Methods and systems for non-destructive testing of a battery cell separator

Abstract

A system (10) for detecting the presence of a metallic particle in a separator (12) comprising: - means (1) for emitting a microwave beam (2); - means (7) for moving the separator through the microwave beam; - a plurality of contiguous diodes (5) sensitive to electromagnetic waves from said beam, this plurality being arranged to capture a reflected electromagnetic wave from said microwave beam or an electromagnetic wave transmitted by the separator from said microwave beam; - a device (6) configured to detect the presence of a metallic particle in the separator - when a reflected wave from said beam (2) is captured by a diode of said plurality arranged to capture a reflected electromagnetic wave; or - when the beam (2) is captured only by a portion of said plurality arranged to capture a transmitted electromagnetic wave. Figure for the abstract: Fig. 1

Description

Title of the invention: Methods and systems for non-destructive testing of a separator for battery cells

[0001] The present invention relates to methods and systems for non-destructive testing of a separator upstream of the assembly of battery cells, and more particularly to methods and systems for detecting the presence of a metallic object in a separator intended to be placed between two electrodes of opposite polarities of a battery cell.

[0002] In a battery, the separator is a key element that insulates and prevents two electrodes of opposite polarities from directly touching each other, while allowing the passage of ions between these two electrodes. Direct contact between the two electrodes could lead to an internal short circuit and, consequently, damage to the battery. Direct contact between the two electrodes prevents the battery from performing its function of sustainable storage of electrical energy.

[0003] This separator is in the form of a thin membrane, an assembly of insulating fibers or a thin electronically insulating and porous film which is placed, in a known manner, by stacking or by winding between a positive electrode or cathode and a negative electrode or anode.

[0004] However, during the production of the separator (extrusion, mechanical drawing) or to carry out the assembly of the cell, the separator is, most often, pulled from a supply reel and is made to pass through several machines in a production line, before it is placed between the two electrodes of opposite polarities. During these operations, the separator is particularly exposed to the risk of depositing metallic objects such as metal splinters from surrounding devices. Conductive particles can, in fact, detach from these devices and become fixed on / in the separator. In addition, the processes for producing non-woven, woven or membrane separators inevitably include equipment consisting of numerous moving metallic parts (bearings, rollers, knives, or calenders for example) which can release conductive particles into the separator.

[0005] The presence of a metal object in the separator can lead to its piercing and the two electrodes of opposite polarities coming into direct contact, in other words to a short circuit of the battery. This short circuit may not be detected during an initial electrical test because the electrodes may not yet have reached their final thickness and may not clearly touch the metal object. Such products can thus be delivered to the customer.

[0006] It is known from the state of the art to use an image sensor to detect the presence of objects in the separator before its insertion between two electrodes of opposite polarities. However, this sensor does not make it possible to distinguish between conductive objects and other inclusions that are not detrimental to the operation of the battery cells. On the other hand, control of the separator based on real-time processing of the acquired images may impose limits on the speed of movement of this separator. In addition, existing image analysis solutions are not sufficiently sensitive to detect small metallic objects (a few microns, i.e. the thickness of the separator), in particular less than 200 qm, especially when the separator is moving rapidly.

[0007] It is also known to use magnetically sensitive detection means. A disadvantage of these means is that they do not detect non-magnetic objects, although they may be electrically conductive such as copper or stainless steel.

[0008] An object of the present invention is to remedy the aforementioned drawbacks.

[0009] To this end, there is proposed, firstly, a system for detecting the presence of a metal particle in a separator intended to be arranged between two electrodes of opposite polarities, this system comprising - transmission means capable of emitting a beam of microwaves; - scrolling means for scrolling the separator in the microwave beam; - reception means sensitive to the electromagnetic waves of said microwave beam, these reception means being arranged to capture, during the movement of the separator in the microwave beam, an electromagnetic wave reflected from said microwave beam or an electromagnetic wave transmitted by the separator of said microwave beam; - an electronic processing device configured to detect the presence of a metal particle in the separator when a reflected wave from said microwave beam is picked up by the receiving means arranged to pick up an electromagnetic wave reflected from said microwave beam; or - when the microwave beam is only picked up by part of the reception means arranged to pick up an electromagnetic wave transmitted from said microwave beam.

