Patent GB-1482950-A (GB)
Title: Apparatus for generating radiation
IPC: H01S3/09
Filed: 1974-08-21
Abstract: 1482950 Lamps FUSION SYSTEMS CORP 21 Aug 1974 [22 Aug 1973] 36677/74 Heading F4R [Also in Divisions H1 and H4] A source of u.v. or visible light comprises a sealed envelope containing a plasma-forming medium, a source of microwave energy, and means for coupling the energy to the medium to excite the latter to a state in which it emits light. In a first embodiment, Figs. 2 and 3, the envelope 19, which is tubular and contains an appropriate mixture of gases such as mercury and xenon, is supported inside a microwave chamber composed of a reflector 17 of elliptical cross-section and a wire mesh screen 22 which closes the mouth of the reflector. The reflector is made of polished anodized aluminium which is opaque to microwaves but provides maximum u.v. reflectivity, and the screen has a mesh size which transmits about 90% of the u.v. but reflects most of the microwave radiation. The optimum mesh size is stated to be 1/40 to 1/50 inch using 0À001 inch tungsten wire but a # inch mesh using 0À011 inch copper wire is contemplated. The source 2 of microwave energy is preferably a magnetron or klystron operating at 2450 MHz and providing 120 pulses per second, and the energy is transmitted to the microwave chamber by a rectangular to circular S-Band waveguide section 3 which terminates in a flange 4 bolted to a corresponding flange 5 at one end of the chamber. The other end of the chamber terminates in a flange 11 bolted to a flange 12 carrying a flange collar 15 to attenuate the escape of energy. The lamp envelope 19, which forms the inner conductor of a coaxial microwave cavity, may be supported by coaxial extensions 20, 21 resting on brackets 7, 14 attached adjustably to the respective flanges 5, 11 or by radial extensions (54, Figs. 11 and 12, not shown). The apparatus is intended for use in curing paints and inks, objects 28 to be irradiated being moved beneath the mesh screen 22 by a conveyer 29. The elliptical reflector 17 may be replaced by a reflector of parabolic section (40, Fig. 6, not shown) enclosing an envelope (41) of semicircular section, or by a reflector of semicircular section (43, Fig. 7, not shown) closed by a mesh screen (45) also of semicircular section. In a further modification (Fig. 8, not shown) the reflector (46) is of circular section and completely surrounds a lamp envelope (47) of annular section, the object to be irradiated being placed inside the hollow core (48) of the envelope. Figs. 9 and 10, not shown, disclose a reflector (49) in the form of a paraboloid of revolution containing a lamp envelope (50) and closed by a mesh screen (51). Various methods of cooling the apparatus using air and/or water are described. In a second embodiment, Fig. 13, the magnetron 66 or klystron is mounted inside a power head which is bolted directly to the microwave chamber by means of a flange 68 at the end of a circular waveguide section 65. The section 65 contains a quarter wave tuning stub 63 and/or a quarter wave fixed reflector 67. A power head may be mounted at each end of the chamber, the two microwave sources being run on alternate 60 cycle pulses. Two sources operated in this manner may be mounted in a single power head. In a third embodiment, Figs. 19 and 20, the microwave power source is coupled into the top of the microwave chamber instead of the end. The chamber, which comprises lamp tube 100, elliptical reflector 101, and mesh screen 102, is closed at each end by a mesh screen 120 so that a plurality of the devices may be assembled end-to-end to form a unit of any desired length. The magnetron dome 105, and possibly a quarter-wave tuning plate 104, are mounted in a waveguide section 103 comprising three longitudinally extending walls at right angles to one another and the top of the reflector 101. Microwave energy enters the chamber through one or more slot antennae 116 in the reflector which may be provided with sliding covers for tuning purposes. Pre-heater elements 112 are provided to ensure that the lamp starts instantly when the power source is switched on. The apparatus is protected by an outer housing 107, and cooling air circulates through a duct 113, through portions of the waveguide section 103 made of mesh (not shown), and through a slot 108 at the top of the reflector which is covered by mesh 109. The magnetron is air or water cooled. In a modification (Figs. 15 and 16, not shown) two parallel waveguide structures (73, 78) are mounted on the reflector (70) at different angular positions about the axis of the lamp envelope (72). In a further modification (Figs. 17 and 18, not shown) two curved waveguide structures (86, 89) are mounted around the reflector (82) at different axial positions.