Device, system and method for heating and / or drying a material layer using microwaves, filter element, and use of the device

Abstract

The invention relates to a device (100), a system and a method for heating and / or drying a material layer, in particular an electrically conductive material layer, using microwaves. The device (100) comprises: - at least two waveguides (10a, 10b) which are arranged parallel to one another; - at least one microwave source for coupling microwaves into the at least two waveguides (10a, 10b); and - a filter element (20) which forms a guide channel (30) with the at least two waveguides (10a, 10b), wherein the guide channel (30) allows the material layer to be guided through the at least two waveguides (10a, 10b) and the filter element (20) in a guide plane (E), and wherein the filter element (20) has at least one waveguide decoupling filter (25), which is in each case arranged between two adjacent waveguides (10a, 10b) of the at least two waveguides (10a, 10b) and is designed to electromagnetically decouple the adjacent waveguides (10a, 10b). The present invention also relates to a filter element (20) and to a use of the device (100) according to the invention.

Description

[0001] Applicant: Karlsruhe Institute of Technology, a public corporation “Device, system and method for heating and / or drying a layer of material using microwaves, filter element, and use of the device”

[0002] MB&P code: K07712WO - ksc / msc

[0003] Description

[0004] The invention relates to a device, a system, and a method for heating and / or drying a material layer, particularly an electrically conductive one, using microwaves. The invention further relates to a filter element, particularly for use in the device according to the invention, and to a use of the device.

[0005] For example, in battery and / or fuel cell manufacturing, it is necessary to dry the electrode materials used in the batteries or fuel cells. Conventionally, the electrodes are applied to a substrate (e.g., made of aluminum or copper) and heated using hot air and / or radiant heaters. However, drying such materials with these conventional methods is very energy- and time-intensive. Industrial systems for drying electrode materials are typically up to 100 meters long to achieve acceptable production rates. Previous attempts to dry electrodes using microwaves have failed, primarily because these electrode materials inherently possess significant electrical conductivity, resulting in insufficient microwave penetration depth for efficient heating.For example, the penetration depth of microwaves in good electrical conductors (such as silver, copper, gold or aluminum) using the industrial frequency of 2.45 GHz is in the range of a few micrometers.

[0006] It is therefore an object of the present invention to improve the heating and / or drying of material layers, in particular material layers with good electrical conductivity (e.g., at least 10 S / m). This object is achieved by the subject matter of the dependent claims.

[0007] Advantageous embodiments are the subject of the dependent claims.

[0008] A first independent aspect of solving the problem concerns a device for heating and / or drying a material layer using microwaves, comprising: at least two waveguides arranged parallel to each other; at least one microwave source for coupling microwaves into the at least two waveguides; and a filter element which forms a guide channel with the at least two waveguides, wherein the guide channel enables the material layer to be guided through the at least two waveguides and the filter element in a guide plane, and wherein the filter element includes at least one waveguide decoupling filter (or...a waveguide decoupling filter structure) which is arranged and designed between two adjacent waveguides of the at least two waveguides to electromagnetically decouple the adjacent waveguides (between which one of the at least one waveguide decoupling filter is arranged).

[0009] The material layer to be heated or dried can be an electrically conductive material layer, such as an electrode layer (especially for batteries and / or fuel cells). For example, the material layer can have an electrical conductivity of at least 10 S / m, in particular at least 100 S / m, and in particular at least T10. 3 S / m, in particular at least T10 4 S / m, in particular at least T10 5 S / m, or in particular at least T10 6The material layer to be heated or dried can be applied to a substrate. The substrate can be electrically insulating (e.g., a plastic film) or electrically conductive or metallic (e.g., aluminum or copper foil). In particular, the material layer can be in the form of a material strip or film. The heating and / or drying process includes, or is in particular, inductive heating, meaning that the heating and / or drying is carried out (essentially) with the aid of a magnetic field (microwaves).

[0010] For the purposes of this description, "microwaves" refers to electromagnetic waves, particularly in a frequency range of 300 MHz and 300 GHz, or a wavelength range of 1 mm to 1 m. For example, microwaves in the industrial frequency band at 2.45 GHz can be used for the device or method described herein.

[0011] In this description, "waveguide" refers specifically to a waveguide for guiding electromagnetic waves or microwaves. Preferably, the waveguides are rectangular waveguides or rectangular hollow conductors. It is understood, however, that other waveguides or hollow conductors capable of guiding microwaves can also be used. The at least two waveguides are arranged parallel to each other, particularly with respect to their longitudinal axes and / or a wave propagation direction, and have the same cross-sectional geometry.

[0012] The "microwave source" can be, for example, a microwave oscillator (e.g., a magnetron) or a (particularly adjustable) microwave amplifier (e.g., a klystron, traveling-wave tube, or a semiconductor-based microwave amplifier). In particular, the device can comprise at least two microwave sources. Specifically, each of the at least two waveguides can have its own associated microwave source. Thus, the device can, for example, comprise as many microwave sources as waveguides. However, it is also possible for the number of waveguides and the number of microwave sources to differ. This is the case, for example, if the power from one microwave source is coupled into more than one waveguide, or if the power from several microwave sources is first combined and then the combined power is coupled into a waveguide.The "filter element" is made of an electrically conductive material, preferably a metal such as aluminum, copper, or brass. For example, the filter element can be made of a stainless steel sheet, particularly with a coating of, for example, gold and / or silver. Specifically, a waveguide decoupling filter belonging to two adjacent waveguides is arranged such that a first end section (or a first end) of a connecting channel belonging to this waveguide decoupling filter opens into a longitudinal slot of the first of the adjacent waveguides, and a second end section of said connecting channel opens into a longitudinal slot of the second waveguide of the adjacent waveguides. The connecting channel belonging to a waveguide decoupling filter is part of the guide channel.The guide channel is formed in particular by longitudinal slots in the waveguides and the connecting channels of the waveguide decoupling filters arranged between two adjacent waveguides.

[0013] In this description, "adjacent waveguides" refers specifically to immediately adjacent waveguides, i.e., two waveguides between which no further waveguide is arranged. In particular, each waveguide decoupling filter represents a connecting element between any two adjacent waveguides, wherein the connecting element comprises a channel or connecting channel. The connecting or guiding channel has a height that is greater than or equal to the thickness of the material layer to be heated or dried and / or of a support on which the material layer to be heated or dried is located. The connecting or guiding channel has a width that is greater than or equal to the width of the material layer to be heated or dried and / or of a support on which the material layer to be heated or dried is located.The connecting channel has a length that corresponds to the distance between the adjacent waveguides.

[0014] In particular, each waveguide decoupling filter has a connecting channel through which the material layer to be heated or dried can be passed (or transported). The material layer can thus be transported, at least partially, from one of the at least two waveguides to an adjacent waveguide.

[0015] In particular, each pair of adjacent waveguides of at least two waveguides is mechanically and electrically connected to each other via the filter element or via a waveguide decoupling filter of the filter element (belonging to the adjacent waveguides). Each waveguide decoupling filter is designed to electromagnetically decouple the waveguides connected by the respective waveguide decoupling filter. In particular, this means that the electromagnetic wave propagating in the connecting or guide channel is almost completely reflected by the waveguide decoupling filter (acting as an impedance converter), resulting in virtually no power being coupled from one waveguide to its adjacent waveguide. The individual waveguides thus behave essentially as if they were each closed (i.e., in particular, without any opening or...(would not have a slot for transporting the layer of material to be heated or dried).

[0016] In addition to at least one waveguide decoupling filter or waveguide decoupling filter structure, the device preferably comprises one or more further filters or filter structures, namely, in particular, an input filter (or an input filter structure) and / or an output filter (or an output filter structure). The input filter is specifically designed to introduce the material layer (essentially) without leakage radiation into a first of the at least two waveguides. Accordingly, the input filter can also be referred to as a layer introduction filter. The output filter is specifically designed to guide the material layer out of a further or last of the at least two waveguides (essentially) without leakage radiation. Accordingly, the output filter can also be referred to as a layer discharge filter.Preferably, the input filter and / or the output filter each have a filter structure that is similar to or identical with the waveguide decoupling filter structure. The input filter serves to electromagnetically decouple the waveguide arranged at an input of the device (also referred to as the first waveguide of the device in this description) from its surroundings. Similarly, the output filter serves to electromagnetically decouple the waveguide arranged at an output of the device (also referred to as the last waveguide of the device in this description) from its surroundings. The "input" of the device is understood to be a region of the device into which the material layer to be heated or dried can be introduced. Similarly, the "output" of the device is understood to be a region of the device into which the material layer to be heated or dried can be introduced.The material layer to be dried can be conveyed out of the device. In particular, the input filter and / or the output filter each have a structure with a plurality of hollow longitudinal and transverse channels, each of which is open at a first end of these longitudinal or transverse channels (which faces the guide channel of the filter element) and closed or short-circuited at an opposite second end of these longitudinal or transverse channels (which faces away from the guide channel of the filter element), and which each have a dimension (in particular depth) in a direction perpendicular to the longitudinal axis of the waveguides (and / or perpendicular to the flow or transport direction of the material layer) that corresponds to an odd multiple of a quarter of the wavelength of a microwave coupled into the waveguides for heating and / or drying the material layer.In particular, depending on the intensity of the leakage radiation present, several input and / or output filter structures can be arranged in series. The input filter and the output filter each contribute to preventing the microwave from escaping the waveguides. Specifically, the input filter and the output filter each serve to decouple the waveguides from the environment and thus prevent leakage radiation.

