WO1996013157A1

WO1996013157A1 - Apparatus for generating microwave radiation

Info

Publication number: WO1996013157A1
Application number: PCT/NL1995/000352
Authority: WO
Inventors: Wilhelmus Johannes Boks
Original assignee: Wilhelmus Johannes Boks
Priority date: 1994-10-13
Filing date: 1995-10-13
Publication date: 1996-05-09
Also published as: NL9401694A; AU3755895A

Abstract

An apparatus for generating microwave radiation comprises: generator means for generating electromagnetic energy with a frequency content in the microwave range; antenna means which are adapted to receive this energy and to transmit microwave radiation; and transfer means for transferring said energy from the generator means to the antenna means. In order to utilize the available energy as effectively as possible and to reduce to a minimum any possible danger to other organisms in the surrouding area, an apparatus is recommended in which the antenna means comprise a directional antenna.

Description

APPARATUS FOR GENERATING MICROWAVE RADIATION

The invention relates to an apparatus for generating microwave radiation, which apparatus comprises: generator means for generating electromagnetic energy with a frequency content in the microwave range; antenna means which are adapted to receive this energy and to transmit microwave radiation; and transfer means for transferring said energy from the generator means to the antenna means. Such an apparatus according to the inven- tion can be used for a wide diversity of applications. The apparatus can for instance be used for accelerated drying of lacquer, paint or the like applied to a sur¬ face. The invention can also be applied for drying wood. A further important application can be found in the influencing of life processes, for example the growth of living organisms. Plant growth can be enhanced when a low intensity radiation is used. When high to very high intensity radiation is used the invention can be effec¬ tively used for controlling harmful living organisms. Envisaged here for instance is the control of insects such as long-horned beetles, locusts, cockroaches or rats in sewage systems. The invention can also be deployed for controlling insects in for instance timber constructions. In the same context the invention can be used for con- trolling weeds and for defoliation purposes. Fungi and other micro-organisms can also be effectively controlled with the invention.

The invention makes it possible to dispense with the use of chemical control means, particularly poisons. Thermal treatments such as deep-freezing and heating, which require a relatively large amount of energy, can also be dispensed with according to the invention.

The control of harmful organisms implies the control of organisms which are harmful to humans, whether for health reasons or also for material and economic reasons.

Yet another application of the invention is distance irradiating of a radioluminescent body. As example hereof can be given a transparent body, for instance suspended from a balloon, which is filled with a relatively easily ionizable gas such as is also used for gas discharge applications. Inert gases in particular, such as helium, neon, argon and krypton, are known in this respect. Through irradiation with microwave radiation with an apparatus according to the invention, such a gas ionizing under the influence of the received radiation can transmit light, with which desired effects can be realized. Since the radiation generated by the apparatus according to the invention can be dangerous to humans in some conditions, steps must be taken to prevent for instance operative personnel being irradiated. Use can be made for example of an effective screening. If the apparatus according to the invention is used for instance to control fungi and wood-damaging insects in old buildings such as churches, the windows through which radiation can pass are then preferably covered with metal gauze, the mesh of which is so small relative to the wavelength of the applied microwave radiation that the gauze provides an effective screening from the radiation.

In order to utilize the available energy as effectively as possible and to reduce to a minimum any possible danger to other organisms in the surrounding area, an apparatus is recommended in which the antenna means comprise a directional antenna. Use can be made for instance of an embodiment in which the directional anten¬ na comprises a horn antenna.

Another variant displays the special feature that the directional antenna comprises a parabolic reflector. A parabolic reflector can also be used in combination with a horn antenna. A practical, advantageous variant is that in which the directional antenna comprises adjusting means for adjusting the directional characteristic of the antenna. Such an embodiment can comprise for instance a combination of a horn antenna and a parabolic reflector which optionally co-act via an additional interposed reflector with a flat, hyperbolic or parabolic shape. An adaptation of the directional characteristic can be carried out by displacing the said components relative to each other. It is also possible to achieve herewith that the beam of microwave rays leaving the antenna means converges such that a maximum radiation intensity is realized in a selected zone for treatment. Beyond this zone the beam will diverge and with increasing distance therefore also display a lower intensity of radiation.

