GB1230402A - - Google Patents

Abstract

1,230,402. Electrostatic transducers. THERMO ELECTRON CORP. 2 April, 1968 [15 May, 1967], No. 15917/68. Heading H4J. In an electrostatic transducer comprising a pair of electrodes at least one of which is an electret having a dielectric surface confronting the other electrode and a metallized opposite surface, the diaphragm electrode is prevented from sticking to the fixed electrode by a grid of supporting elements on the surface of the fixed electrode spacing the diaphragm from the fixed electrode. As shown in Fig. 2, the transducer comprises a metal back-plate 19 mounted on flange 15 of plastics base 13, and perforated so that the space between it and base 13 serves as a compression chamber. A mesh of fine wires 23, or an array of raised posts, is secured to or integral with back-plate 19, and prevents electret diaphragm 25 from coming in contact with the back-plate. The diaphragm is held in place by the rim 31 of protective metal screen 33 and cap 35. Two metal back-plate and electret diaphragm assemblies may be arranged back to back (Fig. 5, not shown) for use in a pressure gradient operated microphone having a figure of eight directional response pattern. In Fig. 7 the perforated back-plate 93 is an electret metallized at 95 and supported by plastics screen 89 on non-porous insulating base 81. The opposite surface of the electret back-plate is embossed to provide the grid of support elements 101. The diaphragm is metallized plastics foil or thin metal foil 105. An embodiment of the transducer for use in conditions of variable temperature and humidity, utilizing a two-part housing, is described (Fig. 8, not shown).