Technical Field

The present disclosure relates to a device for microwave treatment of material. Background

A known device for microwave treatment of material is disclosed in the patent SE466281 , wherein the device comprises a plurality of microwave generators adapted to heat the material that is treated. A fan blows cooling air passed the microwave generators. The heated air that has passed the microwave generators continues into a space wherein the material is treated by the microwaves. The microwaves react with dipoles, such as water molecules, in the material. The heated air that enters the treatment space is used for removal of moisture that is a result of the microwave treatment.

When the material passes through the device, the material will eventually become dryer, i.e. there will be less dipoles for the microwave to react with. The energy density in the space wherein the material is treated will raise and there is a risk that the microwave generators are damaged due to re-radiation of microwaves.

The microwave generator normally comprises a generator, a

magnetron and a waveguide. For microwave generators with large effects, the generator and the magnetron may be connected to a circulator wherein re-radiated energy is transported from the waveguide to an extra load to avoid damage on the magnetron. However, this solution is not applicable on a small effect microwave generator, such as disclosed in SE466281 , since it would be too complicated and bulky.

Consequently, there is a need for a device that protects the microwave generator from damage due to re-radiated microwaves in an effective easy manner. Summary

It is an object of the present invention to provide an improved solution that alleviates the mentioned drawbacks with present devices. Furthermore, it is an object to provide a device for microwave treatment of material.

This is achieved by providing a device for microwave treatment of a material, wherein the device defines a treatment space for receiving the material to be treated by the microwaves. The device comprises at least one microwave-generating unit arranged outside the treatment space and adapted to provide microwaves into the treatment space for treating the material, a microwave absorbent, and a housing made of a non-microwave transparent material, in which housing the microwave absorbent is arranged. The housing is provided with a plurality of openings for microwaves to pass through to the microwave absorbent.

By providing a microwave absorbent, excessive microwaves may be absorbed by the microwave absorbent instead of risking damage to a magnetron in the microwave-generating unit due to re-radiation. When treating the material in the treatment space, the material may be irradiated by microwaves that may react with dipoles, such as water molecules, in the material. The material may thereby be heated. Alternatively, the device may be used for sanitation of the material. Concurrently with the material drying, the amount of dipoles in the material may decrease such that excessive microwaves may be left in the treatment space, re-radiating from the material and the energy density in the treatment space may increase. Further along with an increasing energy density, the openings in the housing may be adapted to start leaking the excessive microwaves into the housing to be absorbed by the microwave absorbent. The amount of microwaves entering the housing may increase along with an increased energy density level in the treatment space. To avoid that the excessive microwaves may re-radiate to a magnetron in the microwave-generating unit, the microwave absorbent may be adapted to comprise dipoles that may react with the microwaves. To control the amount of microwaves that may be absorbed, the housing may prevent microwaves from being absorbed before the energy density in the treatment space reaches a predetermined level. The predetermined level of the energy density may be set by the shape and dimension of the openings in the housing. The device according to the invention may provide a way of absorbing excessive energy in the treatment space that is not complex, bulky or expensive. Except for the openings in the housing, the interior of the housing in which the microwave absorbent extends may be isolated from microwaves. The non-microwave transparent material of the housing may be stainless steel, aluminum or the like. The microwave-generating unit may comprise a magnetron, a generator for generating power to the magnetron, and a waveguide for distributing the microwaves into the treatment space. The treatment space may be defined as a space, the interior of a chamber or housing, or the like, adapted to receive the material to be treated, and adapted to receive microwaves from the microwave-generating units.

In one embodiment, the housing may be arranged in the treatment space, forming a channel in which the microwave absorbent may be arranged.

By arranging the housing in the treatment space, the excessive microwaves may easily reach the housing and the absorbent when the energy density in the treatment space increases.

In one embodiment, the microwave absorbent may be a water-filled tube of microwave transparent material.

