Arrangement and method for processing a material using electromagnetic heating

Abstract

An arrangement (100) for processing a material, the arrangement comprising: a pair of press plates (210, 220) adapted to receive a workpiece (140) of the material to be processed therebetween, wherein the press plates are arranged to apply a pressure (290) on the workpiece, a transmission line (300) embedded in at least one of the press plates, the transmission line being arranged to guide and emit electromagnetic radiation therethrough to generate standing waves for heating the workpiece; a source (110) for generating electromagnetic radiation, the source being connected to the transmission line via a transmission line (180) to couple the electromagnetic radiation into the transmission line; a plurality of temperature sensors (160) configured to detect a temperature distribution of the workpiece; a control unit (150) connected to the source and the plurality of sensors, wherein the control unit is configured to adjust the electromagnetic radiation generated by the source based on the detected temperature distribution of the workpiece.

Description

ARRANGEMENT AND METHOD FOR PROCESSING A MATERIAL USINGELECTROMAGNETIC HEATINGTechnical Field

[0001] The present disclosure relates to the field of material treatment or processing and advanced manufacturing. More specifically, an arrangement and method for processing a material using electromagnetic radiation, e.g. radiofrequency (RF) and / or microwave (MW) energy together with application of pressure.Background

[0002] The subject matter herein relates generally to microwave applicators, specifically focusing on the development and utilization of devices designed to apply microwave energy to a given target or material. This field encompasses various applications, including but not limited to industrial processes, and other contexts where microwave energy serves as a high-efficiency and clean energy heating method. Microwave heating has found applications in diverse sectors due to its ability to provide rapid heating.

[0003] Microwave heating chambers have been commonly employed, yet their limitations in terms of influencing the heating environment and achieving uniformity pose significant challenges, especially in industrial settings. As a result, there is a pressing need for innovative microwave applicators capable of overcoming these drawbacks and providing efficient, uniform heating solutions. The microwave oven heats workpieces within a chamber by exposing materials to electromagnetic radiation. The waves within the microwave oven reflect within the chamber and cause standing waves, resulting from waves with identical frequency and amplitude interfering with each other while traveling in opposite directions. The standing wave creates nodes, being the positions on the standing wave where the wave stays in a fixed position over time because of destructive interference. The standing wave further creates antinodes, being the positions on the standing wave where the wave vibrates with a maximum amplitude. Due to the fact that no energy is delivered at the nodes whereas the energy of a single wave is delivered at the antinodes, the heating becomes uneven.

[0004] However, in the practical application of microwave heating, challenges have been encountered, particularly regarding the uniformity of heating for the targeted objects or materials. The traditional methods, such as using heating chambers, often fall short in achieving consistent and homogeneous heating, leading to inefficiencies and limitations in industrial processes. To address these challenges, several methods have been explored in the prior art.

[0005] WO 2022 / 063674 Al, incorporated herein by reference, describes a method and arrangement for processing a workpiece by means of emitted electromagnetic radiation. A number of microwave sources are controlled to adjust the heating pattern in real time during execution of the process, to achieve a reliable and efficient processing of the workpiece.

[0006] The problem of uneven or non-homogeneous heating of materials is addressed e.g. in US 2018 / 0098381 Al. The document describes approaches which apply energy to an arbitrary workpiece placed in a chamber for heating using evaluative feedback or deterministic planning to thereby solve the problem of uneven heating in a microwave oven. In some approaches, the evaluative feedback involves an evaluation of the workpiece by sensing a surface temperature distribution for the workpiece using an infrared sensor which is given to a control system.

[0007] EP2767389A1 discloses a double-belt heating press comprising a pair of roller tables for conveying a work piece and microwave heating units with rod-shaped microwave antennae disposed as radiation sources in voids between support tubes for the rollers.

[0008] DE102017121732A1 discloses a device for microwave treatment of products introducing a novel coaxial conductor configuration designed for optimal and uniform heating. Featuring an electrically conductive inner conductor enveloped by a spaced outer conductor with openings in the outer conductor. The standing waves enhance the exposure efficiency, aligning openings with electric field strength nodes, having multiple openings at intervals spaced by half-wavelength and multiples of half-wavelengths, i.e. a slotted coaxial cable with one shorted end and opening spaced by half-wavelength and multiplesof half-wavelengths. This slotted coaxial cable is inserted in a treatment room for industrial microwave heating processes.

