Metal detector

Abstract

The invention relates to a metal detector for detecting at least one metal target in a detection area, the detector including: · at least one receiving coil arranged to detect a magnetic field originating from the detection area and to generate a signal corresponding to the magnetic field, referred to as "detection signal"; and · a detection unit (24) including: - a filtering module (28) arranged to receive the detection signal as input and to filter this signal according to at least first and second filtering configurations, the second filtering configuration having a shorter temporal support than the first filtering configuration; and - a control module arranged to control the filtering module (28) on the basis of at least one data item contained in the detection signal and providing information on the presence of a metal object.

Description

Description Title of the invention: METAL DETECTOR technical field

[0001] The invention relates to the general field of portable electromagnetic metal detectors. Technological background

[0002] Such detectors are used primarily for recreational purposes, for example, to search for and discriminate between metallic objects buried in the ground, such as coins, jewelry, treasures, or gold nuggets, but also by professionals, for example, in demining, ballistics research, or locating pipes in the construction industry. These examples are not exhaustive. Modern handheld metal detectors allow the user not only to locate but also to identify a target buried in the ground.

[0003] Metal detectors are essentially divided into "passive" and "active" metal detectors.

[0004] Passive metal detectors capture and evaluate distortions in the Earth's magnetic field. Active metal detectors, on the other hand, produce an electromagnetic field during their emission phase, which induces eddy currents in metals.

[0005] The magnetometer is a passive detector that emits no signal. Specifically, it detects anomalies in the Earth's magnetic field, based on the assumption that the Earth's magnetic field is inherently homogeneous. Thus, any metallic particle, magnetized by the Earth's field, disturbs this homogeneity to varying degrees, depending on its size, position, and metallurgical properties. The basic principle of a magnetometer relies on two coils sensitive to magnetic fields, connected in opposite phase to ensure that the magnetic field is measured as zero. If one of the coils encounters a disturbing field, the difference ceases to be zero, generating a voltage that allows for the localization and differentiation of a metallic object.

[0006] Typically, active metal detectors consist of an electromagnetic detection head, also called a search coil, which is the active part of the detector. This head is usually mounted at the end of a handle. The detection head is generally disc-shaped because it contains one or more inductive coils that can generate an incident electromagnetic field and receive a magnetic field modified by the immediate environment.

[0007] The detection head can also incorporate control electronics, adapted to generate an alternating electromagnetic signal that creates the incident electromagnetic field, and to process a received electromagnetic detection signal corresponding to the resulting magnetic field. This processing enables the detection and discrimination of any metallic objects exposed to the incident electromagnetic field. Alternatively, the detection head may incorporate only part of the electronics for processing the received electromagnetic detection signal, for example, a preamplifier, with the remaining electronics housed in a separate control unit to which the detection head is connected.

[0008] In portable electromagnetic detectors operating in continuous wave mode, also called continuous wave (CW) detectors, an alternating magnetic field is emitted continuously, and detection can be based on the variations in amplitude and phase between the frequency components of the emitted signal and those of the received signal. More specifically, CW detectors use the measurement of the amplitude and phase of the different components of the alternating electromagnetic signal emitted by at least one transmitting coil powered by an electrical voltage, and the components of the electromagnetic signal received by one or more receiving coils arranged close to the transmitting coil. At least one frequency of the signal emitted by the transmitting coil is generally below 100 kHz. In some designs, the transmitting coil and the receiving coil(s) are a single coil.

[0009] The induction balance (IB) principle allows for the measurement of very small changes in the properties of a medium by induction. This is achieved by arranging the coils... The transmitting and receiving coils are designed so that the mutual inductance of the receiving and transmitting coils is as low as possible. This minimizes the electromagnetic field measured in the absence of a target. The coupling of the two coils is such that the signal received by the receiving coil is practically zero when no metallic element is placed within the transmitting coil's field. Since signal conditioning electronics often have a saturation amplitude, this optimizes the dynamic range of the measurement signal by measuring only the variations in the resulting electromagnetic field.

[0010] The most common configuration is the "double D" head, but other configurations are possible, for example with concentric coils, or by placing the coils at 90° to each other, or with auxiliary coils used to generate a compensation field, or with other geometries.

[0011] Furthermore, there are other types of metal detectors that, instead of operating in the "frequency" domain, operate in the "time" domain. In this case, it is not the frequency components of the emitted and received signals that are analyzed, but rather the shape of the received signal. This may seem similar because there is a correspondence (via Fourier transforms) between the time and frequency domains. However, this comparison can be misleading because time analysis is generally performed during a relaxation time when induction phenomena do not manifest in the same way. This often involves a different way of generating the emitted magnetic field.Indeed, while in the case of a CW detector the signal is emitted continuously, in the case of a pulsed induction (or "PI") detector, a pulsed signal is generated for a few tens of microseconds (ps) in the detection head, then the transmitting coil is released (or relaxed) and the signal received after this magnetic excitation of the ambient medium is analyzed. The same coil can then be used alternately to generate a pulse and to analyze the received field. But it is also possible to use two coils, namely one for transmission and the other for reception, in various configurations (for example, the configuration...). (the aforementioned "double D" method, or others). In all cases, the received signal can be seen as the sum of different exponential decays that are representative of the medium in which the operation is taking place. Signals associated with soils or salt water generally have rapid exponential decays, with time constants of less than a few ps, while the targets of interest have longer time constants. Obviously, the excitation signal must be renewed periodically (generally with a recurrence of about 1 kHz) and the received signal is "averaged" for use, but the processing is done in the time domain and not in the frequency domain.

[0012] We can also have detectors that work simultaneously in both modes, namely frequency analysis and time analysis.

[0013] During a metal detecting session, the user walks around a designated area, sweeping the ground with the handheld detector using the handle, thus avoiding the need to bend or stoop. Specifically, they stand upright and move the search coil parallel to the ground with the handle, sweeping the search head from left to right, then right to left, and so on. This method is well-suited to dynamic detectors, often found in recreational handheld detectors. A static mode is also possible for detectors that don't require this swinging motion. The transmitting coil produces a magnetic field which, at the level of a potentially fixed metallic target, varies over time due to the relative movement of the search head with respect to the target.This magnetic field generates eddy currents in the metallic target that we are trying to detect.

[0014] These currents in turn generate magnetic fields that are captured by the receiving coil (which is sometimes the same as the transmitting coil). The received electromagnetic signal, also called the target detection signal or simply the detection signal in what follows, has a response that varies as the detection head moves over the target, proportionally to the magnetic fields produced by the circulation of eddy currents generated in the target and received by the detection head. The received electromagnetic signal is then processed by the receiving electronics, in order to isolate the component of the detection signal associated with the target sought and to separate it from undesirable or parasitic components, such as industrial, meteorological, ground-related, magnetic field, parasitic objects, etc.