[0010] Various additional features may be provided, alone or in combination: - the receiving means comprise a plurality of contiguous diodes sensitive to the electromagnetic waves of said microwave beam, the electronic processing device being configured to detect the presence of a metal particle in the separator - when a reflected wave of said microwave beam is picked up by a diode of said plurality arranged to pick up an electromagnetic wave reflected from said microwave beam; or - when the microwave beam is only picked up by a portion of said plurality arranged to pick up an electromagnetic wave transmitted from said microwave beam - the transmitting means comprise a phased array antenna configured to illuminate the moving separator at a predefined scanning speed of the microwave beam; - the electronic processing device is, furthermore, configured to determine the position, in the separator, of a detected metal particle present in this separator, this position corresponding, according to the direction of the emitted microwave beam, to the position, in said plurality arranged to capture a reflected electromagnetic wave, of the diode having captured a reflected electromagnetic wave of said microwave beam; - the electronic processing device is, furthermore, configured to determine the position, in the separator, of a detected metal particle present in this separator, this position corresponding, according to the direction of the emitted microwave beam, to the position, in said plurality arranged to pick up a transmitted electromagnetic wave, of a diode of said plurality not having picked up an electromagnetic wave transmitted from said microwave beam; - the contiguous diodes and / or the emission means are supported by layers of a material absorbing electromagnetic waves from the microwave beam; - the scrolling means comprise two rotating rollers located on either side of the emission means.

[0011] Secondly, a battery cell assembly machine comprising the system presented above is provided.

[0012] Thirdly, a method is proposed for detecting the presence of a metal particle in a separator intended to be arranged between two electrodes of opposite polarities, this method comprising the following steps: - emission of a microwave beam; - scrolling of the separator in the microwave beam; - capture, during the movement of the separator in the microwave beam, by a diode of a plurality of contiguous diodes sensitive to the electromagnetic waves of said microwave beam, of an electromagnetic wave reflected from said microwave beam when this plurality is arranged to capture an electromagnetic wave reflected from said microwave beam, or of a transmitted electromagnetic wave by the splitter of said microwave beam when said plurality is arranged to pick up an electromagnetic wave transmitted by the splitter of said microwave beam; - detection, by an electronic processing device, of the presence of a metal particle in the separator when a reflected wave of said microwave beam is picked up by a diode of said plurality arranged to pick up an electromagnetic wave reflected from said microwave beam; or - when the microwave beam is only picked up by a portion of said plurality arranged to pick up an electromagnetic wave transmitted from said microwave beam.

[0013] Various additional features may be provided, alone or in combination: - the method presented above further comprises a step of determining the position, in the separator, of a detected metal particle present in this separator, this position corresponding, according to the direction of the emitted microwave beam, to the position, in said plurality arranged to capture a reflected electromagnetic wave, of a diode having captured an electromagnetic wave reflected from said microwave beam; - the method presented above further comprises a step of determining the position, in the separator, of a detected metal particle present in this separator, this position corresponding, according to the direction of the emitted microwave beam, to the position, in said plurality arranged to pick up a transmitted electromagnetic wave, of a diode of said plurality not having picked up an electromagnetic wave transmitted from said microwave beam.

[0014] Other characteristics and advantages of the invention will appear more clearly and concretely on reading the following description of embodiments, which is given with reference to the appended drawings in which:

[0015] Figure [Fig. 1] schematically illustrates a system for detecting the presence of a metal particle in a separator intended to be arranged between two electrodes of opposite polarities according to a first embodiment;

[0016] Figure [Fig.2] schematically illustrates a system for detecting the presence of a metal particle in a separator intended to be placed between two electrodes of opposite polarities according to a second embodiment;

[0017] Figure [Fig.3] schematically illustrates steps of a method for detecting the presence of a metal particle in a separator intended to be placed between two electrodes of opposite polarities according to various embodiments.

[0018] Referring to Figures 1 and 2, there is shown a system 10 for detecting the presence of a metal particle 11 in a separator 12 intended to be arranged between two electrodes of opposite polarities. This system 10 comprises emission means 1 capable of emitting a beam 2 of microwaves, scrolling means 7 making it possible to scroll the separator 12 in the emitted beam 2 of microwaves and reception means 3 sensitive to the electromagnetic waves of the beam 2 of microwaves to capture electromagnetic waves of this beam 2 of microwaves during the scrolling of the separator 12 in this beam of microwaves. An electronic processing device 6 is configured to detect, from the measurements from the reception means 3, the presence of a metal particle 11 in the separator 12.