By providing the microwave absorbent as a water-filled tube, the excessive microwaves may react with the water in the tube when the microwaves have entered the channel. The tube may be made of a microwave transparent material, such as polythene. When the microwaves react with the water molecules, the water may be heated. The energy from the microwaves may thereby be transformed to heat in the water.

In a further embodiment, the device further may comprise an accumulator in connection with said microwave absorbent.

The microwave absorbent may be in connection with an accumulator. If the microwave-absorbent is a water-filled tube, the water-filled tube may be in fluid connection with an accumulator, and the heated water in the tube may be transported away from the microwave absorbent. The accumulator may be located outside the housing. The accumulator may store the energy provided to the water by the microwaves. A pump may be connected to the water-filled tube and the accumulator, adapted to circulate the water through the tube and the accumulator.

In another embodiment, the device further may comprise a

temperature detecting unit for detecting the temperature of the water in the water-filled tube, and a controller device for controlling the operation of the at least one microwave-generating unit based on said detected temperature.

The device may comprise a plurality of microwave-generating units. To control the total amount of energy provided to the material to be treated, the microwave-generating units may be switched on and off during the treatment. The device may comprise a controller that controls the operation, i.e. the on and off states, of the microwave-generating units. The controller may receive input signals from a temperature detecting unit regarding the treatment space for basis of the controlling operation. In one embodiment, the temperature of the water in the microwave absorbent and/or the accumulator may function as an input to the controlling of the operation of the microwave-generating units. Such temperature information may be provided by the temperature detecting unit. When the energy density in the treatment space increases and the amount of excessive microwaves that is absorbed by the microwave absorbent increases, the temperature in the microwave absorbent may increase. The temperature of the water in the water-filled tube and/or the water in the accumulator may thereby increase. By measuring the

temperature of the water, information of the energy density in the treatment space may thereby be provided. This information may be used for controlling the operation of the microwave-generating units.

In one embodiment, the device may comprise a ventilation

arrangement adapted to provide cooling air to the microwave-generating unit and air into the treatment space, and wherein the ventilation arrangement may be formed to guide air that have passed the at least one microwave- generating unit into the treatment space.

The air that may be provided into the treatment space may remove moisture that may leave the material when it is heated. By using the air for cooling the microwave-generating unit also to the treatment space, an effective ventilation arrangement may be achieved. The air that is guided passed the microwave-generating unit may be heated when it cools the unit. When the air reaches the treatment space it may be used for drying the material, i.e. transporting the vaporized water that may be a result of the reaction between the microwaves and the water molecules in the material. The heat from the microwave-generating unit may thereby be reused in the treatment space.

In a further embodiment, the ventilation arrangement may be formed such that air guided to the treatment space is adapted to enter the treatment space through the plurality of openings in the housing.

The air flow adapted to enter the treatment space may thereby be controlled by the openings in the housing. The air that is guided to pass through the openings may have been heated by the microwave-generating unit. The air may be used for transporting vaporized water from the treatment space. By guiding the air to the treatment space through the housing, the air may further pass the microwave absorbent. When the microwave absorbent absorbs energy from the excessive microwaves, the microwave absorbent may be heated. When the air passes the microwave absorbent it may be further heated. A further heated air may increase its ability to absorb moisture in the treatment space. The openings in the housing may in an alternative embodiment comprise a first and a second set of openings, wherein the first set of openings may be adapted for letting microwaves into the channel, and the second set of openings may be adapted to letting air into the treatment space. The first set of openings may be covered with a plate of microwave transparent material to prevent air from passing said first set of openings.

In another embodiment, the device further may comprise a ventilation arrangement adapted to provide air for cooling the at least one microwave- generating unit, and wherein the ventilation arrangement may comprise an air mixture chamber adapted to receive the air for cooling the at least one microwave-generating unit, and wherein the air mixture chamber may be adapted to supply air to the treatment space.