[0015] To achieve this, the receiving electronics conventionally include ground discrimination and suppression modules.

[0016] Discrimination refers to the processing applied to the detection signal that allows the presence of one or more types of materials to be detected, or even their type to be identified. This discrimination can be achieved, for example, by measuring and analyzing the ratio between the received reactive and resistive signals. Discrimination can be used to identify soil and / or unwanted metallic objects, also referred to as parasitic objects or debris in the following text. It should be noted that a parasitic object can be of the same nature as a target. In the context of the invention, a parasitic object is an object whose signal masks that of a target.

[0017] Ground suppression reduces or even eliminates the ground-related component of the detection signal. It can be achieved using several techniques, as described below. Generally, ground suppression is accomplished by combining at least two of these techniques: one based on the relative uniformity of the ground and the other on the electromagnetic properties of the ground. Each technique often only reduces the ground response while minimizing the target response to a lesser extent. Techniques based on the relative uniformity of the ground are suitable for dynamic detectors, that is, detectors whose operation requires continuous movement of the search head through a sweeping motion.

[0018] The suppression can be achieved using a specific antenna (traditionally in figure-eight) or its electronic equivalent having two loops as described in particular in application WO2007147199. This antenna makes it possible to suppress soils considered homogeneous using two loops arranged to subtract a uniform field.

[0019] Suppression can be achieved using a combination demodulator. This combination modifies the gain according to the characteristic frequency of the desired target. For a CW detector, the combination is usually performed between signals received at several frequencies.

[0020] The discrimination method described above can also be used. In this case, the discrimination process classifies the target as ground. With such a technique, the ground might obscure targets mixed with it.

[0021] The suppression can also be achieved using a filtering module. Assuming the ground is essentially uniform, a high-pass or, more traditionally, band-pass filter is applied to suppress the slowest spectral components corresponding to the assumed slow variations in the ground.

[0022] Applications US4128803, US4514692, US4700139, US7148692, US9207315, and US11067715 introduce improvements to metal detectors. These improvements aim to enhance ground suppression, signal quality for discrimination, and sensitivity to a wider range of targets.

[0023] Generally, the user can choose the cutoff frequency to adapt the filtering to the scanning speed and / or the uniformity of the soil type. This cutoff frequency can be set independently or in conjunction with a set of parameters to simplify detector operation. This parameter is called reactivity or "recovery speed" depending on the manufacturer.

[0024] A low cutoff frequency will only slightly suppress the ground signal. However, it will reduce detection signals less and maintain a wide detection range. Conversely, a high cutoff frequency will suppress the ground signal more, at the expense of the detector's range.

[0025] Signal trail is a common problem caused by filtering techniques. Filtering spreads the temporal response of a signal over time, resulting in the mixing of two closely related signals.

[0026] Also, when two targets are located close to each other, they generate relatively similar time signals when scanning their environment. Depending on the gap and the filtering used, the representative data of said targets may be mixed in the detection signal received by the detector.

[0027] During detection, targets of varying sizes may be encountered in close proximity. In some cases, the targets may be of the same type, for example, an anti-personnel mine near an anti-tank mine. This configuration risks obscuring the presence of the anti-personnel mine from the operator, thus placing them in a dangerous situation. In other, more common scenarios, in addition to the intended target, other metallic objects may be encountered. Generally, these extraneous objects are not rejected by the filtering module but by the discrimination function. The filtering module may therefore mix the components related to the detected metallic objects and potentially obscure the intended target.

[0028] The publication entitled MINHAS SHAHAB FAIZ ET AL: "Minimizing Soil Mineralization Effects in Pulse Induced Metal Detector Through Dual Adaptive Filter-Based Compensation to Detect Low Metal Contents" plans to use a servo algorithm to compensate for the effects of soil mineralization, by learning the response of the mineralization content in the soil, including the presence of bricks forming part of the soil, through supervised learning.

[0029] This masking problem is recurring. Indeed, it is common for large extraneous objects to be shallowly buried while the targets of interest are both smaller and buried deeper.

[0030] There is therefore a need to further improve metal detectors, in particular to improve the detection of the target of interest in the presence of one or more extraneous metallic objects in its vicinity. Summary of the invention

[0031] The invention aims to achieve this objective and relates to a metal detector for detecting at least one metallic target within a detection zone, referred to as the "target of interest," said metal detector comprising - At least one receiving coil arranged to detect a magnetic field from the detection zone and to generate a signal corresponding to said magnetic field, called "detection signal", - A detection unit configured to process said detection signal so as to detect the presence of a target of interest and possibly its type, said detection unit comprising: o A filtering module arranged to receive the detection signal as input and to filter the latter according to at least first and second filtering configurations, the second filtering configuration having a narrower time support than the first filtering configuration, o A control module arranged to control the filtering module according to at least one piece of information contained in the detection signal and indicating the presence of a metallic object, referred to as a "parasitic object", said metallic object having a signal power greater than a predefined power threshold,said control module in such a way as to apply the second filtering configuration to the detection signal so as to attenuate at least one component of the detection signal relating to said parasitic object.

[0032] In particular, it can be predicted that when the filtering module is operating with the first filtering configuration and a spurious object is detected, the second filtering configuration, which has a shorter time support than the first filtering configuration, is applied to the detection signal in such a way as to reduce the temporal trace of the spurious object. This reduces or eliminates the risk of the spurious object masking a target of interest that might be close to it.

[0033] A "target of interest" is a metallic target sought by the user, which the detector will discriminate from other types of metallic targets encountered in the detection zone. This discrimination can be based on fixed criteria or criteria configurable by the user. Generally, the target of interest can be a non-ferrous metal. Depending on the user, the target of interest may be an object made of gold, silver, or even a meteorite. These examples are not exhaustive.

[0034] The target of interest may be buried within the detection zone.

[0035] The extraneous object is a metallic target that may obscure a nearby metallic target (target of interest). In one embodiment, the extraneous object and / or the target of interest may be a ferrous target.

[0036] A target (parasitic object or target of interest) is detected based on the amplitude (or power) of the detection signal. The type of material of the target (e.g., ferrous, gold, or silver) can be detected based on a signal indicating the type of metal. Alternatively, the type of material of the target can be detected based on the resistive and / or reactive components of the detection signal.

[0037] The term "detection signal" refers to a digital signal representing the detected magnetic field. In the following, the detection signal may correspond to the detection signal as provided by the receiving coil(s) or to a signal resulting from pre-processing of said provided signal. This pre-processing may include, for example, amplification and / or demodulation of the signal. The detection signal may be single-frequency. The detection signal may also be analog.

[0038] In what follows, the term "parasitic object" means a metallic object present in the vicinity of the target of interest that generates a signal, preferably stronger than said target.