[0009] CN212137954U discloses a leakage coaxial device for uniform heating of solid material wherein two sets of coaxial cables equipped with slits are arranged horizontally with the object to be processed in a layered pattern and at intervals to increase the homogeneity of heating solid materials. It is then expected that the arrangement of the coaxial cable induces the emission of electromagnetic waves, creating a uniformly distributed electric field outside the coaxial cable, ensuring even heating of the solid material.

[0010] In addition, there is usually a need to apply pressure while heating a material, and thus a mold or press plates are generally used to shape the material that is heated. This mold is generally constructed in metal, although other molds may be realized in a material permeable to electromagnetic radiation such as glass fiber composite material or ceramics. However, in the vast majority of cases, metallic molds or press plates are used to apply pressure on the material to be processed. This makes it challenging to guide and couple the electromagnetic energy to the material to be processed as there is no direct line of sight to an antenna, as it would be the case in an open enclosure, without the mold or press plates.

[0011] Hence, there is an interest to improve methods and arrangements of the prior art in order to provide efficient methods and arrangements for material processing, and in particular for the purpose of obtaining a desired heating and / or curing of materials and advanced manufacturing.Summary of Invention

[0012] An objective of the present disclosure is therefore to provide improved solutions for material treatment. In particular, it is of interest to provide efficient methods and arrangements for the purpose of material processing, such as obtaining a desired heating and / or curing of materials relating to an even or uneven i.e., heterogeneous or homogeneous heating and / or heating of a certain (desired) location of the material and a variation of the heating profile in time.

[0013] According to a first aspect of the present disclosure, there is provided an arrangement for processing a material. The arrangement comprises: a pair of press plates adapted to receive a workpiece of the material to be processed therebetween, wherein the press plates are arranged to apply a pressure on the workpiece; a transmission line embedded in at least one of the press plates, the transmission line being arranged to guide and emit electromagnetic radiation therethrough to generate standing waves for heating the workpiece; a source for generating electromagnetic radiation, the source being connected to the transmission line via a transmission line to couple the electromagnetic radiation into the transmission line; a plurality of temperature sensors configured to detect a temperature distribution of the workpiece; and a control unit connected to the source and the plurality of sensors, wherein the control unit is configured to adjust the electromagnetic radiation generated by the source based on the detected temperature distribution of the workpiece.

[0014] By means of the transmission line embedded in the press plate, the arrangement of the present disclosure combines heating and application of pressure to process a workpiece of a material to be processed in a single processing step. The temperature sensors allow for adaptive control of the heating to achieve an efficient and uniform heating pattern of the workpiece.

[0015] In one embodiment, the transmission line comprises a plurality of grooves formed in the at least one press plate and facing towards or away from the workpiece, each groove containing an inner conductor and an insulating material, wherein the inner conductor is at least partially surrounded by an outer conducting shield to allow leakage of the electromagnetic radiation. The grooves facilitate embedding of the transmission line in the press plate.

[0016] In one embodiment, the at least one press plate is made of conductive material and further comprises a cover plate made of conductive material comprising one or more slots, wherein the groove and cover plate together constitute the outer conducting shield of the transmission line. Using the conductive material in the press plate and cover plate as the outer conducting shield of the transmission line reduces the material needed and further simplifies embedding.

[0017] In one embodiment, the at least one press plate comprises a ground plane made of conductive material and arranged on a side of the press plate facing away from the workpiece, and a cover plate made of non-conductive material, wherein the ground plane constitutes the outer conducting shield of the transmission line. The common ground plane enables provision of a single outer conducting shield, thereby facilitating manufacture. The electromagnetic transparent cover plate allows for increased leakage of electromagnetic waves to heat the workpiece, whilst providing a fluid tight seal to protect the transmission line.

[0018] In one embodiment, the source is connected to the transmission line at opposite ends thereof for coupling of the electromagnetic radiation. The open-ended configuration of the transmission line allows feeding electromagnetic radiation from both ends. This enables changing the position and intervals of the nodes / antinodes of the standing waves in a continuous and flexible manner.

[0019] In one embodiment, the transmission line is arranged in a serpentine pattern in the at least one press plate. By means of the serpentine pattern, a uniform distribution of the transmission line in the press plate is achieved.

[0020] In one embodiment, the arrangement comprises a plurality of transmission lines arranged substantially in parallel, each transmission line being connected to the source via a transmission line for coupling of electromagnetic radiation. The plurality of transmission lines allows for individual control of the generation and emission of electromagnetic radiation in each separate transmission line.

