Primary Research On Lift-off Characteristics Of Soft Eddy Current Displacement Sensitive Component

The probes of traditional eddy current sensor are made of metal coil-winding, having become soft and slim with the development of preparation process, but the probes are still rigid. Furthermore, the traditional eddy current sensor probes can only be applied to the situations in which the measured object is metal conductor. So the kind of non-contact displacement measurement sensor which is soft and can be applied to the situations in which the measured object is insulator is urgent needed. Based on this background, this paper researched a kind of soft displacement sensor based on eddy current effect. In this thesis, sensitive components and films using carbon nanotube/silicone rubber composites were prepared. This material does not contain any metal and it has good mechanical and electrical properties.The main contents of this thesis include the following items:(1) Spiral-type composites coils were prepared. The mass ratio of conductive phase and matrix phase ranges from 0.001 to 0.20, and the number of circles ranges from 3 to 9. Composites films were also prepared. And its length is 7cm, width is 7cm, thickness is 2mm. The mass ratio ranges from 0.01 to 0.24.(2) The effect of mass ratio and frequency on impedance characteristic and eddy current characteristic of the composites coils was analyzed. The result of experiments shows that with the increasing of mass ratio, the impedance amplitude, impedance angle and parallel equivalent resistance decrease but the parallel equivalent capacity increases. The impedance amplitude, impedance angle, parallel equivalent resistance and capacity decrease when frequency increases. The eddy current characteristics are as follows:When the measured object is not the same, the impedance amplitude, impedance angle, parallel equivalent resistance and capacity reflect basically the same lift-off characteristic under different mass ratio of composites coils and frequency. The impedance amplitude, impedance angle and parallel equivalent resistance monotonically increase with the increasing of lift-off, and the parallel equivalent capacity decrease with the increasing of lift-off.(3) The noise, sensitivity and resolution were analyzed quantitatively. The noise of coils is lower than 2.3%. With the increasing of mass ratio, sensitivity and resolution of coils first increase and then decrease, and reach the maximum when the mass ratio is 0.04. When the lift-off changes from 0 to 0.5mm, resolution of the spiral-type coils reaches 0.05mm, the sensitivity reaches 1.7 kΩ/mm.(4) The conductive model of the composites coils was researched preliminarily. The relation between the tunneling effect and the eddy current effect was established.After analyzing the eddy current properties of the composites coils, it has been found that at certain range of lift-off, the coils’ impedance amplitude varies monotonically and the resolution reaches 0.05mm. This thesis preliminary verified the feasibility to use the composites coils and films to realize non-contact displacement measurement. The composites coils and films can also be applied to the situations in which the measured object is insulator.