GB1110021A - Microwave irradiation technique - Google Patents

Abstract

1,110,021. Microwave heating. LITTON INDUSTRIES Inc. 17 May, 1965 [15 May, 1964], No. 20860/65. Heading H5H. [Also in Division E1] Microwave irradiation equipment is mounted upon a vehicle, to permit material deposited upon a road surface to be heat treated during movement of the equipment along the road. Apparatus for applying and rapidly drying markings on road surfaces includes-mounted, in order, along a vehicle (Figs. 4 and 5, not shown) which may be less than one foot in height and is drawn along the road-an infrared preheater (54) for drying the road surface if wet; a paint gun (58) for spraying a paint which has a conductivity of greater than 5 millimhos per cm.; a dispenser (60) for dropping reflecting beads into the wet paint marking; and a series of microwave irradiating slow-wave structures (12A to 12F), each formed of a rectangular waveguide, Figs. 1 and 2, which has its lowermost wall 34 of insulating material, and includes a plurality of transversely extending interdigitated vanes 14, such that substantial radiation of energy downwards from the structure occurs only in the presence of electrically lossy material external to but closely adjacent the lower wall. In the absence of such lossy material, the microwave power is absorbed in dummy loads. In order to provide substantially uniform heating despite non- uniformity in the intensity distribution of the radiated energy transverse to the axes of the waveguide, and despite the decrease in radiated intensity in passing from the input to the output end of each waveguide, the latter are arranged at an angle to the vehicle axis (Fig. 5, not shown), and are mounted in an inclined position (Fig. 8, not shown), such that the output end of each guide approaches closest to the road surface; alternatively, they may be horizontally mounted, and the interdigitated vanes arranged with a spacing which increases toward the output end of the guide (Fig. 10, not shown). The vanes may be either enlarged, as shown in Fig. 2, or tapered, at their lower ends, to influence the radiation intensity and distribution; air may be supplied under pressure to the waveguides, escaping through spaced orifices 41<SP>1</SP> in their lower walls, to drive off vapours released from the drying paint; and the vehicle may be supplied with conductive wire cloth safety shields hung from its sides, to reduce escape of radiation. Control circuitry may be provided to adjust the power source, or the height of the slow wave structures above the roadway, in dependence upon the temperature of the dummy loads, the speed of the vehicle, or the presence of substantial reflected energy, e.g. as produced by the passage of the vehicle over a manhole. Examples of paint compositions having a conductivity permitting the use of the above apparatus and method are referred to.