Portable detection system including magnetostatic sensor

Abstract

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

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 caused by various attacks in public places has led to the need to detect assault rifle-type weapons at the entrances of public places such as stadiums, concert halls, department stores, etc.

[0003] Currently, such checks are 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 post attached to a base, the post being equipped with at least one static magneto sensor, for example three static magneto sensors distributed over the entire height of the post. Each sensor is configured to generate a (voltage) signal representative of the strength of the electromagnetic field detected. These barriers are used in particular 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 high, since prisoners are generally not allowed to use any metal or magnetic material.

[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 WO 2011 / 020148 describes a system for detecting a target object, the system comprising: a separate detector comprising at least one magnetic system configured to generate a signal representative of the detected magnetic field strength; and a processing unit 20 configured to receive the signal generated by the magnetic sensor. The document relates in particular to the field of coil detectors, which are combined with another detection technology to improve detection.

[0011] Document US2018 / 012465 describes a detection system according to the preamble of claim 1. In particular, the document describes a detection system comprising detectors, each detector comprising at least one magnetic sensor configured to generate a signal representative of the strength of the detected magnetic field, 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 the document is equal to half of their sensitivity distance. In this way, the detectors are independent and their sensitivity can be reduced.

[0012] 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 the signals generated by the gradiometers. The processor calculates an average value of the collected signals to obtain a measure of background noise. The average value is then subtracted from the signal generated by the gradiometer to eliminate the noise. Summary of the invention

[0013] The object of the present invention is therefore to propose a detection system that can be quickly installed and disassembled, for example at the entrance of a public place, which is able to reliably distinguish small objects including magnetic components (such as smartphones) and detect assault rifles, while having a reasonable size.

[0014] To this end, the present invention proposes a detection system for a target object, the system comprising:

[0015] - a first detector comprising at least one first magnetic sensor configured to generate a signal representative of a detected magnetic field strength,

[0016] a second detector, separate from the first detector and comprising at least one second magnetic sensor configured to generate a signal representative of the detected magnetic field strength

[0017] - 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.

[0018] - It also comprises at least one communication interface configured to transmit the signals generated by the first and / or second magnetic sensor to the processing unit. Furthermore, the processing unit is configured to determine the average value of the signals generated by the magnetic sensors of the first and second detectors and, when said average value is greater than a predetermined threshold, to send an instruction to generate an alarm.

[0019] Certain preferred but non-limiting aspects of the above detection system are used alone or in combination as follows:

[0020] - The processing unit is configured to determine an arithmetic or geometric mean of the signal.

[0021] - The communication interface is a wireless communication interface.

[0022] - The first and second detectors are portable.

[0023] - the detection system further comprises a third detector comprising at least one third magnetic sensor configured to detect a magnetic field and to generate a signal representative of the strength of the magnetic field detected in this way, and wherein the first detector and the second detector form a first gate and the second detector and the third detector together form a second gate.

[0024] - a processing unit is housed in each of the first and second detectors, and the processing unit housed in the second detector is configured to: on the one hand calculate the average value of the signals generated by the magnetic sensors of the second and third detectors, and on the other hand transmit a signal representing the magnetic field strength detected by the second magnetic sensor and the average value of the signal thus calculated to the processing unit of the first detector via a communication interface.

[0025] 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:

[0026] S1: the first and / or the second magnetic sensor generates a signal indicating the strength of the magnetic field,

[0027] S2: Calculating the average value of the signals generated by the first and second magnetic sensors, and

[0028] S4: comparing the average value with a predetermined threshold, and

[0029] S5: When the average value is greater than a predetermined threshold, an instruction to generate an alarm is sent.

[0030] Certain preferred but non-limiting aspects of the above detection methods are used alone or in combination as follows:

[0031] The method further comprises, before step S4, a step S3 of correcting the mean value calculated in step S2 so as to obtain a corrected mean value by applying the attenuation coefficient to the mean value of step S2, said corrected mean value being used for implementing step S4.

