Portable detection system including magnetostatic sensor

Abstract

The present invention relates to a detection system (1) for a target object, comprising: - a first and a second detector (10, 20), the detectors having magnetic sensors (5), the magnetic sensors being configured to detect a magnetic field and to generate a signal indicating the strength of the magnetic field, - a processing unit (6), the processing unit being configured to receive a signal indicating the strength of the magnetic field detected by the sensor (5), and - a communication interface (7), the interface being configured to send the signal generated by the magnetic sensor (5) to the processing unit (6), the processing unit (6) being further configured to determine a correction value of the signal generated by the magnetic sensor (5) of the first and second detectors (10, 20), and to send an instruction to generate an alarm when the correction value is greater than a predetermined threshold.

Description

Technical Field

[0001] The present invention relates to the field of object detection, and more particularly to the detection of objects containing magnetized or ferromagnetic components. Background Art

[0002] The current climate of various attacks in public places has created a need to detect assault rifle type weapons at the entrances of public places such as stadiums, concert halls, department stores, etc.

[0003] Currently, such detection is usually performed by security personnel equipped with manually operated portable detectors that are moved along the body and around the belongings of the person wishing to enter the various public places of interest. However, such checks are lengthy and cumbersome, and the number of persons wishing to enter the relevant places is often too large to be checked in a satisfactory manner.

[0004] There are also proposals to install permanent doors at the entrances of various public places. These doors are suitable for situations where a fixed installation is required. However, such installations require a lot of work and are not suitable for public places such as stadiums, concert halls and department stores. In public places, however, a certain amount of space must be left for possible barrier-free emergency exits, which requires the use of portable systems.

[0005] It has also been proposed to use portable, independent barriers comprising static magneto sensors. Such barriers generally comprise a column attached to a base, the column being equipped with at least one static magneto sensor, for example three static magneto sensors distributed over the entire height of the column. Each sensor is configured to generate a (voltage) signal representative of the strength of the detected electromagnetic field. These barriers are particularly used in prisons to detect whether prisoners are carrying magnetic objects, in particular mobile phones. For this purpose, the sensitivity of the magnetic sensors may be very high, since prisoners are generally not allowed to use any metal or magnetic materials.

[0006] In order to increase the sensitivity of these barriers, it is also proposed to use them in pairs to form gates. Specifically, the sensitivity of the sensors decreases exponentially with distance. The advantage of such barriers is that they are portable and do not require any installation work to be performed. In addition, since current assault rifles are made of ferromagnetic materials and are large in size, the disturbance they generate in the earth's electromagnetic field is sufficient to be detected by these sensors.

[0007] However, unlike in prisons, people often wear or carry metal objects that may include magnetized or ferromagnetic parts, in most cases smartphones containing magnetized chips. However, the autonomous magnetic field of a smartphone is roughly equivalent to the disturbance of the earth's electromagnetic field generated by the passage of an assault rifle. Therefore, the barrier alarm will be systematically triggered when these people pass through the barrier, even without an assault rifle. Therefore, it is necessary to be able to distinguish between smartphones and assault rifles to ensure that the barrier can detect these weapons.

[0008] Therefore, it has been proposed in document WO 2017 / 141022 to add a spacing zone to each barrier to guide the inspected person so that he or she passes through the middle of the door formed by the barriers, where the sensitivity of the door formed by a pair of barriers is relatively uniform. Specifically, the sensitivity of the static magnetic sensor is inversely proportional to the distance, and the sensor close to the barrier is more sensitive than the sensor in the center, but the excessive sensitivity near the barrier causes almost all false alarms. Therefore, the presence of the spacing zone can prevent the inspected person from getting too close to the barrier and ensure that they stay in the middle of the door, where the sensitivity is lower and more uniform.

[0009] However, this increase in the distance between the barriers makes the gates sensitive to environmental disturbances, since the signal at this distance is weaker relative to the barriers and therefore more like that generated by the surrounding elements. In addition, the barriers thus obtained are more difficult to transport, since they are much heavier and larger than the earliest ones. Finally, in cases where several gates must be built, especially at the entrances of stadiums or large concert halls, the assembly formed by each pair of barriers is very bulky, thus limiting the number of gates that can be built.

[0010] Document US2018 / 012465 describes a detection system according to the preamble of claim 1, comprising detectors, each of which comprises at least one magnetic sensor configured to generate a signal representative of the strength of the magnetic field detected, and, for each detector, a processing unit configured to receive a signal representative of the strength of the magnetic field detected by the sensor. In the case where the magnetic field generated at the detector is inversely proportional to the cube of the sensitivity distance r of the detector, the distance between the two detectors of the system of this document is equal to half of their sensitivity distance. In this way, the detectors are independent and their sensitivity can be reduced.

[0011] Document US2006 / 197523 describes a system for detecting an object comprising several detectors, each of which comprises a plurality of gradiometers; and a processor configured to collect signals generated by the gradiometers. The processor calculates an average value of the collected signals to obtain a measurement of background noise. The average value is then subtracted from the signal generated by the gradiometer to eliminate the noise. Summary of the invention

[0012] Therefore, the object of the present invention is to propose a detection system that can be quickly installed and disassembled, for example at the entrance of a public place, which detection system can reliably distinguish small objects including magnetic components (such as smartphones) and detect small assault rifles.

[0013] To this end, the present invention proposes a detection system for a target object, the system comprising:

[0014] a first detector comprising at least one first magnetic sensor configured to generate a signal representative of a detected magnetic field strength,

[0015] a second detector, separate from the first detector and comprising at least one second magnetic sensor, the second magnetic sensor being configured to generate a signal representative of a detected magnetic field strength, and

[0016] a processing unit configured to receive said signal representing the strength of the magnetic field detected by said first magnetic sensor and / or said second magnetic sensor,

[0017] The detection system further comprises at least one communication interface configured to send the signal generated by the first and / or the second magnetic sensor to the processing unit. In addition, the processing unit is configured to determine a correction value of the signal generated by the magnetic sensors of the first and second detectors by applying an attenuation coefficient to the signal generated by the one or more magnetic sensors, and to send an instruction to generate an alarm when the correction value is greater than a predetermined threshold.

[0018] Certain preferred but non-limiting aspects of the above detection system are used alone or in combination as follows:

[0019] The communication interface is a wireless communication interface.

[0020] The first and second detectors are portable.

[0021] The system also includes a third detector, which includes at least one third magnetic sensor, which is configured to detect a magnetic field and generate a signal representing the strength of the magnetic field detected in this way, and the first detector and the second detector form a first gate, and the second detector and the third detector together form a second gate.

[0022] The processing unit is housed in each of the first and second detectors, and the processing unit housed in the second detector is configured, on the one hand, to calculate correction values ​​of the signals generated by the magnetic sensors of the second and third detectors by applying an attenuation coefficient to the signals generated by the second and third magnetic sensors, and on the other hand, to send a signal representing the magnetic field strength detected by the second magnetic sensor and the correction value of the signal calculated in this manner to the processing unit of the first detector via the communication interface.

[0023] According to a second aspect, the present invention further proposes a method for detecting a target object using the above detection system, the detection method comprising the following steps:

[0024] S1: the first and / or the second magnetic sensor generates a signal indicating the strength of the magnetic field,

[0025] S3: calculating correction values ​​for the signals generated by the first and the second magnetic sensors by applying an attenuation coefficient to the signals generated by the one or more magnetic sensors during step S1;

[0026] S4: Compare the correction value with a predetermined threshold, and

[0027] S5: When the correction value is greater than the predetermined threshold, an instruction to generate an alarm is sent.