[0019] Here, the term microwave beam 2 is understood to mean a field or a zone of electromagnetic radiation at one or more predefined frequencies in the microwave domain. This microwave beam 2 is, in one embodiment, emitted by one or more antennas (a patch antenna and / or a horn antenna for example) coupled to a microwave radiation source or by an electromagnetic wave reflector configured to at least partially reflect a microwave beam incident thereon. The emission means 1 are dimensioned so that the emitted microwave beam 2 preferably illuminates the separator 12 as it moves along its entire width. In one embodiment, the microwave beam 2 has a rectangular section.

[0020] In one embodiment, the transmission means 1 comprise an array of antennas configured to radiate a beam 2 of microwaves. This array is, for example, a uniform linear array of antennas arranged perpendicular to the direction of travel of the separator 12 (in the direction of the width of the separator 12 in travel). Alternatively, the transmission means 1 comprise a two-dimensional array of antennas.

[0021] In another embodiment, the transmission means 1 comprise a phased array antenna. Such an antenna advantageously makes it possible to illuminate the separator 12 in a direction that can be adjusted by means of a phase control device. The direction of the microwave beam 2 is effected by electronic scanning. In one embodiment, the phased array antenna is configured to illuminate the separator 12 as it moves along at a predefined scanning speed of the microwave beam 2. This scanning speed is preferably linked to the speed of movement of the separator 12.

[0022] In another embodiment, the emission means 1 comprise a rotating reflector arranged to reflect an incident microwave beam so that the reflected microwave beam scans the separator 12 as it moves along its width. The rotation speed of the reflector is preferably linked to the separator scroll speed 12.

[0023] The scrolling means 7 comprise, in one embodiment, two rotating rollers arranged to bring the separator 12 to be controlled into the microwave beam 2. The two rotating rollers are located on either side of the emission means 1. In one embodiment, the scrolling means 7 are two successive rotating rollers of a battery cell assembly machine. The two rollers are not necessarily specific to the system 10, but may be part of a battery cell assembly machine already in place. The system 10 can, thus, be easily integrated into an existing battery cell assembly machine.

[0024] The receiving means 3 comprise a plurality of contiguous diodes 5 sensitive to the electromagnetic waves of said microwave beam 2. Each of these diodes 5 is capable of capturing an electromagnetic wave of the microwave beam 2 by converting the energy or intensity of this electromagnetic wave into an electrical signal, such as a Schottky diode or, more generally, any other diode capable of delivering an electrical current linked to the electromagnetic background energy to which this diode 5 is subjected.

[0025] The contiguous diodes 5 are regularly distributed over a surface to capture electromagnetic waves from the microwave beam 2 at almost any point on this surface. The contiguous diodes 5 form, in one embodiment, a carpet 4 of diodes. In this carpet 4, the diodes 5 are arranged in a matrix following a regular pattern of rows and columns of contiguous diodes 5. The surface density (i.e. per unit area) of the contiguous diodes 5 is chosen so as to be able to capture an electromagnetic wave at almost any point on said carpet 4. This density defines, in fact, the detection resolution of the system 10. The greater this density, the higher the detection sensitivity of the metal particles 11. A carpet 4 of contiguous diodes 5 advantageously makes it possible to have fine spatial sampling for the detection of fine metal particles 11 in the separator 12.In the attached figures, the dimensions of the diodes 5 are enlarged for obvious reasons of clarity. The dimensions of the carpet 4 of contiguous diodes 5 are chosen so that this carpet 4 makes it possible to take readings of the microwave beam 2 over the entire width of the separator 12.

[0026] Advantageously, a phased array antenna or a rotating reflector configured to illuminate the moving separator 12 in a variable direction further improves the detection resolution of the reception means 3.

[0027] In a first embodiment illustrated by [Fig.l], the contiguous diodes 5 are arranged to capture, during the movement of the separator 12 in the microwave beam 2, an electromagnetic wave transmitted by the separator 12 of the beam 2 microwaves. For this, the carpet 4 of contiguous diodes 5 is arranged opposite the emission means 1 so as to be able to capture electromagnetic waves during the movement of the separator 12 in the microwave beam between the emission means and this carpet 4 of contiguous diodes 5. The movement means 7 cause the separator 12 to move between, on the one hand, the emission means 1 and, on the other hand, the reception means 3. Given the nature of reciprocal emission-reception, the relative arrangement of the emission means 1 with respect to the carpet 4 of contiguous diodes 5 in [Fig.l] is therefore given for illustrative purposes only. More generally, the emission means 1 and the contiguous diodes 5 are arranged on either side of the separator 12 in scrolling fashion so that these contiguous diodes 5 can capture electromagnetic waves from the microwave beam 2 passing through the separator 12.