[0039] By "attenuate at least one component of the detection signal relating to said parasitic object", we mean that the component relating to the parasitic object, present in the detection signal, is attenuated, or even removed, in the output signal of the filtering module.

[0040] The detection signal filtering can initially be performed according to a user-defined configuration. The invention then offers the possibility of adapting this filtering to the conditions encountered in the field in order to prevent the target of interest from being masked by interfering objects present in its vicinity. For example, if an interfering object generating a strong signal is detected, the control unit adapts the detection signal filtering by applying the second filtering configuration to the detection signal. Applying the second filtering configuration makes it possible to attenuate, or even eliminate, the signal. The detector eliminates the component of the detection signal related to this unwanted object. This consequently prevents the masking of the target of interest. Furthermore, unlike prior art detectors, the detector according to the invention allows the use of filtering to both eliminate the ground component of the signal and attenuate the signal components related to interfering objects, when necessary. This avoids the mixing of components related to the different metallic objects described above.

[0041] The claimed detector thus maintains a detection depth while preventing the target of interest from being masked by larger, nearby extraneous objects. The detector enables spatial separation of the target of interest while maintaining equivalent sensitivity.

[0042] The control module automatically adjusts the filtering as needed, without requiring user intervention. This improves detection performance and / or makes the detector easier to use, even for inexperienced users.

[0043] Advantageously, the control module is configured to deliver a substantially continuous output signal from said filtering module during a configuration change.

[0044] Compared with prior art metal object detectors, the component relating to the parasitic object initially present in the detection signal is attenuated or even eliminated in the output signal of the filtering module.

[0045] In the publication entitled MINHAS SHAHAB FAIZ ET AL: "Minimizing Soil Mineralization Effects in Pulse Induced Metal Detector Through Dual Adaptive Filter-Based Compensation to Detect Low Metal Contents", hereinafter “MINHAS”, the supervised algorithm does not respect the principle of time invariance and is therefore not a filter.

[0046] MINHAS does not address the potential masking of a target by another nearby target. As a reminder, a target is a metallic object. MINHAS takes into account the presence of bricks forming part of the ground. However, in the field of metal detection, a brick, which is raw, dried, or baked clay, corresponds to a type of soil whose... Characteristics are evolving rapidly. For example, MIHAS takes into account the presence of a brick for adapting the detector to the ground, but this brick is not a metallic object and is therefore not a target.

[0047] In the field of filtering, a time support corresponds to the time during which the output of a filter is considered significant (by reference to a target to be detected in the field of detectors).

[0048] In the case of a metal detector, which is a system that has very high signal dynamics (sometimes greater than 100dB), the term "significant" can thus correspond to "above the detection threshold of a target".

[0049] According to a first definition (i), the temporal support can thus correspond to the duration (including any possible crossing of the detection threshold in both directions, as illustrated for example in Figure 7 or Figure 8 shown below) during which the response to a (Dirac) pulse with an amplitude corresponding to the maximum amplitude acceptable by the detector remains greater than or equal to the detection threshold. Beyond this duration, the response remains below said detection threshold.

[0050] In other words, according to the first definition (i), the time support can correspond to the duration of the response beyond which the absolute amplitude of the impulse response (Dirac delta function) of a strong signal remains below the detection threshold. A strong signal corresponds to the maximum amplitude acceptable to the system such that the detector's detection system is not saturated. This maximum amplitude depends, for example, on the linearity limit of the amplification chain, the maximum amplitude of any ADC, and / or the maximum amplitude of the digital signals.

[0051] According to a second definition (ii), the time support can be defined as the duration, including any crossing of the threshold in both directions, such that the absolute value of the impulse response (response to a Dirac impulse of a strong signal) is greater than or equal to the absolute value of the maximum amplitude (acceptable by the detector) minus 100 dB. Beyond this duration, the impulse response remains below said threshold corresponding to the absolute value of the maximum amplitude minus 100 dB.

[0052] Thus, to simplify the technical characterization of the temporal medium, the temporal medium can be defined as the duration (including a possible crossing in both directions of the threshold) during which the absolute value of the impulse response is greater than the threshold corresponding to the absolute value of the maximum amplitude minus 100dB.

[0053] The temporal support can be mathematically defined as follows:

[0054] Either In other words, H MAX is the maximum of the absolute value of the impulse response.

[0055] Either In other words, T MAX is the last instant exceeding the threshold of -100dB with respect to H MAX lOOdB Therefore, we have the properties | / r(t)l < 10 ~ ' H MAX ,Vt E ] MAX ; + °°[ lOOdB and | / i(T M ^)| > 10 20 ■ H MAX IQOdB

[0056] Let T MIN = min(t) such that \h(t) | > 10 20 ■ H MAX In other words, T MIN is the first instant exceeding the threshold of -100dB with respect to H MAX

[0057] Time support = T MAX — T MIN

[0058] with h(t) being the impulse response.

[0059] We can also define the temporal support as equal to Tmax - Tmin with: Tmin: the instant at which the impulse response exceeds the sensitivity (detection threshold) of the detector; and Tmax: the point at which the response will no longer exceed the sensitivity.

[0060] This sensitivity, also called capacitance, can also be defined as the detector's detection threshold below which at least 99% of the signals are generated by noise from the detector's components. In other words, the contribution of the detector's electronics to the received signal for a signal amplitude less than or equal to the detector's detection threshold is at least 99%.

[0061] The temporal support can be defined as the duration during which the amplitude of the response of a target (parasitic object or target of interest) is greater than or equal to a given threshold value corresponding to the detection sensitivity of the detector.

[0062] According to one particular aspect, the sensitivity or detection capacity of the detector is a manufacturer's data that can possibly be configured according to the user.

[0063] According to one embodiment, the filter is an infinite impulse response filter, and more particularly a filter whose impulse response decreases according to a decreasing exponential envelope.

[0064] According to one embodiment, a first filter is considered to have a shorter time support than a second filter, if said first filter satisfies at least one of the following propositions: - its temporal support in the sense of the first definition (i) is shorter than that of the second; - or its temporal support in the sense of the first definition (ii) is shorter than that of the second; - or if it satisfies equation A Max \VA e [0 Max],3to |vt e [t0; +oo[,| / i2(t)| < II, hi and h2 being the impulse response of the first and second filters, respectively. A being the amplitude of h1 or h2.

[0065] As an example, and as illustrated in Figure 9 below, the impulse response of a filter with a cutoff frequency of 8 Hz decays more rapidly than that of a filter with a cutoff frequency of 2 Hz. For all amplitudes A below the crossover amplitude (corresponding to A iax in the formula above), obtained at time te (corresponding to time to for A = A iax in the formula above) of the two response curves, the impulse response of the filter with a cutoff frequency of 8 Hz is lower than the impulse response of the filter with a cutoff frequency of 2 Hz.