[0028] Certain preferred but non-limiting aspects of the above detection method are used alone or in combination as follows:

[0029] The method further comprises, before step S4, a step S2 of calculating an average value of the correction values, wherein the average value of the correction values ​​is used to implement step S4.

[0030] The method further comprises, before step S3, a step S2 of calculating an average value of the signals generated by the first and second magnetic sensors, the average value being used to implement step S3.

[0031] The correction step S3 includes the following sub-steps:

[0032] S31: determining a maximum value of the signals generated by the first magnetic sensor and the second magnetic sensor,

[0033] S32: determining a minimum value of the signals generated by the first magnetic sensor and the second magnetic sensor,

[0034] S32: Calculate the ratio of the maximum value to the minimum value determined in this way,

[0035] S34: comparing the ratio with a first threshold and a second threshold, the second threshold being higher than the first threshold,

[0036] S35: inferring the attenuation coefficient,

[0037] When the ratio is less than a first threshold, the attenuation coefficient is equal to a first value; when the ratio is greater than the second threshold, the attenuation coefficient is equal to a second value different from the first value; and when the ratio is between the first threshold and the second threshold, the attenuation coefficient is equal to a value between the first value and the second value.

[0038] When the ratio is between the first threshold and the second threshold, the attenuation coefficient is a linear function that depends on the ratio.

[0039] When the ratio is between the first threshold and the second threshold, the first value is equal to 1, the second value is equal to 0.1, and the attenuation coefficient is defined by the following function:

[0040] -0.03*R+1.9

[0041] Where R is the value of the ratio.

[0042] The first detector comprises at least two first magnetic sensors, the second detector comprises at least two second magnetic sensors, each first magnetic sensor being associated with a given second magnetic sensor to form a pair, and wherein the steps S1 to S4 are applied to each pair.

[0043] The detection system also includes a third detector, which includes at least one third magnetic sensor, and the third magnetic sensor is configured to detect a magnetic field and generate a signal representing the strength of the magnetic field detected in this manner. The detection method also includes a step of calculating correction values ​​of the signals generated by the second and third magnetic sensors by applying an attenuation coefficient to the signals generated by the second and third magnetic sensors before the step S5 of generating an alarm.

[0044] The method further comprises, after the step of calculating correction values ​​of the signals generated by the second and third magnetic sensors, a step of inferring one or more gates formed by the first and second detectors detecting the magnetic field on the one hand and by the second and third detectors detecting the magnetic field on the other hand, based on the correction values ​​of the signals generated by the first and second magnetic sensors and the correction values ​​of the signals generated by the second and third magnetic sensors.

[0045] The step of inferring the one or more gates comprises the following sub-steps:

[0046] multiplying the correction value calculated based on the signals of the second and third sensors by a safety factor,

[0047] comparing the correction value calculated based on the signals generated by the first and second sensors with the product of the correction value calculated based on the second and third sensors and the safety factor,

[0048] multiplying the safety factor by a correction value calculated based on the signals of the first and second sensors,

[0049] The correction value calculated based on the signals generated by the second sensor and the third sensor is compared to the product of the correction value calculated based on the first sensor and the second sensor and the safety factor.

[0050] If the correction value calculated based on the signals generated by the first and second sensors is greater than the product of the correction value calculated based on the signals of the second and third sensors and the safety factor, step S5 is implemented only by the first and second detectors.

[0051] If the correction value calculated based on the signals generated by the second and third sensors is greater than the product of the correction value calculated based on the signals of the second and third sensors and the safety factor, step S5 is implemented only by the second and third detectors.

[0052] The first detector and the second detector each comprise a processing unit, and wherein:

[0053] the step of calculating said correction values ​​of said signals generated by said second and third magnetic sensors being performed by said processing unit of said second detector,

[0054] the step of calculating said correction values ​​for said signals generated by said first and second magnetic sensors is performed by said processing unit of said first detector, and

[0055] The step of inferring one or more pairs of detectors that detected the magnetic field is performed by the processing unit of the second detector and the processing unit of the first detector.

[0056] The detection system further includes a fourth detector, the fourth detector includes at least one fourth magnetic sensor, the fourth magnetic sensor is configured to detect a magnetic field and generate a signal representing the strength of the magnetic field detected in this way, and the detection method further includes the following sub-steps:

[0057] calculating correction values ​​for the signals generated by the third and fourth magnetic sensors by applying an attenuation coefficient to the signals generated by the third and fourth magnetic sensors,

[0058] multiplying the correction values ​​of the signals generated by the third and fourth magnetic sensors by the safety factor,

[0059] comparing the correction values ​​of the signals generated by the second and third sensors with the product of the correction values ​​of the signals generated by the third and fourth magnetic sensors and the safety factor,

[0060] comparing the correction values ​​of the signals generated by the third and fourth sensors with the product of the correction values ​​of the signals generated by the second and third magnetic sensors and the safety factor,

[0061] One or more pairs of detectors are inferred from among the first, second, third and fourth detectors that detect the magnetic field.

[0062] If the correction value of the signals generated by the second and third sensors is greater than the product of the correction value of the signals generated by the third and fourth magnetic sensors and the safety factor, step S5 is implemented only by the second and third detectors.

[0063] If the correction value of the signal generated by the third and fourth sensors is greater than the product of the correction value of the signal generated by the second and third magnetic sensors and the safety factor, step S5 is implemented only by the third and fourth detectors. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Other characteristics, objects and advantages of the invention will become more apparent on reading the following detailed description and with reference to the accompanying drawings, given by way of non-limiting examples, in which:

[0065] Figure 1 is a schematic diagram of an example of a detector that can be used in a detection system according to the present invention.

[0066] Figure 2 An exemplary embodiment of a detection system according to the invention comprising two detectors is shown.

[0067] Figure 3 An exemplary embodiment of a detection system according to the invention is shown which comprises three detectors which together form two doors, in one of which a check of a person is performed.

[0068] Figure 4An exemplary embodiment of a detection system according to the invention is shown comprising m detectors which together form m-1 gates.

[0069] Figure 5 is a block diagram illustrating the general steps of an example of a detection method according to the present invention.

[0070] Figure 6 is a block diagram showing the sub-steps of correcting the signal value.

[0071] Figure 7 is a block diagram showing steps of an example of a detection method according to the present invention in the case where the detection system includes at least four detectors (n-2, n-1, n and n+1).

[0072] Figure 8a The signal strength of a detection system according to the prior art comprising two detectors 130 cm apart is shown.

[0073] Figure 8b The signal strength of a detection system according to an embodiment of the invention is shown, comprising two detectors 130 cm apart and comprising a processing unit configured to calculate an average of the signals generated by the sensors of the two detectors.

[0074] Figure 8c The signal strength of a detection system 1 according to an embodiment of the invention is shown, comprising two detectors 130 cm apart and comprising a processing unit configured to calculate an average value of the signals generated by the sensors of the two detectors. DETAILED DESCRIPTION

[0075] A system 1 for detecting a target object, in particular for detecting an object containing a large volume of ferromagnetic material (e.g. an assault rifle), comprising:

[0076] at least one first and second detector 10, 20 which together form a door,

[0077] at least one processing unit 6, and

[0078] At least one communication interface 7.

[0079] Each detector 10, 20 comprises at least one magnetic sensor 5. The term "magnetic" (or magnetostatic) is understood herein to refer to a passive sensor configured to detect the magnetic field naturally surrounding an object containing iron or any ferromagnetic component, as opposed to, for example, an inductive coil.

