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 battery cell separator

[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 component that isolates and prevents two electrodes of opposite polarities from directly touching, while allowing the passage of ions between these two electrodes. Direct contact between the two electrodes could cause an internal short circuit and, consequently, damage to the battery. Direct contact between the two electrodes prevents the battery from fulfilling its function of long-term 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 winding between a positive electrode or cathode and a negative electrode or anode.

[0004] However, during the manufacturing of the separator (extrusion, mechanical drawing) or during cell assembly, the separator is most often pulled from a feed reel and passes through several machines in a production line before being placed between the two electrodes of opposite polarities. During these operations, the separator is particularly exposed to the risk of the deposition of metallic objects such as metal fragments from surrounding equipment. Conductive particles can, in fact, detach from this equipment and become embedded in the separator. Furthermore, the manufacturing processes for non-woven, woven, or membrane separators inevitably include equipment consisting of numerous moving metallic parts (bearings, rollers, knives, or calenders, for example) that can release conductive particles into the separator.

[0005] The presence of a metallic object in the separator can lead to its perforation and direct contact between the two electrodes of opposite polarities, in other words, a short circuit in 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 be making direct contact with the metallic object. Such products can therefore be delivered to the customer.

[0006] It is known in the prior 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 cannot distinguish between conductive objects and other inclusions that are not detrimental to the operation of the battery cells. On the other hand, separator control based on real-time processing of acquired images can impose limits on the separator's speed. Moreover, existing image analysis solutions are not sensitive enough to detect small metallic objects (a few microns regardless of the separator's thickness), particularly those smaller than 200 µm, 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] One object of the present invention is to remedy the aforementioned drawbacks.

[0009] To this end, a system is proposed, firstly, for detecting the presence of a metallic particle in a separator intended to be placed between two electrodes of opposite polarities, this system comprising - emission means capable of emitting a microwave beam; - means of scrolling to allow the separator to be scrolled in the microwave beam; - receiving means sensitive to electromagnetic waves of said microwave beam, these receiving means being arranged to capture, during the passage 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 metallic particle in the separator when a reflected wave from said microwave beam is captured by receiving means arranged to capture a reflected electromagnetic wave from said microwave beam; or - when the microwave beam is only captured by a part of the receiving means arranged to capture 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 device of the process is configured to detect the presence of a metallic particle in the separator - when a reflected wave from said microwave beam is captured by a diode of said plurality arranged to capture a reflected electromagnetic wave from said microwave beam; 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 - the transmission means include a phase-controlled array antenna configured to illuminate the scrolling separator at a predefined microwave beam scanning speed; - the electronic processing device is further configured to determine the position, in the separator, of a detected metallic 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 further configured to determine the position, in the separator, of a detected metallic 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 transmitted electromagnetic wave, of a diode of said plurality not having captured a transmitted electromagnetic wave from said microwave beam; - the adjacent 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 proposed.

[0012] Thirdly, a method is proposed for detecting the presence of a metallic particle in a separator intended to be placed between two electrodes of opposite polarities, this method comprising the following steps - emission of a microwave beam; - movement of the separator through the microwave beam; - capture, during the passage of the separator in the microwave beam, by a diode of a plurality of contiguous diodes sensitive to 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 from an electromagnetic wave transmitted by the separator of said microwave beam when said plurality is arranged to capture an electromagnetic wave transmitted by the separator of said microwave beam; - detection, by an electronic processing device, of the presence of a metallic particle in the separator when a reflected wave from said microwave beam is captured by a diode of said plurality arranged to capture a reflected electromagnetic wave from said microwave beam; 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.

[0013] Various additional features may be provided, alone or in combination: - the process presented above further includes a step of determining the position, in the separator, of a detected metallic 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 a reflected electromagnetic wave from said microwave beam; - the process presented above further includes a step of determining the position, in the separator, of a detected metallic 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 transmitted electromagnetic wave, of a diode of said plurality not having captured a transmitted electromagnetic wave from said microwave beam.