[0032] - Correction step S3 comprises the following sub-steps:

[0033] S31: determining a maximum value of the signals generated by the first magnetic sensor and the second magnetic sensor,

[0034] S32: determining a minimum value of the signals generated by the first magnetic sensor and the second magnetic sensor,

[0035] S32: Calculate the ratio of the maximum value to the minimum value determined in this way,

[0036] S34: comparing the ratio with a first threshold and a second threshold, the second threshold being higher than the first threshold,

[0037] S35: inferring the attenuation coefficient,

[0038] 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.

[0039] - When the ratio is between the first threshold and the second threshold, the attenuation coefficient is a linear function depending on the ratio.

[0040] 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 when the ratio is between the first threshold and the second threshold:

[0041] -0.03*R+1.9

[0042] Where R is the value of the ratio.

[0043] - said first detector comprises at least two first magnetic sensors, said 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 said steps S1 to S4 are applied to each pair.

[0044] -The detection system further comprises a third detector comprising at least one third magnetic sensor, the third magnetic sensor being configured to detect a magnetic field and to generate a signal representing the strength of the magnetic field thus detected, the detection method further comprising, prior to the step S5 of generating an alarm, a step of calculating an average value of the signals generated by the second magnetic sensor and the third magnetic sensor.

[0045] - the method further comprises, after the step of calculating the average value of the signals generated by the second and third magnetic sensors, a step of deducing, based on the average value of the signals generated by the first and second magnetic sensors and the average value of the signals generated by the second and third magnetic sensors, 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.

[0046] -The step of inferring one or more gates comprises the following sub-steps:

[0047] ■Multiply the average value calculated based on the signals of the second and third sensors by a safety factor,

[0048] ■ compare the average value calculated based on the signals generated by the first sensor and the second sensor with the product of the average value calculated based on the signals of the second sensor and the third sensor and the safety factor,

[0049] ■Multiply the average value calculated based on the signals of the first and second sensors by a safety factor,

[0050] ■ Comparing the average value calculated based on the signals generated by the second sensor and the third sensor with the product of the average value calculated based on the signals of the first sensor and the second sensor and the safety factor.

[0051] - Step S5 is performed by said first and second detectors only if the average value calculated based on said signals generated by said first and second sensors is greater than the product of the average value calculated based on said signals of said second and third sensors and said safety factor.

[0052] - Step S5 is performed by said second and third detectors only if the average value calculated based on said signals generated by said second and third sensors is greater than the product of the average value calculated based on said signals of said second and third sensors and said safety factor.

[0053] - the first detector and the second detector each comprise a processing unit, and wherein:

[0054] ■ the step of calculating the average value of the signals generated by the second and third magnetic sensors is performed by the processing unit of the second detector,

[0055] ■ the step of calculating the average value of the signals generated by the first and second magnetic sensors is performed by the processing unit of the first detector, and

[0056] ■ 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.

[0057] The detection system further comprises a fourth detector, the fourth detector comprising at least one fourth magnetic sensor, the fourth magnetic sensor being 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 further comprises the following sub-steps:

[0058] ■ Calculate the average value of the signals generated by the third magnetic sensor and the fourth magnetic sensor,

[0059] ■ multiplying the average of the signals generated by the third and fourth magnetic sensors by the safety factor,

[0060] ■ comparing the average value of the signals generated by the second and third sensors with the product of the average value of the signals generated by the third and fourth magnetic sensors and the safety factor,

[0061] ■ comparing the average value of the signals generated by the third and fourth sensors with the product of the average value of the signals generated by the second and third magnetic sensors and the safety factor,

[0062] ■ Inferring one or more pairs of detectors from among said first, second, third and fourth detectors detecting said magnetic field.

[0063] - Step S5 is performed by said second and said third detectors only if the average value of said signals generated by said second and third sensors is greater than the product of the average value of said signals generated by said third and fourth magnetic sensors and said safety factor.

[0064] - Step S5 is performed by said third and said fourth detector only if the average value of said signals generated by said third and fourth sensors is greater than the product of the average value of said signals generated by said second and third magnetic sensors and said safety factor. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] 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:

[0066] 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.

[0067] Figure 2 An exemplary embodiment of a detection system according to the invention comprising two detectors is shown.

[0068] Figure 3 An exemplary embodiment of a detection system according to the invention is shown which comprises three detectors which together form two doors, within one of which a check of a person is performed.