[0028] The electric current from a diode 5 indicates the electromagnetic energy, at this point of the carpet 4 of contiguous diodes 5, of the beam 2 of microwaves passing through the separator 12. Each of the contiguous diodes 5 provides a measurement, at the point where this diode 5 is located in the carpet 4, of the beam 2 of microwaves passing through the separator 12. The presence of a metal particle 11 in the separator 12 causes, at its location in the separator 12, a modification in the propagation of the beam 2 of microwaves. The metal particle 11 prevents, at its location in the separator 12, at least partially the transmission of the electromagnetic waves of the beam 2 of microwaves. The waves of the beam 2 of microwaves undergo reflections and / or diffraction effects when they impact a metal particle 11 in the separator 12.The microwave radiation from the emission means 1 is, most often, reflected by the metal particle 11 at its location in the separator 12. The presence of a metal particle 11 in the separator 12 therefore has the effect of making at least one corresponding diode 5 of the belt 4 non-passing so as to reveal the presence of this metal particle 11. This diode 5 is in the shadow of the metal particle 11, relative to the beam 2 of microwaves passing through the separator 12. On the other hand, outside the position of the metal particle 11 in the separator 12, the beam 2 of microwaves propagates through the separator 12 in scrolling order to the belt of contiguous diodes 5. As a result, advantageously, the belt 4 of contiguous diodes 5 makes it possible to have a clear two-dimensional image of the beam 2 of microwaves passing through the separator 12 in scrolling order.

[0029] Based on the data from the contiguous diodes 5 arranged to capture an electromagnetic wave transmitted from the microwave beam 2, the electronic processing device 6 makes it possible, by comparing the intensity of the electric current from each diode 5 and / or the evolution of this intensity with predefined threshold values, to determine whether the microwave beam is only captured by a portion of the contiguous diodes 5 arranged to capture an electromagnetic wave transmitted from said beam 2. of microwaves. In other words, the electronic processing device 6 determines whether there is a diode 5 which has not picked up an electromagnetic wave transmitted by the splitter 12 of the beam 2 of microwaves.

[0030] When the microwave beam is only picked up by a portion of the contiguous diodes 5 arranged to pick up an electromagnetic wave transmitted from the microwave beam 2, the electronic processing device 6 detects the presence of a metal particle 11 in the separator 12. Upon reading the coordinates of the non-passing diode 5 (or, more generally, whose electrical current intensity at its output is below an expected intensity) in the belt 4, the electronic processing device 6 is able to determine, as a function of the direction of the emitted microwave beam 2, the corresponding position of the metal particle 11 detected in the separator 12.The position, in the separator 12, of a detected metallic particle 11 present in the separator 12, corresponds, according to the direction of the beam 2 of microwaves emitted, to the position, in the mat 4 arranged to capture a transmitted electromagnetic wave, of the diode 5 which has not captured an electromagnetic wave transmitted from the beam 2 of microwaves.

[0031] In one embodiment, the dimensions of the metal particle 11 can be estimated from the number of adjacent diodes 5 having revealed the presence of this metal particle 11.

[0032] Given the direction of the microwave beam 2, when no position in the separator 12 does not correspond to the position in the mat 4 of a non-passing diode 5 (i.e. generating an electric current of intensity lower than a predefined threshold value), the electronic processing device 6 does not deduce the presence of a metallic particle 11 in the separator.

[0033] In a second embodiment illustrated by [Fig. 2], the contiguous diodes 5 are arranged to capture, during the movement of the separator 12 in the microwave beam 2, an electromagnetic wave reflected from the microwave beam 2. In this case, the system 10 operates in reflection mode in which the electronic processing device 6 detects the presence of a metal particle 11 in the separator 12 when a reflected wave from the microwave beam 2 is captured by a diode 5 of the belt 4 arranged to capture an electromagnetic wave reflected from the microwave beam 2. The position, in the separator 12, of a detected metallic particle 11 present in this separator 12, corresponding, according to the direction of the beam 2 of microwaves emitted, to the position, in the carpet 4 of contiguous diodes 5 arranged to capture a reflected electromagnetic wave, of the diode having captured an electromagnetic wave reflected from the beam 2 of microwaves.

[0034] The emission means 1 on the one hand and the contiguous diodes 5 on the other hand are arranged on the same side with respect to the separator 12 in scrolling to be controlled. so that any one of these contiguous diodes 5 can capture an electromagnetic wave reflected from the microwave beam 2 by a possible metallic particle 11 in the separator 12. Such a configuration has an advantage in the case of a lack of access to a face of the separator 12 during movement.