[0066] According to one embodiment, the second configuration is applied until the end of the temporal support of the response of the parasitic object according to the first filtering configuration.

[0067] In one embodiment, the control module is configured to switch the filtering module from its first configuration to at least its second configuration when the detection signal has a power (or amplitude) greater than a threshold value (strong signal level) corresponding to the detection of a spurious object. In particular, this threshold value (strong signal level) is greater than the sensitivity (detection threshold) of the detector.

[0068] According to one embodiment, the second filtering configuration has a bandwidth, for example 8Hz, greater than the bandwidth of the first filtering configuration, for example 2Hz. Otherwise That said, the first configuration has greater frequency selectivity than the second configuration.

[0069] According to one embodiment, the filtering module includes a bandpass or lowpass filter whose bandwidth, or cutoff frequency, preferably at 3dB, is less than or equal to 40Hz, preferably less than or equal to 25Hz. Such a design is particularly suitable for a metal detector-type system that is swept, i.e. moved, by hand.

[0070] According to one embodiment, the filtering module includes a bandpass filter whose bandwidth, preferably at 3dB, varies from 1 Hz to 25Hz, preferably 2 Hz to 25 Hz.

[0071] For example, the first filtering configuration has a bandwidth (at 3dB) of 1 Hz and the second filtering configuration has a bandwidth (at 3dB) of 25 Hz. In other words, the filter's bandwidth is increased when going from the first configuration to the second configuration.

[0072] According to one embodiment, the detection unit is configured to perform a step of removing the soil component and / or electromagnetic interference from the detection signal.

[0073] In one embodiment, the control module is configured to command the switch from the first filtering configuration to the second filtering configuration during target detection, i.e., at least when the amplitude of the detected signal exceeds a given amplitude (upward slope of the amplitude). Additional means can be used to refine the detection, and a hold function for applying the second configuration can be added.

[0074] In one embodiment, the switch from the first configuration to the second filtering configuration is performed before the end of the time support period for the response of the spurious object according to the first filtering configuration. In particular, the switch is performed rapidly compared to the duration of the time support period for the response according to the first filtering configuration.

[0075] According to one embodiment, when the filtering module includes two filters, one corresponding to the first filtering configuration and the other to the second filtering configuration, the two filters are run in parallel and the control module selects the outputs of the two filters by combining them. The output time of one or both filters depends on the desired filtering configuration. This design allows for pre-loaded filters and rapid switching between configurations without relying on filter stabilization time. This minimizes discontinuity in the output sound.

[0076] Advantageously, the invention is independent of the type of detection. The detector according to the invention can be single-frequency.

[0077] The detector according to the invention can be multi-frequency.

[0078] The detector according to the invention can be temporal.

[0079] The detector according to the invention can be hybrid.

[0080] Preferably, this information data corresponds to information representative of the power (or amplitude), particularly the Euclidean power, of the detection signal. Euclidean power refers to a measure of the detection signal's power based on the Euclidean norm, namely the square root of the sum of the squares of the signals.

[0081] Preferably, the control module is configured to control the filtering module in such a way as to: - apply the first filtering configuration to the detection signal by default, and - when the control module detects the presence of the parasitic object, apply the second filtering configuration, in particular in parallel or as a replacement, of the first filtering configuration.

[0082] In some embodiments, the detector may include at least one demodulator.

[0083] The said demodulator can be arranged to receive the detection signal as input and to apply demodulation to said detection signal.

[0084] Alternatively, the demodulator is configured to apply demodulation to the signal at the output of the filtering module. Preferably, the input of the demodulator is connected to the output of the filtering module.

[0085] The term "connected" refers to a direct or indirect connection between the input of the demodulator and the output of the filtering module.

[0086] In some embodiments, the filtering module comprises at least two distinct first and second filters, the first filter being arranged to filter the detection signal according to the first filtering configuration so as to generate a first filtered signal and the second filter being faster (i.e. presenting a shorter time support) than the first filter and being arranged to filter the detection signal according to the second filtering configuration so as to generate a second filtered signal.

[0087] Preferably, the time support of the second filter is less broad than the time support of the first filter.

[0088] This relative characteristic of temporal media can be defined by the formula, A Max \VA e [0; Max ],at o |vt e[t0; +oo[,| / i2(t)| < | / ii(t)|, hi and h2 being the impulse response of the first and second filters, respectively. A being the amplitude of h1 or h2. For sufficiently small amplitudes, also called tolerance, the impulse response of the second filter is always shorter than that of the first filter, up to this tolerance.

[0089] Because detector signals have high dynamic ranges, it can be useful to compare two filters by comparing the decay rates of their responses. The formula above allows for the classification of decay rates to facilitate the technical characterization of a temporal media hierarchy.

[0090] In one embodiment, the filtering module exhibits a zero response for a DC component of the input signal. Preferably, the filtering module includes a delay line connected to the second filter, said delay line being arranged to compensate for any latency differences between the two filters.

[0091] Preferably, the time support of the second filter is less broad than the time support of the component relating to the parasitic object.

[0092] Preferably, the time support of the second filter has a width of less than 500 ms, especially less than 400 ms, better less than 300 ms.

[0093] Preferably, the first and / or second filter is a low-cut filter. By way of example, the first and / or second filter may be chosen from a differentiator, a series of differentiators, a high-pass filter, a band-pass filter, a low-pass filter, or a combination of at least two of these.

[0094] Preferably, the application of the second filtering configuration is maintained for a duration at least equal to the detection duration of the spurious object, preferably for a duration greater than or equal to the detection duration of the spurious object + 30 ms.

[0095] In one embodiment, following the application of the second filtering configuration, the first filtering configuration is reapplied (or selected) at a time corresponding to when an information signal (detection) indicating the presence of the unwanted object disappears (is cut off), preferably plus a given dwell time. The moment when the information signal indicating the presence of the target unwanted object is cut off, i.e., when the unwanted object is no longer detected, can correspond to the time at which the amplitude of the signal filtered according to the second configuration falls below a given threshold, which can correspond to the detection threshold of the unwanted object (at which point the switch from the first configuration to the second configuration was triggered). It can be assumed that this given threshold is different from the detection threshold of the unwanted object.It can be predicted that the given threshold will be between the sensitivity threshold of the detector and the detection threshold of the parasitic object from which the switch from the first configuration to the second configuration was triggered.

[0096] In some embodiments, the control module is arranged to control the filtering module so as to: o Deliver as output, in particular by default, the first filtered signal, and o When the presence of a parasitic object is detected, deliver as output the second filtered signal or a combination, in particular linear, of the first and second filtered signals.

[0097] Preferably, the filtering module also includes a combiner configured to receive the first and second filtered signals as input and to output a combination, in particular a linear combination, of the aforementioned filtered signals. The control module is advantageously configured to determine the weighting values ​​associated with this combination. These weighting values ​​preferably range from 0 to 1, with the sum of the aforementioned values ​​equal to 1.

