A simple estimation formula for a crack depth using the RCS dip

In this paper, we have proposed a simple estimation formula for the crack depth by using the RCS dip. This estimation formula is based on finding in our previous study that the monostatic RCS return by a crack sharply decreases at certain frequencies and is derived empirically from our extensive numerical calculation. Then test measurements had been made for check validity of our estimation formula. Time domain gating process has been utilized to extract only the desired RCS return by a crack from the measured responses. It had been found that thus processed RCS dip in the frequency domain agrees well with the theoretically predicted one.