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

Abstract

The invention relates to a system (10) for detecting the presence of a metal particle in a separator (12) intended to be arranged between two electrodes having opposite polarities in a battery cell, the system comprising: - means (1) capable of emitting a microwave beam (2); - means (7) for moving the separator into the microwave beam; - a plurality of contiguous diodes (5) that are sensitive to the electromagnetic waves of the beam, this plurality being arranged so as to capture a reflected electromagnetic wave of the microwave beam or an electromagnetic wave of the microwave beam transmitted by the separator; - a device (6) configured to detect the presence of a metal particle in the separator - when a reflected wave of the beam (2) is captured by a diode of the plurality arranged so as to capture a reflected electromagnetic wave; or - when the beam (2) is captured only by a portion of the plurality arranged so as to capture a transmitted electromagnetic wave.

Description

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 ions to pass between these two electrodes. Direct contact between the two electrodes could cause an internal short circuit and, consequently, damage the battery. Direct contact between the two electrodes prevents the battery from performing 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 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 assemble 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 shards from surrounding devices. Conductive particles can, in fact, detach from these devices and attach themselves to / 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 perforation and direct contact between the two electrodes of opposite polarities, 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 have yet reached their final thickness and may not clearly touch the metal object. Such products can therefore 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 scrolling speed 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 μm, especially when the separator is scrolling 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 can 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 of a battery cell, this system comprising - emission means capable of emitting a microwave beam; - scrolling means making it possible to scroll the separator in the microwave beam; - reception means sensitive to the electromagnetic waves of said microwave beam, these reception means being arranged to pick up, during the scrolling 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 of 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 picked up only by a part of the receiving 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 a reflected electromagnetic wave of said microwave beam; or- when the microwave beam is picked up only by a portion of said plurality arranged to pick up a transmitted electromagnetic wave of 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 pick up a reflected electromagnetic wave, of the diode having picked up 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 a transmitted electromagnetic wave of 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 proposed.

[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 of a battery cell, this method comprising the following steps: - emission of a microwave beam; - movement 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 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 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 picked up only by a part 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 a reflected electromagnetic wave of 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] the figure 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] the figure 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 second embodiment;

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

[0018] Referring to Figures 1 and 2, there is shown a system10 for detecting the presence of a metallic particle11 in a separator12 intended to be arranged between two electrodes of opposite polarities. This system10 comprises transmission means1 capable of emitting a beam2 of microwaves, movement means7 for moving the separator12 in the emitted beam2 of microwaves and reception means3 sensitive to the electromagnetic waves of the beam2 of microwaves to capture electromagnetic waves of this beam2 of microwaves during the movement of the separator12 in this beam of microwaves. An electronic processing device6 is configured to detect, from the measurements from the reception means3, the presence of a metallic particle11 in the separator12.

[0019] Here, the term “microwave beam” is understood to mean a field or area of ​​electromagnetic radiation at one or more predefined frequencies in the microwave domain. This microwave beam 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 are dimensioned so that the emitted microwave beam preferably illuminates the separator moving across its entire width. In one embodiment, the microwave beam has a rectangular cross-section.

[0020] In one embodiment, the transmission means1 comprise an array of antennas configured to radiate a beam2 of microwaves. This array is, for example, a uniform linear array of antennas arranged perpendicular to the direction of travel of the separator12 (in the direction of the width of the separator12 during travel). Alternatively, the transmission means1 comprise a two-dimensional array of antennas.

[0021] In another embodiment, the transmission means1 comprise a phased array antenna. Such an antenna advantageously makes it possible to illuminate the separator12 in an adjustable direction by means of a phase control device. The direction of the microwave beam2 is carried out by electronic scanning. In one embodiment, the phased array antenna is configured to illuminate the separator12 in motion at a predefined scanning speed of the microwave beam2. This scanning speed is preferably linked to the speed of movement of the separator12.

[0022] In another embodiment, the emission means1 comprise a rotating reflector arranged to reflect an incident microwave beam so that the reflected microwave beam scans the separator12 as it moves across its width. The rotation speed of the reflector is preferably linked to the movement speed of the separator12.

[0023] The scrolling means7 comprise, in one embodiment, two rotating rollers arranged to bring the separator12 to be inspected into the microwave beam2. The two rotating rollers are located on either side of the emission means1. In one embodiment, the scrolling means7 are two successive rotating rollers of a battery cell assembly machine. The two rollers are not necessarily specific to the system10, but may be part of an existing battery cell assembly machine. The system10 can thus be easily integrated into an existing battery cell assembly machine.

[0024] The receiving means3 comprise a plurality of contiguous diodes5 sensitive to the electromagnetic waves of said microwave beam2. Each of these diodes5 is capable of capturing an electromagnetic wave of the microwave beam2 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 energy of the electromagnetic wave to which this diode5 is subjected.