[0014] Other features and advantages of the invention will become clearer and more concrete upon reading the following description of embodiments, which is made with reference to the accompanying drawings in which:

[0015] Figure [Fig. 1] schematically illustrates a system for detecting the presence of a metallic particle in a separator intended to be disposed 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 metallic particle in a separator intended to be disposed 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 metallic particle in a separator intended to be placed between two electrodes of opposite polarities according to various embodiments.

[0018] With reference to Figures 1 and 2, a system 10 is shown for detecting the presence of a metallic particle 11 in a separator 12 intended to be placed between two electrodes of opposite polarities. This system 10 comprises emission means 1 for emitting a microwave beam 2, scrolling means 7 for scrolling the separator 12 through the emitted microwave beam 2, and receiving means 3 sensitive to the electromagnetic waves of the microwave beam 2 for capturing electromagnetic waves from this microwave beam 2 as the separator 12 scrolls through this microwave beam. An electronic processing device 6 is configured to detect, from the measurements obtained from the receiving means 3, the presence of a metallic particle 11 in the separator 12.

[0019] Here, a microwave beam 2 is understood to mean a field or zone of electromagnetic radiation at one or more predefined frequencies in the microwave range. In one embodiment, this microwave beam 2 is 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 reflect at least partially a microwave beam incident upon it. The emission means 1 are dimensioned so that the emitted microwave beam 2 illuminates, preferably, the moving separator 12 across its entire width. In one embodiment, the microwave beam 2 has a rectangular cross-section.

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

[0021] In another embodiment, the transmission means 1 comprise a phase-controlled array antenna. Advantageously, such an antenna allows the separator 12 to be illuminated in an adjustable direction by means of a phase-control device. The direction of the microwave beam 2 is determined by electronic scanning. In one embodiment, the phase-controlled array antenna is configured to illuminate the moving separator 12 at a predefined scanning speed of the microwave beam 2. This scanning speed is preferably linked to the speed at which the separator 12 moves.

[0022] In another embodiment, the emission means 1 comprise a rotating reflector arranged to reflect an incident microwave beam such that the reflected microwave beam performs a scan of the separator 12 in scrolling across its width. The rotation speed of the reflector is preferably linked to the scrolling speed of the separator 12.

[0023] In one embodiment, the scrolling means 7 comprise two rotating rollers arranged to bring the separator 12 to be inspected into the microwave beam 2. The two rotating rollers are located on either side of the emitting 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 an existing battery cell assembly machine. 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 from 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 electric current related 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 virtually any point on this surface. In one embodiment, the contiguous diodes 5 form a diode array 4. In this array 4, the diodes 5 are arranged in a matrix according to 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 virtually any point of said array 4. This density, in effect, defines the detection resolution of the system 10. The higher this density, the greater the sensitivity for detecting metallic particles 11. An array 4 of contiguous diodes 5 advantageously allows for fine spatial sampling for the detection of fine metallic 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 array 4 of contiguous diodes 5 are chosen so that this array 4 allows measurements of the microwave beam 2 to be taken over the entire width of the separator 12.

[0026] Advantageously, a phase-controlled array antenna or a rotating reflector configured to illuminate the scrolling separator 12 in a variable direction further improves the detection resolution of the receiving means 3.