The air mixture chamber may provide an equalization of the

temperature of the air that is adapted to enter the treatment space. The device may comprise a plurality of microwave-generating units. The cooling air from all these units may enter a common air mixture chamber. The air that leaves the air mixture chamber may thereby be mixed such that the temperature is equalized. The plurality of microwave-generating units may be switched on and off periodically to control the treatment process in the treatment space. The temperature of the cooling air from each microwave- generating unit may thereby vary over time. The air mixture chamber may avoid that the temperature of the air adapted to enter the treatment space may vary too much. It may further avoid that too cold air may enter the treatment space.

In a further embodiment, the ventilation arrangement may be adapted to supply additional air to the air mixture chamber.

The additional air may be supplied from an air supply unit, such as a fan. The fan may be a part of the ventilation arrangement and may further be adapted to supply the cooling air to the at least one microwave-generating unit. The additional air may not be guided passed any microwave-generating unit before it is adapted to enter the air mixture chamber. The additional air may thereby be used for controlling the temperature of the air that leaves the air mixture chamber into the treatment space.

In a yet further embodiment, an accumulator in connection with the microwave absorbent may be arranged in the air mixture chamber such that the air in the air mixture chamber may be adapted to be heated by the accumulator.

The energy from the excessive microwaves that is absorbed by the microwave absorbent may be stored in an accumulator. An increased amount of absorbed microwaves may provide an increased temperature in the microwave absorbent and the accumulator. By arranging the accumulator in the air mixture chamber, the heat from the accumulator may be used for heating the air that is adapted to enter the treatment space. Thereby, the excessive energy in the treatment space may be reused as heat.

In one embodiment, the size of the openings in the housing may be in the range between 7-12 mm in diameter. The size and shape of the openings in the housing may control the amount of microwaves that may pass into the channel when the energy density in the treatment space increases. With an opening size of 6 mm or less, no or almost no microwaves may be able to pass through the openings. With too large opening size, too much microwaves may enter the channel. The size of the openings may set the amount of microwaves that may be absorbed by the microwave absorbent at a certain energy density level. The most suitable size of the openings may vary for different applications.

In another embodiment, the device further may comprise a ventilation arrangement adapted to provide cooling air to the microwave-generating unit and air into the treatment space, and a dehumidifier adapted to receive air from the treatment space.

When using the device for heating/drying the material, the air that is guided to the treatment space may be used for removing moisture, i.e.

vaporized water, which may be a result of the microwaves reacting with dipoles in the material. The moisture may be removed such that it may not continue to moisten the material, and such that the drying operation of the material may be efficient. The device may comprise an air removal channel adapted to lead the moisturized air away from the treatment space. The moisturized air may further be adapted to be dried by a dehumidifier such that dry air is received. The dry air may thereby be reused in the ventilation arrangement, providing efficient ventilation in the device.

In yet another embodiment, the material to be treated may be adapted to be moved in a longitudinal direction through the treatment space in the device and to be treated by microwaves from the at least one microwave- generating unit along its movement through the device, and wherein the microwave absorbent and the housing may extend in a direction transverse to the longitudinal direction.

The material that may pass through the device to be treated by the microwaves may be moved by a transportation device along with the longitudinal direction. The transportation device may be a conveying belt. Along with the movement through the device, the material may be adapted to be treated by at least one microwave-generating unit. The treatment space may have a width in a direction transverse to the longitudinal direction. The at least one microwave-generating unit may provide microwaves along the width of the treatment space such that all material that may be moved through the device may be treated by the microwaves. Further, the microwave absorbent and the housing may extend across the width of the treatment space.

Thereby, the energy density level may be kept at a suitable level across the whole width of the treatment space. The device may comprise a plurality of microwave-generating units at different positions along the longitudinal direction of the treatment space. Further, the device may comprise a plurality of microwave absorbents and housings extending across the width of the treatment space at different positions along the longitudinal direction of the treatment space. Each microwave absorbent and housing may be arranged adjacent to at least one microwave-generating unit.