[0017] The present invention enables the particularly efficient and uniform heating and drying of material layers using microwaves. It allows for the use of inductive heating and drying based on a microwave magnetic field. Specifically, the filter element or waveguide decoupling filter allows for the electromagnetic decoupling of adjacent waveguides, thereby achieving a very precisely defined single-mode field distribution (e.g., the TE10 mode) within the waveguides. This results in uniform heating and drying of the material layer. The invention allows for the provision of systems that are scalable to any number of parallel waveguides in the direction of travel of the material layer to be heated or dried.

[0018] In particular, wave propagation can be based (essentially and / or exclusively) on a single (predefined or predetermined) mode, e.g., the fundamental mode TE10. Accordingly, a predefined or predetermined field distribution can also be present. Specifically, a regular resonant field in a predefined or predetermined mode, e.g., the TEw fundamental mode, can be generated by the filter element. Advantageously, therefore, no mode conversion is required or provided within the scope of the present invention, in which the field distribution would be (more or less) left to chance.

[0019] The waveguides are preferably aligned orthogonally to the direction of travel or transport of the material layer to be heated and / or dried. The waveguides are operated in resonance. In other words, resonant waveguides are used. The operating principle described within the scope of the invention is therefore based primarily on resonance and not on a traveling wave. This resonance is made possible primarily by the filter element. In other words, the resonance condition is created primarily by the filter element. The filter element serves, in particular, to match the impedance.

[0020] In a preferred embodiment, the device comprises a guide or transport unit for generating relative movement between the material layer to be heated or dried and the guide channel in the guide plane. The guide unit can, for example, be a conveyor belt system. In particular, the guide unit can include transport rollers by means of which the material layer can be guided or transported through the guide channel of the device, and / or the device or the guide channel of the device can be moved relative to the material layer.

[0021] In a further preferred embodiment, each waveguide has two opposing longitudinal slots through which the material layer can be passed, the longitudinal slots of the waveguides being arranged such that the guide plane runs through each longitudinal slot. Preferably, the longitudinal slots (or longitudinal axes of the longitudinal slots) of each of the at least two waveguides extend parallel to a longitudinal axis of the waveguide. In other words, the longitudinal slots of each of the at least two waveguides extend from a first axial end section to a second axial end section of the respective waveguide. Preferably, the longitudinal slots (or longitudinal axes of the longitudinal slots) of each of the at least two waveguides extend parallel to a propagation direction of the microwaves in the respective waveguide. The guide plane extends parallel to the longitudinal slots (or longitudinal axes of the longitudinal slots).The material layer's direction of travel or transport is parallel to the guide plane and perpendicular to the longitudinal slots (or their longitudinal axes). The waveguides can, for example, be rectangular waveguides. In this case, specifically when the waveguides each have a rectangular cross-section, the two longitudinal slots of a waveguide are formed on opposite walls along one long side of the waveguide. The longitudinal slots of the waveguides are, in particular, a component of the guide channel in the guide plane.

[0022] The longitudinal slots of the waveguides are preferably arranged such that, in a plane or the guide plane (particularly in a region of the guide plane) between the opposing longitudinal slots of the respective waveguide, the RMS value of an electric field present in the respective waveguide due to microwaves coupled into the respective waveguide (for the purpose of heating and / or drying) is minimal and / or smaller than a predetermined threshold value for the electric field. The predetermined threshold value for the electric field is preferably 20%, more preferably 10%, and even more preferably 5% of a maximum RMS value of the electric field of the microwaves coupled into the waveguide. Preferably, the RMS value of the electric field (in this plane) is zero. Alternatively or additionally, the longitudinal slots of the waveguides are preferably arranged such that, in a plane or the guide plane, the RMS value of the electric field is approximately zero.The effective value of a magnetic field present in the respective waveguide (due to microwaves coupled into the waveguide for heating and / or drying) is maximum and / or greater than a predetermined threshold value for the magnetic field. The predetermined threshold value for the magnetic field is preferably 80%, more preferably 90%, and even more preferably 95% of the maximum effective value of the magnetic field of the microwaves coupled into the waveguide. The maximum effective value depends in particular on the microwave power coupled into the waveguide. The coupled microwave power, in turn, is selected depending in particular on the temperature increase to be achieved in the respective waveguide pair and / or the absorption behavior of the material layer.The terms "minimal" and "maximum" refer to the dependence of the RMS value of an electric or magnetic field on the position of the longitudinal slots (especially relative to the respective waveguide) and / or the position of the guide plane (especially relative to the waveguides). The position of the longitudinal slots or the position of the guide plane can be defined, for example, by a distance from a longitudinal axis of the waveguide and / or by a distance from a side face or side wall of the waveguide (especially parallel to the longitudinal axis of the waveguide). In particular, the RMS value of an electric field present due to microwaves coupled into the respective waveguide (for the purpose of heating and / or drying) is minimal with respect to a position of the longitudinal slots of the waveguides and / or a position of the guide plane relative to the waveguides.Alternatively or additionally, the RMS value of a magnetic field present due to microwaves coupled into the respective waveguides (for the purpose of heating and / or drying) is maximized with respect to a position of the longitudinal slots of the waveguides and / or a position of the guide plane relative to the waveguides. An "RMS value" is understood, as is common in electrical engineering, to be the root mean square of a time-varying physical quantity (here, the electric or magnetic field of the microwaves). In particular, the RMS value of the variable physical quantity is as large as the value of an equivalent quantity that would dissipate the same electrical energy in a resistive load over a representative period of time as the time-varying quantity.In particular, the RMS value of a sinusoidal electric field coupled into the waveguides in the form of microwaves is 1 / V² of the amplitude of the electric field. Similarly, the RMS value of a sinusoidal magnetic field coupled into the waveguides in the form of microwaves is 1 / V² of the amplitude of the magnetic field.

[0023] In a further preferred embodiment, the guide channel (and / or the guide plane) is positioned relative to the waveguides depending on a microwave mode provided (and / or predetermined) for heating and / or drying the material layer. Similarly, the longitudinal slots are also positioned in the respective waveguide depending on a microwave mode provided (and / or predetermined) for heating and / or drying the material layer.

[0024] In a further preferred embodiment, the guide channel and / or the guide plane extends decentrally through the at least two waveguides. Accordingly, the longitudinal slots are also arranged decentrally in the waveguides. In other words, the guide channel and / or the guide plane preferably does not extend centrally through the waveguides, i.e., in particular not through the centers of the individual waveguides. The longitudinal slots are also preferably not arranged centrally in the waveguides and, in particular, do not extend through the centers of the individual waveguides. In other words, the guide channel or the guide plane is preferably spaced apart from a center and / or a central plane of the waveguide with respect to each of the at least two waveguides. The reason for this is that the waveguides are preferably operated in a fundamental mode, particularly preferably in the TE10 mode. If a rectangular waveguide is used, for example,When operated in TE10 mode, a high or maximum effective electric field is present in the center and / or in a central plane of the waveguide. If an electrically conductive material layer is guided through such a region of the waveguide where a high or maximum electric field is present, the microwaves in the waveguide, particularly in this region, are no longer able to propagate. Effective and uniform heating and / or drying of an electrically conductive material layer is therefore not possible under such conditions. Preferably, the guide channel thus runs through regions of the waveguide where the electric field (or its RMS value) is minimal or ideally zero, and where, preferably, the magnetic field (or its RMS value) is maximal. When a rectangular waveguide is operated in TE10 mode, such a region, where the electric field (or its RMS value) is minimal or ideally zero, is present in the center and / or in a central plane of the waveguide.The point where the effective value (RMS value) is minimal and the magnetic field (or its RMS value) is maximal is found in or in the immediate vicinity of the waveguide face or side wall spanned by the shortest side (i.e., the side in the y-direction) and the longest side (i.e., the side in the z-direction) of the waveguide. The z-direction is parallel to the longitudinal axis of the waveguide and thus also parallel to the direction of microwave propagation within the waveguide. The y-direction is the direction perpendicular to the longitudinal axis and perpendicular to the direction of microwave propagation within the waveguide, and in which a short side of the waveguide extends. The x-direction is the direction perpendicular to the longitudinal axis and perpendicular to the direction of microwave propagation within the waveguide, and in which a longer side of the waveguide (compared to the short side) extends.Preferably, the guide channel and / or the guide plane runs parallel to and / or in the immediate vicinity of those side faces of the (rectangular) waveguides that extend in the yz-plane. In particular, the guide channel runs through a region of an upper or lower side face, i.e., preferably in the region of one of the two narrow side faces of the at least two, preferably rectangular, waveguides. In particular, one side wall of each of the at least two waveguides (preferably a side wall in the yz-plane) can be formed by the guide channel. In particular, the (electrically conductive) material layer in the guide channel, which is to be heated and / or dried, can assume the function of the waveguide wall.In this way, the magnetic field (and not the electric field) of the microwaves coupled into the waveguides can be used primarily for heating and / or drying the material layer. In other words, the heating and / or drying of the material layer can advantageously be carried out inductively, so that the device is particularly suitable for heating and / or drying electrically conductive material layers.