[0027] In a first embodiment illustrated by [Fig. 1], the contiguous diodes 5 are arranged to capture, during the passage of the separator 12 in the beam 2 of Microwaves, an electromagnetic wave transmitted by the separator 12 of the microwave beam 2. For this purpose, the array 4 of contiguous diodes 5 is positioned opposite the transmitting means 1 so as to capture electromagnetic waves as the separator 12 moves through the microwave beam between the transmitting means and this array 4 of contiguous diodes 5. The moving means 7 move the separator 12 between, on the one hand, the transmitting means 1 and, on the other hand, the receiving means 3. Given the reciprocal nature of transmission and reception, the relative arrangement of the transmitting means 1 with respect to the array 4 of contiguous diodes 5 in [Fig. 1] is therefore given for illustrative purposes only.More generally, the emitting means 1 and the adjacent diodes 5 are arranged on either side of the scrolling separator 12 so that these adjacent 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 that point in the array 4 of adjacent diodes 5, of the microwave beam 2 passing through the separator 12. Each of the adjacent diodes 5 provides a measurement, at the point where that diode 5 is located in the array 4, of the microwave beam 2 passing through the separator 12. The presence of a metallic particle 11 in the separator 12 causes, at that point in the separator 12, a modification in the propagation of the microwave beam 2. The metallic particle 11 prevents, at its location in the separator 12, at least partially the transmission of electromagnetic waves from the microwave beam 2.The microwave beam 2 undergoes reflections and / or diffraction effects when it strikes a metallic particle 11 in the separator 12. The microwave radiation from the emission means 1 is most often reflected by the metallic particle 11 at its location in the separator 12. The presence of a metallic particle 11 in the separator 12 therefore renders at least one corresponding diode 5 of the mat 4 non-conducting, thus revealing the presence of this metallic particle 11. This diode 5 lies in the shadow of the metallic particle 11, with respect to the microwave beam 2 passing through the separator 12. Conversely, outside the position of the metallic particle 11 in the separator 12, the microwave beam 2 propagates through the separator 12 in a forward motion to the adjacent mat of diodes 5.The advantageous result is that the array 4 of contiguous diodes 5 allows for a clear two-dimensional image of the microwave beam 2 passing through the separator 12 in motion.

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

[0030] When the microwave beam is captured by only a part of the contiguous diodes 5 arranged to capture an electromagnetic wave transmitted from the microwave beam 2, the electronic processing device 6 detects the presence of a metallic particle 11 in the separator 12. By reading the coordinates of the non-conducting diode 5 (or, more generally, whose electrical current intensity at its output is below an expected intensity) in the mat 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 metallic 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 emitted microwave beam 2, to the position, in the mat 4 arranged to capture a transmitted electromagnetic wave, of the diode 5 which has not captured a transmitted electromagnetic wave from the microwave beam 2.

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

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

[0033] In a second embodiment illustrated by [Fig. 2], the adjacent diodes 5 are arranged to capture, as the separator 12 passes through the microwave beam 2, a reflected electromagnetic wave 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 metallic particle 11 in the separator 12 when a reflected wave from the microwave beam 2 is captured by a diode 5 of the mat 4 arranged to capture a reflected electromagnetic wave 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 emitted microwave beam 2, to the position, in the mat 4 of contiguous diodes 5 arranged to capture a reflected electromagnetic wave, of the diode which has captured a reflected electromagnetic wave from the microwave beam 2.

[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 sliding separator 12 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 one face of the sliding separator 12.

[0035] The system 10 measures the transmission of the separator 12 in 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 considered. These embodiments utilize the transparency of the separator 12 to microwave radiation and the obstruction or reflection properties of microwave radiation by any 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. The emitting means 1 and the adjacent diodes 5 are preferably arranged quite close to the moving separator 12, at a distance on the order of the wavelength, so that the electromagnetic energy of the microwave beam 2 is not dissipated.

[0037] To prevent the receiving means 3 from picking up unwanted waves, the adjacent diodes 5 and / or the transmitting means 1 are preferably supported by layers of a material that absorbs 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 transmitting means 1 in the case of the second embodiment described above) to minimize the interactions of the support frame with the microwave beam 2 in the manner of an anechoic chamber. A tunnel-like configuration of the opposite lateral faces through which the separator 12 passes further improves the coupling of the transmitting and receiving means 1 and 3.

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

[0039] Referring to [Fig. 3], steps of a method employing the means described above for detecting the presence of a metallic particle 11 in a separator 12 intended to be placed between two electrodes of opposite polarities are shown. This method comprises a step 31 of emitting a microwave beam 2, and a step 32 of moving the separator 12 through the microwave beam.

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

[0041] During a detection step 34, a metallic particle 11 is estimated to be present in the separator 12 when a reflected wave from the microwave beam 2 is captured by a diode 5 of the contiguous diodes arranged to capture a reflected electromagnetic wave from the microwave beam 2, or when the microwave beam is captured only by a part of the contiguous diodes 5 arranged to capture a transmitted electromagnetic wave from the microwave beam 2.