[0098] Preferably, the maximum excursion of the control module is dependent on the maximum power of the detection signal.

[0099] Preferably, the maximum excursion is defined so that the signal representing the distance to the target is monotonic with respect to distance. [000100] Preferably, the control module is arranged to determine the weights of the aforementioned combination as a function of information representative of the power of the signal component relating to the parasitic object. [000101] Preferably, the control module is configured to determine the weighting values ​​of the two signals so as to obtain a substantially monotonous sound level. [000102] Preferably, the control module is configured to control the combiner so as to apply by default a value of 1 to the weighting associated with the first filtering function. [000103] Also, the signal delivered by the filtering module can correspond to a combination, in particular linear, of the first and second filtered signals, the weight associated with each filtered signal can go from 0 to 1. The default values ​​of the weights can correspond to 1 for the weight associated with the first filtered signal and 0 for the weight of the second filtered signal. [000104] In embodiments, the detector may further include a discrimination module arranged to receive as input the signal at the output of the filtering module, said discrimination module being configured to process the input signal of the latter and to detect the presence of one or more metallic objects. [000105] The discrimination module can be configured to determine information indicating the type of metallic object detected. [000106] In this way, the information data can correspond to information indicating the type of metallic object detected. [000107] In embodiments, the detector may include more than two filtered signals. [000108] In embodiments, the signal delivered by the filtering module may correspond to a combination, in particular linear, of at least three filtered signals. [000109] In some embodiments, the filtering module comprises a single configurable filter adapted to filter the detection signal according to at least the first and second configurations, said single filter having at least one adjustment parameter for its time support, the control module being arranged to adjust the value of the adjustment parameter according to said data contained in the detection signal. Preferably, the adjustment parameter for the time support comprises at least eight distinct values. [000110] The single filter can be continuously configurable. [000111] Alternatively, the single filter has a configuration granularity allowing for at least two steps, better six steps, even better eight steps, for example ten steps, between the first configuration and the second configuration. [000112] The single filter may correspond to a low-cut filter. By way of example, the single filter may be chosen from a derivatizer, a series of derivatizers, a high-pass filter, a band-pass filter, a low-pass filter, or a combination of at least two of these. [000113] The output of the single filter can be used by the discrimination module to calculate the information data. [000114] The data contained in the discrimination signal is advantageously used by the control module to analyze the presence of a strong component related to a spurious object. Upon detection of a spurious object, the control module commands the single filter to reduce its time support and adopt the second filtering configuration. [000115] The detector may include at least one transmitting coil arranged to generate an incident magnetic field. [000116] According to one embodiment, the detection unit is configured to remove the component of the signal corresponding to the ground and / or electromagnetic interference. [000117] According to one embodiment, the filtering module is a time-invariant filtering module. According to another embodiment, the filtering module is linear and time-invariant. [000118] According to one embodiment, the modification of the filtering configuration can be carried out by modifying the coefficients and / or the number of coefficients of the filter or by changing the topology, for example from an HR type filter to an Fl R type filter. [000119] According to one embodiment, the first filter, the second filter and / or the single filter is a low-cut filter. [000120] According to one embodiment, the first filter, the second filter and / or the single filter is a low-pass filter. Brief description of the figures [000121] The following description, with reference to the accompanying drawings, given by way of non-limiting examples, will clearly explain what the invention consists of and how it can be implemented. In the accompanying figures: [000122] [fig. 1] Figure 1 schematically represents a detector according to the invention during a detection session conducted by a user; [000123] [fig. 2] Figure 2 is a functional diagram representing, in the form of a block diagram, the architecture of the detector of Figure 1; [000124] [fig. 3] Figure 3 represents a processing unit according to a first embodiment; [000125] [fig. 4] Figure 4 represents a processing unit according to a second embodiment; [000126] [fig. 5] Figure 5 represents a processing unit according to a third embodiment; and [000127] [fig. 6] Figure 6 is an example of curves representing the sound level likely to be generated by the detector according to the invention. [000128] [Fig.7] Figure 7 is a graph showing a signal amplitude curve as a function of time which is an example of impulse response, for which the time support has been highlighted, the dashed lines representing a detection threshold value. [000129] [Fig.8] Figure 8 is a graph showing another signal amplitude curve as a function of time which is another example of impulse response, for which the time support has been highlighted, the dashed lines representing a detection threshold value. [000130] [Fig.9] Figure 9 is a graph showing a first impulse response of a signal filtered with a low-pass filter of a given cutoff frequency (first filtering configuration), and a second impulse response of the signal filtered with a low-pass filter (second filtering configuration) whose cutoff frequency is greater than that of the first filter, to show that the time support of the second response (obtained with the filter whose bandwidth is the widest) is shorter than that of the first response. [000131] [Fig. 10] Figure 10 is a graph representing the response seen by the detector head for two targets close to each other during a scan before filtering (i.e., with noise). A curve corresponding to the response of the two targets without noise is also shown. [000132] [Fig.11] Figure 11 is a graph representing two responses (the residual noise also being shown) after filtering, for the two targets close to each other in Figure 10, one response resulting from the use of a low-pass filter with a cutoff frequency of 2Hz (first filtering configuration), and the other response resulting from the use of a low-pass filter with a cutoff frequency of 8Hz (second filtering configuration). [000133] [Fig.12] Figure 12 is a graph which takes up the responses of Figure 11, on which is added the combined response (combined filter) corresponding to the selection for the output of the filtering module of the first filtering configuration (2Hz in this example) until the rise of the amplitude to the value ACR, then to the selection of the second filtering configuration (8Hz in this example) from said value ACR and until a time t3 corresponding to the time t2 when the amplitude falls below the value ACR plus a holding time DM. [000134] [Fig.13] Figure 13 is a graph illustrating the response of a weak target with filter configuration switching. Description of method(s) of implementation [000135] In the figures, and unless otherwise specified, identical elements shall bear the same reference symbols. [000136] Figure 1 shows an example of a metal detector 10 for detecting at least one metallic target within a detection zone, referred to as the "target of interest". As illustrated, the detector 10 comprises three elements communicating with each other via analog, digital, wired, or wireless links, for example, a radio link. These three elements correspond to: - a detection disc 11 or detection head which incorporates the transmitting and / or receiving coil(s); - a control module 12, also called a remote control, which allows you to configure all the various functions of the detector using a suitable human-machine interface (or HMI, from the English "Human-Machine Interface"); - an audio playback device 13, which may be a wired headset or preferably a wireless headset, one or more loudspeakers, a haptic feedback system or a bone conduction device, comprising electroacoustic transducers (for example one for each ear) capable of reproducing the detection signal in a form audible to the user. The audio playback device 13 is not required and can be replaced by the control module 12. Nevertheless, device 13 is the preferred playback method due to the sensitivity and dynamics of the human ear compared to other human sensory organs. [000137] In the illustrated example, all or part of the electronics for managing retransmission, reception, and processing detection signals to achieve target detection and discrimination may be integrated into the detection head, or into the remote control, or may be distributed between the detection head and the remote control. [000138] In addition, the detector generally comprises a shaft 15 having a handle and an armrest. The end of the shaft 15 opposite the armrest and the handle is adapted to support the detection disc, which can be removably coupled to it. The remote control 12 is adapted to be attached to the shaft 15, just in