[0021] In one embodiment, the plurality of temperature sensors comprises an array of thermocouples and / or ultrasonic transducers arranged on one or both of the press plates, an optical fiber sensor embedded in one or both of the press plates, cover plates, or a combination thereof. The present arrangement allows for selecting or combining the optimal sensor type for the given configuration, depending e.g. on prerequisites of the material to be processed.

[0022] In one embodiment, the press plates define an open or closed cavity therebetween for receiving the workpiece. An open cavity may be used for workpieceswhich do not require application of pressure on all sides, e.g. for curing of glued laminated timber, whereas closed cavities are preferred for molding processes wherein a particular shape of the workpiece is desired.

[0023] In one embodiment, a surface of the press plates facing the workpiece is flat or curved. The flat or curved surface enables shaping the workpiece to a desired geometry.

[0024] In one embodiment, the control unit is configured to adjust the phase, amplitude, frequency and / or power of the electromagnetic radiation.

[0025] In a second aspect of the present disclosure, there is provided a method for processing a material, the method comprising the steps of: arranging a workpiece of the material to be processed between a pair of press plates; applying a pressure on the workpiece by means of the press plates; generating electromagnetic radiation from a source and coupling the electromagnetic radiation into a transmission line embedded in at least one of the press plates, the transmission line being arranged to guide and emit electromagnetic radiation therethrough to generate standing waves for heating the workpiece; detecting a temperature distribution of the workpiece by means of a plurality of temperature sensors; and adjusting the electromagnetic radiation generated by the source based on the detected temperature distribution of the workpiece.

[0026] In one embodiment, adjusting the electromagnetic radiation comprises adjusting the phase, amplitude, frequency and / or power of the electromagnetic radiation.

[0027] In one embodiment, the electromagnetic radiation is coupled into the transmission line from opposite ends thereof.

[0028] In one embodiment, the workpiece comprises glued laminated timber (glulam), laminated stock (lamstock) lumber, laminated wood, solid wood boards, multi-layer panels or scantlings, posts, and beams, engineered wood products like particleboard, mediumdensity fiberboard (MDF), and oriented strand board (OSB), fiberglass composites, ceramics, and other polymers.Brief Description of Drawings

[0029] The disclosure is now described, by way of example, with reference to the accompanying drawings, in which:Fig. 1 shows a schematic view of an arrangement according to the present disclosure. Fig. 2 shows a cross-sectional view of an arrangement according to one embodiment of the present disclosure.Fig. 3 shows an exploded top view of a press plate according to the present disclosure. Fig. 4 shows top views of alternative slot arrangements in a cover plate according to the present disclosure.Fig. 5 shows a cross-sectional view of an arrangement according to another embodiment of the present disclosure.Fig. 6. shows a cross-sectional view of an arrangement according to another embodiment of the present disclosure.Fig. 7 shows a schematic view of a transmission line according to the present disclosure, as well as an exemplary resulting standing wave.Fig. 8 shows diagrams of heating patterns used in an arrangement according to the present disclosure.Detailed Description

[0030] In the following, a detailed description of method and arrangement according to the present disclosure is presented. In the drawing figures, like reference numerals designate identical or corresponding elements throughout the several figures. It will be appreciated that these figures are for illustration only and do not in any way restrict the scope of the present disclosure. Also, it is to be understood that the phraseology and terminology used herein is for the purpose of description and should not be regarded as limiting. The use of ‘including’, ‘comprising’, or ‘having’ and variations thereof herein is meant to encompass the items listed thereafter and equivalents thereof as well as additional items. Unless specified or limited otherwise, the terms ‘mounted’, ‘connected’, ‘supported’, and ‘coupled’ and variations thereof are used broadly and encompass both direct and indirect mountings, connections, supports, and couplings. Further, ‘connected’ and ‘coupled’ are not restricted to physical or mechanical connections or couplings.

[0031] To the extent that the figures illustrate diagrams of the functional blocks of various embodiments, the functional blocks are not necessarily indicative of the division between hardware circuitry. For example, one or more of the functional blocks (e.g., processors or memories) may be implemented in a single item of hardware (e.g., a general- purpose signal processor or a block of random-access memory, hard disk, or the like) or multiple items of hardware. Similarly, the programs may be standalone programs, may be incorporated as subroutines in an operating system, may be functions in an installed software package, and the like. It should be understood that the various embodiments are not limited to the arrangements and instrumentality shown in the drawings.