[0069] Figure 4 An exemplary embodiment of a detection system according to the invention is shown comprising m detectors which together form m-1 gates.

[0070] Figure 5 is a block diagram showing general steps of an example of a detection method according to the present invention.

[0071] Figure 6 is a block diagram showing the sub-steps of correcting the signal value.

[0072] 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).

[0073] Figure 8a The signal strength of a detection system according to the prior art comprising two detectors 130 cm apart is shown.

[0074] 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.

[0075] 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

[0076] 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:

[0077] - at least one first and second detector 10, 20 which together form a door,

[0078] - at least one processing unit 6, and

[0079] - At least one communication interface 7.

[0080] 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.

[0081] More precisely, the first detector 10 comprises at least one first magnetic sensor 5, preferably at least two, for example three first magnetic sensors 5, and the second detector 20 comprises at least one second magnetic sensor 5. Preferably, the second detector 20 and the first detector 10 each comprise as many sensors 5 as possible.

[0082] Each magnetic sensor 5 is configured to detect a magnetic field and generate a signal representative of 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.

[0083] In one embodiment, each magnetic sensor 5 is configured to detect magnetic field strength along three orthogonal axes.

[0084] 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.

[0085] 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.

[0086] The magnetic sensors 5 are distributed over the entire height of the column 3 to ensure detection of the target object between the feet and the head of the person being inspected 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.

[0087] 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.

[0088] The system 1 further comprises at least one processing unit 6 configured to receive a signal representative of the strength of the magnetic field generated by the first magnetic sensor 5 and / or the second magnetic sensor 5 .

[0089] The processing unit 6 then determines the mean value of the signals generated by the magnetic sensors 5 of the first and second detectors 10 , 20 and, when said mean value is greater than a predetermined threshold, sends an instruction for emitting an alarm.

[0090] In one embodiment, the processing unit 6 determines an arithmetic mean of the signals, which corresponds to the sum of the signal values ​​divided by the number of signals.

[0091] In a variant, the processing unit 6 determines a geometric mean of the signals, which corresponds to the square root of the product of the signals.

[0092] 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.

[0093] In this embodiment, the processing unit 6 can be attached, for example, to the column 3 of the associated detector or, in a variant, to the base 4 thereof.

[0094] Alternatively, 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 in order to process the signals through its communication interface 7.

[0095] In one embodiment, the processing unit 6 may include:

[0096] - an analog-to-digital converter A / D configured to convert the analog (voltage) signal generated by the magnetic sensor 5 into a digital signal

[0097] a digital signal processor DSP configured to generate a digital signal converted in this way, and

[0098] - A system management microcomputer SMM configured to receive the digital signal generated by the DSP and compare it with a predetermined threshold value.

[0099] 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 may 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.

[0100] 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 detection program, performing diagnostics on one or more detectors, loading updates and the like.

[0101] Finally, the SMM is connected to the human-machine interface HMI.

[0102] Each detector 10, 20 of the detection system 1 further comprises 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 to send a signal generated by one or more magnetic sensors 5 of the other detector. 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.

[0103] 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.

[0104] 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 one and the same detection system 1 form a pair of substantially identical ones.

[0105] 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.

[0106] 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 .

[0107] 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), making it possible to 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.

[0108] As will be seen below, this configuration is achieved by the fact that the processing unit 6 of the second detector 20, which is 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.

[0109] More precisely, the processing unit 6 of the second detector 20 is configured to:

[0110] (i) calculating the average (corrected where applicable) or corrected value of the signals generated by the second magnetic sensor and the third magnetic sensor 5, and

[0111] (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 .

[0112] Of course, the operator can also use four detectors according to the present invention to form two gates, and sharing the second detector 20 is not necessary for detecting the target object.

[0113] 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.

[0114] 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.

[0115] When the detectors 10, 20, 30 of the detection system 1 are paired, the address used by a given detector when forming 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:

[0116] - The address of the second detector 20 is stored in the memory of the third detector 30

[0117] - during the parameterization performed by the detection system 1, the addresses of the first detector and the third detector 30 are stored in the memory of the second detector 20, and

[0118] The address of the second detector 20 is stored in the memory of the first detector 10 .