front of the handle as shown in Figure 1. [000139] It is possible to decompose the architecture of detector 10 in the manner that will be described below with reference to the functional diagram in Figure 2. [000140] This functional breakdown allows us to distinguish the main functions performed by the detector, but it is not limiting to how these functions are implemented at the hardware level. Some functions may be grouped together or, conversely, separated into specific hardware components, which may also implement additional functions that are not considered here because they are not essential for describing embodiments of the invention. Digital components may be implemented in an analog manner unless otherwise specified. [000141] The detector comprises an electromagnetic transmission / reception assembly 21, including the coil(s), namely at least one receiving coil and optionally at least one transmitting coil, it being understood that these two coils may also be one. This assembly 21 is mounted in the detection head 11 of Figure 1. [000142] The detector also includes an analog front-end module and a digital front-end module. The assembly 22 of these two front-end modules ensures the emission (Tx) of the incident magnetic field. [000143] In the receive direction (Rx), the front-end modules 22 perform the transposition of the analog signals adapted to the coils into signals, particularly at very low frequencies (generally below 50 Hz), representative of the speed at which the detection head passes over the target. This transposition can be carried out in different ways depending on the type of detector. Frequency transposition is generally applied for frequency-analyzing detectors, which can be achieved, for example, by demodulation and associated filtering. For a time-domain detector, the transposition is usually performed by integrating time windows. Most often, the analog front-end module integrates the power amplifiers of the transmit chain (Tx) and the low-noise amplifiers of the receive chains (Rx).Traditionally, frequency detectors are called VLF detectors, which stands for the frequency band from 3 kHz to 30 kHz. However, lower frequencies, and especially higher frequencies—that is, frequencies in a wider range than the VLF band, for example, between 1 kHz and 150 kHz—can also be used for metal detection in specific searches. This is why we refer to it as an "extended" VLF band. The analog front-end module can also... integrate the demodulators, but the demodulators are most often made in the digital front-end module for narrowband detectors. [000144] The person skilled in the art will also appreciate that the analog / digital separation depends on the design of the equipment, and is not limited, in practice, by the examples considered here. [000145] The detector further comprises a detection unit 24, which is adapted to apply detection treatments in order to determine the presence and possibly the type of the metallic target of interest. [000146] The detection unit 24 can be implemented in the form of a miniaturized electronic circuit, which allows it, in certain metal detectors, to be integrated into the detection disc 11. Such a circuit is suitable for digitizing and analyzing the detection signals and for producing the detection data and the discrimination data, this data then being sent, in particular in real time, to the user interface 25, for example by digital radio link as shown in Figure 1 or by wired connection, for sound playback by the audio headset 13 and possibly, in addition, for display on the remote control 12. [000147] The performance of detector 10 may be affected by the different levels of soil mineralization that may be encountered depending on the application. These may include, for example, naturally occurring magnetic mineralizations such as iron oxide, ferrites, and magnetites. They may also include localized mineralizations linked to former sites of human occupation (which are also magnetic), such as hearths, terracotta, ferrites, slag, etc. Finally, they may include coastal mineralizations, which can range from magnetic (black sands) to electrically conductive (salt water), depending on the beach and region. [000148] Detection is also affected by electromagnetic interference (or EMI, from the English "Electromagnetic interference") which is widespread, particularly in urban areas (high voltage line, electrical transformer, electric fence, power lines, radio relays, mobile phones, computers, televisions, other metal detectors operating nearby, etc.), as well as by metallic pollution. [000149] In particular, detection may be disrupted by the presence of unwanted metallic objects which may obscure the target of interest. [000150] The detection unit 24 includes a filtering module 28 which filters the ground component of the detection signal. The module attenuates the component of the detection signal related to one or more parasitic metallic object(s) significantly larger than the target of interest and present in its vicinity. [000151] As will be described later, the filtering module 28 is arranged to receive the detection signal as input and to filter it according to at least two first and second filtering configurations, the second filtering configuration having a shorter time support than the first filtering configuration. Advantageously, the filtering adaptation is maintained for a duration at least equal to the detection duration of the spurious object, preferably for a duration greater than or equal to the detection duration of the spurious object + 30 ms. The filtering adaptation, in particular the application of the second filtering function, occurs over a duration shorter than the detection duration of the target of interest + 30 ms. [000152] The detection unit 24 further comprises a control module 30 arranged to control the filtering module 28 based on at least one piece of data indicating the presence of a parasitic object. This data may correspond to the power, for example Euclidean, of the detection signal so as to adapt the filtering applied to the detection signal in order to attenuate at least a power of the detection signal relative to at least one metallic object considered undesirable. [000153] In the illustrated example, the detection unit 24 further includes an optional discrimination module 29 which receives as input the signal from the output of the filtering module 28. Such a discrimination module is optional. The discrimination module 29 is configured to process the input signal and to detect the presence of one or more metallic objects and, optionally, their type. The discrimination module is capable of determining information on the type of metallic object detected and, optionally, whether said object corresponds to the target of interest or to a spurious object. [000154] When the detector includes the aforementioned discrimination module, the information data can be output data from the discrimination module. In this embodiment, the output data from the module discrimination can correspond to information indicating the type of metallic object detected and possibly whether the metallic object corresponds to the target of interest or whether it is a parasitic object. [000155] The detector includes a human-machine interface, also called a user interface 25 (or HMI). The user interface 25 allows the equipment to be configured, on the one hand, and provides information indicating the possible presence of metallic targets and, possibly, information relating to their identification, as well as, potentially, detection aids to assist the user in their search, on the other hand. As already mentioned in the introduction, audio playback is the most commonly used interface for this purpose, and it is primarily this interface that is the subject of the present invention. The user interface 25 thus includes the headphones 13 of Figure 1 and / or any other electroacoustic transducer, for example, one or more loudspeakers. [000156] However, all or part of the aforementioned information can also be displayed in another form, for example, visible on a screen. The user interface 25 includes the remote control 12 (Figure 1) for this purpose. The remote control also allows the user to adjust the main detection settings such as sensitivity, discrimination, ground effects, tones, the frequency(ies) used for the signals emitted and processed by the detection head, volume, etc., as well as to select factory programs or those previously created by the user using the remote control. [000157] Figures 3 to 5 illustrate embodiments of the detection unit 24 according to the invention. [000158] In the embodiment illustrated in Figure 3, the filtering module 28 comprises a single configurable filter 40a capable of filtering the detection signal according to at least the first and second configurations. This single filter 40a comprises at least one adjustment parameter for setting its time support. The control module is arranged to adjust the value of this adjustment parameter according to said information data. Preferably, the temporal support adjustment parameter has at least eight distinct values. [000159] The unique 40a filter can be continuously configurable. [000160] Alternatively, the single filter 40a has a configuration granularity allowing at least ten steps between the first configuration and the second configuration. [000161] In the illustrated example, the single filter 40a corresponds to a low-cut filter. [000162] In the embodiment illustrated in Figure 4, the filtering module 28 comprises two separate filters 40b and 40c. The first filter filters the detection signal according to the first filtering configuration so as to generate a first filtered signal. [000163] The second filter 40c is faster than the first filter 40b and filters the detection signal according to the