[0025] In principle, it is possible to arrange the longitudinal slots of the waveguide and the filter element such that the guide channel runs centrally through the waveguide. In this case, when using the preferred TE10 mode, the material layer is guided through a maximum of the electric field strength. This has the advantage that the longitudinal slots in the waveguide do not influence wall currents, and thus no microwaves are coupled out of the waveguide through the slots. However, such an arrangement is primarily suitable for heating and / or drying dielectric layers. This is because, as mentioned above, electrically conductive layers positioned at the maximum of the electric field strength prevent the microwave field from propagating in this region.This means that with material layers several tens of centimeters wide, certain areas of these layers (namely, those located too far from the microwave source) within the waveguide can no longer be reached by the microwaves and therefore cannot be heated. Even with material layers 10 cm wide or less, the microwaves are attenuated so strongly across the width of the layer, given electrical conductivities on the order of 100 S / m, that microwave heating would no longer be effective due to the resulting high temperature gradient. Therefore, for electrically conductive material layers (especially those several tens of centimeters wide, e.g., 100 cm and more), it is advantageous to route the material layer through a magnetic field maximum rather than an electric field maximum within the waveguide.In other words, in these cases it is advantageous to use inductive heating instead of dielectric heating. As has been shown within the scope of the present invention, such inductive heating is possible in a particularly uniform manner, especially by using one or more filters for electromagnetic decoupling of adjacent waveguides. In particular, the filter element serves to impedance-match off-center slots in the waveguides (which would conventionally have been considered "electromagnetically unfavorable slots") in order to reduce the disturbance of the electromagnetic field in the waveguides. The filter element allows a regular resonant field to form in a predefined or predetermined mode, e.g., the TEw fundamental mode.

[0026] In a further preferred embodiment, the filter element comprises at least one microwave trap, in particular at least one quarter-wave trap. Specifically, the at least one waveguide decoupling filter is designed to function as a microwave trap, in particular a quarter-wave trap. Such a microwave trap enables electromagnetic decoupling of two adjacent waveguides.

[0027] In a further preferred embodiment, the filter element or the at least one waveguide decoupling filter has a waffle iron structure. Alternatively or additionally, the filter element or the at least one waveguide decoupling filter comprises a structure with a plurality of hollow longitudinal and transverse channels, each of which is open at a first end (of these longitudinal or transverse channels), which is particularly facing the connecting or guide channel of the filter element, and closed or short-circuited at an opposite second end (of these longitudinal or transverse channels), which is particularly facing away from the connecting or guide channel of the filter element, and which each extends in a direction perpendicular to the longitudinal axis of the waveguide (and / or perpendicular to the flow or...).The waveguides (in the direction of transport of the material layer) have a dimension (especially depth) that corresponds to an odd multiple of a quarter of the wavelength of a microwave coupled into the waveguides for heating and / or drying the material layer. In this way, the electromagnetic wave propagating in the connecting or guiding channel is almost completely reflected by the waveguide decoupling filter (which acts primarily as an impedance converter), resulting in virtually no power being transferred from one waveguide to the adjacent waveguide.

[0028] In a further preferred embodiment, each waveguide, particularly at an end section of the respective waveguide facing away from the respective microwave source (which is also referred to in this description as the second axial end section of the respective waveguide), has a short circuit or a short-circuit element (or reflection element) for reflecting microwaves within the respective waveguide, preferably displaceable in the axial direction of the waveguide. The short circuits or short-circuit elements of two adjacent waveguides are preferably arranged axially offset from each other by an odd multiple of one-quarter of the wavelength of a microwave coupled into the waveguides for heating and / or drying the material layer.In the event that the device comprises N waveguides, the short circuits or short-circuit elements of each adjacent waveguide of the N waveguides can be in. axial direction of the waveguides each around the wavelength of one each into the Waveguides for heating and / or drying the material layer are arranged offset from one another by the microwaves coupled in, where N is a natural integer with N > 2. Short circuits or short-circuiting elements can be used to create a standing electromagnetic wave in each waveguide. By offsetting the short circuits or short-circuiting elements as described above, particularly uniform heating and / or drying of the material layer can be advantageously achieved. It should be noted that the lengths of the individual waveguides can be identical or different (taking into account the microwave frequency and the geometry of the device). The offset position of the short circuits or short-circuiting elements is the primary factor in achieving uniform heating and / or drying.

[0029] In a further preferred embodiment, a coupling and reflection element, or iris, is arranged at a first axial end section of each of the at least two waveguides for coupling a microwave into the respective waveguide and reflecting the microwave inside the respective waveguide. Such an iris, which functions as a kind of aperture, is conventionally used in waveguides to correct impedance mismatch and to prevent harmful reflections. The iris can be, for example, inductive, capacitive, or resonant. For instance, an iris can comprise a thin metal plate, which is arranged in the waveguide, in particular transversely to the direction of propagation, and which in particular represents a discontinuity in the wave propagation.Within the scope of the invention, the iris does not serve to correct a mismatch, but rather, in particular, as a coupling element into a (downstream) waveguide, which preferably has a short circuit at its end. In this way, a waveguide resonator can be realized. The length of the waveguide resonator (distance between the iris and the short circuit) preferably corresponds to an integer multiple of half the microwave length. Alternatively or additionally, a short-circuit slider (displaceable in the axial direction of the waveguide) for reflecting the microwave within the respective waveguide is preferably arranged at a second axial end section of each of the at least two waveguides. For the purposes of this description, the first axial end section of a waveguide is understood to be the end section designed to couple a microwave into the waveguide.The second axial end section of the waveguide is opposite the first axial end section. Using the iris and / or the short-circuiting slider, it is advantageous to create a standing wave in each waveguide, causing the waveguide to function as a resonator. This significantly increases the efficiency of heating and / or drying.

[0030] In a further preferred embodiment, the device comprises a wavelength testing device for each waveguide for determining any difference between the actual wavelength of a microwave present in the respective waveguide and a predetermined target wavelength. The wavelength testing device particularly comprises two measuring probes, which can be attached to or are attached to the respective waveguide for coupling out a measurement signal (in particular, a power signal) and which are spaced apart in an axial direction of the respective waveguide at a distance corresponding to a multiple of half the target wavelength. Furthermore, the device preferably comprises a wavelength adjustment device for adapting the actual wavelength to the target wavelength based on the determined difference. In particular, the wavelength adjustment device is designed to adjust the frequency or...The wavelength of the microwaves coupled into the waveguides is to be changed or adjusted. In particular, the wavelength adjustment device can include a control unit designed to adjust one or more frequencies of the at least one microwave source and / or the position of the shorting sliders. In the resonant design using an iris, if the wavelength in the resonator changes (e.g., due to a minimal change in the guide plane of the material layer and / or the waveguide cross-section as a result of thermal expansion), the wavelength must also be adjusted by changing the frequency. If the length of the resonator changes in the resonant design (e.g., due to thermal expansion), the position of the shorting slider must be changed so that the resonator is resonant again at the target wavelength.

[0031] In a further preferred embodiment, the device comprises at least one signal transmission unit designed to transmit one or more feedback signals from the at least two waveguides (10a, 10b) to the at least one microwave source, in particular from each waveguide to its respective associated microwave source. In particular, a signal (especially frequency and / or power) can be coupled out at a suitable location in a (resonant) waveguide. This coupled-out signal and / or a modified signal based on the coupled-out signal can be transmitted as a feedback signal to the at least one microwave source (or the at least one microwave amplifier). By means of the signal transmission, or...Feedback can be used to regulate the frequency and / or power of at least one microwave source. In particular, the difference to a predefined resonant frequency at the at least one microwave source can be compensated for. Signal transmission can be wired or wireless. Specifically, the operating frequency of the at least one microwave source (or the at least one microwave amplifier) ​​can be automatically set or adjusted to a predefined resonant frequency. In other words, the signal transmission makes it possible to "lock" the operating frequency of the at least one microwave source to the predefined resonant frequency. This significantly simplifies the adjustment of the operating frequency and makes the device more efficient.

[0032] The scalability of the device in the direction perpendicular to the direction of travel or transport of the material layer to be heated or dried (i.e., scalability with respect to the width of the material layer) is generally limited by the electrical conductivity of the material layers, since the power of the microwaves decreases with the direction of propagation due to absorption in the material layer. To avoid a power gradient and thus also a possible gradient in heating as much as possible, it is advantageous for the device to have an associated microwave source for each waveguide, and for the microwave sources to be arranged alternately from one waveguide to the next, i.e., on opposite sides or axial ends of the waveguides. For example, if a microwave source belonging to a waveguide is located at a first (e.g.,If a microwave source is arranged at the left axial end of the waveguide, a microwave source belonging to an adjacent waveguide is preferably arranged at a second axial end (e.g., the right axial end) of the adjacent waveguide, opposite the first axial end. Thus, in a further preferred embodiment, the device comprises an associated microwave source for each waveguide, wherein the microwave sources belonging to any two adjacent waveguides are each arranged at different (in particular, opposite) axial ends of the waveguides. In other words, the microwave sources of adjacent waveguides are arranged alternately at the axial ends of the respective waveguides. In this way, the most uniform possible heating or drying (in a direction perpendicular to the direction of passage or transport) can be achieved when the material layer is passed through the guide channel of the device.In a preferred embodiment, the guide channel passes through a region of an upper or lower side surface of the at least two waveguides.