[0119] 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.

[0120] 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.

[0121] Both detectors are identical and each comprises a processing unit 6 and a communication interface 7 .

[0122] Of course, the present invention should be modified mutatis mutandis 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 (e.g., 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, rather than being accommodated in the first detector 10.

[0123] 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 an average value and / or a correction value of the signal, while the term "slave detector" should be understood to mean another detector of the given gate.

[0124] 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.

[0125] 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 differing.

[0126] 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 comprises 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.

[0127] During step S2, the processing unit 6 of the main detector then calculates the average of the signals generated by each pair of magnetic sensors 5. Here, the processing unit 6 therefore calculates a first average corresponding to the first pair of the pair of first and second magnetic sensors 5, and a second average corresponding to the second pair.

[0128] 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 values ​​of the signals of the two magnetic sensors 5 .

[0129] As mentioned above, the processing unit 6 can calculate the arithmetic mean of the signal or, in a variant, the geometric mean.

[0130] In a variant, the processing unit 6 may implement step S3 of correcting the signal generated by each magnetic sensor 5 by applying an attenuation coefficient to said signal, instead of calculating the average value of the signals of each pair of magnetic sensors 5 .

[0131] This correction step S3 thus makes it possible to attenuate the signals generated by the magnetic sensor 5 of the detection system 1 by applying correction coefficients to these signals according to their values. More precisely, when the target object is close to one of the detectors 10, 20 of greater sensitivity, the purpose of the correction is to attenuate the signal in order to reduce the weight of this signal in the detection.

[0132] 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.

[0133] 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.

[0134] 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. Therefore:

[0135] - when the ratio is less than a first threshold, the attenuation coefficient may be equal to a first value,

[0136] - when the ratio is greater than a second threshold, the attenuation coefficient may be equal to a second value that is smaller than the first value, and

[0137] 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.

[0138] 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.

[0139] A relative virtual uniformity between the two detectors is thereby obtained.

[0140] By way of non-limiting example, 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 when the ratio is between the first threshold and the second threshold the attenuation coefficient may be defined by the following function:

[0141] -0.03*R+1.9

[0142] Where R is the value of the ratio.

[0143] 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.

[0144] In another variant, the processing unit 6 immediately 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 ).

[0145] 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 ).

[0146] 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).

[0147] 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).

[0148] During a fifth step S5 , the processing unit 6 compares the calculated value with a predetermined threshold value.

[0149] The calculated value used by the processing unit 6 during the fifth step S5 can be the average value of the signals generated by the paired magnetic sensors 5 and the average value obtained in step S2, or the average value corrected by applying the attenuation coefficient in the following step S3. When the average value (corrected average value, where applicable) is greater than a predetermined threshold value, 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.

[0150] In a variant, 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.

[0151] 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.

[0152] In the variant, 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 emitter 8. As previously indicated, the processing unit 6 can send an instruction to emit an alarm to the emitters 8 of the first detector 10 and / or the second detector 20.

[0153] 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.

[0154] 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.

[0155] 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.

[0156] 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 mean of the corrected values ​​of the signals generated by the sensors of the two detectors.

[0157] 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 intensity between the two detectors of the detection system.

[0158] Example

[0159] The following table is a comparative example of the same target object through 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.

[0160] 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 essentially corresponds to the interference caused by the presence of an AK47 type assault rifle in the middle of the door.

[0161]

[0162]

[0163] In the table, "Limit diameter [mm]" corresponds to the minimum diameter in millimeters, from which the tested detection system 1 emits an alarm signal.

[0164] 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, it is possible to distinguish between a target object having a magnetic field equivalent to that of an iron ball of approximately 62 mm and an object 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, and during this test the detectors were 130 cm apart).

[0165] When 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 identify 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).

[0166] Therefore, even if the passing position of the inspected person 2 is not in the middle of the two detectors, the detection system according to the present invention (configurations (ii) and (iii)) is able to distinguish between small-sized objects (even if these small-sized objects include magnetic components, such as smartphones) and large-volume target objects such as assault rifles.

[0167] 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.