[0080] More precisely, the first detector 10 includes at least one first magnetic sensor 5, preferably at least two, for example three first magnetic sensors 5, and the second detector 20 includes at least one second magnetic sensor 5. Preferably, the second detector 20 and the first detector 10 each include as many sensors 5 as possible.

[0081] Each magnetic sensor 5 is configured to detect a magnetic field and generate a signal representing the strength of the magnetic field detected in this way. In one embodiment, the signal is a voltage whose value is proportional to the strength of the detected magnetic field.

[0082] In one embodiment, each magnetic sensor 5 is configured to detect magnetic field strength along three orthogonal axes.

[0083] Each detector 10, 20 further comprises a column 3, which is configured to be placed on the ground, for example via a base 4. Preferably, the column 3 has a height substantially equal to the average height of a person 2, for example about 1.70m to 2.0m.

[0084] The assembly formed by the column 3 and its base 4 is portable, i.e. it is not explicitly anchored to the ground and can be transported by an operator. Where applicable, each detector 10, 20 can be equipped with a handle to facilitate transportation. The handle can in particular be attached to the base 4.

[0085] The magnetic sensors 5 are distributed over the entire height of the column 3 to ensure detection of target objects between the feet and the head of the inspected person 2. For example, each column 3 may be equipped with three magnetic sensors 5 distributed between the base 4 and the free end of the column 3.

[0086] Finally, within one and the same detection system 1 , the magnetic sensors of the detectors 10 , 20 are positioned in pairs at the same height, thereby forming pairs of sensors 5 facing each other.

[0087] The system 1 further comprises at least one processing unit 6 configured to receive a signal representing the strength of a magnetic field generated by the first magnetic sensor 5 and / or the second magnetic sensor 5. The processing unit 6 then determines a correction value for the signal generated by the magnetic sensor 5 of the first and second detectors 10, 20 by applying an attenuation coefficient to the signal generated by one or more magnetic sensors 5 during step S1, and sends an instruction to generate an alarm when the correction value is greater than a predetermined threshold.

[0088] In one embodiment, the processing unit 6 calculates the average value of the signals generated by the magnetic sensors 5 of the first and second detectors 10, 20 and then applies the correction step to this average value. Alternatively, the processing unit 6 may first determine the correction values ​​of these signals and then calculate the average value of these correction values.

[0089] The processing unit 6 can determine the arithmetic mean of the signals, corresponding to the sum of the signal values ​​divided by the number of signals, or, in a variant, the geometric mean of the signals, corresponding to the square root of the product of the signals.

[0090] In one embodiment, the processing unit 6 may be incorporated into one of the first detector 10 and the second detector 20. Preferably, each detector 10, 20 comprises an integrated processing unit 6. The term "integrated" should be understood to mean that the processing unit 6 is part of the detector 10, 20 and is not a separate component connected to the system 1.

[0091] In this embodiment, the processing unit 6 can be attached, for example, to the upright 3 of the associated detector or, in a variant, to the base 4 thereof.

[0092] In a variation of this embodiment, the processing unit 6 may be placed at a distance from the first and second detectors 10, 20. The detectors 10, 20 then transmit the signals generated by their magnetic sensors 5 to the processing unit 6 for processing the signals through its communication interface 7.

[0093] In one embodiment, the processing unit 6 may include:

[0094] Analog-to-digital converter A / D, which is configured to convert the analog (voltage) signal generated by the magnetic sensor 5 into a digital signal

[0095] a digital signal processor DSP configured to generate a digital signal converted in this manner, and

[0096] The system management microcomputer SMM is configured to receive the digital signal generated by the DSP and compare it with a predetermined threshold.

[0097] The SMM is connected to at least one transmitter 8 configured to generate an alarm signal, such as a sound transmitter 8 configured to generate an acoustic signal and / or a lamp configured to generate an optical signal (LED, flash light, etc.). The transmitter 8 can be included in the detector 10, 20, or in a variant, worn by the operator (earphones, etc.), in which case the processing unit 6 sends a command to generate an alarm to the remote transmitter 8 via the communication interface 7 of the corresponding detector 10, 20.

[0098] Furthermore, the SMM is connected to an asynchronous interface UART to allow the processing unit 6 to be connected to a computer (or equivalent) to allow various actions including controlling the probe program, performing diagnostics on one or more probes, loading updates and the like.

[0099] Finally, the SMM is connected to the human-machine interface HMI.

[0100] Each detector 10, 20 of the detection system 1 also includes a communication interface 7, which is configured to allow one of the detectors 10, 20 of the system 1 to communicate with another of the detectors 20, 10 of the system 1 and send the other detector a signal generated by one or more magnetic sensors 5 thereof. For each detector 10, 20, the communication interface 7 can be connected to a DSP (such as a DSP) of the processing unit 6 of the detector 10, 20. Figure 1 as shown), and can also be connected to its SMM and its alarm transmitter 8.

[0101] The communication interface 7 preferably comprises a wireless interface to facilitate the installation of the detection system 1 , for example an interface of the Wi-Fi or Bluetooth type performing optical, radio, infrared or inductive communication, etc. In a variant, the communication interface 7 may be a wired interface.

[0102] Where applicable, the detection system 1 may comprise a larger number of detectors so as to form a set of gates, each gate being formed by two adjacent detectors. Preferably, the detectors of a detection system 1 are substantially identical forming a pair.

[0103] For example, the detection system 1 may comprise a third detector 30 comprising at least one third magnetic sensor 5 configured to detect a magnetic field and to generate a signal representative of the strength of the magnetic field detected in this way.

[0104] Similar to the first and second detectors 10 , 20 , the third detector 30 may comprise a stand 3 attached to a base 4 and equipped with one or more third magnetic sensors 5 and a communication interface 7 and, where applicable, a processing unit 6 .

[0105] In order to form a plurality of doors, the invention proposes placing a first detector 10, a second detector 20 and a third detector 30 side by side to form two doors. More precisely, the first door is formed by the first detector 10 and the second detector 20, while the second door is formed by the second detector 20 and the third detector 30. In the system, two separate doors are thus formed using one and the same detector (here the second detector 20), which can significantly reduce the volume of the detection system 1 compared to the system proposed, for example, in document WO 2017 / 141022. The system is easier to install.

[0106] As will be seen below, this configuration is achieved by the fact that the processing unit 6 of the second detector 20 located between the first detector 10 and the second detector 20 can be configured to both process the signals generated by one or more sensors 5 of the third detector 30 and communicate with the first detector 10, so that the detection system 1 is able to determine the door in which the target object is detected even if the magnetic sensor 5 performs scalar rather than vector detection.

[0107] More precisely, the processing unit 6 of the second detector 20 is configured to:

[0108] (i) calculating a correction value (or average value, where applicable) or an average value of the signals generated by the second and third magnetic sensors 5, and,

[0109] (ii) When the calculated value is greater than a predetermined threshold, a signal representing the magnetic field strength detected by the one or more second magnetic sensors 5 and the calculated value are sent to the processing unit 6 of the first detector 10 via the communication interface 7 .

[0110] Of course, the operator can also use four detectors according to the present invention to form two doors, and the shared second detector 20 is not necessary for detecting the target object.

