first magnetic sensor when it is not disturbed by ferromagnetic material. The data processing module determines whether ferromagnetic material exists in the detection area based on each of the sensing signals and the reference signal.

9. The system as described in claim 8, characterized in that, The reference signal is generated by sensing the low-frequency bias magnetic field signal using a second magnetic sensor. The second magnetic sensor is positioned at a location where the low-frequency bias magnetic field can be effectively sensed and where there is no interference from ferromagnetic materials.

10. The system as described in claim 8 or 9, characterized in that, The data processing module extracts a voltage signal that is only related to the phase difference between each sensing signal and the reference signal using phase-sensitive detection technology, and determines whether the low-frequency bias magnetic field is distorted in the detection area based on the voltage signal. If distortion is confirmed, ferromagnetic material is present in the detection area.

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