This can be a practical solution from a safety viewpoint.

A specific embodiment has the special feature that the energy generated by the antenna produces a power density in an irradiated object of 50-100 W/dm³. Said range ensures a very effective control of the microorganisms for treating.

Depending on the frequency and the associated wave¬ length of the applied microwave radiation, it may occur that for instance relatively elongate microorganisms are irradiated by the microwave radiation such that the energy dissipated in the relevant organism is insuffi¬ cient to kill this organism. This is associated with the unfavourable polarization direction of the transmitted radiation possible in this situation. To obviate this drawback the apparatus preferably comprises rotation means for continuously rotating the polarization direc¬ tion of the microwave radiation, for example with a frequency in the range of 0.5-2 Hz. This rotation of the plane of polarization can be induced by electronic means, in which case the arrange¬ ment can in principle be stationary. A mechanical embodi¬ ment will however be simpler in which the rotation means are adapted to rotate at least a part of the antenna means and in which use is for instance made of a motor which keeps a used horn antenna in continuous rotation.

A particular variant has the special feature that the said frequency is a frequency officially allowed for heating purposes.

Great effectiveness of the heating by the microwave radiation can be obtained with an embodiment in which the generator means are adapted to be switched on and off with a selected time sequence. There could for example be an effective relative operating period of 10^'3- 10-*.

A specific embodiment comprises temperature measuring means which are adapted to measure the temperature of an irradiated object at a distance, which measuring means are connected to the generator and/or antenna means for adjusting the intensity of radiation at the position of the object measured by the temperature measuring means. The temperature of the irradiated object can be controlled herewith. It is thus possible to effectively prevent not only a temperature which is too low, which makes the treatment less effective, but also a temperature which is too high, which can cause damage to an object. Since the applied radiation can also be dangerous to humans, it may be necessary to have operative personnel wear protective clothing. From safety considerations however, a variant of the apparatus according to the invention can be provided with radiation measuring means for measuring the quantity representative of the intensity of radiation at a selected measuring point, for example the field intensity of the microwave radiation, and for switching off the apparatus when it is determined that a pre-selected value has been exceeded. It is noted generally that the invention is not limited to specific generator means for generating the microwave energy. A magnetron, a travelling wave tube (which has the advantage of being adjustable) , a backward wave oscillator and a multi-chamber klystron can for instance be considered suitable.

As examples of effectively operating frequencies can be mentioned 2450 MHz and 5800 MHz. It will be apparent that the design of the antenna means must correspond with the frequency applied.

For treating a comparatively large object it is useful to embody the antenna means such that they perform for instance a scanning movement over the object for treating under the control of a control unit. The control will take place in this case such that the treatment of every point of the object takes place with a preselected intensity of radiation and for a preselected time period. The invention will now be elucidated with reference to the annexed drawing of a random embodiment of the apparatus according to the invention. In the drawing: figure 1 shows partly schematically and partly in perspective view an apparatus according to the invention; and figure 2 shows on enlarged scale a schematic cross-sectional view of a part of the apparatus according to figure 1.

The figures show an apparatus 1 for killing harmful organisms. In this embodiment the apparatus comprises a housing 3 which is carried by a stand 2 and in which is incorporated a magnetron 4 with an output of 10 kW. Under the control of a central control unit 5 the magnetron 4 receives electrical power supply via a supply line 6 which incorporates an on/off switch 14. A cooling circuit for the magnetron 4 comprises a radiator 7 with fan 8, a pump 9 for the cooling medium, an expansion tank 10, a supply conduit 11 and a return conduit 12. The power supply unit receives via input connections 15 three-phase power supply from a mains supply suitable for this purpose, in particular a 380 V mains. The power is supplied via a transformer 16 and a rectifier 17. The on/off switch can be considered as a main switch and operates both the magnetron 4 and the central control unit 5, which can be embodied for example as a personal computer. In a manner to be described hereinafter, the line 18 between the switch 14 and the control unit 5 can serve for a mutual control.

