GB837063A - Improvements in or relating to high frequency furnaces - Google Patents

Abstract

837,063. Dielectric heating. PATELHOLD PATENTVERWERTUNGS- & ELEKTROHOLDING A. G. April 16, 1958 [April 16, 1957], No. 12080/58. Class 39(3) A high frequency furnace where the material to be treated or heated e.g. food is located in a hollow chamber bounded by metal walls into which H.F. electromagnetic radiation is introduced e.g. by a wave guide L, means G2 are arranged in the chamber adjacent a wall D at which the radiation is introduced for varying the polarization direction of the H.F. radiation in order to reduce standing waves in the chamber and a second such means G1 is disposed adjacent an opposite wall B of the chamber. Thus a polarization grid G1 is arranged parallel to the wall B at a distance therefrom of a quarter of a wave length of the radiation or of an odd multiple of this value, the parallel conductors of this grid having a direction displaced by 45 degrees with respect to the polarization direction EO of the radiation. The direction of polarization E1 of the energy reflected from the wall B is then displaced by 90 degrees with respect to that EO of the entering radiation. When the radiation enters the chamber through a wave guide L, a polarization grid GO is arranged at the end of the wave guide with parallel conductors directed perpendicular to the direction of polarization of the introduced radiation, in order to prevent entry of radiation reflected from the wall B into the waveguide; but the grid GO is not required when the H.F. radiation is introduced by a coupling loop or by a dipole. The second polarization grid G2 is arranged parallel to the wall D through which the radiation is introduced at a distance of a quarter of a wave length or an odd multiple of this number therefrom, the conductors of the grid having a direction at 45 degrees to the polarization direction EO of the entering radiation i.e. parallel or perpendicular to the conductors of the grid G1. The grid G2 leaves the opening for the introduction of the radiation free. The chamber may be of quadrangular or of cylindrical cross-section. The polarization grid G1 may be spaced at one eighth of a wave length from the wall B, and then the reflected wave has circular polarization. The distance from the wall of at least one polarization grid may be variable. The grid may comprise parallel strips of material having a high dielectric constant and may support the material -under treatment. The H.F. energy may be fed into the chamber at several points from one or more H.F. generators. Thus a second wave guide may be provided in the wall B opposite the wave guide L to introduce a radiation with a direction of polarization perpendicular to the direction EO of the radiation entering by wave guide L, and the supply may come from independent generators giving different frequencies.