[0033] In a preferred embodiment, one side wall of each of the at least two waveguides is formed by the guide channel.

[0034] In a preferred embodiment, the guide channel is designed and / or arranged such that the material layer to be heated and / or dried in the guide channel takes on the function of a waveguide wall.

[0035] Another independent aspect for solving the problem relates to a system for (in particular, on both sides) heating and / or drying a material layer, comprising: at least two devices according to the invention; and a (common) guide unit for generating a relative movement between the material layer and a common guide channel in a common guide plane, wherein the at least two devices are arranged such that all guide planes of the at least two devices coincide and form the common guide plane, and that the common guide channel is formed by the guide channels of the at least two devices.

[0036] Preferably, the at least two devices according to the invention comprise a plurality, in particular an even number (e.g., 2, 4, 6, 8, etc.), of devices according to the invention. With the aid of the guide unit, which can, for example, be a conveying unit, the material layer can be guided, in particular at least partially, simultaneously or sequentially, through each of the at least two devices (e.g., similar to a conveyor belt). Preferably, the guide channel (and thus also the guide planes and the longitudinal slots) of the at least two devices according to the invention each run parallel to and in close proximity to a side surface of the respective waveguide (preferably rectangular waveguide). By a suitable arrangement of the at least two devices according to the invention, it is advantageously possible to heat and / or dry the material layer not only on one side, but also on both sides or double sides.

[0037] Bilateral or double-sided heating and / or drying can be achieved, for example, by the system comprising at least one first device and at least one second device according to the invention, wherein the at least one first and the at least one second device according to the invention are arranged such that their guide planes coincide or form the common guide plane. The guide channel (and thus also the guide plane and the longitudinal slots) of the at least one first device and the guide channel (and thus also the guide plane and the longitudinal slots) of the at least one second device according to the invention preferably each run parallel to and in close proximity to a side surface of the respective waveguide (preferably rectangular waveguide).Preferably, the at least one second device according to the invention is arranged in a mirror-symmetrical manner with respect to the common guide plane relative to the at least one first device according to the invention. In other words, each of the at least one second device according to the invention is preferably arranged in a mirror-symmetrical manner with respect to the common guide plane relative to its respective first device according to the invention. In particular, the filter structures of the waveguide decoupling filters are arranged both above and below the common guide channel in this embodiment. Thus, it is advantageously possible to heat or dry both sides of the material layer simultaneously.

[0038] Alternatively or additionally, double-sided heating and / or drying can be achieved by having a first (e.g., upper) side surface of the waveguides (preferably rectangular waveguides) in a subset (preferably half) of the at least two devices of the system according to the invention run parallel to and in the immediate vicinity of the respective guide channel (and thus also to the guide plane and the longitudinal slots), while in the remaining (preferably the other half) of the at least two devices according to the invention, a second (e.g., lower) side surface of the waveguides (preferably rectangular waveguides) runs parallel to and in the immediate vicinity of the respective guide channel (and thus also to the guide plane and the longitudinal slots), wherein the second side surface of the waveguides is opposite the first side surface of the waveguides.In other words, the at least two devices are arranged in such a way that, for all devices from a subset of the at least two devices, a first side surface of the waveguides of these devices runs parallel to and in the immediate vicinity of the common guide channel, and that, for the remaining devices of the at least two devices, a second side surface of the waveguides of these remaining devices runs parallel to and in the immediate vicinity of the common guide channel, wherein the first and second side surfaces of the waveguides are opposite side surfaces of the waveguides.

[0039] In a preferred embodiment, the system thus comprises at least one first device according to the invention and at least one second device according to the invention, wherein, according to a first variant, the at least one first device according to the invention and the at least one second device according to the invention are arranged in a mirror-image fashion relative to each other. In particular, in this first variant, the at least one first and the at least one second device according to the invention of the system are offset from each other and / or (with respect to a flow direction of the material layer) arranged one after the other or one after the other. In particular, in this first variant, all devices according to the invention of the system are offset from each other and / or (with respect to a flow direction of the material layer) arranged one after the other.According to a second embodiment, the at least one second device according to the invention is arranged in a mirror-symmetrical manner with respect to the common guide plane relative to the at least one first device according to the invention. In particular, in this second embodiment, each of the at least one second device according to the invention is arranged in a mirror-symmetrical manner with respect to the common guide plane relative to a first device according to the invention belonging to the respective second device according to the invention. In the context of this description, such a mirror-symmetrical arrangement means in particular that each of the at least one second device according to the invention can be mapped onto a first device according to the invention belonging to the respective second device according to the invention by means of a reflection across the common guide plane. In particular, in this second embodiment, the devices according to the invention are arranged such that the object to be heated or...The material layer to be dried passes through the system simultaneously through a first device according to the invention and a second device according to the invention. In particular, one of the at least one first device according to the invention and one belonging to the at least one second device according to the invention (with respect to a flow direction of the material layer) are not arranged one behind the other, but one above the other. In both the first and the second variant, the material layer, particularly when passing through the individual devices according to the invention, can advantageously be separated on one side of the material layer by the at least one first device according to the invention or a subset (e.g., half) of the at least two devices of the system and by the at least one second device according to the invention or by the remaining (e.g.,(the other half) of the system, at least two devices on the second side of the material layer, which faces the first side of the material layer, are heated or dried. While the heating and / or drying of the first and second sides of the material layer occurs sequentially in the first variant described above, in the second variant described above both sides of the material layer are heated or dried simultaneously.

[0040] Another independent aspect of solving the problem relates to a filter element (particularly for use in a device according to the invention) comprising: a connecting channel designed to connect two parallel waveguides and to guide a material layer from one of the two waveguides to the other; and a filter structure (waveguide decoupling filter or waveguide decoupling filter structure) designed to electromagnetically decouple the two waveguides. In a preferred embodiment, the filter element comprises a further filter structure, namely an inlet filter structure, which is arranged and designed to introduce the material layer into a (first) waveguide (essentially) without leakage radiation.Alternatively or additionally, the filter element comprises a further filter structure, namely an output filter structure, which is arranged and designed to guide the material layer out of a (further or second) waveguide (essentially) without leakage radiation. In particular, the input filter structure is arranged at a first end section of the filter element and the output filter structure at a second end section of the filter element. The waveguide decoupling filter structure is specifically arranged between the input filter structure and the output filter structure.

[0041] Another independent aspect for solving the problem concerns a method for heating and / or drying a layer of material, comprising the following steps:

[0042] Provision of a device according to the invention;

[0043] Coupling microwaves into the at least two waveguides by means of the at least one microwave source; and

[0044] Guiding the material layer through the guide channel.

[0045] The material layer to be heated and / or dried is guided through the guide channel, in particular by a relative movement of the device and the material layer to be dried. This guiding of the material layer through the guide channel can be achieved by moving or transporting the material layer relative to the device and / or by moving the device relative to the material layer.

[0046] In a preferred embodiment, the method comprises the steps of: determining, for each of the waveguides, any difference between an actual wavelength of a microwave present in the respective waveguide and a predetermined target wavelength; and optionally adjusting the actual wavelength based on the determined

[0047] Difference. Another independent aspect for solving the problem concerns the use of a device according to the invention for heating and / or drying a material layer, particularly an electrically conductive one, in particular by induction. In particular, the material layer comprises or is an electrode material for batteries and / or fuel cells.

[0048] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified, but also individually or in other combinations, without leaving the scope of the present invention.

[0049] The descriptions of the embodiments of the first aspect given above also apply to the aforementioned further independent aspects and, in particular, to preferred embodiments thereof. In particular, the descriptions given above and below of the embodiments of the other independent aspects also apply to an independent aspect of the present invention and to preferred embodiments thereof.

[0050] The following section describes, by way of example, individual embodiments for solving the problem, illustrated by the figures. Some of the described embodiments exhibit features that are not strictly necessary for carrying out the claimed subject matter, but which provide desirable properties in certain applications. Thus, embodiments that do not possess all the features of the embodiments described below are also considered to be disclosed within the scope of the described technical teaching. Furthermore, to avoid unnecessary repetition, certain features are mentioned only in relation to some of the embodiments described below. It should therefore be noted that the individual embodiments should be considered not only individually, but also in combination.From this overview, the person skilled in the art will recognize that individual embodiments can also be modified by incorporating one or more features from other embodiments. It should be noted that a systematic combination of individual embodiments with one or more features described in relation to other embodiments may be desirable and useful, and should therefore be considered and also be regarded as covered by the description.