[0032] Fig. 1 schematically shows an arrangement 100 for processing a material according to an exemplifying embodiment of the present disclosure. The arrangement 100 comprises a source 110 for generating signals at radio frequency, RF, range of 30 kHz - 300 MHz and / or at microwave frequency, MW, range of 300 MHz - 300 GHz. It should be noted that the source 110 is merely schematically indicated in their function, implementation, etc. The source 110, such as unit, emitter or the like, may comprise any components for the purpose of generating electromagnetic radiation, such as e.g. signal generators, (pre-) amplifiers, etc. The signal generated by the source 110 is further delayed and attenuated by phase shifters and attenuators 120, respectively.

[0033] Yet another alternative to dephase and attenuate the signal emanating from the source 110, is in using vector modulators, exhibiting two fundamental capabilities, namely amplitude and phase modulation. The combination of amplitude and phase modulation allows vector modulators to finely manipulate both the magnitude and timing of the incoming signal. A vector modulator operates by manipulating the amplitude and phase of a signal using In-phase (I) and Quadrature (Q) signals. The I and Q signals represent two orthogonal components of the modulated signal, corresponding to the real and imaginary parts of a complex number. The I and Q signals are provided in base band or even as DC voltage, and are used as input to mixer the diphase and attenuate the incoming signal. The I and Q signals are often generated using digital -to-analog erters (DACs), and the combined signal is produced by a vector summing network.

[0034] One particular characteristic at the core of the implementation of arrangement 100 is that the distribution of signals from 110 via transmission line(s) 180 is coherent inphase. Phase coherent signals refer to signals that have the same frequency and are perfectly aligned in phase. In-phase signals share the same phase, meaning their waveforms reach their maximum and minimum values simultaneously. Coherence ensures that the signals maintain a constant phase relationship over time. This relationship does not need to be absolute but consistent and repeatable over time, as the repeatability of the phase modulation is required for the subsequent standing wave manipulation where this alignment is used to achieve an additive effect, where the amplitudes of the signals arrive in phase and reinforce each other.

[0035] The frequency of the source 110 in the arrangement 100 may be selected and / or adapted in the radio frequency, RF, range of 30 kHz - 300 MHz and / or a microwave frequency, MW, range of 300 MHz - 300 GHz for the purposes of the method and / or adapted to one or more properties of the workpiece 140 to be processed in the method.

[0036] The arrangement 100 further comprises preamplifiers and amplifiers 130. The primary function of a pre-amplifier is to elevate the input signal level, making it suitable for further amplification by a larger power amplifier, which has an operational minimum signal level. The amplifiers 130 operate at higher power levels, and come in various classes, each with specific characteristics, and power transformation efficiencies, i.e. from DC to RF.

[0037] The arrangement 100 comprises a mold structure 200 with a pair of press plates 210, 220, defining a cavity for a material to be processed or workpiece 140 to be positioned therebetween. The arrangement 100 further comprises a transmission line 300, configured to guide and emit electromagnetic radiation in a radio frequency, RF, range of 30 kHz - 300 MHz and / or a microwave frequency, MW, range of 300 MHz - 300 GHz. The frequency of the electromagnetic radiation emitted by the transmission line 300 of the arrangement 100 may be selected and / or adapted for the purposes of the method and / or adapted to one or more properties of the workpiece 140.

[0038] The arrangement 100 in Fig. 1 comprises two plates 210, 220 between which the workpiece 140 is arranged, such that the workpiece 140 is exposed to the electromagnetic radiation from the transmission line 300 during operation of thearrangement 100. The transmission line 300 is connected to amplifiers and preamplifiers 130 as to rise the power of the signal source 110 to adequate power levels, i.e. in the range of 250 W, 500 W, 1 kW and more. The size of the plates could be of 10 cm, I m, 10 m to even 100 m in length and width. Larger the size, more power amplifiers would be required, and it is foreseen to have a typical power density of 100 W per 0.25 m2, where even larger power densities are considered, as 1 kW per 0.25 m2, 5 kW per 0.25 m2and 10 kW per 0.25 m2and even more. In the context of the present invention, the term “transmission line” is to be interpreted as a cable or structure designed to conduct electromagnetic waves in a contained manner. The transmission line may be an open or slotted coaxial structure, or a planar structure with conductors and / or insulators being flat and arranged parallel to each other.

