Impedance variation of the gap sensing coil-type conductive polymer composite in the compressive loading and stress relaxation phases

Abstract

The coil made of conductive polymer composite has the potential to be utilized as the flexible contactless gap and compressive stress sensor. To solve the problem of the stress measurement in the compressive loading and relaxation phases, the impedance-changes of the coil-type composite at the contactless stage and the loading and relaxation phases have been studied. The data at the contactless stage show that the amplitude/angle is attenuated/enlarged when the gap decreases. The data at the compression stage show that the impedance amplitude/angle is attenuated/enlarged when the stress increases in the loading phase and decays/grows exponentially with time in the relaxation phase. The spring-dashpot models for the compressive impedance relaxations have been established. The changing-ratio of the impedance in the loading phase is far higher than that in the relaxation phase; the changing-ratio decreases with time in the relaxation phase; and therefore there is a changing-ratio-threshold which can be used to judge whether the coil-type composite is in the loading or relaxation phase. Accordingly, a procedure to measure the gap and the stress in the loading and relaxation phases has been designed. The aforementioned results have laid preliminarily the foundations to use the coil-type composite to measure the stress and the gap.