In one embodiment, the treatment space may extend in a longitudinal direction of the device, and wherein the device may comprise an additional microwave absorbent arranged at a longitudinal end of the treatment space, and wherein the additional microwave absorbent may extend in a direction transverse to the longitudinal direction.

By arranging an additional microwave absorbent at a longitudinal end of the treatment space, microwaves may be prevented from leaving the treatment space and the device if they are not absorbed by the material. The additional microwave absorbent may extend in the direction transverse to the longitudinal direction, such that the whole width of the treatment space is covered by the additional microwave absorbent.

In a further embodiment, the additional microwave absorbent may be a water-filled tube of a microwave transparent material.

The additional water-filled tube may be in fluid communication with other water-filled tubes in the device and with a common accumulator. By connecting all microwaves absorbents in the device with each other and with a common accumulator, an absorbent arrangement throughout the complete device/treatment space may be achieved, wherein all excessive energy in the treatment space may be stored in the accumulator. A pump may be provided in the absorbent arrangement to circulate water through the tubes and accumulator.

In another embodiment, the dimension of the openings in the housing may be adjustable.

By providing the possibility to adjust the size of the openings in the housing, the amount of microwaves that may be absorbed by the microwave absorbent may be controlled. There may be several ways to provide an adjustable opening size. One way may be to provide the openings as triangle shaped openings, wherein a covering member may be attached at a side of the triangle and moveable such that the size of the triangle may be adjusted.

Brief Description of the Drawings

The invention will in the following be described in more detail with reference to the enclosed drawings, wherein:

Fig 1 a shows a schematic cross-sectional view of a device according to an embodiment of the invention.

Fig 1 b shows a schematic cross-sectional view of a device according to an embodiment of the invention.

Fig 1 c shows a schematic cross-sectional view of a device according to an embodiment of the invention.

Fig 1 d shows a perspective view of a housing according to an embodiment of the invention.

Fig 2a shows a schematic cross-sectional view of a device according to an embodiment of the invention.

Fig 2b shows a schematic cross-sectional view of a tube arrangement according to an embodiment of the invention.

Fig 2c shows a schematic cross-sectional view of a ventilation arrangement according to an embodiment of the invention.

Fig 2d shows a schematic cross-sectional view of a ventilation arrangement according to an embodiment of the invention.

Fig 3a shows a schematic cross-sectional view of a device according to an embodiment of the invention. Fig 3b shows a schematic cross-sectional view of a device according to an embodiment of the invention.

Description of Embodiments

The present invention will be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. In the drawings, like numbers refer to like elements.

Fig 1 a illustrates a device 1 according to an embodiment of the invention. An energy deck 2 is arranged above a treatment space 3. Material to be treated in the device 1 is adapted to be moved through the treatment space 3, below the energy deck 2. In the energy deck 2, a microwave- generating unit 10 is arranged for supplying microwaves 14, comprising a magnetron 1 1 , a waveguide 13 and a generator 12. The microwaves 14 are generated by the magnetron 1 1 and distributed into the treatment space 3 by the waveguide 13. The generator 12 is adapted to generate power to the magnetron 1 1 . The magnetron 1 1 and generator 12 may be of conventional technology. The microwaves 14 react with dipoles in the material that passes below the energy deck 2. In the treatment space 3, a channel is formed by a housing 20. The housing 20 is attached to an underside of the energy deck 2 in a microwave sealed manner. Microwaves 15 may enter the channel through openings 29 on a bottom side 20a of the housing 20. The openings 29 are directed towards the material adapted to pass through the treatment space 3. The size of the openings 29 is preferable between 7-12 mm. The shape and size of the openings 29 may be adjusted to suit a particular application.

