For the quantitative description of electromagnetic coupling between probe coils of eddy-current sensor and detected material, an improved transformer model was presented based on the transformer model that was brought out by DARKO V. By dividing the whole probe coils and eddy-current distributed areas in detected material in both axial and radical directions, the improved transformer model included all coil units, which were regarded as primary sides, and eddy-current units, which were regarded as secondary sides. The output impedance of probe coils was derived by solving voltage equations for all coil units and eddy current units. The comparison between calculation results from both transformer models and experimental results proved the validation of improved transformer model. It is proved that the improved transformer model, with relatively simple principles and accurate calculation results consistent with experiments, provides a convenient method to quantitatively analyze the influence of variables on output impedance of probe coil and a reference for design and application of eddy-current sensor．
LV Yun-teng, ZHU Chang-sheng. Improved transformer model for output impedance of eddy-current sensor probe. JOURNAL OF ZHEJIANG UNIVERSITY (ENGINEERING SCIENCE), 2014, 48(5): 882-888.
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