Vol. 111, Issue 12, December 2009, pp. 25-37

Stray Capacitances of an Air-Cored Eddy Current Sensor

¹Yi Jia, ²Henning Heuer, ²Susanne Hillmann, ²Norbert Meyendorf

¹Department of Mechanical Engineering

University of Puerto Rico, Mayaguez, PR 00680, USA

²Fraunhofer Institute for Non-Destructive Testing
Maria-Reiche Strasse 2, 01109 Dresden, Germany

Tel.: 787-832-4040 ext 3482, fax: 787-265-3817

E-mail: jia0@me.uprm.edu

Received: 10 September 2009   /Accepted:  22 December 2009   /Published:  30 December 2009

Abstract: Stray capacitance of an air-cored eddy current sensor is one of the most crucial issues for successful development of an eddy current based residual stress assessment technology at frequency above 50 MHz. A two dimensional finite element model and an equivalent lumped capacitance network have been developed to accurately quantify overall stray capacitances of an air-cored eddy current sensor with specimen being tested. A baseline model was used to evaluate sensor design parameters, including the effects of pitch distance, trace width, trace thickness, number of turns, inner diameter, substrate thickness, lift-off distance, and dielectric constant of shim on the stray capacitances of the sensor. The results clearly indicate that an appropriate sensor design parameters could reduce the stray capacitance and improve the sensor performance. This research opens up a new design space to minimize stray capacitance effect and improve the sensor sensitivity and its lift-off uncertainty at elevated high frequencies.

Keywords: Stray capacitance, Eddy current sensor, Finite element, Residual stress assessment

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