[0035] The system 10 measures the transmission of the separator 12 while scrolling in the first embodiment and its reflection in the second embodiment.

[0036] A third embodiment combining the embodiments presented above can, of course, be envisaged. These embodiments use the transparency of the separator 12 to microwave radiation and the properties of obstruction or reflection of the microwave radiation by a possible metallic particle 11 present in the separator 12. The detection of a metallic particle 11 in the separator 12 can therefore be carried out by observing its transmission, its reflection, or both at the same time. The emission means 1 and the contiguous diodes 5 are, preferably, arranged fairly close to the moving separator 12, at a distance of the order of the wavelength so that the electromagnetic energy of the microwave beam 2 is not dissipated.

[0037] In order to prevent the reception means 3 from picking up parasitic waves, the contiguous diodes 5 and / or the transmission means 1 are preferably supported by layers of a material absorbing electromagnetic waves from the microwave beam 2. These layers cover the inner faces of the support frame of the system 10 (in particular, the face opposite the transmission means 1 in the case of the second embodiment presented above) to minimize the interactions of the support frame with the microwave beam 2 in the manner of an anechoic chamber. A tunnel conformation of the opposite lateral faces through which the separator 12 passes further improves the coupling of the transmission and reception means 1, 3.

[0038] Upon detection of a metal particle 11 in the separator 12, the electronic processing device 6 is, in one embodiment, configured to generate an alert intended for a supervision device and / or control signals intended for a device located downstream in the battery cell assembly line to eliminate the detected metal particle 11 or isolate the section of the separator 12 integrating this metal particle 11.

[0039] Referring to [Fig. 3], steps of a method implementing the means presented above are shown for detecting the presence of a metal particle 11 in a separator 12 intended to be arranged between two electrodes of opposite polarities. This method comprises a step 31 of emitting a beam 2 of microwaves, a step 32 of moving the separator 12 in the microwave beam.

[0040] During the scrolling of the separator 12 in the beam 2 of microwaves, a step 33 of capturing an electromagnetic wave reflected from the beam 2 of microwaves or of an electromagnetic wave transmitted by the separator 12 of the beam 2 of microwaves is implemented by at least one diode 5 of the mat 4 of contiguous diodes 5 sensitive to the electromagnetic waves of the beam 2 of microwaves.

[0041] During a detection step 34, a metal particle 11 is estimated to be present in the separator 12 when a reflected wave of the microwave beam 2 is picked up by a diode 5 of the contiguous diodes arranged to pick up an electromagnetic wave reflected from the microwave beam 2, or when the microwave beam is picked up only by a portion of the contiguous diodes 5 arranged to pick up an electromagnetic wave transmitted from the microwave beam 2.

[0042] During a location step 35, the electronic processing device 6 determines the position, in the separator 12, of a detected metal particle 11 present in the separator 12. This position corresponds, according to the direction of the beam 2 of microwaves emitted, to the position, in the carpet of contiguous diodes 5 arranged to pick up a transmitted electromagnetic wave, of the diode that has not picked up a transmitted electromagnetic wave of the beam 2 of microwaves. In the case of operation in reflection mode, the position of the detected metal particle 11 present in the separator 12 corresponds, according to the direction of the beam 2 of microwaves emitted, to the position, in the carpet 4 of contiguous diodes 5 arranged to pick up a reflected electromagnetic wave, of the diode that picked up a reflected electromagnetic wave of the beam 2 of microwaves.

[0043] Advantageously, the embodiments presented above allow non-destructive testing of the separator 12 (without physical contact with the separator), implementing an excitation signal in the form of a microwave beam and a mat of contiguous diodes 5 to observe the transmission and / or reflection of the moving separator 12. Without disturbing the production flow, the system 10 can be integrated into a free space between two successive rotating rollers upstream of the assembly of the battery cells where at least one face of the moving separator is accessible.

[0044] The methods and systems presented above are suitable for high running speeds of the separator 12.