[0111] Each detector 10, 20 may also include identification means and a memory to allow association and communication with other detectors of the detection system 1 and implementation of the detection method S. For example, when the detectors 10, 20, 30 forming the detection system 1 are paired, each detector 10, 20, 30 may be assigned an address, which may be set when the detectors 10, 20, 30 are manufactured or programmed. In one embodiment, the address of each detector 10, 20, 30 is fixed, i.e., non-modifiable, to limit operational errors of the detection system 1 and facilitate after-sales service.

[0112] An example of an address may include a character chain, which may be formed in particular by a given number (eg eight) of hexadecimal pairs.

[0113] When the detectors 10, 20, 30 of the detection system 1 are paired, the address used when a given detector forms a gate is stored in the memory of the given detector. For example, in the case where the detection system 1 comprises a first detector 10, a second detector 20 and a third detector 30, during parameterization of the detection system:

[0114] The address of the second detector 20 is stored in the memory of the third detector 30.

[0115] During parameterization of the detection system, the addresses of the first detector 10 and the third detector 30 are stored in the memory of the second detector 20, and

[0116] The address of the second detector 20 is stored in the memory of the first detector 10 .

[0117] An example of a detection method S using a detection system 1 according to the invention comprising two detectors 10 , 20 will now be described.

[0118] For ease of reading the description, the detection system 1 includes a first detector 10 and a second detector 20, and the first detector 10 and the second detector 20 respectively include two first magnetic sensors 5 and two second magnetic sensors 5. The first and second magnetic sensors 5 form two pairs of magnetic sensors 5, each pair including a first sensor 5 and a second sensor 5. Preferably, one pair includes a first magnetic sensor 5 and a second magnetic sensor 5, each sensor being placed near the free end of the column 3 of the first detector 10 and the second detector 20, and the other pair includes a first magnetic sensor 5 and a second magnetic sensor 5 respectively placed near the base 4 thereof.

[0119] Both detectors are identical and each comprise a processing unit 6 and a communication interface 7 .

[0120] Of course, the present invention should be modified accordingly in the case where the detector includes a different number of magnetic sensors 5. In particular, the detector may include only a single magnetic sensor 5, or include more than two magnetic sensors 5 (for example, three magnetic sensors 5). In addition, the second detector 20 may not include the processing unit 6, or in a variant, the processing unit 6 may be placed at a distance from the detector instead of being accommodated in the first detector 10.

[0121] During a preliminary step, the first detector 10 and the second detector 20 are paired to associate them and to configure them to be each assigned a function in the detection method S. For example, the first detector 10 can be configured as a master detector and the second detector 20 can be configured as a slave detector. The "master detector" of a given gate should be understood to mean the detector whose processing unit 6 is configured to calculate a correction value and / or an average value of the signal, while the term "slave detector" should be understood to mean another detector of said given gate.

[0122] During a first step S1 , at least one of the first and second magnetic sensors 5 generates a signal representative of the magnetic field strength.

[0123] In practice, when a magnetic field is detected by one of the magnetic sensors 5 of the detection system 1 , all magnetic sensors 5 of the system generate a signal representative of the strength of the detected magnetic field, only the power of the signal generated by each sensor 5 differs.

[0124] The signals generated by the first and second magnetic sensors 5 are sent to the processing unit 6, where appropriate, through the communication interface 7 of the first detector 10 and / or the second detector 20. In the example, the first detector 10 is the main detector and includes the processing unit 6, the signal of the second magnetic sensor 5 is sent to the first detector 10 through the communication interface 7 of the second detector 20, and the signal of the first magnetic sensor 5 can be sent directly to the first detector 10 through the first magnetic sensor 5.

[0125] During step S3, the processing unit calculates a correction value for the signal generated by each magnetic sensor 5 by applying the attenuation coefficient to said signal. Thus, here, the processing unit 6 calculates a first correction value corresponding to the first magnetic sensor of the pair consisting of the first and second magnetic sensors 5, and then calculates a second correction value corresponding to the second magnetic sensor of the pair.

[0126] This so-called calibration step S3 thus makes it possible to attenuate the signals generated by the magnetic sensor 5 of the detection system 1 by applying a correction factor to these signals as a function of their value. More precisely, the purpose of the calibration is to attenuate the signal when the target object is close to one of the detectors 10, 20 of greater sensitivity, so as to reduce the weight of this signal in the detection.

[0127] To this end, during sub-steps S31 and S32 , for each pair of magnetic sensors 5 , the processing unit 6 determines the maximum and minimum values ​​among the signals generated by the first magnetic sensor 5 and the second magnetic sensor 5 at a given time.

[0128] During a third sub-step S33 , the processing unit 6 calculates the ratio of the maximum value to the minimum value determined in this way and then, during a fourth sub-step S34 , compares this ratio with a determined threshold value and deduces therefrom the value of the attenuation coefficient to be applied to the signal value.

[0129] For example, the processing unit 6 may specifically compare the ratio with a first threshold and a second threshold, wherein the second threshold is greater than the first threshold, and infer the attenuation coefficient therefrom.

[0130] When the ratio is less than a first threshold, the attenuation coefficient may be equal to a first value,

[0131] When the ratio is greater than a second threshold, the attenuation coefficient may be equal to a second value that is less than the first value, and

[0132] When the ratio is between the first threshold and the second threshold, the attenuation coefficient may be equal to a value between the first value and the second value. In particular, when the ratio is between the first threshold and the second threshold, the attenuation coefficient may be a linear function depending on the ratio.

[0133] By using the ratio between the maximum and minimum values, it is possible to determine whether a target object that generates a magnetic field or interferes with the Earth's electromagnetic field is placed near one of the detectors. In this case, the value of the ratio is greater than the second threshold, and the applied attenuation coefficient is equal to the second value, which is less than the first value. On the contrary, when the target object is located in the middle of the two detectors, the sensitivity in this area of ​​the gate is lower. This is manifested by the fact that the ratio of the maximum to the minimum value is also lower. Therefore, the attenuation coefficient can be higher, while the resulting attenuation coefficient is lower.

[0134] A relative virtual homogeneity between the two detectors is thereby obtained.

[0135] By way of non-limiting example, when the ratio is between a first threshold and a second threshold, the first threshold may be equal to 30, the second threshold may be equal to 60, the first value may be equal to 1, the second value may be equal to 0.1, and the attenuation coefficient may be defined by the following function:

[0136] -0.03*R+1.9

[0137] Where R is the value of the ratio.

[0138] In other words, when the ratio is less than 30, the attenuation coefficient may be equal to 1; when the ratio is greater than 60, the attenuation coefficient may be equal to 0.1; and when the ratio is between 30 and 60, the attenuation coefficient may be equal to 0.03*R+1.9.

[0139] In a variant embodiment, instead of calculating the correction value of the signal of each pair of magnetic sensors 5, the processing unit 6 of the main detector can calculate the average value (step S2) of the signal generated by each pair of magnetic sensors 5. Therefore, here, the processing unit 6 calculates a first average value corresponding to the first magnetic sensor in the pair consisting of the first and second magnetic sensors 5, and a second average value corresponding to the second magnetic sensor in the pair.

[0140] Of course, when each detector comprises only a single sensor 5 , the processing unit 6 calculates in step S2 only a single average value corresponding to the average value of the signals of the two magnetic sensors 5 .

[0141] As mentioned above, the processing unit 6 can calculate the arithmetic mean of the signal or, in a variant, the geometric mean.

[0142] In another variant embodiment, the processing unit 6 calculates the mean value of the signals of each pair of magnetic sensors 5 (step S2 ) and implements a step of correcting said signals (step S3 ).

