Mutual impedance of air-cored coils above a conducting plate

Abstract

The change in mutual impedance ΔZ12 due to eddy-current induction is considered for an arbitrary pair of air-cored coils located above a conducting plate. A general expression is derived for ΔZ12 and applied to the specific case of cylindrical coils with rectangular cross-section. A series of closed-form expressions for ΔZ12 is presented for the geometries that cover all of the possible coil configurations for which the orientation of the individual coils is either normal or tangential to the plate. Expressions are also obtained for ΔZ12 in the dipole limit and the results are compared with earlier work for dipole loops. The validity of the theory is tested against experimental measurements for representative high-symmetry coil systems above an aluminium-alloy plate. The theoretical calculations and experimental results are in excellent agreement over the experimental frequency range 100 Hz–50 kHz. The significance of the results for eddy-current non-destructive inspection using driver–pickup coils is discussed.

Transient response of a driver-pickup coil probe in transient eddy current testing

“…al. [2]. The correction brought forth in this work incorporates the additional self-inductance and material coupling effects associated with the pickup.…”

“…It is relatively inexpensive, fast and reliable in comparison with other inspection technologies. These qualities make eddy current a desirable inspection method in industry [2,3], where it is employed to monitor the structural health of industrial assets. To this end, considerable efforts have been made to develop mathematical models that enable the interpretation of inspection data.…”

“…In transient eddy current experiments, for instance, agreement with experimental data is limited to later times when feedback effects become less prominent [11]. In other cases, authors often assume non-magnetic samples for experimental validation [1][2][3][4], constrained sample geometries [11], and resort to fitted parameters [3] or convenient smoothing functions [9]. In some instances [9][10][11][12][13], analytical models have been presented with limited or no experimental support.…”

Coupling Impedance Between Planar Coils Inside a Layered Media

“…Mutual impedance between coils is also modified by the layered media. It should also be noted that resistive coupling occurs in the presence of at least one conductive layer, as is shown in studies concerning the coupling of two circular turns located between two half-space media [19] or the coupling between two ring-type coils above a halfspace conductive medium [20].…”

“…Considering that A N is zero, the product between the matrix T + (k ρ ) and the vector of coefficients when (20) is introduced into (19) leads to a the following expression…”