[0051] Short the

[0052] Figure 1 shows a schematic sketch of a rectangular waveguide 10, which has a long side a and a short side b, with electric and magnetic field lines drawn for the TE10 mode;

[0053] Figure 2 shows schematic drawings of the distribution of the electric and magnetic field in a rectangular waveguide 10, which is operated in the TE10 mode;

[0054] Figure 3a shows a simulated areal power density in an electrically conductive layer for two electrically separated rectangular waveguides 10a and 10b, each with a short circuit on the right side and a microwave source on the left side;

[0055] Figure 3b shows a schematic drawing of two waveguides 10a and 10b connected by a channel in a top view and the resulting power density distribution in an electrically conductive layer;

[0056] Figure 4a shows a schematic drawing of the cross-section of a device 100 according to a preferred embodiment of the invention;

[0057] Figure 4b shows a schematic drawing of the device 100 of Figure 4a in a perspective view; Figure 5a shows a schematic drawing of the cross-section of a device 100 according to a further preferred embodiment of the invention;

[0058] Figure 5b shows a schematic drawing of the device 100 from Figure 5a in a perspective view;

[0059] Figure 6 shows a schematic drawing of two adjacent waveguides 10a and 10b, which are connected and electromagnetically decoupled by a filter element 20, in a top view, as well as the resulting power density distribution in an electrically conductive layer;

[0060] Figure 7a shows an exemplary first and second power density in the conductive material layer, which is formed in a first and second waveguide 10a and 10b of a device 100 according to the invention, as well as a superposition of the first and second power densities, which corresponds to the total power absorbed by the material layer after passing through the device 100, wherein the first waveguide 10a has the same height as the second waveguide 10b;

[0061] Figure 7b shows a first and second power density in the conductive material layer, which is formed in a first and second waveguide 10a and 10b of a device 100 according to the invention, respectively, as well as a superposition of the first and second power densities, which corresponds to the total power absorbed by the material layer after passing through the device 100, wherein the second waveguide 10b has a height that is 1 mm lower than that of the first waveguide 10a. Detailed description of the drawings

[0062] The positional references chosen in the present description, such as top, bottom, left, right, side, etc., each refer to the figure directly described and illustrated and should be applied analogously to the new position in the event of a change in position.

[0063] Figure 1 shows a schematic sketch of a rectangular waveguide 10, which has a long side a and a short side b. In this description, the dimension a is also referred to as the height of the waveguide. The dimension b is also referred to as the width of the waveguide. In standard rectangular waveguides, the field distribution of the electromagnetic fields can be calculated very precisely with knowledge of the waveguide geometry and the frequency. Figure 1 shows the distribution of the electric field (field vector E) and the magnetic field (field vector H). The electric field exhibits a sinusoidal field distribution in the axial direction (z-direction) at the center of the waveguide (i.e., at x = a / 2). Similarly, the magnetic field exhibits a sinusoidal field distribution in the axial direction at one or the other side wall (i.e., at x = 0 or x = a).

[0064] As can be seen in Figure 1, the z-direction is parallel to the longitudinal axis of the waveguide 10, along which an electromagnetic wave propagates within the waveguide 10. The z-direction thus indicates the direction of propagation of an electromagnetic wave or microwave. The x-direction is the direction perpendicular to the longitudinal axis (and therefore perpendicular to the direction of propagation of the electromagnetic waves in the waveguide 10), and in which the long side of the waveguide 10 extends with height a. The y-direction is the direction perpendicular to the longitudinal axis (and therefore perpendicular to the direction of propagation of the electromagnetic waves in the waveguide 10), and in which the short side of the waveguide 10 extends with width b.

[0065] For the electric field strength E y in the y-direction and for the magnetic field strength El z In the z-direction, the following applies: E y = E o sin (— z) for x = a / 2 ,

[0066] H z = H o sin (— z) for x = 0 or x = a , where EQ is the amplitude of the electric field, H o an amplitude of the magnetic field, and A z to denote a wavelength of the electromagnetic wave in the z-direction.

[0067] Figure 2 shows schematic drawings of the distribution of the electric and magnetic fields in a rectangular waveguide 10, which is operated in TE10 mode. In the upper left part of the figure, the waveguide 10 is shown in the (x, y, z) coordinate system, with three different cross-sectional planes 1, 2, and 3 through the waveguide 10 indicated by dashed lines. In the depicted rectangular waveguide 10, as in Figure 1, a long side of the rectangular waveguide cross-section extends along the x-direction, and a short side of the rectangular waveguide cross-section extends along the y-direction. The z-direction corresponds to the longitudinal axis of the waveguide 10, and thus to the direction of wave propagation. The upper right part of the figure shows the distribution of the electric and magnetic fields in cross-sectional plane 1.The lower right image shows the distribution of the electric and magnetic fields in section plane 2. The lower left image of Figure 2 shows the distribution of the electric and magnetic fields in section plane 3. The dashed arrows represent the magnetic field, and the solid arrows represent the electric field. The dots represent the magnetic or electric field leading into or out of the plane of the drawing. The upper right and lower right images, with section planes 1 and 2 respectively, each represent a direction of propagation of the electromagnetic wave in the waveguide 10. The lower left image, with section plane 3, represents a cross-section of the waveguide 10.

[0068] The heating of dielectric materials is primarily caused by the electric field, so heating is most efficient when the material or material layer to be heated is positioned at the maximum of the electric field. In the case of a rectangular waveguide operating in TE10 mode, as shown in Figure 2, dielectric heating is therefore most efficient when the material to be heated is positioned at half the height of the waveguide 10 (or in the section plane 2). Heating electrically conductive materials or material layers is not possible at this position, partly because the electromagnetic field is shielded by the conductive layer at this point, thus preventing the TE10 mode from propagating in the waveguide 10.If, on the other hand, an electrically conductive material layer is positioned on or in the region of a wall of the waveguide 10 that extends in the yz-plane, i.e., on or in the region of the left or right wall of the waveguide 10 shown in Figure 2, where the magnetic field along the axis of the short-circuited waveguide 10 has a cosine-shaped field distribution, inductive heating by means of eddy currents induced in the material layer by the alternating magnetic field is possible. Such a region of the waveguide 10, in which a magnetic field but no electric field is present, can be seen in the upper right part of Figure 2, which shows the section plane 1 of the waveguide 10, at both the upper and lower walls of the waveguide 10. Advantageously, in these regions, a microwave in the waveguide 10 in the TE10 mode remains fully propagable, unlike in the case described previously.

[0069] To heat electrically conductive material layers, it is therefore advantageous to position a longitudinal slot for guiding the electrically conductive material layer in regions of the waveguide 10 where a high (or maximum) magnetic field and a low (or minimum) electric field are present. Preferably, longitudinal slots 15 of the waveguide 10 are provided in the immediate vicinity of side walls of the waveguide 10, which extend in the yz plane. These longitudinal slots 15 each run along the z-direction and close to x = 0 or x = a. Possible positions of the longitudinal slots 15 are indicated by a thin dotted line in the upper sections of Figure 2. The material layer to be heated (not shown in Figure 2) is guided along the y-direction through the waveguide 10 (or through the longitudinal slots of the waveguide 10).

[0070] Possible flow directions D are indicated in the upper left part of Figure 2.

[0071] As shown in Figure 2, the preferred TE10 mode is used as an example for heating and / or drying a material layer. It is understood that, in principle, higher-order modes can also be used. To utilize inductive heating, the longitudinal slots can be positioned, depending on the microwave mode used for heating and / or drying the material layer, in regions of the waveguide 10 where the magnetic field of the microwave (or an RMS value of the magnetic field) is at its maximum and the electric field of the microwave (or an RMS value of the electric field) is at its minimum (e.g., in the yz-plane at the center of the waveguide x = a / 2 for a TE20 mode).

[0072] Figure 3a shows a simulated areal power density in a conductive layer for two electrically isolated rectangular waveguides 10a and 10b, each with a short circuit on the right side and a microwave source (not explicitly shown in Figure 3a for simplicity) on the left side. As can be seen in Figure 3a, the waveguides 10a and 10b, short-circuited on one side, are offset by a quarter of the wavelength A and A, respectively. z The microwaves used are arranged offset from each other. As can be seen in Figure 3a, such an arrangement, in which a layer of material to be heated is passed vertically (e.g., from top to bottom) through the waveguides 10a and 10b, results in a perfectly uniform power density distribution. In particular, the following applies to a power P generated on the basis of the two waveguides 10a and 10b:

[0073] To heat a conductive layer during continuous operation, waveguides 10a and 10b must be opened and connected by longitudinal slots with a length at least equal to the width of the material layer to be heated. Since this significantly disrupts the wall currents of waveguide 10a, the fields couple through the channel into the adjacent waveguide 10b (see Figure 3b). Figure 3b shows a schematic top view of two waveguides 10a and 10b connected by a channel, as well as the resulting power density distribution in an electrically conductive layer. The field excited in the upper waveguide 10a passes through the connecting channel into the adjacent waveguide 10b. Predicting the field and homogenizing the power density distribution is no longer easily possible after the necessary slots are installed.