[0143] To this end, after calculating the average value of the signals of each pair of magnetic sensors 5 (step S2 ), the processing unit 6 can apply the attenuation coefficient to the average value calculated in this way (step S3 ).

[0144] Alternatively, the processing unit 6 may first apply the attenuation coefficient to the signal of each pair of magnetic sensors 5 (step S3) and then calculate the average value of the corrected signals of each pair of magnetic sensors 5 (step S2, applied to the corrected signals, not the signals generated by the magnetic sensors 5).

[0145] The attenuation coefficient may be the same as the attenuation coefficient described previously (equal to the first value, the second value, or a function of the ratio, depending on the value of the ratio).

[0146] During a fifth step S5 , the processing unit 6 compares the calculated value with a predetermined threshold value.

[0147] The calculated value used by the processing unit 6 during the fifth step S5 can be the corrected value of the signal generated by the paired magnetic sensors 5 and the corrected value obtained in step S3, or the value corrected and averaged by implementing the attenuation coefficient applied in step S2. When the corrected value (where applicable, the corrected average value) is greater than a predetermined threshold, during a sixth step S6, the processing unit 6 sends an instruction to emit an alarm (light, sound alarm, etc.) to at least one transmitter 8. Preferably, the processing unit 6 sends the instruction to emit an alarm to the transmitters 8 of the first detector 10 and the second detector 20 (via the communication interface 7), thereby emitting one or more alarms on both sides of the door. In a variant, only one or more transmitters 8 of one of the detectors 10, 20 can receive the emission instruction of the processing unit 6.

[0148] Alternatively, when the processing unit 6 determines only the corrected values ​​of the signals without taking their average value, the sum of the corrected values ​​of the signals (rather than their average value) is compared with a predetermined threshold value during step S5. Of course, the signals generated by the sensors 5 are first added and then the correction step S3 is applied to the sum of the values.

[0149] Alternatively, instead of calculating the sum of the correction values ​​of the signal, the processing unit 6 can determine the maximum value of the correction signal and compare the maximum value determined in this way with a threshold value during step S5. In a similar manner to the previous description, the maximum value of the signal generated by the sensor 5 can first be determined and then the correction step S3 can be applied to this maximum value.

[0150] In this alternative, the processing unit 6 compares the sum of the corrected values ​​(or the corrected maximum value) of the signals of the same pair of magnetic sensors 5 with a predetermined threshold. When the sum (or the corrected maximum value) is greater than the predetermined threshold, during a sixth step S6, the processing unit 6 sends an instruction to emit an alarm (light, sound alarm, etc.) to at least one transmitter 8. As previously indicated, the processing unit 6 can send an instruction to emit an alarm to the transmitter 8 of the first detector 10 and / or the second detector 20.

[0151] Figure 8a , 8b 8a and 8c show the intensity of the measurement signals of the four detection systems as a function of the distance relative to the detector.

[0152] Figure 8a The situation of a detection system according to the prior art comprising two detectors 130 cm apart is shown. In this figure, the intensity represented corresponds to the maximum value of the signal generated by the sensors of the two detectors.

[0153] Figure 8b The case of a detection system 1 according to an embodiment of the invention comprising two detectors 130 cm apart and comprising a processing unit is shown. In this figure, the intensity represented corresponds to the average value of the signals generated by the sensors of the two detectors.

[0154] Figure 8c The case of a detection system 1 according to an embodiment of the invention comprising two detectors 130 cm apart and comprising a processing unit is shown. In this figure, the intensity represented corresponds to the average of the corrected values ​​of the signals generated by the sensors of the two detectors.

[0155] It is evident from this figure that by calculating the mean value and, where applicable, applying the attenuation factor during the step of correcting the mean value, a simple determination of the signal maximum ( Figure 8a ) can homogenize the signal strength between the two detectors of the detection system.

[0156] Example

[0157] The following table is a comparative example of detecting the same target object by three configurations of the detection system, namely (i) a detection system 1 comprising only one detector, (ii) a detection system 1 comprising two detectors 130 cm apart according to a first embodiment of the present invention, wherein an average value of the signal is calculated; and (iii) a detection system 1 comprising two detectors 130 cm apart according to a second embodiment of the present invention, wherein an average value of the signal is calculated and the average value is corrected to determine whether an alarm must be triggered.

[0158] In this example, the sensitivity SE of the three configurations of the detection system has been set to 85% (equivalent to 1400mV). In other words, the sensitivity has been set so that the predetermined threshold is equal to 1400mV. The system has been parameterized so that at this sensitivity, the passage of a sphere with a diameter of 75mm at a height of one meter from the ground will not generate any alarm in the following cases: when passing at 65cm from a single detector (first configuration (i)), or when passing in the middle of two detectors (second and third configurations (ii) (iii)). In other words, a diameter of 75mm is the limiting detection diameter of the system under test. Specifically, the interference of the electromagnetic field of an iron ball with a diameter of 75mm substantially corresponds to the interference caused by the presence of an AK47-type assault rifle in the middle of the door.

[0159]

[0160]

[0161] In the table, "Limit diameter [mm]" corresponds to the minimum diameter in millimeters, from which the detected detection system 1 emits an alarm signal.

[0162] Tests have shown that, in the case where the detection system 1 comprises two detectors forming a gate (configurations (ii) and (iii)) and the processing unit 6 calculates the average value of the signals generated by the magnetic sensors 5 of these detectors, a target object having a magnetic field equivalent to that of an approximately 62 mm iron ball can be distinguished from objects of smaller size (such as a smartphone) even if the target object is 50 cm away from one of the detectors (in practice, the distance through the center is already very far, during this test the detectors were 130 cm apart).

[0163] In the case where the processing unit 6 of the detection system 1 further applies a correction step S2 to the average value of the signal (configuration (iii)), the detection system 1 is able to distinguish a target object having a magnetic field equivalent to that of an approximately 64 mm iron ball even if the target object is 25 cm away from one of the detectors (i.e., very close to the detectors because the detectors were 130 cm apart during this test).

[0164] Therefore, even if the passing position of the inspected person 2 is not in the middle of the two detectors, the detection system (configurations (ii) and (iii)) according to the present invention is able to distinguish small-sized objects from large-volume target objects such as assault rifles, even if these small-sized objects include magnetic components (such as smartphones).

[0165] The present invention is also applicable to the case where the detection system 1 includes three or more detectors to form a plurality of doors, and two adjacent doors share the same detector. An example of a method of detecting a target object using such a detection system 1 will now be described.

[0166] To facilitate reading of this embodiment, the detection system 1 includes three detectors, each of which includes two magnetic sensors 5 ( Figure 3 ). In other words, the detection system 1 includes first, second and third detectors 10, 20, 30, which respectively include two first, two second and two third magnetic sensors 5. The second detector 20 forms a first door with the first detector 10 and a second door with the third detector 30. Therefore, the second detector 20 is located between the first detector 10 and the third detector 30.

[0167] The three detectors are identical and therefore each comprises a processing unit 6 and a communication interface 7. Of course, in a variant, the processing unit 6 may be placed at a distance from the detectors, rather than being incorporated into the detectors. In this case, the signals generated by the magnetic sensor 5 of a given detector are sent to the remote processing unit 6 via the detector's communication interface 7, so that the processing unit 6 applies the detection algorithm to these signals and then sends any instructions requiring the generation of an alarm to the detector's transmitter 8 via the corresponding communication interface 7 in the detector.