[0039] During operation of the arrangement 100, the workpiece 140 is heated by the electromagnetic radiation emitted by the transmission line 300. The workpiece 140, is merely schematically indicated in Fig. 1 for reasons of simplicity, and it will be appreciated that the innovative concept of the present disclosure may be applied to substantially any kind of item. Hence, the workpiece 140 may constitute substantially any kind of material, product, sample, etc. susceptible to heating using electromagnetic radiation, and may take on different forms, shapes or configurations. Examples of workpieces to be processed include glued laminated timber (glulam), laminated stock (lamstock) lumber, laminated wood, solid wood boards, multi-layer panels or scantlings, posts, and beams include engineered wood products like particleboard, medium-density fiberboard (MDF), and oriented strand board (OSB). Additionally, materials such as fiberglass composites, ceramics, and other polymers can also be processed using the arrangement 100.

[0040] The arrangement 100 in Fig. 1 further comprises a plurality of temperature sensors 160 for sensing a temperature distribution of the workpiece 140. It will be appreciated that the number of sensors 160 of the arrangement 100 is arbitrary. Furthermore, the positioning of the sensor(s) 160 in the arrangement 100 is arbitrary. Hence, the disclosure of the sensors 160 and their position in the arrangement 100 is for illustrative purposes only and serves for an increased understanding of the operation of thearrangement 100. Preferably, the temperature sensors 160 are positioned as an array to capture the temperature distribution over the whole workpiece 140.

[0041] Fig. 1 further shows a control unit 150 of the arrangement 100. The control unit 150, which is schematically indicated, is connected to the RF / MW source 110 via an analogue or digital communication line 175 and is also connected to the temperature sensors 160 at different locations by analogue or digital communication line(s) 170. This configuration provides the required feedback in terms of temperature measured over time and in space. This measured temperature feedback, T(x,y,t) where x and y are the space coordinates and t, the time is later compared to the desired temperature setting, R(x,y,t) also defined in space and time with the same variables x,y and t. This temperature setting is further illustrated in Fig. 8. Processing the control error, E(x,y,t) = T(x,y,t) - R(x,y,t) with regards to the measured temperature feedback and reference setting allows the control unit 150 to set the parameters of the phase shifters and attenuators 120, via analogue or digital communication line(s) 190 and also to set the operating frequency of the source 110, via analogue or digital communication line 175. The control unit 150 is configured to control the heating of the workpiece 140 via the transmission line 300 receiving electromagnetic energy from the amplifiers 130 and coupling it via the transmission line 300 to the workpiece 140.

[0042] The temperature feedback signals are used in order to compute the next control action. Now, a central processing unit 150 controls those frequencies and phases based on differences between a reference heatmap and a temperature feedback heatmap. This computation deploys methods of automatic control and machine learning. Control actions are chosen from a collection of feasible settings, e.g. in a similar manner to the control method disclosed in WO 2022 / 063674 Al, which is incorporated herein by reference. Each setting defines the frequency, phase and amplitudes of the signals feeding the amplifiers 130. This allows one to work with complex constraints, unlike many other control approaches. The choice of the next setting to be applied, is directly dependent on the control error which consists of the difference between the reconstructed heatmap and the reference frame for the next instance.

[0043] Referring now to Figs. 2 and 3, there is shown a cross-sectional views, of the mold structure 200 according to two embodiments of the present disclosure, illustrating thetransmission line 300. This novel transmission line 300 is designed for heating a dielectric material within molds 200 or press plates 210, 220. This configuration is slightly different from a conventional transmission line such as a coaxial cable, as it may be realized by shaping or configuring the mold / press plate(s) itself and does not require the use of a regular cable.

[0044] The press plates 210, 220 can be made of a conductive (metallic) material, but other materials are also foreseen such as glass fiber composite material or ceramics and may further comprise a coating of conductive material or a separate metallic ground plane, as will be explained in more detail below. The two press plates 210, 220 are arranged to apply a pressure to the workpiece 140 for shaping or maintaining a shape of the workpiece 140, as illustrated by arrows 290 in Fig. 2. The surface of the press plates 210, 220 facing the workpiece 140 may be substantially flat in order to achieve or maintain a flat shape of the workpiece 140. In other embodiments, the press plates 210, 220 may also comprise additional sides (not shown) to define a closed cavity, thus forming a mold structure 200, and exhibit press plate movement in both top-to-bottom and bottom-to-top directions, as well as left-to-right and right-to-left movements. Various potential configurations and shapes of the surface of the press plates 210, 220 facing the workpiece 140 are conceivable, such as convex or concave or combinations thereof to more complex shapes. For example, one press plate may be convex and the other concave to obtain a corresponding curved geometry of the workpiece 140 after processing.