Air is supplied to the energy deck 2 for cooling the magnetron 1 1 . The energy deck 2 further comprises an air mixture chamber 30. The air 31 that is directed towards the magnetron 1 1 enters the air mixture chamber 30 after it has passed the magnetron 1 1 . At the bottom side of the energy deck, openings are provided to enable air flow from the air mixture chamber 30 into the channel. The air 33 that leaves the air mixture chamber 30 enters the treatment space through the openings 29 in the housing 20. Optionally, an additional air flow 32 is supplied to the air mixture chamber. The additional air 32 is provided from the same source as the cooling air 31 to the magnetron 1 1 . By supplying additional air 32 and mixing all air in the air mixture chamber 30, the temperature of the air 33 that is supplied to the treatment space 3 may be controlled.

Inside the housing 20, a microwave absorbent 21 is arranged. The microwaves 14 that are supplied to the treatment space 3 by the waveguide 12 are directed towards the material that passes through the treatment space 3. The material is dried by the reaction with the microwaves 14. If the material passing below the energy deck 2 comprises a low amount of dipoles, not all microwaves 14 supplied to the treatment space 3 can react with the material. Excessive microwaves 15 will thereby re-radiate from the material and the energy density in the treatments space 3 will increase. Without any

microwave absorbent 21 , the excessive microwaves 15 could reach and damage the magnetron 1 1 . In the present invention, the excessive

microwaves 15 enter the channel through the openings 29 in the surface 20a of the housing 20. The microwave absorbent 21 absorbs the microwaves 15 and stores the energy from them. The energy density in the treatment space 3 is thereby kept at a suitable level. The microwave absorbent 21 may comprise any material comprising dipoles and suitable for absorbing the energy from the microwaves 15. Such material could be water, ore or iron. In the illustrated embodiment, the microwave absorbent 21 comprises a water- filled tube. The tube 21 is made of a microwave transparent material, such as polythene. The water in the tube 21 reacts with the excessive microwaves 15 and absorbs the energy. The water in the tube 21 is thereby heated.

In the air mixture chamber 30 in the energy deck 2, an accumulator 23 provided as a heat exchanger 23 is provided. The heat exchanger 23 is in fluid connection with the tube via pipes 22. A pump 26 (not shown) circulates the water through the tube 21 , the pipes 22 and the heat exchanger 23. The energy from the excessive microwaves 15, stored in the water as heat is transported to the heat exchanger 23. By arranging the heat exchanger 23 in the air mixture chamber 30, the energy from the excessive microwaves 15 may be reused for heating the air in the air mixture chamber 30. The air 33 supplied to the treatment space 3 is adapted for drying and removal of moisture in the treatment space 3. It is thereby an advantage if the air 33 supplied to the treatment space 3 is heated.

In a case wherein the microwave absorbent comprises a solid material instead of water, the microwave absorbent is heated by the excessive microwaves, and the air 33 passing the microwave absorbent towards the treatment space 3 is heated by the microwave absorbent.

As shown in figs 1 b and 1 c, the energy deck 2 may comprise a plurality of microwave-generating units 10a-c. The microwave-generating units 10a-c share the same air mixture chamber 30, heat exchanger 23 and microwave absorbent 21 . During treatment of the material, each magnetron 1 1 a-c will be switched on and off from time to time to control the total energy supply to the treatment space 3. When a magnetron 1 1 a-c is switched off, less heat will be generated by the magnetron 1 1 a-c, providing a varying temperature of the cooling air 31 a-c that cools the magnetron 1 1 a-c. By use of the air mixture chamber 30, the air 33 that reaches the treatment space 3 will not vary in the same amount since the air flows 31 a-c from the magnetrons 1 1 a-c are mixed and the temperatures are equalized. The air 33 to the treatment space 3 passes through openings 30a in a bottom surface of the air mixture chamber 30, which may also be a bottom surface of the energy deck 2. The air thereby enters the housing 20 and may continue through the openings 29 in the housing 20 to the treatment space 3.

Excessive microwaves 15 from all microwave-generating units 10a-c in the energy deck 2 are absorbed by the microwave absorbent 21 . The energy absorbed by the absorbent 21 is transported to the heat exchanger 23 and reused in the air mixture chamber 30.