[0168] Of course, with necessary modifications, the present invention is also applicable to the following cases: that is, the system includes only two detectors that together form a single door, or includes a larger number of detectors (for example, n detectors, n is an integer) that together form n-1 doors. The detector may also include only a single magnetic sensor 5, or include more than two magnetic sensors 5 (for example, three magnetic sensors 5).

[0169] During a preliminary step, the first, second and third detectors 10, 20, 30 are paired to associate them and configured to each be assigned a function in the detection method S. For example, for a first door, the first detector 10 can be configured as a master detector, while the second detector 20 can be configured as a slave detector. For a second door, the second detector 20 is configured as a master detector, while the third detector 30 is configured as a slave detector. During pairing, the identification means of each detector of the system (usually referred to as its address) can also be entered and stored in the memory of each adjacent detector. Thus, the identification mechanism of the first detector 10 is entered into the second detector 20, while the identification mechanism of the second detector 20 is entered into the first detector 10 to allow them to be paired. In the same way, the identification mechanism of the second detector 20 is entered into the third detector 30, while the identification mechanism of the third detector 30 is entered into the second detector 20.

[0170] During a first step, at least one of the first, second and third magnetic sensors 5 detects a magnetic field and generates a signal representative of the strength of the magnetic field detected in this way.

[0171] In practice, all magnetic sensors 5 of the same door continuously or periodically generate signals representing the strength of the magnetic field, and only the power of the signal generated by each sensor 5 is different.

[0172] In the remainder of this document, an example in which signals are generated by two second magnetic sensors 5 and two third magnetic sensors 5 is described to illustrate the steps of method S.

[0173] The signals generated by the magnetic sensors 5 are then sent to the processing unit 6 of the main detector of the door in question, where appropriate by means of the communication interface 7. In the example described, the signals generated by the three magnetic sensors 5 are sent to the processing unit 6 of the second detector 20 via the communication interface 7 of the third detector 30. The signals generated by the second magnetic sensor 5 are themselves sent directly to the processing unit 6 of the second detector 20 (note that if the processing unit 6 is external, the signals are sent via its communication interface 7).

[0174] During the second step, the processing unit 6 of the main detector of the door in question, here the second detector 20, calculates a correction value for the signal generated by each magnetic sensor 5 by applying the attenuation coefficient to said signal (step S3). Thus, here the processing unit 6 calculates a first correction value corresponding to the first magnetic sensor of the pair formed by the second and third magnetic sensors 5, and a second correction value corresponding to the second magnetic sensor of the pair.

[0175] The processing unit 6 then calculates a value corresponding to the sum of the values ​​of the signals corrected in this way (or in a variant determines, for each pair of sensors 5, the maximum of the corrected signals). This correction step has already been described above with respect to sub-steps S31 to S35 and will not be repeated here.

[0176] Alternatively, instead of calculating the correction value for the signal of each pair of magnetic sensors 5, the processing unit 6 may calculate the average value PGS[2,3] of the signals generated by each pair of magnetic sensors 5. Thus, here, the processing unit 6 calculates a first average value corresponding to the first magnetic sensor of the pair consisting of the second and third magnetic sensors 5, and a second average value corresponding to the second magnetic sensor of the pair.

[0177] Of course, when each detector comprises only a single sensor 5 , the processing unit 6 calculates only a single average value corresponding to the average value of the signals of the two magnetic sensors 5 .

[0178] As mentioned above, the processing unit 6 can calculate the arithmetic mean of the signal or, in a variant, the geometric mean.

[0179] In another variant embodiment, the processing unit 6 can immediately calculate the mean value of the signals of each pair of magnetic sensors 5 and implement the step of correcting said signals as described above to obtain a corrected mean value.

[0180] In a similar manner to that already described, the correction step S2 may be applied to the signal generated by the sensor 5, either to the sum of the signals (or to the maximum value of the signals), or to the average value of the signals.

[0181] During the third step, when one of the values ​​PGS[2,3] calculated in the second step is greater than a predetermined threshold, the processing unit 6 of the second detector 20 sends the calculated value PGS[2,3] to the processing unit 6 of the first detector 10 on the one hand, and sends the signal generated by its second magnetic sensor 5 to the processing unit 6 of the first detector 10 on the other hand.

[0182] During the fourth step, simultaneously with the third step, the processing unit 6 of the first detector 10 calculates the value PGS[1,2] based on the signals generated by each pair of magnetic sensors 5 of the first door. The value calculation performed by the processing unit 6 of the first detector 10 is the same as the value calculation performed by the processing unit 6 of the second detector 20. In other words, when one of the main detectors calculates a correction value (corresponding to the sum of the correction values, the maximum value of the correction or the average value of the correction, respectively), the other main detectors perform the same calculation (the sum of the correction values, the maximum value of the correction or the average value of the correction, respectively).

[0183] Here, the processing unit 6 of the first detector 10, for example, calculates the average value of the first correction value corresponding to the first magnetic sensor in the pair formed by the first and second magnetic sensors 5, and the average value of the second correction value corresponding to the second magnetic sensor in the pair to obtain the average value of the correction value of the signal.

[0184] When the value PGS[1, 2] calculated by the first detector 10 is less than the predetermined threshold, the processing unit 6 of the first detector 10 does not send any instructions to the transmitter 8 of the first detector 10 or the second detector 10 to generate an alarm.

[0185] On the other hand, when the value PGS[1,2] calculated by the first detector 10 is greater than a predetermined threshold, during the fifth step, the processing unit 6 of the first detector 10 serving as the main detector of the first gate determines whether the target object is detected through the first gate (formed by the first and second detectors 10, 20) or the second gate (formed by the second and third detectors 20, 30).

[0186] For this purpose, processing unit 6 of first detector 10 compares value PGS[2,3] calculated by second detector 20 (sum of corrected values, corrected maximum value or corrected mean value) with value PGS[1,2] calculated by first detector 10 .

[0187] To this end, during a first sub-step, the processing unit 6 of the first detector 10 multiplies the value PGS[2,3] calculated based on the signals generated by the second and third sensors 5 by a predetermined safety factor Ks: Ks*PGS[2,3]. The safety factor Ks is greater than or equal to 1, for example equal to 1.5 or 2.

[0188] In parallel, during the second sub-step, the processing unit 6 of the second detector 10 multiplies the value PGS[1,2] calculated based on the signals generated by the first and second sensors 5 by a predetermined safety factor Ks: Ks*PGS[1,2].

[0189] During the third sub-step, the first detector 10 compares the value PGS[1,2] calculated based on the signals generated by the first and second sensors 5 with the value Ks*PGS[2,3]. If the value PGS[1,2] calculated based on the signals generated by the first and second sensors 5 is less than the value Ks*PGS[2,3] obtained by multiplying the value calculated based on the signals generated by the second and third sensors 5 by the safety factor Ks (i.e., if PGS[1,2]<Ks*PGS[2,3]), then the processing unit 6 of the first detector 10 deletes any instruction requiring an alarm to be generated or does not send the instruction to the transmitter 8 of the first and second detectors 10, 20.

[0190] In parallel, during the fourth sub-step, the second detector 20 compares the value PGS[2,3] with the value Ks*PGS[1,2] obtained by multiplying the value of the signals generated by the first and second signals by Ks. If the value PGS[2,3] calculated based on the signals generated by the second and third sensors 5 is less than the value Ks*PGS[1,2] obtained by multiplying the value calculated based on the signals generated by the first and second sensors 5 by the safety factor Ks (i.e., if PGS[2,3]<Ks*PGS[1,2]), then the processing unit 6 of the second detector 20 deletes any instruction requiring an alarm to be generated or does not send the instruction to the transmitter 8 of the second and third detectors 20, 30. Conversely, if PGS[2,3]>Ks*PGS[1,2], then the second detector 2 sends any instruction requiring an alarm to be generated to the transmitters 8 of the second detector 20 and the third detector 30.