[0045] Referring to Fig. 2, the transmission line 300 can be realized by forming grooves 230 in the press plates of the mold, introducing an inner conductor 310 suspended within an insulator of a low-loss dielectric material 320 or using shims of this low-loss dielectric material 320 to suspend the inner conductor 310 at the center of the groove 230, and covering the groove 230 with a cover plate 240 made of a conductive material. The walls of the groove 230 and the cover plate 240 thus form the outer conducting shield of the transmission line 300. In case of press plates 210, 220 made of non-conductive material, the walls of the groove 230 may be coated with a conductive material to form the outer conducting shield.

[0046] Furthermore, slots 250 are formed in the cover plate 240 to provide an open or slotted structure of the transmission line 300. The slots 250 allow leakage of theelectromagnetic radiation from the transmission line 300. At the positions of the local maxima (antinodes) of the standing waves propagating along the transmission line 300, the heating of the workpiece 140 is maximal. As shown in Figs. 2 and 4, the press plate 210 comprises a plurality of parallel grooves 230, each accommodating a transmission line 300. In one embodiment, a single transmission line 300 is embedded in the press plate 210 arranged e.g. in a serpentine pattern. Alternatively, the press plate 210 comprises a plurality of separate transmission lines 300 arranged substantially in a parallel, wherein each transmission line 300 is connected to the source 110 by a transmission line 180 via separate (pre-) amplifiers 130 and phase shifters / attenuators 120 to receive electromagnetic radiation. This allows for individually controlling the characteristics of the electromagnetic radiation in the separate transmission lines 300. The electromagnetic radiation may be coupled into the transmission line 300 at opposite ends or at only one end thereof. The transmission line 300 may be embedded in both the top and bottom press plates 210, 220, or in only one of the press plates 210, 220, depending on the desired heating pattern to be created as well as the characteristics of the workpiece 140.

[0047] As shown in Fig. 3, the slots 250 may be formed as single continuous slots 250, one for each segment or section of transmission line 300, extending substantially in parallel throughout the length or width of the press plate 210, 220. For other reasons, such as mechanical stability, or reduction of the material protruding the slot 250, slot openings of different number, forms, orientation, spacing and aspect ratios may be used, as illustrated in Fig. 4.

[0048] Referring now to Fig. 5, another embodiment of a transmission line 305 is shown. Similar to the embodiment of Fig. 2, either of both press plate(s) 210, 220 comprise grooves 235 formed therein. An inner conductor 315 is arranged in the groove 235, e.g. in the form of a copper bar. This embodiment differs in that both the grooves 235 and the inner conductors have a substantially rectangular cross-sectional shape, as opposed to the approximately circular cross-sectional shapes in Fig. 2, thus providing a greater surface area of the inner conductor 315 and a larger window for leakage of electromagnetic radiation towards the workpiece 140. The inner conductor 315 is embedded in an insulator of a low-loss dielectric material 325 or using shims of this low-loss dielectric material 325 to suspend the inner conductor 315 at the center of the groove 235. The walls of the groove235 thus form the outer conducting shield of the transmission line 305. In case of press plates 210, 220 made of non-conductive material, the walls of the groove 235 may be coated with a conductive material to form the outer conducting shield. Alternatively, a ground plane may be provided in the form of a metallic plate (not shown) arranged outside the press plate(s) 210, 220, on the side facing away from the workpiece 140. The ground plane forms a common outer conducting shield for all inner conductors 315.

[0049] The grooves 235 with the inner conductors 315 are covered by a cover plate 245 made of a non-conductive material, i.e. which is transparent to electromagnetic radiation. For example, the cover plate 245 may be made of a dielectric plastic material. Suitable materials include polyether ether ketone (PEEK), polytetrafluoroethylene (PTFE) commonly known as Teflon®, aluminum oxide, micas, polypropylene (PE), fluorinated ethylene propylene (FEP) etc. Since the cover plate 245 allows passage of electromagnetic radiation, there is no need to provide slots therein. An advantage of this embodiment is that the combination of rectangular shaped, wider grooves 235 and electromagnetic transparent cover plate 245 allows for increased leakage of electromagnetic waves to heat the workpiece 140, whilst providing a fluid tight seal to protect the transmission line 305 from any liquid (e.g. glue) present together with or in the workpiece 140. An additional spacer layer 255 may be provided between the press plate(s) 210, 220 and the cover plate 245, e.g. for accommodating temperature sensors as will be described further below.