[0074] By using suitable filter structures in the area of ​​the connecting channel, coupling can be largely avoided, and a field distribution comparable to that of an undisturbed waveguide can be obtained. Depending on the process, the required power, and the power that can be installed per waveguide, the system can be expanded with additional waveguides, ideally in pairs or in groups of N waveguides. In the latter case, the waveguides are preferably offset from each other by 1 / (2N) wavelengths so that the material layer to be heated receives the same power input at every point during its passage. The use of suitable filters or filter structures between the adjacent waveguides 10a and 10b fulfills two functions: On the one hand, the passage of the material layer is ensured, and on the other hand, the adjacent waveguides 10a and 10b are decoupled to obtain a standing wave field with defined maxima and minima.

[0075] Figure 4a shows a schematic drawing of the cross-section of a device 100 for heating and / or drying a layer of material (not shown in Figure 4a) according to a preferred embodiment of the invention. The device 100 comprises two waveguides 10a and 10b, which are arranged parallel to each other. Microwaves are coupled into the two waveguides 10a and 10b by means of at least one microwave source (not shown in Figure 4a for simplicity). A waveguide decoupling filter 25 of a filter element 20 is arranged between the two adjacent waveguides 10a and 10b, which forms a guide channel 30 with the two adjacent waveguides 10a and 10b. This guide channel 30 enables the layer of material to be heated to be guided through the two adjacent waveguides 10a and 10b and the filter element 20 in a guide plane E.In addition to the guide channel 30, the filter element 20 has a waveguide decoupling filter or waveguide decoupling filter structure 25, which is designed to electromagnetically decouple the waveguides 10a and 10b connected by the filter element 20. The material layer to be heated can be guided or transported through the guide channel 30 in the direction of flow D. For this purpose, the waveguides 10a and 10b each have two longitudinal slots 15.

[0076] Figure 4b shows a schematic drawing of the device 100 from Figure 4a in a perspective view. To achieve uniform heating of the material layer, which can be guided through the guide channel 30 in the direction of travel D in the guide plane E through the two waveguides 10a and 10b and through the filter element 20, the waveguides 10a and 10b are arranged axially (i.e., in the direction of wave propagation) offset from each other by one-quarter of the wavelength of a microwave used to heat the material layer. In particular, short-circuiting sliders, which are attached to the right end section of the waveguides 10a and 10b for short-circuiting the respective waveguides 10a and 10b, are arranged offset from each other by one-quarter of the wavelength of a microwave used to heat the material layer.

[0077] As a waveguide decoupling filter or waveguide decoupling filter structure 25, chokes (in the form of a waffle iron filter) are used transversely and longitudinally in the connecting channel between the two adjacent waveguides 10a and 10b. These chokes are short-circuited at the end and are a quarter wavelength deep of the microwave used for heating. The wave propagating in the guide channel 30 is almost completely reflected by the filter element 20 or the waveguide decoupling filter 25. This prevents any power from coupling from the first waveguide 10a to the second waveguide 10b, and thus the individual waveguides 10a and 10b behave as if they were closed loops. As a result, in contrast to the example shown in Figure 3b, a standing wave field can form again, similar to that shown in Figure 3a.Figure 5a shows a schematic drawing of the cross-section of a device 100 according to a further preferred embodiment of the invention. Compared to the embodiment shown in Figure 4a, the filter element 20 comprises, in addition to the waveguide decoupling filter 25, two further filters or filter structures, namely an input filter or an input filter structure 26 and / or an output filter or an output filter structure 28. The input filter 26 is designed to introduce the material layer into the first waveguide 10a (essentially) without leakage radiation. The output filter 28 is designed to guide the material layer out of the second waveguide 10b (essentially) without leakage radiation. Otherwise, the above description of the embodiment of Figure 4a also applies to the embodiment of Figure 5a.

[0078] Figure 5b shows a schematic drawing of the device 100 from Figure 5a in a perspective view. Compared to the embodiment shown in Figure 4b, the filter element 20 comprises, in addition to the waveguide decoupling filter 25, two further filters or filter structures, namely an input filter 26 and / or an output filter 28. Otherwise, the above description for the embodiment of Figure 4b also applies to the embodiment of Figure 5b.

[0079] Figures 4a, 4b, 5a and 5b each show only two parallel waveguides 10a and 10b with a waveguide decoupling filter 25 arranged between them. It is understood that the device 100 can also comprise several (in particular any number) parallel waveguides 10 with several waveguide decoupling filters 25, each arranged between two adjacent waveguides 10.

[0080] Figure 6 shows a schematic drawing of two adjacent waveguides 10a and 10b from above, where the waveguides 10a and 10b are connected by a filter element 20 and simultaneously electromagnetically decoupled by the filter element 20 or the waveguide decoupling filter 25, as well as the resulting power density distribution in an electrically conductive layer. As already shown in Figures 4a, 4b, 5a and 5b, the adjacent waveguides 10a and 10b in Figure 6 are also connected by a connecting channel of the filter element 20 and electromagnetically decoupled by a waveguide decoupling filter structure 25 of the filter element 20. The simulated areal power density in the electrically conductive layer exhibits regular maxima and minima, similar to Figure 3a.Due to this uniform distribution of the maxima and minima of the areal power density of an electrically conductive material layer to be heated, a uniform power density in this vertical direction, or direction of travel D, can be achieved when the material layer is passed through the waveguides 10a and 10b in the vertical direction (on average over time). This is particularly true when, as shown in Figure 6, the short-circuiting sliders of the two waveguides 10a and 10b are offset by one quarter of the wavelength of a microwave used to heat the material layer.

[0081] By appropriately optimizing the filter structure 25 between adjacent waveguides 10a and 10b, the waveguides can be sufficiently decoupled from each other so that the distribution of the areal power density on the material layer to be heated approximates the distribution shown in Figure 3a, and consequently, the heating and drying process is sufficiently homogeneous when averaged in the direction of flow D. The results with two waveguides can be scaled to any number of parallel, decoupled waveguides, depending on the heating requirements.

[0082] For the waveguides 10 to function as resonators, they must be short-circuited at both ends. This can be achieved by using an iris in the waveguide at the input end, where the microwaves are coupled in, creating a short circuit on this side as well. At the opposite end, short-circuiting sliders are preferably used to allow for precise adjustment of the resonance in the waveguide 10. This increases the overall efficiency of the device 100, since in the case of resonance, almost all the power is dissipated as heat into the material layer. Additionally, the areal power density distribution across the width of each waveguide 10 can be influenced by adjusting and / or controlling the frequencies of the individual microwave sources.

[0083] In its basic configuration within an industrial plant, the described device 100 can be used either on one or both sides. A layer of material (e.g., a film with a layer to be heated) can be passed over or between several devices 100, similar to a conveyor belt, in order to heat the material applied to the film either on one or both sides.

[0084] The wavelength A zThe temperature of the waveguide 10 is determined by the frequency of the microwave signal and by the height a of the waveguide 10, where the height a is measured from the top of the waveguide 10 to the material layer. If the heights a between two waveguides change during the process, for example due to inhomogeneities in the thickness of the material layer being heated or due to the transport mechanism, this leads to a detuning of the two waveguides relative to each other and thus to inhomogeneous heating. For example, a displacement of the wall by 1 mm in a WR 340 waveguide at 2.45 GHz results in a change in the wavelength A. z from 173.4 mm to 175.5 mm. Over the length of the device or microwave applicator, even small errors quickly lead to strong inhomogeneities due to beat frequencies caused by the slightly different wavelengths (see Figures 7a and 7b).

[0085] Especially when drying thick layers of material, readjusting the wavelength during operation can be helpful or even necessary. This can be achieved, for example, using a wavelength testing device by coupling a measurement signal at two points in the waveguide 10. If these signals are combined appropriately, they superimpose destructively, and the combined measurement signal becomes zero. However, if the wavelength deviates from the desired value, a phase difference of other than 180° exists between the coupled signals at the superposition point, and they do not completely cancel each other out due to the superposition. Preferably, the two coupling points are separated by a multiple of the desired half wavelength. However, other distances can also be achieved through a suitable design of the coupling and superposition structure.In the case of a simply short-circuited waveguide 10, the operating frequency can now be readjusted to achieve the desired wavelength again. If the setup is resonant due to the use of an iris, the length of the resonator can also be adjusted via a shorting slider, in addition to the frequency, to set the resonant frequency to the new operating frequency. In particular, the target wavelength of the resonance can be determined by the position of the shorting slider. Thus, the resonant frequency changes with every change in the waveguide height. Therefore, with every change in the waveguide height, the operating frequency must be adjusted to the current resonant frequency. Only when the operating frequency is identical to the resonant frequency can microwave power be optimally coupled into the resonator.This can be achieved by tracking and adjusting the operating frequency to the resonant frequency, or by coupling a signal from a point on the resonant waveguide and using it as an input signal for the microwave amplifier. This ensures that the operating frequency of the microwave amplifier always automatically adjusts to the resonant frequency defined by the shorting switch or by the current height *a* of the waveguide, assuming a constant resonant wavelength. Alternatively or additionally, the operating frequency can be readjusted by measuring the actual height of the waveguide *10* and analytically calculating the resulting wavelength. Alternatively or additionally, the temperature distribution in the material layer can be measured to readjust the operating frequency. Temperature measurements can be performed, for example, contactlessly using pyrometers or infrared cameras.This can be done after the material layer has left the device or applicator 100, or at any desired time or at predetermined time intervals, by integrating temperature sensors (e.g., pyrometers or infrared cameras) at suitable locations in the waveguides 10. Locations where the magnetic field, and thus the wall currents, are zero are particularly suitable, as the microwave signal is then not affected by disturbances in the waveguide wall. However, since no heating occurs at these locations, the temperature sensors must have suitable wide-angle optics and / or be installed at an angle. If the aperture of the pyrometers or infrared cameras is small (diameter less than one-tenth of the wavelength), they can also be installed where the wall currents are not exactly zero without significantly interfering with the microwave signal.For this purpose, appropriately small holes can be drilled into the waveguide wall with sufficient thickness.