[0191] Then, the operator can easily identify which door (here the second door) has detected the target object.

[0192] It should be noted that applying the safety factor Ks during the comparison of the values calculated by the detectors on either side of a given door provides a margin for the detection of the target object and reduces the risk of false alarms.

[0193] Therefore, the sending of the calculated value (sum of corrected values, corrected maximum value or corrected average value) of the adjacent door (the slave detector is the master detector of the adjacent door) from the detector to the master detector of the door enables the determination of the position of the detected target object. In particular, it should be remembered that the detection by the magnetic sensor 5 is a scalar detection, and the detector shared by two adjacent doors (here referring to the second detector 20) cannot determine on which side the detected target object is located.

[0194] The detection method S of the present invention can be generalized to cover any detection system 1 including m (where m is greater than or equal to 4) detectors, thereby forming m-1 gates, and two adjacent gates share the same detector.

[0195] The detection method S then comprises the same steps as described above in relation to the detection method for the detection system 1 with three detectors. However, in this case, when the detector n-1 calculates a value PGS[n-1;n] greater than the predetermined threshold value AT, the detection method S comprises, in addition to the step of comparing this value PGS[n-1;n] with the value PGS[n-2;n-1] calculated by the detector n-2, the step of comparing this value PGS[n-1;n] with the value PGS[n;n+1] calculated by the detector n, in order to determine the door in which the target object was detected (see Figure 7 ). Where applicable, a safety factor Ks (Ks≥1) is applied to the value PGS[n;n+1] during the comparison step.

[0196] For example, detector n-1 calculates a given value PGS[n-1; n] based on the signals generated by the magnetic sensors of detectors n and n-1, which value is usually a corrected average value. Detector n-1 (slave detector) then sends this calculated value PGS[n-1; n] and the value of the signal generated by its magnetic sensor 5 to detector n-2 (master detector). Detector n-2 then calculates the value PGS[n-2; n-1] based on the values ​​of the signals generated by the magnetic sensors 5 of detectors n-2 and n-1, which value is here a corrected average value. In the same way, detector n (slave detector of detector n-1) calculates the value PGS[n; n+1] and sends this calculated value and the value of the signal generated by its magnetic sensor 5 to detector n-1. If the value calculated by detector n-2 (master detector) is greater than a predetermined threshold, then:

[0197] For detector n-2:

[0198] The value PGS[n-1;n] calculated and sent by detector n-1 is multiplied by the safety factor Ks, and

[0199] Compare the value PGS[n-2;n-1] that has been calculated with the value Ks*PGS[n-1;n] that has been multiplied by the safety factor. If the value PGS[n-2;n-1] that has been calculated is less than the value calculated by detector n-1 multiplied by the coefficient Ks (i.e., PGS[n-2;n-1]<Ks*PGS[n-1;n]), then detector n-2 infers therefrom that the gate formed by detectors n-2 and n-1 does not have to generate any alarm. Therefore, detector n-2 does not send any instruction to the transmitter 8 of detectors n-2 and n-1 to generate an alarm (or, where applicable, an instruction to cancel the transmission of an alarm).

[0200] In parallel, for detector n-1:

[0201] Multiply the value PGS[n-2;n-1] calculated and sent by detector n-2 by the safety factor Ks, and

[0202] Compare the value PGS[n-1;n] that has been calculated with the value Ks*PGS[n-2;n-1] that has been multiplied by the safety factor.

[0203] If the value PGS[n-1;n] that has been calculated is less than the value calculated by detector n-2 multiplied by the coefficient Ks (i.e., PGS[n-1;n]<Ks*PGS[n-2;n-1]), then detector n-1 infers therefrom that the gate formed by detectors n-1 and n does not have to generate any alarm. Therefore, detector n-1 does not send any instruction to the transmitter 8 of detectors n-1 and n to generate an alarm (or, where applicable, an instruction to cancel the transmission of an alarm).

[0204] Multiply the value PGS[n;n+1] calculated and sent by detector n by the safety factor Ks, and

[0205] Compare the value PGS[n-1;n] that has been calculated with the value Ks*PGS[n;n+1] that has been multiplied by the safety factor.

[0206] If the value PGS[n-1;n] that has been calculated is less than the value calculated by detector n multiplied by the coefficient Ks (i.e., PGS[n-1;n]<Ks*PGS[n;n+1]), then detector n-1 infers therefrom that the gate formed by detectors n-1 and n does not have to generate any alarm. Therefore, detector n-1 does not send any instruction to the transmitter 8 of detectors n-1 and n to generate an alarm (or, where applicable, an instruction to cancel the transmission of an alarm).

[0207] In parallel, for detection n:

[0208] Multiply the value PGS[n-1;n] calculated and sent by detector n-1 by the safety factor Ks, and

[0209] Compare the value PGS[n;n + 1] that has been calculated with the value Ks*PGS[n - 1;n] that has been multiplied by the safety factor.

[0210] If the value PGS[n;n + 1] that has been calculated is less than the value calculated by detector n - 1 multiplied by the coefficient Ks (i.e., PGS[n;n + 1]<Ks*PGS[n - 1;n]), then detector n infers therefrom that the door formed by detectors n and n + 1 does not have to generate any alarm. Therefore, detector n does not send any instruction requiring an alarm to be generated (or, where applicable, an instruction to cancel the transmission of an alarm) to the transmitter 8 of detectors n and n + 1.

[0211] It should be noted that when adjacent doors do not share the same detector and are formed by two separate detectors respectively, the detection within each door is completed by a pair of detectors. Therefore, the detectors of a given door do not have to communicate with the detectors of adjacent doors. This is because each door can operate independently and does not have to determine the door through which the target object has passed.

Claims

1. A detection system (1) for a target object, comprising: a first detector (10) comprising at least one first magnetic sensor configured to generate a signal representative of a detected magnetic field strength, a second detector (20) which is separate from the first detector (10) and comprises at least one second magnetic sensor, the second magnetic sensor being configured to generate a signal representing the strength of the detected magnetic field, and a processing unit (6) configured to receive the signal representing the strength of the magnetic field detected by the first magnetic sensor and / or the second magnetic sensor, The detection system (1) is characterized in that: Also comprising at least one communication interface (7), the interface being configured to send the signal generated by the first magnetic sensor and / or the second magnetic sensor to the processing unit (6), and The processing unit (6) is configured to determining a maximum value of the signals generated by the first magnetic sensor and the second magnetic sensor, determining a minimum value of the signals generated by the first magnetic sensor and the second magnetic sensor, calculating a ratio of the maximum value to the minimum value determined in this way, comparing the ratio with a first threshold value and with a second threshold value, the second threshold value being greater than the first threshold value, deducing an attenuation coefficient, the attenuation coefficient being equal to a first value when the ratio is less than the first threshold value, the attenuation coefficient being equal to a second value different from the first value when the ratio is greater than the second threshold value, and the attenuation coefficient being equal to a value between the first value and the second value when the ratio is between the first threshold value and the second threshold value; determining correction values ​​for the signals generated by the magnetic sensors of the first and second detectors (10, 20) by applying an attenuation coefficient to the signals generated by the one or more magnetic sensors, and When the correction value is greater than a predetermined threshold, an instruction to generate an alarm is sent.