[0050] Referring now to Fig. 6, there is shown another embodiment, similar to the one of Fig. 5. In this embodiment, the press plates 210, 220 are made of a non-conductive material which is transparent to electromagnetic radiation, e.g. a dielectric plastic or composite material. Suitable materials include polyether ether ketone (PEEK), polytetrafluoroethylene (PTFE) commonly known as Teflon®, aluminum oxide, micas, polypropylene (PE), fluorinated ethylene propylene (FEP) etc. The grooves 235 are formed on the side of the press plate(s) 210, 220 facing away from the workpiece 140, i.e. opposite to the embodiment of Fig. 5, and with a similar configuration of inner conductors 315 and insulator 325 arranged in the grooves 235. The cover plate 245 is also made of a non- conductive material, e.g. a dielectric plastic or composite material. The configuration of the press plate(s) 210, 220 is provided with an outer conductor in the form of a ground plane265 made of a conductive material, e.g. aluminum, such that the inner conductors 315 are separated from the ground plane 265 by the cover plate 245.

[0051] The temperature sensors 160 may encompass various types alone or in combination, including optical fiber sensor(s) 260, acoustic sensors (e.g. ultrasonic transducers) 270, thermocouples 280, and others, as shown in Fig. 2. The optical fiber sensor 260 provides continuous or localized temperature measurement capabilities. Optical fibers are immune to electromagnetic interference, making this sensing method suitable for integration in the press plates 210, 220. The different types of temperature sensors 260, 270, 280 may be integrated in the press plate 210, 220 or the cover plate 240 or spacer layer 255, in an evenly distributed manner, thus achieving a substantially uniform distribution of measurement points. The temperature sensors 160 play a crucial role in monitoring and capturing the temperature distribution of the workpiece 140 during the processing steps. Their diverse nature allows for flexibility and adaptability to different materials and processing conditions, ensuring accurate and comprehensive temperature data acquisition. The choice of sensors depends on factors such as the workpiece's composition, processing environment, and the precision required for effective control and optimization of the processing parameters.

[0052] Referring now to Fig. 7, there is shown schematically the transmission line 300 connected to (pre-) amplifiers 130 on both ends and at one end an actuator 120 (consisting of phase shifters or vector modulator) which differentially dephase the signal source 110. With this double-sided configuration, it is possible to manipulate the standing waves along this coaxial transmission line, i.e. changing the position of the field maxima along the geometry in order to enhance the exposure efficiency, and thus the heating capabilities of the set-up with the resulting changes in the standing waves distribution due to the change in phase 400. No shorted end and opening spaced by half-wavelength and multiples of half-wavelengths are necessary. Instead, there is a continuous slot structure and feeding power from both ends. This way, the standing waves can be changed along the coaxial transmission line and avoids the need to align openings with electric field strength nodes, having multiple openings at intervals spaced by half-wavelength and multiples of halfwavelengths. Thus, the present solution provides a much greater flexibility in the rearrangement of the standing wave maxima.

[0053] Referring now to Fig. 8, there is shown how heating patterns vary over time, i.e. following parameter (t) in diagram (a) and spatially, i.e. following parameters (x,y) in diagram (b), where t is the time and x and y are the space coordinates, respectively. The temperature measured over time and in space, is then T(x,y,t). This measured temperature T(x,y,t) is later compared to the desired reference temperature settings R(t) and R(x,y,t), respectively, the difference is taken as feedback for computing the next steps in adjusting the settings by the control unit 150 for heating of the workpiece 140. The heating patterns are a complex function of the past applied electrical field. This electrical field can be changed by changing the phase of the signals emitted by the slots 250 of the transmission lines 300. This is a complex relation, possibly affected by impurities of the involved materials.

[0054] Heating patterns can be homogenous, heterogenous, or variable in time. Arrangement displays a reference heating pattern in time R(t) and space and time R(x,y,t). Alternatively, this heating pattern can also be expressed in space, making it effectively a collection of frames of a reference video. This reference video may indicate homogeneous heating strategies, sawtooth heating strategies or focused heating strategies varying over time: the reference video may be arbitrary, and should be specified by the operator, and as dictated by the case at hand.