[0086] Figure 7a shows an exemplary first and second power density and power loss density, respectively, in the conductive material layer, which is formed in a first and second waveguide 10a and 10b of a device 100 according to the invention, as well as a superposition of the first and second power densities, which corresponds to the total power absorbed by the material layer after passing through the device 100, wherein the first waveguide 10a has the same height as the second waveguide 10b. The "amplitude" shown on the high-value axis in the diagram corresponds to the power density distribution in the material layer, and the length I shown on the low-value axis corresponds to the width of the material layer to be heated and / or dried, or the length I of the waveguides under the material layer. As can be seen in Figure 7a, the sum of signals 1 and 2 is constant.Figure 7b also shows a first and second power density in the conductive material layer, which is formed in a first and second waveguide 10a and 10b of a device 100 according to the invention, respectively, as well as a superposition of the first and second power densities, which corresponds to the total power absorbed by the material layer after passing through the device 100, wherein the second waveguide 10b has a height that is 1 mm lower than that of the first waveguide 10a. In particular, in the second waveguide 10b, compared to the first waveguide 10a, one wall of the waveguide has been moved inwards by 1 mm. The superposition or sum of the two signals is no longer constant in this case, but rather represents a beat frequency.To detect such an adverse case, a wavelength testing device can be used, which, for example, taps out and / or measures the microwave signal at two suitable points within a waveguide. By comparing the measured values, a deviation of the actual wavelength from the target wavelength can be determined. Using a wavelength adjustment device, the actual wavelength can be adjusted to the target wavelength based on the determined deviation.

[0087] The following are examples of some features, properties and advantages of a device 100 described herein, which is also referred to as a microwave applicator in the context of this description:

[0088] By using a microwave applicator, in which a material layer to be heated (e.g., an electrode layer) is precisely positioned at the maximum of a magnetic field, this material layer can be efficiently dried by inductive heating. In a short-circuit waveguide arrangement, where the material layer is guided along its narrow side, i.e., at the maximum of the magnetic field in the TE10 mode, the material layer along the waveguide experiences sinusoidal excitation of eddy currents due to the resulting standing wave, and thus heating due to its electrical resistance. If the material layer is exposed to a field or heating pattern shifted by a quarter wavelength in a subsequent or adjacent waveguide, the total energy input across the material layer along its path results in an ideal, very uniform energy input, and thus very homogeneous heating.The problem that arises here, however, is that for a continuous process, a longitudinal slot must be made in the waveguide for sample passage at a point where the wall currents are at their maximum. This causes microwave power to couple out of the waveguide, preventing the formation of a standing wave along the waveguide as occurs in the case of a closed waveguide. With a series of waveguide arrays, each offset by a quarter wavelength, the pronounced coupling of microwave power from one waveguide to the adjacent waveguides prevents homogeneous heating of the material layer averaged over the entire passage. This problem is now solved, in particular, by using suitable filter structures between the waveguides.

[0089] The arrangement of short-circuited waveguides with a standing wave field is opened at the side by a slot where the magnetic field is strongest. The slotted waveguides are metallically connected to each other, creating a channel of sufficient height through all waveguides for the electrically conductive material layers to be heated. To decouple the waveguides from each other from a microwave perspective, filter structures are inserted between them. This allows the standing wave field in one waveguide to be shifted by exactly one-quarter of the wavelength relative to the adjacent waveguides. When using multiple waveguides, other shift lengths can be utilized, resulting in uniform heating across the entire heating path and the entire width of the layer.In addition to a short circuit at the waveguide end, an iris can also be used at the waveguide input. This creates a waveguide resonator, which means that, unlike in an arrangement without an iris, the coupled wave is not only reflected once at the waveguide end, but is reflected back and forth multiple times between the short circuit and the iris. This allows the microwave power to be coupled more efficiently into the layer being heated. This increases the efficiency of the process, especially when the electrical conductivity of the material layer being heated is high.

[0090] By using semiconductor microwave amplifiers, waveguide imbalances can be addressed by selectively varying the microwave frequency. If an iris is used at the waveguide input and a resonator with sufficient quality is created, efficient coupling of microwave power is possible by tuning the microwave source to its resonant frequency. The use of a magnetron (vacuum tubes and oscillators) as a microwave source is therefore limited primarily to low-quality waveguide resonators, in which case the resonators can be tuned to the operating frequency of the specific magnetron used. This can be achieved, in particular, by using short-circuit sliders.Semiconductor microwave amplifiers as microwave sources offer the advantage that wavelength fluctuations, for example due to changes in layer thickness, can be easily compensated for by adjusting the frequency. Such fluctuations can be detected by coupling out reference signals at suitable points along the waveguide. If material layers to be heated are applied to both sides of a metallic substrate, the longitudinal slots for material passage can be positioned alternately on opposite sides of the waveguide.

[0091] Within the scope of the present invention, it has been found in particular that microwaves can be used to heat and / or dry electrically conductive material layers, especially electrode materials for batteries or fuel cells.

[0092] While conventional devices for heating and / or drying a material layer using microwaves aim for a central routing of the material layer to be heated and / or dried at a maximum of the electric field strength in the TEw fundamental mode, the present invention has been recognized in particular that, when a central routing of an electrically conductive material layer (e.g., a conductive electrode path) is used, the material layer to be heated and / or dried must not have excessively high electrical conductivity, as this would otherwise shield the electric field. In particular, the present invention has been recognized that, for example,When a waveguide is split in the middle, creating two (rectangular) waveguides parallel to each other, wave propagation in the TEw mode is no longer possible, provided the material layer used has high electrical conductivity. In particular, highly electrically conductive traces or layers made of materials such as aluminum or copper (for example, with an electrically conductive coating) cannot be easily heated if the layer to be heated and / or dried is routed through the center of the waveguide. If such an electrically conductive layer is positioned at the point of maximum electric field strength (along its length) within the waveguide, virtually no microwave energy is absorbed, as the penetration depth in the material is too low.The magnetic field is too weak in the material layer, causing the material or material layer to act like a reflector. Therefore, the field can no longer propagate in the fundamental mode TE10 within the given dimensions. To heat and / or dry electrically conductive material layers, the present disclosure proposes, in particular, the use of inductive heating and / or drying of the material layer (i.e., heating and / or drying the material layer using the magnetic field of microwaves). As mentioned above, it can be provided that the electrically conductive material layer to be heated and / or dried (e.g., with a less conductive layer applied to it) directly forms one of the short sidewalls of the waveguide. At this point (i.e., one of the short sidewalls of the waveguide), the magnetic field maximum in the fundamental mode TE10 is located.The currents induced in the surface of the sidewall cause it to heat up due to the increased electrical resistance of the less or poorly conductive layer. To achieve a continuous, path-like guidance according to this principle, the waveguides are preferably longitudinally slotted at this point (i.e., at least on one of the short sidewalls of the waveguide), creating a gap through which the path or material layer can run.

[0093] Preferably, the waveguides are slotted at the edge of the wider side wall, rather than in the middle. However, this initially presents a considerable problem with regard to the TEw fundamental mode. This is because the magnetic field has a maximum here, resulting in non-zero induced wall currents perpendicular to the waveguide (see Figures 1 and 2). These currents are disrupted by the slot, causing microwaves to radiate from the slot and preventing the TEw mode from resonating as desired (see Figure 3b). This is not a problem with conventional devices that have slots in the middle, since the transverse component of the current density on the waveguide's side faces is zero in the middle, and the longitudinal component is also hardly affected by the central slot. This prevents microwaves from escaping, provided the slot is sufficiently narrow. Therefore, a central, elongated slot in the waveguide does not impede the propagation of the TEw mode.As is thus provided for in conventional devices, the layer to be heated can optimally absorb the energy at the maximum of the electric field. However, this requires that the material layer to be heated and / or dried does not disrupt the field too much, which would be the case with increased electrical conductivity of the layer combined with a very shallow penetration depth in the material. Therefore, this principle, as conventionally used, is only feasible with dielectric layers on dielectric substrates.

[0094] To enable resonant propagation of the TEw fundamental mode despite a decentralized and thus conventionally "electromagnetically unfavorable" slot position (especially near the narrow side wall of the waveguide), the present disclosure proposes the use of a specially developed filter element. This filter element serves, in particular, to make resonance in the fundamental mode possible in the first place (see Figure 6). Specifically, the filter element proposed herein effects an impedance transformation of the air gap between the side walls of the hollow or waveguide and the (electrically conductive) material layer to be heated and / or dried. In particular, the filter element thus acts like a short circuit for the electromagnetic wave.Thus, the propagation of the TEw fundamental mode becomes possible again, especially when the (electrically conductive) material layer to be heated and / or dried forms a side wall of the hollow or waveguide.