second filtering configuration to generate a second filtered signal. The time span of the second filter 40b is narrower than the time span of the component related to the parasitic object. [000164] In the illustrated example, the first and / or second filter is a low-cut filter. [000165] The filtering module 28 further includes a delay line 42 connected to the second filter 40c, as illustrated, and allows compensation for any differences in latency between the two filters 40b and 40c. The optional discrimination module 29 is connected on one side to the filtering module 28, and on the other side to the control module 30. Also, depending on the output data of the discrimination module 28, the control module adapts the filtering in order to avoid masking the target of interest by a parasitic metallic object. [000166] Also, the control module is arranged to control the filtering module so as to: o Deliver at output, in particular by default, the first filtered signal at the output of the first 40b filter, and o When the presence of a parasitic object is detected, output the second filtered signal resulting from the second filter 40c or a combination of the two filtered signals from the two filters 40b and 40c. [000167] The filtering module 28 further comprises a combiner 44 arranged to receive the first and second filtered signals as input and to output a combination, in particular a linear combination, of the aforementioned filtered signals. The control module 30 is advantageously configured to determine the weighting values ​​associated with each filtered signal in said combination. These weighting values ​​range from 0 to 1, with the sum of the aforementioned values ​​equal to 1. The weights of the aforementioned combination are preferably determined based on at least one piece of information relating to the power of the signal component associated with the parasitic object. [000168] In the illustrated embodiment, the control module 30 is arranged to control the combiner 44 so as to apply a default value of 1 to the weight associated with the first filtered signal. In other words, the filtering module 28 delivers the first filtered signal by default. [000169] Also, the signal delivered by the filtering module 28 corresponds to a combination, in particular a linear one, of the first and second filtered signals. The default values ​​of the weights are 1 for the weight associated with the first filtered signal and 0 for the weight of the second filtered signal. [000170] Advantageously, the control module determines the values ​​of the weights associated with the filters 40a and 40b so as to obtain a substantially monotonous sound level, as illustrated in Figure 6. [000171] Filters 40b and 40c have different signal-to-noise ratios. In terms of signal-to-noise ratio, we hear AWGN (additive white Gaussian noise), which is representative of the thermal noise received by the receiving electronics. The faster 40c filter has a narrower bandwidth and therefore a lower signal-to-noise ratio than filter 40a. Generally, the sound level is a function of the signal strength. The operator's audio perception therefore differs depending on the filter, whether it be noise, a target, or both. [000172] Figure 6 shows representative curves of the sound level of the target of interest as a function of its depth. Curve A corresponds to the first filter 40b. Curve B corresponds to the second filter 40c. Switching at a fixed threshold without weighting corresponds to curve C. As illustrated, when switching from filter 40b to the second filter 40c without weighting, the sound level is not monotonic. This can affect the user's perception. Curve D, on the other hand, shows a transition weighted by the detection level of the component related to the unwanted object. As can be seen, such weighting makes it possible to obtain a monotonic sound level. [000173] Figure 5 illustrates an example of a detection unit 24 according to a second embodiment. [000174] In the illustrated example, the information data used by the control module 30 is calculated from the second filtered signal at the output of the second filter 40c. [000175] In this embodiment, the detection unit includes an additional discrimination module 43. This additional discrimination module 43 is connected to both the second filter 40c and the control module 30. Such a configuration has the advantage of allowing the filtering adaptation to be triggered earlier. This makes it possible to improve the aforementioned masking effects upstream (temporally), and more particularly the masking at the beginning of the filtering process. [000176] Figure 9 is a graph showing a dashed curve corresponding to an example of the impulse response (amplitude as a function of time) provided by a low-pass filter with a cutoff frequency of 2 Hz; and a solid curve corresponding to an example of the impulse response provided by a low-pass filter with a cutoff frequency of 8 Hz. The impulse response of the 8 Hz filter decays more rapidly than that of the 2 Hz filter. In particular, for amplitudes lower than the crossover amplitude obtained at time t of the two response curves (8 Hz and 2 Hz), the response of the low-pass filter with a cutoff frequency of 8 Hz remains lower than that of the low-pass filter with a cutoff frequency of 2 Hz for a time t later than the time at which the curves intersect. [000177] It can be observed that the impulse response decays more rapidly for the low-pass filter with the highest cutoff frequency. In other words, the wider the bandwidth, the smaller the time support. [000178] Figure 10 illustrates the response provided by the detector for two nearby targets before filtering. The target responses are noisy, and the filtering module reduces or even eliminates the noise. [000179] Figure 11 is a graph illustrating the response provided by the 2 Hz cutoff frequency low-pass filter for two nearby targets, as well as the response provided by the 8 Hz cutoff frequency low-pass filter for the same two nearby targets. The As line, which indicates a detection threshold of the system, shows that with a wider bandwidth filter (8 Hz compared to 2 Hz in this example), the two targets can be better distinguished. [000180] Figure 12 illustrates the controlled switching between filtering configurations. The control module commands the switch from the first filtering configuration to the second filtering configuration when the amplitude exceeds a given threshold. The amplitude used to control the switch can be the amplitude of the detection signal (input signal) or the filtered signal, depending on the first or second configuration. [000181] Figure 12 also illustrates the reverse switching, from the second configuration of the filtering module to the first filtering configuration when the amplitude falls below a given threshold. Advantageously, the reverse switching is triggered after a predefined time following the falling below the given threshold. In other words, the second configuration is maintained for a given time after the falling below the given threshold. [000182] In particular, in the example of Figure 12, it can be observed that up to time t1, the first filtering configuration is used, since beyond time t1 and up to time t3 the second configuration is activated and maintained. From time t3 onwards, the detection unit (the filtering module) switches back to the first configuration. Time t2 corresponds to the crossing below a given threshold value, for example the ACR value. which marks the time at which the DM (predefined) maintenance duration is activated. This given threshold value may differ from the ACR value. This given threshold value may be between the As sensitivity and the ACR value. [000183] It can be observed that, for the output signal of the filtering module corresponding to the "combined filter" curve, in the initial configuration (first configuration), the output signal follows the "2Hz Filter >>" curve. At the crossover point during the rise of the response, the configuration switches to the "8Hz Filter >>" curve (second configuration). A threshold value (higher than the sensitivity) different from the crossover amplitude can be chosen to trigger the switch. This switch is triggered as soon as the signal amplitude exceeds a certain absolute threshold. Then, the hold time DM is applied at time t2. This duration manages the delay of the response to the first configuration ("2Hz Filter >>"). In practice, this delay prevents prematurely switching back to the initial configuration (first configuration) before the delay of the signal from the first configuration ("2Hz Filter >>") dissipates. [000184] It can thus be foreseen that the control module selects the output of one and / or the other configuration according to the amplitude and applies a time delay to ensure a smooth transition. [000185] Figure 13 is a graph representing the response for a low-amplitude signal. The low-amplitude signal after filtering does not exceed the ACR threshold. Switching is not triggered, thus preserving the detection capability (i.e., the range or depth of detection) that would have been degraded by the second filtering configuration. [000186] Of course, the invention is not limited to the examples described. [000187] The filtering module can be arranged to switch continuously from the first configuration to the second configuration. In such an embodiment, the filtering module may not include a combiner. [000188] The detector may not include a discrimination module. [000189] The detector may be a dynamic type metal detector (motion detection), with frequency and / or time-domain analysis methods. The detector can also be a metal detector of the type metal detector where the detector is a fixed gantry and the targets move, for example to detect the presence of foreign metal on a feed conveyor.

