Impedance Change of Non-Contact Gap Sensor Coil Made of Conductive Polymer Composite Under Compression and Decompression

Flexible sensor coil, made of carbon nanotubes and silicone rubber, can measure gaps and stress. During the noncontact process, the impedance amplitude/angle increases as the gap decreases, reaching a critical value at the zero-gap point, differentiating it from the compression/decompression process. During loading, the impedance increases with stress buildup. During unloading, the impedance angle drops; while the impedance amplitude increases sharply when unloading to the target stress of 0.3, 0.2, and 0.1 MPa, and decreases sharply when unloading to 0 MPa with a change rate of less than -0.002 s−1. In the relaxation stage, the impedance amplitude/angle shows an exponential decay trend, and the impedance amplitude change rate ranges from 0 to -0.002 s−1. Therefore, a method to measure gaps and stress has been developed by utilizing the critical value and the change rate, laying a preliminary foundation for monitoring gaps and stress with the sensor coil.