Via a so-called insulator 20 which is cooled via a cooling circuit 19 and which provides a nominal desired load of the magnetron, the microwave energy generated by a wave conductor 21 of the magnetron 4 is transferred to a rotatable coupling piece, or rotary joint, 22 to a second wave conductor 23, on the end of which is fixed a horn antenna 24. By means of means which are not drawn the horn antenna 24 is held with the second wave conduc¬ tor in a rotating movement around the central axis 25. An effective rotation of the plane of polarization of the microwave radiation leaving the horn antenna hereby takes place. This radiation is directed onto a flat sub-reflec¬ tor 26 which directs radiation onto a parabolic reflector 27. It can be seen from the drawing that the housing

3 is supported by the stand 2 via two servo-motors with associated transmissions, 28 and 29 respectively, which are controlled by the control unit 5 via associated lines 30, 31. The servo-motor 28 provides a rotation around the central axis 32 of a leg 33 bearing the housing 3, while servo-motor 29 can provide a rotation of the housing 3 in perpendicular direction thereof round the central axis defined by motor 29. Through these two degrees of freedom the central control unit 5 can control the movement of the beam of electromagnetic radiation generated by the reflector 27 such that it performs a scanning movement over an object for treating.

The reflector 27 is supported by the housing 3 and in turn carries servo-motors 34 which can be controlled by the control unit 5 in a manner not shown. These servo-motors each carry a screw spindle 35. Nut elements 35 carrying the sub-reflector 5 co-act with these screw spindles. The position of sub-reflector 5 can thus be varied by operating the servo-motors 34. An effective adaptation of focus and the directional characteristic of the antenna 24, 26,27 can be effected herewith. The parabolic reflector 27 bears a device 36 for measuring at a distance the temperature of a treated object, or at least the zone at which the microwave beam is directed, on the basis of infrared radiation. The temperature information is transferred via a line 37 to the central control unit 5, which can adjust the effec¬ tive relative operating time of the magnetron.

Not shown in the drawing are radiation measuring means for measuring the quantity representing the radiation intensity at a selected measuring point. Analogously to the temperature measuring device 36 such a device can likewise be used for measuring a possibly dangerous radiation intensity in a space in which for instance operative personnel may be present. On the basis of a specific relevant norm being exceeded, the central control unit 5 can switch off the magnetron 4 via the line 18. The apparatus can only be set into operation again by the intervention of operative personnel.

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Claims

1. Apparatus for generating microwave radiation, which apparatus comprises: generator means for generating electromagnetic energy with a frequency content in the microwave range; antenna means which are adapted to receive this energy and to transmit microwave radiation; and transfer means for transferring said energy from the generator means to the antenna means.

2. Apparatus as claimed in claim 1, wherein the antenna means comprise a directional antenna.

3. Apparatus as claimed in claim 2, wherein the directional antenna is a horn antenna.

4. Apparatus as claimed in claim 2, wherein the directional antenna comprises a parabolic reflector.

5. Apparatus as claimed in claim 1, wherein the directional antenna comprises adjustment means for adjusting the directional characteristic of the antenna.

6. Apparatus as claimed in claim 1, wherein the energy generated by the antenna produces a power density in an irradiated object of 50-100 W/dm³.

7. Apparatus as claimed in claim 1, comprising rotation means for continuously rotating the polarization direction of the microwave radiation, for example with a frequency in the range of 0.5-2 Hz.

8. Apparatus as claimed in claim 1, wherein the rotation means are adapted to rotate at least a part of the antenna means.

9. Apparatus as claimed in claim 1, wherein said frequency is a frequency made free for heating purposes.

10. Apparatus as claimed in claim 1, wherein the generator means are adapted to be switched on and off with a selected time sequence.

11. Apparatus as claimed in claim 1, comprising temperature measuring means which are adapted to measure the temperature of an irradiated object at a distance, which measuring means are connected to the generator and/or antenna means for adjusting the intensity of radiation at the position of the object measured by the temperature measuring means.

12. Apparatus as claimed in claim 1, comprising radiation measuring means for measuring the quantity representative of the intensity of radiation at a selected measuring point, for example the field intensity of the microwave radiation and for switching off the apparatus when it is determined that a pre-selected value has been exceeded.

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