Claims

Claims

1. System (10) for detecting the presence of a metal particle (11) in a separator (12) intended to be arranged between two electrodes of opposite polarities, this system (10) comprising - emission means (1) capable of emitting a beam (2) of microwaves; - scrolling means (7) making it possible to scroll the separator (12) in the beam (2) of microwaves; - reception means (3) sensitive to the electromagnetic waves of said beam (2) of microwaves, these reception means (3) being arranged to pick up, during the scrolling of the separator (12) in the beam (2) of microwaves, an electromagnetic wave reflected from said beam (2) of microwaves or an electromagnetic wave transmitted by the separator (12) of said beam (2) of microwaves;- an electronic processing device (6) configured to detect the presence of a metal particle (11) in the separator (12) - when a reflected wave of said microwave beam (2) is picked up by the receiving means (3) arranged to pick up an electromagnetic wave reflected from said microwave beam (2); or - when the microwave beam is picked up only by a portion of the receiving means (3) arranged to pick up an electromagnetic wave transmitted from said microwave beam (2).;

2. System according to the preceding claim, characterized in that the receiving means (3) comprise a plurality of contiguous diodes (5) sensitive to the electromagnetic waves of said microwave beam (2), the electronic processing device (6) being configured to detect the presence of a metallic particle (11) in the separator (12) - when a reflected wave of said microwave beam (2) is picked up by a diode of said plurality arranged to pick up a reflected electromagnetic wave of said microwave beam (2); or - when the microwave beam is picked up only by a part of said plurality arranged to pick up a transmitted electromagnetic wave of said microwave beam (2).

3. System according to claim 1 or 2, characterized in that the transmission means (1) comprise a phased array antenna configured to illuminate the scrolling separator (12) at a predefined scanning speed of the microwave beam (2).

4. System according to claim 2 or 3, characterized in that the electronic processing device (6) is, in addition, configured to determine the position, in the separator (12), of a detected metallic particle (11) present in this separator (12), this position corresponding, according to the direction of the beam (2) of microwaves emitted, to the position, in said plurality arranged to capture a reflected electromagnetic wave, of a diode having captured an electromagnetic wave reflected from said beam (2) of microwaves.

5. System according to claim 2 or 3, characterized in that the electronic processing device (6) is, in addition, configured to determine the position, in the separator, of a detected metallic particle (11) present in this separator (12), this position corresponding, according to the direction of the beam (2) of microwaves emitted, to the position, in said plurality arranged to capture a transmitted electromagnetic wave, of a diode which has not captured an electromagnetic wave transmitted from said beam (2) of microwaves.

6. System according to any one of the preceding claims, characterized in that the receiving means (3) and / or the transmitting means (1) are supported by layers of a material absorbing electromagnetic waves from the microwave beam (2).

7. System according to any one of the preceding claims, characterized in that the scrolling means (7) comprise two rotating rollers located on either side of the emission means (1).

8. A battery cell assembly machine comprising the system (10) of any preceding claim.

9. Method for detecting the presence of a metal particle (11) in a separator (12) intended to be arranged between two electrodes of opposite polarities, this method comprising the following steps - emission (31) of a beam (2) of microwaves; - movement (32) of the separator (12) in the beam (2) of microwaves - capture (33), during the movement of the separator (12) in the beam (2) of microwaves, by a diode (5) of a plurality of contiguous diodes (4) sensitive to the electromagnetic waves of said beam (2) of microwaves, of an electromagnetic wave reflected from said beam (2) of microwaves when this plurality is arranged to capture an electromagnetic wave reflected from said beam (2) of microwaves, or of a electromagnetic wave transmitted by the separator (12) of said microwave beam (2) when said plurality is arranged to pick up an electromagnetic wave transmitted by the separator (12) of said microwave beam (2), - detection (34), by an electronic processing device (6), of the presence of a metallic particle (11) in the separator (12) - when a reflected wave of said microwave beam (2) is picked up by a diode of said plurality arranged to pick up an electromagnetic wave reflected from said microwave beam (2); or - when the microwave beam is only captured by a part of said plurality arranged to capture an electromagnetic wave transmitted from said microwave beam (2).

10. Method according to the preceding claim, characterized in that it further comprises a step of determining (35) the position, in the separator (12), of a detected metallic particle (11) present in this separator (12), this position corresponding, according to the direction of the beam (2) of microwaves emitted, to the position, in said plurality arranged to capture a reflected electromagnetic wave, of a diode having captured an electromagnetic wave reflected from said beam (2) of microwaves.

11. Method according to claim 9 or 10, characterized in that it further comprises a step of determining the position, in the separator, of a detected metallic particle (11) present in this separator (12), this position corresponding, according to the direction of the beam (2) of microwaves emitted, to the position, in said plurality arranged to capture a transmitted electromagnetic wave, of a diode which has not captured an electromagnetic wave transmitted from said beam (2) of microwaves.

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