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This paper describes the backside defect searching by means of the low frequency ∞ coil excitation. The low frequency ∞ coil excitation confronts to a noise processing problem in the practical tests. To overcome this difficulty, this paper employs two methodologies. One is an averaged sum and the other is the Fourier transform signal processing methods to reduce the higher frequency components compared to the excitation one. Thus, we have succeeded in enhancing the S/N ratio and detecting the signals caused by the backside defects of the targets. As a result, we have elucidated that the backside defect searching is possible by employing the low frequency excitation to our ∞ coil. Experimental as well as numerical verification along with intensive three-dimensional finite element method are carried out to confirm our results.