The energy deck 2 is supplied with air from an external air supply. In the energy deck 2, the incoming cooling air 31 is distributed to each of the magnetrons 1 1 . There may also be more than one inlet for additional air 32 to the air mixture chamber 30. Fig 1 d illustrates an alternative embodiment wherein air 33 to the treatment space 3 is adapted to pass through the housing 20 though a first set of openings 60, and the excessive microwaves 15 are adapted to pass through the housing 20 through a second set of openings 61 . The first set of openings 60 is provided on a bottom surface 20a of the housing 20. In this embodiment, the first set of openings 60 is of a size such that the microwaves 15 will not pass through. Such size may be approximately 5 mm. The second set of openings 61 may comprise openings at two sides 20b of the housing 20. At an inner side of the housing 20, the second set of openings 61 is covered with a microwave transparent material 62. The air 33 passing through the housing 20 may thereby not pass through the second set of openings 61 . Further, at least one adjustable strip 63 is arranged at the second set of openings 61 . The second set of openings 61 comprises triangle shaped openings. Each side of the triangle shape is between 15-20 mm long. By adjusting the position of the strip 63 along the direction 64, the size of the triangle shaped openings 61 may be adjusted. The strip 63 can be set to cover a portion of each triangle shaped opening 61 . The strip 63 is of a non- microwave transparent material. The amount of excessive microwaves 15 that may enter the housing 20 through the second set of openings 61 to reach the microwave absorbent 21 may thereby be adjusted. The larger openings for the excessive microwaves 15, the larger amount of excessive microwaves 15 will find its way in to the absorbent 21 . The larger amount of excessive microwaves 15 finding its way to the microwave absorbent 21 , the lower energy density level will be kept in the treatment space 3.

Fig 2a illustrates a device 1 according to the invention comprising three energy decks 2 arranged after each other in a longitudinal direction X of the device. The material to be treated is transported through the treatment space 3 by a conveyor belt 40. The material passes all energy decks 2 and all waveguides 13 supplying microwaves 14. The housings 20 with microwave absorbents 21 are arranged transverse to the longitudinal direction X of the device 1 at each energy deck 2.

Each energy deck 2 may comprise a plurality of fastening means (not shown) for arrangement of waveguides, generators and magnetrons for the microwave-generating units. The fastening means are identical for each of the parts, i.e. waveguide, generator and magnetron. Thereby, the position of each part can be varied in each energy deck 2. When a plurality of energy decks 2 are arranged next to each other, the location of the waveguides 13, i.e. the location of the microwave 14 supplies from the energy deck 2, can be varied. This enables a more even supply of microwaves 14 along the width of the treatment space 3 throughout the whole device 1 .

The device 2 comprises an air supply provided as a fan 35. The fan 35 supplies cooling air 31 to the magnetrons 1 1 in each energy deck 2. In each energy deck 2, the cooling air 31 passes the magnetrons 1 1 and enters the air mixture chamber 30 before entering the treatment space 3 through the housing 20.

The microwave absorbents 21 in the energy decks 2 are further shown in fig 2b. In this embodiment, a central accumulator, i.e. heat exchanger 25, is provided in the device 1 , which heat exchanger 25 is in fluid connection with all microwave absorbents 21 in the device. The microwave absorbents 21 are connected to the heat exchanger 25 via pipes 22. A pump 26 is provided for circulating the water through the pipes 22, microwave absorbents 21 and heat exchanger 25.

Further, the device comprises a plurality of additional microwave absorbents 24. These are arranged at the longitudinal ends of the device. The plurality of additional microwave absorbents 24 may be arranged both above and below the conveyor belt 40 transporting the material. The purpose of the additional microwave absorbents 24 is to absorb excessive microwaves 15 that otherwise may have been able to leave the treatment space 3. The additional microwave absorbents 24 extend transverse to the longitudinal direction of the treatment space. The additional microwave absorbents 24 are in fluid connection with the microwave absorbents 21 and the heat exchanger 25 via pipes 22.

