GB1016435A - Improvements relating to the dielectric heating of materials - Google Patents

Abstract

1,016,435. Microwave heating apparatus. ASSOCIATED ELECTRICAL INDUSTRIES Ltd. April 11, 1963 [May 9, 1962], No. 17875/62. Addition to 893,936. Heading H5H. [Also in Division H1] Dielectric heating of material is effected by radio frequency energy in a waveguide 5A or cavity which is terminated at each end in an effective open-circuit 5B, the energy being supplied at approximately the cut-off frequency for the waveguide or cavity which is then " tuned " to cut-off at this applied frequency, In the form shown, the terminations are sections 5B of waveguide of greater depth G2 than the depth G1 of the main portion 5A which is provided with choked slots for the passage of strip material to be heated. Energy is fed by way of coaxial cables 19 and 17 to a loop 15 enclosed in a dome 21, e.g. of P.T.F.E. The inner conductor of the coaxial cable 17 consists of a group of wires spaced around the periphery of a circle so that the end of the inner conductor together with the loop 15 can be rotated through a small angle. Coarse tuning of the waveguide 5A is effected by a longitudinal rod 23 eccentrically mounted on spindles 25 one of which carries a knob 27 and pointer 29. Fine tuning is effected by a longitudinal rod 33 mounted on rods 35 which are coupled to the operating shaft of a thrust motor (not shown). The difference in signals provided by two probes 39 spaced #/4 along the feeder 19 in the presence of standing waves due to the waveguide 5A being off-tune is fed to a coil of the motor to reset the fine tuning rod 33 automatically. A stabilizing negative feed-back signal proportional to the rate of change of position of the rod 33 is obtained from a second coil in the thrust motor. Limit switches associated with the rod 33 provide an indication by coloured lamps when resetting of the coarse tuning rod 23 is necessary. This may be effected manually or automatically.