GB1342672A - Microwave apparatus - Google Patents

Abstract

1342672 Microwave ovens GENERAL CORP 1 June 1971 [1 June 1970] 18389/71 Heading H5H In order to eliminate escape of energy from a micro-wave oven if the door is lightly open, the door or its frame incorporates a resonant cavity which effectively short-circuits any escaping wave energy. In one form the door 5 has a metal shield plate 15 which, in the closed position, abuts against a corresponding plate 7 on the oven. This is surrounded by a metal frame 8, the faces 8a, 8b of which provide a stepped formation and of which the face 8a forms a second seal with the inner face of portion 12c of a metal shield member 12 incorporated in the door. A cavity 13, extending around the member 12, is of a depth equal to one quarter wavelength and its upper edge is a further quarter wavelength from the edge 19 of the oven enclosure. The bottom 12a of the cavity is thus one half wavelength from the edge 19 and provides an effective shortcircuit for energy escaping between surfaces 15, 20 if the door is slightly open. As an additional precaution, a wave absorbing insert 11, of rubber loaded with ferrite, may be fitted in a recess 10 in the face 8a. The arrangement is of particular value where the microwave generator is automatically switched off by opening the door of the oven, as it prevents the escape of energy in the interval before the switch takes effect. In an alternative embodiment, see Fig. 4 (not shown), the cavity is incorporated in the door frame instead of the door itself and it is also suggested, see Fig. 3 (not shown), that the metal-to-metal contact between the members 15, 7 may not be essential. In any of the constructions the cavity 13 may be sealed by a cover member of suitable material, to prevent the ingress of dust.