Referring back to fig 2a, the device 1 may optionally be provided with a plurality of mechanical microwave traps 19. The purpose of the mechanical microwave traps 19 is to complement the microwave absorbent function of the additional microwave absorbents 24 at the longitudinal ends of the device 1 .

As seen in fig 2c, the fan or fans 35 in the device provide air 34 to the energy decks 2. The air 37 that is adapted to transport moisture from the treatment space 3 is guided through air outlet channels 36 back to the fans 35. Along its way back to the fans, the air 37 is guided to pass a dehumidifier 27 and the heat exchanger 25. The dehumidifier 27 removes the moisture in the air 37 transported from the treatment space 3, such that the air can be reused in the device. In an embodiment wherein each energy deck 2 comprises a heat exchanger 23, the heat exchanger 25 at the fans 35 may be removed.

By providing the air outlet channels 36 along the longitudinal extension direction X of the device, the air 33 that is provided into the treatment space 3 may be guided in a direction transverse to the longitudinal direction X to reach the air outlet channels 36. The air 33 thereby leaves the treatment space 3 as fast as possible. If the air 33 would travel along the longitudinal direction X inside the treatments space 3, the moisture intercepted by the air 33 when entering the treatment space 3 could moisten the material present in the treatment space 3. In this embodiment, the air 33 and its intercepted moisture exits the treatments space 3 into the air outlet channels 36 as fast as possible.

The dehumidifier 27 is provided as an accumulator that provides cooling water from an external water cooling compressor assembly for dehumidification of the air. Optionally, an extra cooling accumulator 28 is provided which is connected to an extra accumulator in the water cooling compressor assembly, which extra cooling accumulator 28 is adapted to use cold in exterior air. During cold weather, exterior air can be used to lower the compressor load in the external water cooling compressor assembly.

Fig 2d illustrates a device adapted to be coupled to an external air supply (not shown). The air 37 that is guided from the treatment space 3 by the air outlet channels 36 is adapted to leave the device through air outlets 39. The air 34 supplied to the energy decks 2 is adapted to enter the device through air inlets 38. At the external air supply, the air may pass a dehumidifier and a heat exchanger. An alternative embodiment may be a combination of the embodiments in figs 2c and 2d, wherein the air is supplied by an external air supply, but wherein the device comprises a heat exchanger 25 and a dehumidifier 27.

Fig 3 illustrates an alternative embodiment of the invention, wherein microwaves 14 may be used for a sanitation treatment of material. The device 4 comprises a plurality of treatment decks 5. The treatment decks 5 are placed on top of each other. The number of treatment decks 5 may be adapted to a present application. Different applications may need different total effect from the treatment decks 5. In a top surface and bottom surface of each treatment deck 5 there is an opening 51 . Through the openings 51 a tube 52 extends. The tube 52 could be a flexible tube. The material to be treated in the device 4 is adapted to pass through the tube 52. With an oval tube 52, a larger area of the tube 52 is exposed to the microwaves 14. To hold the tube 52 in place in the treatment decks 5, each treatment deck 5 is provided with two microwave transparent plates 53.

At two opposite ends of each treatment deck 5 an energy deck is provided each comprising a plurality of microwave-generating units 10. The microwaves 14 supplied by the microwave-generating units 10 are directed towards the tube 52 extending through the treatment decks 5. In each treatment deck 5, at least one microwave absorbent 21 is arranged.

Preferably each treatment deck 5 comprises two microwave absorbents 21 , one at each opposite end wherein an energy deck with microwave-generating units 10 is arranged. The at least one microwave absorbent 21 is arranged in a direction transverse to the extending direction of the tube 52. Each microwave absorbent 21 is covered by a housing 20 provided with a plurality of openings 29. The openings 29 are adapted to let excessive microwaves 15 into the housing 20, to the microwave absorbent 21 , when the energy density in the treatment deck 5 increases. The microwave absorbents 21 are adapted to absorb excessive microwaves 15 that are not absorbed by the material to be treated, passing through the tube 52.