[0168] 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 comprises first, second and third detectors 10, 20, 30, which respectively comprise 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.

[0169] 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 sensors 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 a 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.

[0170] 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).

[0171] 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 the 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 the 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, and 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, and the identification mechanism of the third detector 30 is entered into the second detector 20.

[0172] 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.

[0173] 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.

[0174] 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.

[0175] 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).

[0176] During a second step, the processing unit 6 of the main detector of the door in question, here the second detector 20, calculates the mean value PGS[2,3] of the signals generated by each pair of magnetic sensors 5. Thus, here the processing unit 6 calculates a first mean value corresponding to the first magnetic sensor of the pair formed by the second and third magnetic sensors 5, and a second mean 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 a variant, the processing unit 6 may implement the following steps: correct the signal generated by each magnetic sensor 5 by applying the attenuation coefficient to the signal, and then calculate the value corresponding to the sum of the signal values ​​thus corrected (or in a variant, for each pair of sensors 5, determine the maximum value of the corrected signal), instead of calculating the average value of the signal of each pair of magnetic sensors 5. Since the correction step has been described above with respect to sub-steps S31 to S35, it will not be described in further detail here. In another variant, the processing unit 6 may immediately calculate the average value of the signal of each pair of magnetic sensors 5 and implement the step of correcting the signal as described above so as to obtain the corrected average 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 the average value (or, respectively, the corrected average value, the value corresponding to the sum of the correction values, or the maximum correction value), the other main detectors perform the same calculation (calculate the average value, the corrected average value, the value corresponding to the sum of the correction values, or the maximum correction value, respectively).

[0183] Here, the processing unit 6 of the first detector 10 calculates, for example, a first average value corresponding to the first magnetic sensor in the pair of the first and second magnetic sensors 5 and a second average value corresponding to the second magnetic sensor in the pair to obtain an average 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, which is 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] To this end, the processing unit 6 of the first detector 10 compares the value PGS[2,3] (average value, sum or maximum corrected value, corrected or uncorrected) calculated by the second detector 20 with the value PGS[1,2] calculated by the first detector 10.

[0187] To this end, during the 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 that requires 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 signal 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]), the processing unit 6 of the second detector 20 deletes any instruction requiring the generation of an alarm or does not send the instruction to the transmitter 8 of the second and third detectors 20, 30. On the contrary, if PGS[2,3]>Ks*PGS[1,2], the second detector 2 sends any instruction requiring the generation of an alarm to the transmitter 8 of the second detector 20 and the third detector 30.

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

[0192] It is noted that the application of a 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 target objects and reduces the risk of false alarms.

[0193] Thus, the slave detector of a door sends to the master detector of the door the calculated values ​​(average value with or without correction, or the sum of the correction values) of the adjacent door, of which the detector is the master detector, making it possible to determine the position of the detected target object. In particular, it should be remembered that the detection of the magnetic sensor 5 is a scalar detection and that the detector common to two adjacent doors (here 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, 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 detection method S also comprises 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 typically an average value (corrected where appropriate). Then, detector n - 1 (the slave detector) sends this calculated value PGS[n - 1;n] and the value of the signal generated by its magnetic sensor 5 to detector n - 2 (the master detector). Detector n - 2 then calculates a 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 an average value (corrected where appropriate). In the same way, detector n (the 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 (the master detector) is greater than a predetermined threshold, then:

[0197] - For detector n–2:

[0198] ■ Multiply the value PGS[n - 1;n] calculated and sent by detector n - 1 by the safety factor Ks, and

[0199] ■ Compare its already calculated value PGS[n - 2;n - 1] with the value Ks*PGS[n - 1;n] that has been multiplied by the safety factor. If its already calculated value PGS[n - 2;n - 1] is less than the value calculated by detector n - 1 multiplied by the factor Ks (i.e., PGS[n - 2;n - 1]<Ks*PGS[n - 1;n]), then detector n - 2 thereby infers that the gate formed by detectors n - 2 and n - 1 does not have to generate any alarm. Thus, 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 its already calculated value PGS[n - 1;n] with the value Ks*PGS[n - 2;n - 1] that has been multiplied by the safety factor.

