Abstract
This paper describes a liftoff characteristic on backside defect searching by low frequency excitation of the ∞ coil. The low frequency ∞ coil excitation confronts to a noise problem in the practical experiments. To overcome this difficulty, this paper employs a Fourier transform signal processing method to remove the higher frequency noise 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 a liftoff characteristic of the backside defect searching is clarified by employing the low frequency excitation to our ∞ coil. Experimental as well as numerical verification along with intensive three-dimensional finite element method have been carried out to confirm our results.