[0042] During a localization step 35, the electronic processing device 6 determines the position, in the separator 12, of a detected metallic particle 11 present in the separator 12. This position corresponds, according to the direction of the emitted microwave beam 2, to the position, in the array of contiguous diodes 5 arranged to capture a transmitted electromagnetic wave, of the diode that did not capture a transmitted electromagnetic wave from the microwave beam 2. In the case of operation in reflection mode, the position of the detected metallic particle 11 present in the separator 12 corresponds, according to the direction of the emitted microwave beam 2, to the position, in the array of contiguous diodes 5 arranged to capture a reflected electromagnetic wave, of the diode that captured a reflected electromagnetic wave from the microwave beam 2.

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

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

Claims

Demands

1. System (10) for detecting the presence of a metallic particle (11) in a separator (12) intended to be disposed between two electrodes of opposite polarities of a battery cell, said system (10) comprising - emission means (1) capable of emitting a microwave beam (2); - scrolling means (7) for scrolling the separator (12) in the microwave beam (2); - receiving means (3) sensitive to electromagnetic waves from said microwave beam (2), these receiving means (3) being arranged to capture, during the scrolling of the separator (12) in the microwave beam (2), an electromagnetic wave reflected from said microwave beam (2) or an electromagnetic wave transmitted by the separator (12) from said microwave beam (2);- an electronic processing device (6) configured to detect the presence of a metallic particle (11) in the separator (12) - when a reflected wave from said microwave beam (2) is received by the receiving means (3) arranged to receive a reflected electromagnetic wave from said microwave beam (2); or - when the microwave beam is received only by part of the receiving means (3) arranged to receive a transmitted electromagnetic wave 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 electromagnetic waves from 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 from said microwave beam (2) is captured by a diode of said plurality arranged to capture a reflected electromagnetic wave from said microwave beam (2); or - when the microwave beam is captured only by a part of said plurality arranged to capture a transmitted electromagnetic wave from said microwave beam (2).

3. System according to claim 1 or 2, characterized in that the transmitting means (1) comprise a phase-controlled array antenna configured to illuminate the scrolling separator (12) at a predetermined scan rate of the microwave beam (2).

4. System according to claim 2 or 3, characterized in that the electronic processing device (6) is further 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 emitted microwave beam (2), to the position, in said plurality arranged to capture a reflected electromagnetic wave, of a diode having captured a reflected electromagnetic wave from said microwave beam (2).

5. System according to claim 2 or 3, characterized in that the electronic processing device (6) is further 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 emitted microwave beam (2), to the position, in said plurality arranged to capture a transmitted electromagnetic wave, of a diode that has not captured a transmitted electromagnetic wave from said microwave beam (2).

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. Battery cell assembly machine comprising the system (10) of any one of the preceding claims.

9. Method for detecting the presence of a metallic particle (11) in a separator (12) intended to be disposed between two electrodes of opposite polarities of a battery cell, this method comprising the following steps - emission (31) of a microwave beam (2); - sliding (32) of the separator (12) in the microwave beam (2);

10.

11. - capture (33), during the passage of the separator (12) in the microwave beam (2), by a diode (5) of a plurality of contiguous diodes (4) sensitive to electromagnetic waves of said microwave beam (2), of a reflected electromagnetic wave of said microwave beam (2) when this plurality is arranged to capture a reflected electromagnetic wave of said microwave beam (2), or of an electromagnetic wave transmitted by the separator (12) of said microwave beam (2) when said plurality is arranged to capture 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 captured by a diode of said plurality arranged to capture an electromagnetic wave reflected from said microwave beam (2);or - when the microwave beam is captured only by a part of said plurality arranged to capture a transmitted electromagnetic wave from said microwave beam (2). Method according to the preceding claim, characterized in that it further comprises a step of determining 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 emitted microwave beam (2), to the position, in said plurality arranged to capture a reflected electromagnetic wave, of a diode having captured a reflected electromagnetic wave from said microwave beam (2). 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 emitted microwave beam (2), to the position, in said plurality arranged to capture a transmitted electromagnetic wave, of a diode that has not captured a transmitted electromagnetic wave from said microwave beam (2).

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