[0203] If its already calculated value PGS[n - 1;n] is less than the value calculated by detector n - 2 multiplied by the factor Ks

[0204] (i.e., PGS[n - 1;n] < Ks * PGS[n - 2;n - 1]), detector n - 1 then infers that the gate formed by detectors n - 1 and n need not 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, cancel the instruction to transmit an alarm).

[0205] ■ Multiply the value PGS[n;n + 1] calculated and sent by detector n by the safety factor Ks, and

[0206] ■ Compare the value PGS[n - 1;n] it has calculated with the value Ks * PGS[n;n + 1] that has been multiplied by the safety factor.

[0207] If the value PGS[n - 1;n] it has calculated is less than the value calculated by detector n multiplied by the coefficient Ks

[0208] (i.e., PGS[n - 1;n] < Ks * PGS[n;n + 1]), detector n - 1 then infers that the gate formed by detectors n - 1 and n need not 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, cancel the instruction to transmit an alarm).

[0209] - In parallel, for detection n:

[0210] ■ Multiply the value PGS[n - 1;n] calculated and sent by detector n - 1 by the safety factor Ks, and

[0211] ■ Compare the value PGS[n;n + 1] it has calculated with the value Ks * PGS[n - 1;n] that has been multiplied by the safety factor.

[0212] If the value PGS[n;n + 1] it has 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]), detector n then infers that the gate formed by detectors n and n + 1 need not generate any alarm. Therefore, detector n does not send any instruction to the transmitter 8 of detectors n and n + 1 to generate an alarm (or, where applicable, cancel the instruction to transmit an alarm).

[0213] It should be noted that when adjacent gates do not share the same detector and are formed by two separate detectors respectively, the detection within each gate is completed by a pair of detectors. Therefore, the detectors of a given gate need not communicate with the detectors of adjacent gates. This is because each gate can operate independently and need not determine the gate through which the target object has passed.

Claims

1. A detection system (1) for detecting a target object, comprising: - a first detector (10), said first detector (10) comprising: The first column; and at least two first magnetic sensors distributed at the height of the first pillar, each first magnetic sensor being configured to generate a first signal, wherein each first signal represents a detected magnetic field strength; - a second detector (20), which is separate from the first detector (10) and comprises: Second pillar; and at least two second magnetic sensors distributed over the height of the second pillar, each second magnetic sensor being configured to generate a second signal, wherein each second signal represents a detected magnetic field strength and wherein each second magnetic sensor is associated with a given first magnetic sensor to form a pair of magnetic sensors, the first magnetic sensor and the second magnetic sensor of the pair being positioned in pair at the same height facing each other; - at least one processing unit; - at least one communication interface configured to transmit the first signal and / or the second signal to the at least one processing unit; Wherein, the at least one processing unit is configured to: For each pair of magnetic sensors, receiving a corresponding first signal and a second signal; For each pair of magnetic sensors, an average value of the first signal and the second signal is determined, and For each pair of magnetic sensors, the average value is compared with a predetermined threshold and when the average value is greater than the predetermined threshold, an instruction to generate an alarm is sent.

2. The detection system (1) according to claim 1, wherein: The average value is the arithmetic or geometric mean.

3. The detection system (1) according to claim 1 or 2, wherein: The communication interface is a wireless communication interface.

4. The detection system (1) according to claim 1 or 2, wherein: The first detector (10) and the second detector (20) are portable.

5. 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 configured to detect a magnetic field and generate a third signal, wherein the third signal is representative of the strength of the magnetic field thus detected, 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.

6. The detection system (1) according to claim 5, wherein: - the processing unit comprises a first processing unit housed in the first detector and a second processing unit housed in the second detector, and - the second processing unit is configured to calculate an additional average of the second signal and the third signal and to transmit the second signal and the additional average to the first processing unit via a second communication interface.

7. A detection method (S) for detecting a target object using the detection system (1) according to one of claims 1 to 6, the detection method (S) comprising the following steps: The first magnetic sensor and the second magnetic sensor of a pair of magnetic sensors generate the first signal and the second signal respectively; determining an average of the first signal and the second signal; comparing the average value with a predetermined threshold; as well as When the average value is greater than the predetermined threshold, an alarm is generated.

