An Electret Switch

Electrets were fabricated from Teflon®-FEP (copolymer fluorinated ethylene propylene) film of 12 pm ip thickness by heating to 1400C and charging the surface by corona. The attractive force Fa and the repulsive force Fr acting on the movable electrode due to the charge on the surface of the electret were measured using models of (1) the vertical movement system and (2) the hinge movement system, as a function of stroke. Decay of the charge on the surface on the one-side-surface-metallized film was slow compared with the decay in non-metallized film. The attractive force obtained from the hinge movement system was Fa= 3.5 mN when the surface charge density o= 1.8xl0-8 C/cm2, the facing area of the movable electrode S= 4.B cm2, the stroke d= O. 1 mm and the driving voltage VC= 100 V, and the attractive force obtained from vertical movement system was 2.5 mN under the same conditions. The ratio k= Fa/ Fr was always > 1. Based on these results, the electret switches were fabricated by way of trial; variations of the operating voltage and the return voltage were suppressed below 30% when the switches were driven with V0 150 V applied and cycled about one million times.