GB882441A - Improvements in or relating to radio frequency dielectric heating apparatus - Google Patents

Abstract

882,441. Dielectric heating. RADYNE Ltd. Nov. 11, 1959 [Aug. 11, 1958; Feb. 13, 1959], Nos. 25731/58 and 5120/59. Class 39(3) [Also in Group XL(b)] A radiation attenuation duct for radio frequency dielectric heating equipment having a fundamental frequency less than 500 mc/s. includes spaced transverse conductive partitions shaped and arranged to provide a path for passage of material to be heated. The duct 24, Fig. 2, is connected to the wall of a heating compartment 18, the edges of upper and lower partitions 26, 28 being spaced to provide a passage for a conveyer band extending into the compartment. The end member 34, Fig. 4, is provided with a central slot of restricted length. The upper and lower partitions 26, 28 may be staggered in the axial direction of the duct (Fig. 5, not shown). The effect of the partitions is to raise the cut-off frequency of the duct and thus provide attenuation of harmonics below the new cut-off frequency. Further attenuation may be provided by non-inductive resistors 36, 38, Fig. 10, connected between upper and lower partitions and by resistive panels 46 attached to the edges of the partitions 26, 28. These may extend the full width of the duct (Fig. 9, not shown). They may be made of graphite-surfaced resin-bonded paper board or asbestos board. Other materials such as wood, foam rubber, foam polystyrene, textile material or cement mixed with graphite are also stated to be suitable. The resistance of the boards may be arranged to diminish towards the sides of the duct. In the construction of Fig. 8, use is made of transverse resistive boards 42 bolted to the partitions 26, 28 at points 44. In a modification, the partitions have the same form as the end member 34, Fig. 4, whereby a central passage is provided in the duct.. This may be completely enclosed by resistive boards forming an inner duct. Additional attenuation of particular frequencies may be obtained by adding to the end of the duct quarterwavelength extensions having the same section as the aperture in the end member 34. Quarter-wave sections may also be inserted between the duct and the heating compartment or between two or more ducts arranged in series. The conveyer may be made of insulating material. If it is made of metal it is necessary to provide a conductive or capacitative coupling between the conveyer and the duct. Specification 882,442 is referred to.