[0025] The contiguous diodes5 are regularly distributed over a surface to capture electromagnetic waves from the microwave beam2 at almost any point on this surface. The contiguous diodes5 form, in one embodiment, a carpet4 of diodes. In this carpet4, the diodes5 are arranged in a matrix following a regular pattern of rows and columns of contiguous diodes5. The surface density (i.e. per unit area) of the contiguous diodes5 is chosen so as to be able to capture an electromagnetic wave at almost any point on said carpet4. This density defines, in fact, the detection resolution of the system10. The greater this density, the higher the detection sensitivity of metal particles11. A carpet4 of contiguous diodes advantageously allows for fine spatial sampling for the detection of fine metal particles11 in the separator12.In the attached figures, the dimensions of the diodes5 are enlarged for obvious reasons of clarity. The dimensions of the carpet4 of contiguous diodes5 are chosen so that this carpet4 allows measurements of the microwave beam2 to be taken over the entire width of the separator12.

[0026] Advantageously, a phased array antenna or rotating reflector configured to illuminate the scrolling splitter12 in a variable direction further improves the detection resolution of the receiving means3.

[0027] In a first embodiment illustrated by the, the contiguous diodes5 are arranged to capture, during the movement of the separator12 in the beam2 of microwaves, an electromagnetic wave transmitted by the separator12 of the beam2 of microwaves. For this, the carpet4 of contiguous diodes5 is arranged opposite the transmission means1 so as to be able to capture electromagnetic waves during the movement of the separator12 in the beam of microwaves between the transmission means and this carpet4 of contiguous diodes5. The scrolling means7 cause the separator12 to move between, on the one hand, the transmission means1 and, on the other hand, the reception means3. Given the nature of transmission-reception reciprocity, the relative arrangement of the transmission means1 with respect to the carpet4 of contiguous diodes5 on the is therefore given for illustrative purposes only.More generally, the emission means and the adjacent diodes are arranged on either side of the scrolling separator so that these adjacent diodes can capture electromagnetic waves from the microwave beam passing through the separator.

[0028] The electric current from a diode5 indicates the electromagnetic energy, at that point in the carpet4 of contiguous diodes5, of the microwave beam2 passing through the separator12. Each of the contiguous diodes5 provides a measurement, at the point where that diode5 is located in the carpet4, of the microwave beam2 passing through the separator12. The presence of a metal particle11 in the separator12 causes, at its location in the separator12, a change in the propagation of the microwave beam2. The metal particle11 prevents, at its location in the separator12, at least partially the transmission of the electromagnetic waves of the microwave beam2. The waves of the microwave beam2 undergo reflections and / or diffraction effects when they impact a metal particle11 in the separator12. The microwave radiation from the emission means is most often reflected by the metal particle at its location in the separator.The presence of a metallic particle11 in the separator12 therefore has the effect of rendering at least one corresponding diode5 of the belt4 non-passing so as to reveal the presence of this metallic particle11. This diode5 is in the shadow of the metallic particle11, relative to the microwave beam2 passing through the separator12. On the other hand, outside the position of the metallic particle11 in the separator12, the microwave beam2 propagates through the separator12 in scrolling to the belt of contiguous diodes5. The result, advantageously, is that the belt4 of contiguous diodes5 makes it possible to have a clear two-dimensional image of the microwave beam2 passing through the separator12 in scrolling.

[0029] Based on the data from the contiguous diodes5 arranged to capture an electromagnetic wave transmitted from the microwave beam2, the electronic processing device6 makes it possible, by comparing the intensity of the electric current from each diode5 and / or the evolution of this intensity with predefined threshold values, to determine whether the microwave beam is captured only by a portion of the contiguous diodes5 arranged to capture an electromagnetic wave transmitted from said microwave beam2. In other words, the electronic processing device6 determines whether there is a diode5 that has not captured an electromagnetic wave transmitted by the splitter12 of the microwave beam2.

[0030] When the microwave beam is only picked up by a portion of the contiguous diodes5 arranged to pick up an electromagnetic wave transmitted from the microwave beam2, the electronic processing device6 detects the presence of a metallic particle11 in the separator12. By reading the coordinates of the non-passing diode5 (or, more generally, whose electrical current intensity at its output is below an expected intensity) in the belt4, the electronic processing device6 is able to determine, as a function of the direction of the emitted microwave beam2, the corresponding position of the metallic particle11 detected in the separator12.The position, in the separator12, of a detected metallic particle11 present in the separator12, corresponds, according to the direction of the beam2 of microwaves emitted, to the position, in the mat4 arranged to capture a transmitted electromagnetic wave, of the diode5 which has not captured an electromagnetic wave transmitted from the beam2 of microwaves.

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

[0032] Given the direction of the microwave beam2, when no position in the separator12 corresponds to the position in the mat4 of a non-passing diode5 (i.e. generating an electric current of intensity lower than a predefined threshold value), the electronic processing device6 does not deduce the presence of a metallic particle11 in the separator.

