Primary Research On Soft Displacement Sensitive Element Based On Conductive Polymer Composites

It is a key to monitor the displacement between small curved surfaces to ensure the safety of the large defense and industrial equipments. The traditional eddy current sensor probes are made of metal coil-winding, which make the probes rigid that can not satisfy the actual requirement when measure the curved surface gaps. With the preparation technology development in recent years, eddy current coil tend to be be thin and soft, but cost is higher. So the kind of non-contact displacement measurement sensor which is soft and inexpensive is urgent needed.This paper researched a kind of soft displacement-sensitive unit based on eddy current effect. These units are made of carbon nanotube filled silicone rubber. This material does not contain any metal and it has good mechanical and electrical properties. The major work as follows:(1) Omega-type and vortex-type composites coil is prepared. The conductive phase concentration ranges from0.001to0.20, and the number of circles ranges from3to9.(2) The influences of concentration, number of circles and frequency to impedance characteristic and eddy current characteristic of the composites coils is analyzed.The results of experiments show that with the increasing of concentration the impedance amplitude and parallel equivalent resistance decreases but the impedance angle and parallel equivalent capacity are converse. The impedance amplitude, parallel equivalent resistance, impedance angle and parallel equivalent capacity decreases when frequency increases. Impedance amplitude of Omega-type coils shows different lift-off properties.When the lift-off increases, impedance amplitude of concentration0.01,0.12and0.16decrease monotonically; while impedance amplitude of concentration0.04and0.08increase.The vortex-type coils show that with the lift-off increasing impedance mamplitude increase firstly and then decrease. And the lift-off of turning point decrease with concentration increase. The impedance amplitude reduces monotonically when the concentration is0.12,0.16and0.20.(3) The noise, sensitive and resolution is analyzed quantitatively. The noise of the coil is lower than2.8%, with the increasing of the concentration, sensitivity of the coil reduces and the resolution increases. When the range of the lift-off is0to0.5, resolution of the screw-type coils is0.1mm.(4) The conductive mechanism of the composites is researched preliminarily. The relation between the tunneling effect and the eddy current effect is established.(5) After analyzing the eddy current properties of the composites, it has been found that at certain range of lift-off, the composite’s impedance amplitude varies monotonically with the lift-off and the resolution can reach to0.1millimeter. Based on the results aforementioned, the paper verified the feasibility to use the composite coil to realize the non-contact displacement measurement.