The microwave-generating units 10 may be switched on and off periodically during treatment of material to keep a prescribed temperature in the treatment deck 5 and/or the material. Each treatment deck 5 is provided with a temperature detecting unit 54 to provide information about the present temperature. This information may be used for controlling the operation of the microwave-generating units 10.

Each microwave-generating unit 10 comprises a magnetron 1 1 that needs to be cooled. Each energy deck is air sealed such the air in the air sealed spaces does not reach the space wherein the microwaves 14 are supplied. An external air supply provides cooling air 34 into each air sealed energy deck. The cooling air 34 is guided passed the magnetrons 1 1 . After have passed the magnetrons 1 1 the air 37 leaves the energy deck.

The microwave absorbents 21 may be in connection with an external accumulator or heat exchanger to reuse or store the energy absorbed by the microwave absorbents 21 .

Below the treatment decks 5 in the device 4, the device may be provided with a heater 55. The heater 55 is adapted to heat the material to a suitable temperature before leaving the device 4. The device may further be provided with a flow controller 56. The flow controller is adapted to control the flow speed of material through the tube 52. The operation of the flow controller 56 may be based on information from the temperature detecting units 54 in the treatment decks 5.

One embodiment of the invention may be formed as a combination of the embodiments shown in fig 1 and 3. A device similar to the device 4 shown in fig 3 could be used for drying of material passing through the device. Two microwave transparent plates form a shaft through which the material is adapted to pass. The device comprises a plurality of treatment decks put on top of each other. A flexible device may thereby be provided wherein the number of treatment decks could be adjusted for a specific application. In a dryer device, energy decks comprising microwave-generating units are only arranged at one side of each energy deck. A ventilation arrangement provides air into a treatment space, similar to the device in fig 1 , through which treatment space the shaft extends. The air provided into the treatment space is adapted to remove moisture from the treatment space. If the microwave- generating units in each energy deck are arranged in one end of the treatment deck, an air outlet is provided at an opposite end of the treatment deck. The plurality of treatment decks arranged on top of each other may be arranged reversed relative to each other, such that every second energy deck is arranged in one way, and every second in another way. Each treatment deck comprises a microwave absorbent for absorption of excessive microwaves. Each treatment deck may comprise a temperature and/or a humidity detecting device. The flow speed of material through the shaft may be controlled based on information from the temperature and/or the humidity detecting device.

According to an aspect of the invention, the device is provided for microwave treatment of a material, wherein the device defines a treatment space for receiving the material to be treated by the microwaves, the device comprises at least one microwave-generating unit arranged outside the treatment space and adapted to provide microwaves into the treatment space for treating the material, and a ventilation arrangement adapted to provide air for cooling the at least one microwave-generating unit and air into the treatment space, characterized in that the ventilation arrangement comprises an air mixture chamber adapted to receive air provided for cooling of the at least one microwave-generating unit, and wherein the air mixture chamber is adapted to supply air to the treatment space.

The air mixture chamber may provide an equalization of the

temperature of the air that is adapted to enter the treatment space. The device may comprise a plurality of microwave-generating units. The cooling air from all these units may enter a common air mixture chamber. The air that leaves the air mixture chamber may thereby be mixed such that the temperature is equalized. The plurality of microwave-generating units may be switched on and off periodically to control the treatment process in the treatment space. The temperature of the cooling air from each microwave- generating unit may thereby vary over time. The air mixture chamber may avoid that the temperature of the air adapted to enter the treatment space may vary too much. It may further avoid that too cold air may enter the treatment space. In the drawings and specification, there have been disclosed preferred embodiments and examples of the invention and, although specific terms are employed, they are used in a generic and descriptive sense only and not for the purpose of limitation, the scope of the invention being set forth in the following claims.