Claims

33 Demands 1. Metal detector for detecting at least one metallic target within a detection zone, referred to as the "target of interest", said metal detector comprising: - at least one receiving coil (21) arranged to detect a magnetic field coming from the detection zone and to generate a signal corresponding to said magnetic field, called the "detection signal", - a detection unit (24) configured to process said detection signal so as to detect the presence of a target of interest and possibly its type, said detection unit comprising: o a filtering module (28) arranged to receive the detection signal as input and to filter the latter according to at least first and second filtering configurations, the second filtering configuration having a shorter time support than the first filtering configuration, o a control module (30) arranged to control the filtering module (28) according to at least one piece of information contained in the detection signal and indicating the presence of a metallic object, referred to as a "parasitic object", said metallic object having a signal power greater than a predefined power threshold,in order to apply the second filtering configuration to the detection signal so as to attenuate at least one component of the detection signal relating to said parasitic object.

2. Metal detector according to claim 1, wherein the second filtering configuration has a bandwidth, for example 8Hz, greater than the bandwidth of the first filtering configuration, for example 2Hz.

3. Metal detector according to claim 1 or 2, wherein the filtering module comprises a bandpass or lowpass filter, the band 34 pass, or the cutoff frequency, preferably at 3dB, is less than or equal to 40Hz, preferably less than or equal to 25Hz.

4. Metal detector according to claim 3, wherein the filtering module comprises a bandpass filter having a bandwidth, preferably at 3dB, ranging from 1 Hz to 25Hz.

5. Detector according to any one of the preceding claims, wherein the detection unit (24) is configured to perform a step of removing the ground component and / or electromagnetic interference from the detection signal.

6. Detector according to any one of the preceding claims, wherein the time support of a filtering configuration is the duration for which an impulse response to the filtering configuration is significant.

7. Detector according to any one of the preceding claims, wherein the time support is the duration during which the amplitude of the response of a target is greater than or equal to a given threshold value corresponding to the detection sensitivity of the detector.

8. Detector according to any one of the preceding claims, wherein the control module (30) is configured to command the transition from the first filtering configuration to the second filtering configuration during the detection of the parasitic object.

9. Detector according to any one of the preceding claims, wherein said control module (30) is configured to deliver a substantially continuous output signal from said control module (30) during a configuration change.

10. Detector according to any one of the preceding claims, wherein the control module (30) is configured to control the filtering module (28) so as to: - apply the first filtering configuration to the detection signal by default, and - when the control module (30) detects the presence of the parasitic object, apply the second filtering configuration, in particular in combination, in parallel or as a replacement for the first filtering configuration.

11. Detector according to any one of the preceding claims, wherein said information data corresponds to information indicating the power, in particular Euclidean, of the detection signal.

12. Detector according to any one of the preceding claims, wherein the detector further comprises a discrimination module (29) arranged to receive as input the output signal of the filtering module (28), said discrimination module (29) being configured to process the input signal thereof and to detect the presence of one or more metallic objects.

13. Detector according to the preceding claim, wherein said information data corresponds to information indicating the type of object detected.

14. Detector according to any one of the preceding claims, wherein the filtering module (28) comprises at least two separate first and second filters (40b, 40c), the first filter (40b) being arranged to filter the detection signal according to the first filtering configuration so as to generate a first filtered signal, and the second filter (40c) being faster than the first filter (40b) and being arranged to filter the detection signal according to the second filtering configuration so as to generate a second filtered signal.

15. Detector according to claim 14, the filtering module (28) comprising a delay line (42) connected to the second filter (40c), said delay line being arranged to compensate for possible latency differences between the two filters (40b, 40c).

16. Detector according to any one of claims 14 to 15, the filtering module (28) further comprising a combiner (44) arranged: - to receive at least the first and second filtered signals as input, - and to deliver at output a combination, in particular linear, of the aforementioned filtered signals, the control module (30) being preferably configured to determine the weighting values ​​associated with said combination, said weighting values ​​preferably ranging from 0 to 1 with the sum of the aforementioned values ​​equal to 1.

17. Detector according to any one of claims 1 to 13, wherein the filtering module (28) comprises a single configurable filter (40a) adapted to filter the detection signal according to at least the first and second configurations, said single filter (40a) having at least one adjustment parameter for its time support, the control module (30) being arranged to adjust the value of the adjustment parameter according to said information data.

18. Detector according to claim 17, wherein the adjustment parameter of the time support has at least eight distinct values.

19. Detector according to any one of the preceding claims, wherein the maximum excursion of the control module is dependent on the maximum power of the detection signal.

20. Detector according to the preceding claim, wherein the maximum excursion is defined so that the signal representing the distance to the target is monotonic as a function of distance.

21. A detector according to any one of the preceding claims, wherein the application of the second filtering configuration is maintained for a duration at least equal to the detection duration of the spurious object, preferably for a duration greater than or equal to the detection duration of the spurious object plus 30 ms.

22. A detector according to any one of the preceding claims, comprising at least one demodulator, said demodulator being arranged to receive the detection signal as input and to apply demodulation to said detection signal.

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