8. The detection method (S) according to claim 7, further comprising applying an attenuation coefficient to the average value to obtain a corrected average value, the corrected average value being used for comparison with the predetermined threshold value and generating an alarm.

9. The detection method (S) according to claim 8, wherein: The attenuation coefficient is calculated according to the following sub-steps: determining a maximum value of the first signal and the second signal; determining a minimum value of the first signal and the second signal, calculating the ratio of said maximum value to said minimum value thus determined, comparing the ratio to a first threshold and a second threshold, the second threshold being higher than the first threshold, and Inferring the attenuation coefficient, - when the ratio is less than the first threshold, the attenuation coefficient is equal to a first value, - when said ratio is greater than said second threshold, said attenuation coefficient is equal to a second value different from said first value, and - When said ratio is between said first threshold and said second threshold, said attenuation coefficient is equal to a value between said first value and said second value.

10. The detection method (S) according to claim 9, wherein: When the ratio is between the first threshold and the second threshold, the attenuation coefficient is a linear function that depends on the ratio.

11. The detection method (S) according to claim 9 or 10, wherein: 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 when the ratio is between the first threshold and the second threshold: -0.03*R+1.9 Where R is the value of the ratio.

12. The detection method (S) according to one of claims 8 to 10, wherein: The steps of the detection method are applied to each pair of magnetic sensors.

13. The detection method (S) according to one of claims 7 to 10, wherein: The detection system (1) further comprises a third detector (30), the third detector (30) comprising at least one third magnetic sensor, the third magnetic sensor being configured to detect a magnetic field and generate a third signal, wherein the third signal represents the strength of the magnetic field thus detected, and the detection method (S) further comprises a step before generating an alarm: calculating an additional average value of the second signal and the third signal.

14. The detection method (S) according to claim 13 further includes a step after the step of calculating an additional average value of the second signal and the third signal: inferring one or more gates between the gate formed by the first detector (10) and the second detector (20) that have detected the magnetic field and the gate formed by the second detector (20) and the third detector (30) based on the additional average value.

15. The detection method (S) according to claim 14, wherein: The step of inferring the one or more gates comprises the following sub-steps: - multiplying the additional average value by a safety factor (Ks), - comparing said mean value with said additional mean value multiplied by said safety factor (Ks), - multiplying the average value by the safety factor (Ks), - Comparing said additional mean value with said mean value multiplied by said safety factor (Ks).

16. The detection method (S) according to claim 15, wherein: - the first detector (10) and the second detector (20) generate an alarm only when the average value is greater than the additional average value multiplied by the safety factor (Ks), and - The second detector (20) and the third detector (30) generate an alarm only when the additional average value is greater than the average value multiplied by the safety factor (Ks).

17. The detection method according to one of claims 14 to 16, wherein the first detector (10) and the second detector (20) each comprise a processing unit, and wherein: - the step of calculating said additional average value is performed by a processing unit of said second detector (20), - the step of calculating the average value is performed by a processing unit of the first detector (10), and - the step of inferring one or more pairs of detectors that have detected a magnetic field is performed by a processing unit of the second detector (20) and a processing unit of the first detector (10).

18. The detection method (S) according to claim 15, 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 generate a fourth signal, wherein the fourth signal represents the strength of the magnetic field thus detected, and the detection method (S) further comprises the following sub-steps: - calculating a second additional average of the third signal and the fourth signal; - multiplying the second additional average value by the safety factor (Ks); - comparing said additional mean value with said second additional mean value multiplied by said safety factor (Ks), - comparing said second additional mean value with said additional mean value multiplied by said safety factor (Ks), and - inferring one or more pairs of detectors from said first detector (10), said second detector (20), said third detector (30) and said fourth detector (n+1) which have detected a magnetic field.

19. The detection method according to claim 18, wherein: - the second detector (20) and the third detector (30) generate an alarm only when the average value is greater than the second additional average value multiplied by the safety factor (Ks), and - The third detector (30) and the fourth detector (n+1) generate an alarm only when the second additional average value is greater than the additional average value multiplied by the safety factor (Ks).

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