2. The detection system (1) according to claim 1, wherein the communication interface (7) is a wireless communication interface (7).

3. A detection system (1) according to claim 1 or 2, wherein the first and second detectors (10, 20) are portable.

4. The detection system (1) according to claim 1 or 2, further comprising a third detector (30), and wherein: The third detector (30) comprises at least one third magnetic sensor, which is configured to detect a magnetic field and to generate a signal representing the strength of the magnetic field detected in this way, The first detector (10) and the second detector (20) form a first door, and the second detector (20) and the third detector (30) together form a second door.

5. The detection system (1) according to claim 4, wherein: The processing unit (6) is accommodated in each of the first and second detectors (10, 20), The processing unit (6) housed in the second detector (20) is configured to, on the one hand, calculate correction values ​​for the signals generated by the magnetic sensors of the second and third detectors (20, 30) by applying an attenuation coefficient to the signals generated by the second and third magnetic sensors, and, on the other hand, to send a signal representing the magnetic field strength detected by the second magnetic sensor and the correction value of the signal calculated in this way to the processing unit (6) of the first detector (10) via the communication interface (7).

6. A method (S) for detecting a target object using the detection system (1) according to any one of claims 1 to 5, the detection method (S) comprising the following steps: S1: the first and second magnetic sensors generate signals indicating magnetic field strength, S3: calculating correction values ​​for the signals generated by the first and the second magnetic sensors by applying an attenuation coefficient to the signals generated by one or more magnetic sensors during step S1; S4: Compare the correction value with a predetermined threshold, and S5: When the correction value is greater than the predetermined threshold, sending an instruction to generate an alarm, Wherein, step S3 includes the following sub-steps: S31: determining a maximum value of the signals generated by the first magnetic sensor and the second magnetic sensor, S32: determining a minimum value of the signals generated by the first magnetic sensor and the second magnetic sensor, S32: Calculate the ratio of the maximum value to the minimum value determined in this way, S34: comparing the ratio with a first threshold and with a second threshold, the second threshold being greater than the first threshold, S35: inferring the attenuation coefficient, in: When the ratio is less than the first threshold, the attenuation coefficient is equal to a first value; When the ratio is greater than the second threshold, the attenuation coefficient is equal to a second value different from the first value, and When the ratio is between the first threshold and the second threshold, the attenuation coefficient is equal to a value between the first value and the second value.

7. The detection method (S) according to claim 6, further comprising a step S2 of calculating an average value of the correction values ​​before step S4, wherein the average value of the correction values ​​is used to replace the correction values ​​in step S4.

8. The detection method (S) according to claim 6, further comprising a step S2 of calculating an average value of the signals generated by the first and second magnetic sensors before step S3, the average value being used to replace the signal in step S3.

9. The detection method (S) according to claim 6, wherein when the ratio is between the first threshold and the second threshold, the attenuation coefficient is a linear function depending on the ratio.

10. The detection method (S) according to claim 9, wherein when the ratio is between the first threshold and the second threshold, the first value is equal to 1, the second value is equal to 0.1, and the attenuation coefficient is defined by the following function: -0.03*R+1.9 Where R is the value of the ratio.

11. A detection method (S) according to one of claims 7 or 8, wherein the first detector (10) comprises at least two first magnetic sensors, the second detector (20) comprises at least two second magnetic sensors, each first magnetic sensor is associated with a given second magnetic sensor to form a pair, and wherein steps S1 to S4 are applied to each pair.

12. The detection method (S) according to claim 9, wherein the detection system (1) further comprises a third detector (30), wherein the third detector (30) comprises at least one third magnetic sensor, wherein the third magnetic sensor is configured to detect a magnetic field and generate a signal representing the strength of the magnetic field detected in this manner, and the detection method (S) further comprises, before step S5 of generating an alarm, a step of calculating correction values ​​of the signals generated by the second and third magnetic sensors by applying an attenuation coefficient to the signals generated by the second and third magnetic sensors.

13. The detection method (S) according to claim 12 further includes a step of inferring one or more gates formed by the first detector (10) and the second detector (20) that detect the magnetic field on the one hand, and by the second detector (20) and the third detector (30) that detect the magnetic field on the other hand, based on the correction values ​​of the signals generated by the first and second magnetic sensors and the correction values ​​of the signals generated by the second and third magnetic sensors after the step of calculating the correction values ​​of the signals generated by the second and third magnetic sensors.

14. The detection method (S) according to claim 13, wherein the step of inferring the one or more gates comprises the following sub-steps: multiplying the correction value calculated based on the signals of the second and third sensors by a safety factor (Ks), comparing the correction value calculated based on the signals generated by the first and second sensors with the product of the correction value calculated based on the signals of the second and third sensors and the safety factor (Ks), multiplying the safety factor (Ks) by a correction value calculated based on the signals of the first and second sensors, The correction value calculated based on the signals generated by the second sensor and the third sensor is compared with the product of the correction value calculated based on the signals of the first sensor and the second sensor and the safety factor (Ks).

15. The detection method (S) according to claim 14, wherein: Step S5 is performed by the first and second detectors (10, 20) only when the correction value calculated based on the signals generated by the first and second sensors is greater than the product of the correction value calculated based on the signals of the second and third sensors and the safety factor (Ks), and Step S5 is implemented by the second and third detectors (20, 30) only when the correction value calculated based on the signals generated by the second and third sensors is greater than the product of the correction value calculated based on the signals of the second and third sensors and the safety factor (Ks).

16. The method according to any one of claims 13 to 15, wherein the first detector (10) and the second detector (20) each comprise a processing unit (6), and wherein: the step of calculating said correction values ​​for said signals generated by said second and third magnetic sensors being performed by said processing unit (6) of said second detector (20), the step of calculating said correction values ​​for said signals generated by said first and second magnetic sensors is performed by said processing unit (6) of said first detector (10), and The step of inferring one or more pairs of detectors that detected the magnetic field is performed by the processing unit (6) of the second detector (20) and the processing unit (6) of the first detector (10).

17. The detection method (S) according to claim 14, wherein the detection system (1) further comprises a fourth detector (n+1), the fourth detector (n+1) comprising at least one fourth magnetic sensor, the fourth magnetic sensor being configured to detect a magnetic field and to generate a signal representing the strength of the magnetic field detected in this way, the detection method (S) further comprising the following sub-steps: calculating correction values ​​for the signals generated by the third and fourth magnetic sensors by applying an attenuation coefficient to the signals generated by the third and fourth magnetic sensors, multiplying the correction values ​​of the signals generated by the third and fourth magnetic sensors by the safety factor (Ks), comparing the correction values ​​of the signals generated by the second and third sensors with the product of the correction values ​​of the signals generated by the third and fourth magnetic sensors and the safety factor (Ks), comparing the correction values ​​of the signals generated by the third and fourth sensors with the product of the correction values ​​of the signals generated by the second and third magnetic sensors and the safety factor (Ks), One or more pairs of detectors are inferred from among the first, second, third and fourth detectors (10, 20, 30, n+1) detecting the magnetic field.

18. The detection method according to claim 17, wherein: Step S5 is performed by the second and third detectors (20, 30) only when the correction value of the signal generated by the second and third sensors is greater than the product of the correction value of the signal generated by the third and fourth magnetic sensors and the safety factor (Ks), and Step S5 is implemented by the third and fourth detectors (30, n+1) only when the correction value of the signal generated by the third and fourth sensors is greater than the product of the correction value of the signal generated by the second and third magnetic sensors and the safety factor (Ks).

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