[0033] In a second embodiment illustrated by the, the contiguous diodes5 are arranged to capture, as the separator12 moves through the microwave beam2, an electromagnetic wave reflected from the microwave beam2. In this case, the system10 operates in reflection mode in which the electronic processing device6 detects the presence of a metal particle11 in the separator12 when a reflected wave from the microwave beam2 is captured by a diode5 of the belt4 arranged to capture an electromagnetic wave reflected from the microwave beam2. The position, in the separator12, of a detected metal particle11 present in this separator12, corresponding, according to the direction of the emitted microwave beam2, to the position, in the belt4 of contiguous diodes5 arranged to capture a reflected electromagnetic wave, of the diode having captured an electromagnetic wave reflected from the microwave beam2.

[0034] The emission means on the one hand and the adjacent diodes on the other hand are arranged on the same side relative to the moving separator to be controlled so that any one of these adjacent diodes can pick up an electromagnetic wave reflected from the microwave beam by a possible metallic particle in the separator. Such a configuration has an advantage in the case of a lack of access to one face of the moving separator.

[0035] The system10 measures the transmission of the scrolling separator12 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 separator12 to microwave radiation and the properties of obstruction or reflection of the microwave radiation by a possible metallic particle11 present in the separator12. The detection of a metallic particle11 in the separator12 can therefore be carried out by observing its transmission, its reflection, or both at the same time. The emission means1 and the contiguous diodes5 are, preferably, arranged fairly close to the moving separator12, at a distance of the order of the wavelength so that the electromagnetic energy of the microwave beam2 is not dissipated.

[0037] In order to prevent the receiving means3 from picking up parasitic waves, the adjacent diodes5 and / or the transmitting means1 are preferably supported by layers of a material absorbing electromagnetic waves from the microwave beam2. These layers cover the inner faces of the support frame of the system10 (in particular, the face facing the transmitting means1 in the case of the second embodiment presented above) to minimize the interactions of the support frame with the microwave beam2 in the manner of an anechoic chamber. A tunnel conformation of the opposite lateral faces through which the separator12 passes further improves the coupling of the transmitting and receiving means1,3.

[0038] Upon detection of a metal particle in the separator, the electronic processing device 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 metal particle or isolate the section of the separator incorporating this metal particle.

[0039] Referring to the, steps of a method implementing the means presented above are shown for detecting the presence of a metallic particle11 in a separator12 intended to be arranged between two electrodes of opposite polarities. This method comprises a step of emitting31 a beam2 of microwaves, a step of passing32 the separator12 in the microwave beam.

[0040] When the separator12 is moving in the microwave beam2, a step of capturing33 an electromagnetic wave reflected from the microwave beam2 or an electromagnetic wave transmitted by the separator12 of the microwave beam2 is implemented by at least one diode5 of the carpet4 of contiguous diodes5 sensitive to the electromagnetic waves of the microwave beam2.

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

[0042] During a location step35, the electronic processing device6 determines the position, in the separator12, of a detected metal particle11 present in the separator12. This position corresponds, according to the direction of the emitted microwave beam2, to the position, in the carpet of contiguous diodes5 arranged to pick up a transmitted electromagnetic wave, of the diode that has not picked up a transmitted electromagnetic wave from the microwave beam2. In the case of operation in reflection mode, the position of the detected metal particle11 present in the separator12 corresponds, according to the direction of the emitted microwave beam2, to the position, in the carpet4 of contiguous diodes5 arranged to pick up a reflected electromagnetic wave, of the diode that picked up a reflected electromagnetic wave from the microwave beam2.

[0043] Advantageously, the embodiments presented above allow non-destructive testing of the separator12 (without physical contact with the separator), implementing an excitation signal in the form of a microwave beam and a carpet of contiguous diodes5 to observe the transmission and / or reflection of the moving separator12. Without disturbing the production flow, the system10 can be integrated into a free space between two successive rotating rollers ahead 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 running speeds of the separator12.

Claims

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 of a battery cell, 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).; 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 an electromagnetic wave reflected from said microwave beam (2); or - when the microwave beam is picked up only by a part of said plurality arranged to pick up an electromagnetic wave transmitted from said microwave beam (2). System according to claim 1 or 2, characterized in that the transmission means (1) comprise a phased array antenna configured to illuminate the separator (12) moving at a predefined scanning speed of the microwave beam (2). 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. 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. 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). 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). A battery cell assembly machine comprising the system (10) of any preceding claim. Method for detecting the presence of a metallic particle (11) in a separator (12) intended to be arranged between two electrodes of opposite polarities of a battery cell, 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 microwave beam (2), by a diode (5) of a plurality of contiguous diodes (4) sensitive to the electromagnetic waves of said microwave beam (2), of an electromagnetic wave reflected from said microwave beam (2) when this plurality is arranged to capture an electromagnetic wave reflected from 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 metal 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 only picked up by a portion of said plurality arranged to pick up an electromagnetic wave transmitted from said microwave beam (2).; 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. 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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