[0095] The device described herein makes it possible to uniformly heat an electrically conductive material layer with very shallow microwave penetration depth during continuous operation. This is achieved by operating a resonant system, preferably in the TEw fundamental mode. To maximize heating efficiency at shallow penetration depths in electrically conductive materials, the material to be heated and / or dried is positioned at the maximum of the magnetic field to utilize heat losses due to induced surface currents within the material. In particular, unlike conventional devices, mode conversion using dielectric materials on the short sides of the waveguides does not occur; instead, a resonant system in the TEw fundamental mode is realized.The waveguides are therefore slotted, particularly at the maximum of the magnetic field, for continuous operation. A filter is used to adjust the waveguide to achieve the required resonance condition. Reference list.

[0096] 10 Waveguides

[0097] 10a first waveguide

[0098] 10b second waveguide

[0099] 15 longitudinal slots

[0100] 20 filter elements

[0101] 25 Filter structure (waveguide decoupling filter)

[0102] 26 Filter structure (input filter)

[0103] 28 Filter structure (output filter)

[0104] 30 Guide channel a long side of the waveguide cross-section (height of the waveguide) b short side of the waveguide cross-section (width of the waveguide)

[0105] D Direction of travel (transport direction)

[0106] E Management level

Claims

43 Patent claims 1. Device (100) for heating and / or drying a layer of material using microwaves, comprising: at least two waveguides (10a, 10b) arranged parallel to each other; at least one microwave source for coupling microwaves into the at least two waveguides (10a, 10b); and a filter element (20) which forms a guide channel (30) with the at least two waveguides (10a, 10b), wherein the guide channel (30) enables the material layer to be guided through the at least two waveguides (10a, 10b) and the filter element (20) in a guide plane (E), and wherein the filter element (20) has at least one waveguide decoupling filter (25) which is arranged and designed between two adjacent waveguides (10a, 10b) of the at least two waveguides (10a, 10b) to electromagnetically decouple the adjacent waveguides (10a, 10b).

2. Device (100) according to claim 1, further comprising: a guide unit for generating a relative movement between the material layer and the guide channel (30) in the guide plane (E).

3. Device (100) according to claim 1 or 2, wherein each waveguide (10a, 10b) has two opposing longitudinal slots (15) through which the material layer can be passed, wherein the longitudinal slots (15) of the waveguides (10a, 10b) are each arranged such that the guide plane (E) passes through each longitudinal slot (15).

4. Device (100) according to claim 3, wherein the following condition applies in the guide plane (E) between the opposing longitudinal slots (15) of the respective waveguide (10a, 10b): 44 - the RMS value of an electric field present due to microwaves coupled into the respective waveguide (10a, 10b) is minimal and / or smaller than a threshold value specified for the electric field.

5. Device (100) according to claim 3 or 4, wherein the following condition applies in the guide plane (E) between the opposing longitudinal slots (15) of the respective waveguide (10a, 10b): - the RMS value of a magnetic field present due to microwaves coupled into the respective waveguide (10a, 10b) is maximum and / or greater than a threshold value specified for the magnetic field.

6. Device (100) according to one of the preceding claims, wherein the guide channel (30) is positioned relative to the waveguides (10a, 10b) depending on a microwave mode provided for heating and / or drying the material layer.

7. Device (100) according to one of the preceding claims, wherein the guide channel (30) runs decentrally through the at least two waveguides (10a, 10b).

8. Device (100) according to one of the preceding claims, wherein the filter element (20) comprises at least one microwave trap, in particular at least one quarter-wave trap; and / or wherein the at least one waveguide decoupling filter structure (25) is designed to function as a microwave trap, in particular as a quarter-wave trap.

9. Device (100) according to one of the preceding claims, wherein the at least one waveguide decoupling filter (25) has a waffle iron structure.

10. Device (100) according to one of the preceding claims, wherein the at least one waveguide decoupling filter (25) comprises a structure with a plurality of hollow longitudinal and transverse channels, each of which is connected to 45 are open at a first end and closed at an opposite second end, and each of which has a dimension in a direction perpendicular to the longitudinal axis of the waveguides (10a, 10b) that corresponds to an odd multiple of a quarter of the wavelength of a microwave coupled into the waveguides (10a, 10b) for heating and / or drying the material layer.

11. Device (100) according to one of the preceding claims, wherein each waveguide (10a, 10b) has a, preferably displaceable, short-circuiting element for reflecting microwaves within the respective waveguide (10a, 10b).

12. Device (100) according to claim 11, wherein the short-circuiting elements of two adjacent waveguides (10a, 10b) are arranged axially offset from each other by an odd multiple of a quarter of the wavelength of a microwave coupled into the waveguides (10a, 10b) for heating and / or drying the material layer.

13. Device (100) according to claim 11 or 12, wherein the device comprises N waveguides (10) and the short-circuiting elements of adjacent waveguides (10a, 10b) of the N waveguides (10) are each connected in the axial direction of the waveguides (10) by the wavelength of a respective and / or drying of the material layer coupled microwave are arranged offset from each other, where N is a natural integer with N >

2.

14. Device (100) according to one of the preceding claims, wherein an iris for coupling a microwave into the respective waveguide (10a, 10b) and for reflecting the microwave inside the respective waveguide (10a, 10b) is arranged on a first axial end section of each of the at least two waveguides (10a, 10b); and / or wherein a short-circuit slider for reflecting the microwave inside the respective waveguide (10a, 10b) is arranged on a second axial end section of each of the at least two waveguides (10a, 10b).

15. Device (100) according to one of the preceding claims, wherein the device (100) comprises a wavelength testing device for each waveguide (10a, 10b) for determining any difference between an actual wavelength of a microwave present in the respective waveguide (10a, 10b) and a predetermined target wavelength.

16. Device (100) according to claim 15, wherein the wavelength testing device comprises at least two measuring probes which can be attached or are attached to the respective waveguide (10a, 10b) for coupling out a measuring signal and which have a distance from each other in an axial direction of the respective waveguide (10a, 10b) which corresponds to a multiple of half the nominal wavelength.

17. Device (100) according to claim 15 or 16, wherein the device (100) further comprises a wavelength adjustment device for adjusting the actual wavelength to the target wavelength based on the determined difference.

18. Device (100) according to one of the preceding claims, comprising at least one signal transmission unit designed to transmit one or more feedback signals from the at least two waveguides (10a, 10b) to the at least one microwave source.

19. Device (100) according to one of the preceding claims, wherein the device (100) comprises an associated microwave source for each waveguide (10a, 10b), and wherein the microwave sources belonging to each pair of adjacent waveguides (10a, 10b) are arranged at different axial ends of the waveguides (10a, 10b).

20. Device (100) according to one of the preceding claims, wherein the guide channel (30) passes through a region of an upper or lower side surface of the at least two waveguides (10a, 10b).

21. Device (100) according to one of the preceding claims, wherein each side wall of the at least two waveguides (10a, 10b) is formed by the guide channel (30).

22. Device (100) according to one of the preceding claims, wherein the guide channel (30) is designed and / or arranged such that the material layer to be heated and / or dried in the guide channel (30) assumes the function of a waveguide wall.

23. System for heating and / or drying a material layer, comprising at least two devices (100) according to any one of claims 1 and 3 to 22; and a guide unit for generating a relative movement between the material layer and a common guide channel in a common guide plane, wherein the at least two devices (100) are arranged such that all guide planes (E) of the at least two devices (100) coincide and form the common guide plane, and that the common guide channel is formed by the guide channels (30) of the at least two devices (100).

24. System according to claim 23, comprising at least a first device (100) according to any one of claims 1 and 3 to 22 and at least a second device (100) according to any one of claims 1 and 3 to 22.

25. System according to claim 24, wherein the at least one first device (100) and the at least one second device (100) are each arranged in a mirror image of each other.

26. System according to claim 24, wherein the at least one second device (100) is arranged in a mirror-symmetrical manner with respect to the common guide plane relative to the at least one first device (100), and wherein in particular one of the 48 at least one first device (100) and one of at least one second device (100) are arranged one above the other with respect to a through-direction of the material layer.

27. Filter element (20) comprising a connecting channel designed to connect two waveguides (10a, 10b) arranged parallel to each other, and to guide a material layer from one of the two waveguides (10a, 10b) to the other of the two waveguides (10a, 10b); and a filter structure (25) designed to electromagnetically decouple the two waveguides (10a, 10b).

28. Method for heating and / or drying a layer of material, comprising the steps: Providing a device (100) according to any one of claims 1 to 22; Coupling microwaves into the at least two waveguides (10a, 10b) by means of the at least one microwave source; and Guiding the material layer through the guide channel (30).

29. The method of claim 28, further comprising the steps of: determining, for each of the waveguides (10a, 10b), any difference between an actual wavelength of a microwave present in the respective waveguide and a predetermined target wavelength; and any adjustment of the actual wavelength based on the determined difference.

30. Use of a device (100) according to any one of claims 1 to 22 or of a system according to any one of claims 23 to 26 for heating and / or drying a layer of material.

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