[0055] Embodiments of an arrangement and method for processing of a material using electromagnetic heating according to the present disclosure have been described. However, the person skilled in the art realizes that this can be varied within the scope of the appended claims without departing from the inventive idea.

[0056] All the described alternative embodiments above or parts of an embodiment can be freely combined without departing from the inventive idea as long as the combination is not contradictory.

Claims

CLAIMS1. An arrangement (100) for processing a material, the arrangement comprising: a pair of press plates (210, 220) adapted to receive a workpiece (140) of the material to be processed therebetween, wherein the press plates are arranged to apply a pressure (290) on the workpiece, a transmission line (300; 305) embedded in at least one of the press plates, the transmission line being arranged to guide and emit electromagnetic radiation therethrough to generate standing waves for heating the workpiece; a source (110) for generating electromagnetic radiation, the source being connected to the transmission line via a transmission line (180) to couple the electromagnetic radiation into the transmission line; a plurality of temperature sensors (160) configured to detect a temperature distribution of the workpiece; a control unit (150) connected to the source and the plurality of sensors, wherein the control unit is configured to adjust the electromagnetic radiation generated by the source based on the detected temperature distribution of the workpiece.

2. The arrangement according to claim 1, wherein the transmission line comprises a plurality of grooves (230; 235) formed in the at least one press plate and facing towards or away from the workpiece, each groove containing an inner conductor (310; 315) and an insulating material (320; 325), wherein the inner conductor is at least partially surrounded by an outer conducting shield to allow leakage of the electromagnetic radiation.

3. The arrangement according to claim 2, wherein the at least one press plate is made of conductive material and further comprises a cover plate (240) made of conductive material comprising one or more slots (250), wherein the groove and cover plate together constitute the outer conducting shield of the transmission line.

4. The arrangement according to claim 2, wherein the at least one press plate comprises a ground plane made of conductive material and arranged on a side of the press plate facing away from the workpiece, and a cover plate (245) made of non-conductivematerial, wherein the ground plane constitutes the outer conducting shield of the transmission line.

5. The arrangement according to any one of the preceding claims, wherein the source is connected to the transmission line at opposite ends thereof for coupling of the electromagnetic radiation.

6. The arrangement according to any one of the preceding claims, wherein the transmission line is arranged in a serpentine pattern in the at least one press plate.

7. The arrangement according to any one of the preceding claims, comprising a plurality of transmission lines arranged substantially in parallel, each transmission line being connected to the source via a transmission line for coupling of electromagnetic radiation.

8. The arrangement according to any one of the preceding claims, wherein the plurality of temperature sensors comprises an array of thermocouples (280) and / or ultrasonic transducers (270) arranged on one or both of the press plates, an optical fiber sensor (260) embedded in one or both of the press plates, cover plates, or a combination thereof.

9. The arrangement according to any one of the preceding claims, wherein the press plates define an open or closed cavity therebetween for receiving the workpiece.

10. The arrangement according to any one of the preceding claims, wherein a surface of the press plates facing the workpiece is flat or curved.

11. The arrangement according to any one of the preceding claims, wherein the control unit is configured to adjust the phase, amplitude, frequency and / or power of the electromagnetic radiation.

12. A method for processing a material, the method comprising the steps of: arranging a workpiece (140) of the material to be processed between a pair of press plates (210, 220); applying a pressure (290) on the workpiece by means of the press plates;generating electromagnetic radiation from a source (110) and coupling the electromagnetic radiation into a transmission line (300; 305) embedded in at least one of the press plates, the transmission line being arranged to guide and emit electromagnetic radiation therethrough to generate standing waves for heating the workpiece; detecting a temperature distribution of the workpiece by means of a plurality of temperature sensors (160); and adjusting the electromagnetic radiation generated by the source based on the detected temperature distribution of the workpiece.

13. The method according to claim 11, wherein adjusting the electromagnetic radiation comprises adjusting the phase, amplitude, frequency and / or power of the electromagnetic radiation.

14. The method according to claim 11 or 12, wherein the electromagnetic radiation is coupled into the transmission line from opposite ends thereof.

15. The method according to any one of claims 11-14, wherein the workpiece comprises glued laminated timber (glulam), laminated stock (lamstock) lumber, laminated wood, solid wood boards, multi-layer panels or scantlings, posts, and beams, engineered wood products like particleboard, medium-density fiberboard (MDF), and oriented strand board (OSB), fiberglass composites, ceramics, and other polymers.

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