The Thickness/resonance Prediction of an Ultra-thin Layer by the Low-frequency Ul- Trasound

A prediction method of the thickness, resonant space and frequency for the two cases of an ultra-thin layer and the narrow-band frequency spectra has been developed without the appearance of the resonance/anti-resonance. Using the characteristic of straight line and the period of  of the layer phase shift obtained from the measured data, the relations of the line slope with time of flight and resonant space of the layer on the half-space substrate of infinite extent are analyzed. The resonant formulas are derived after the different impedance conditions are considered. Using the relations, the formulas and the curve fitting method, the thickness, resonant space and frequencies can be predicted from the less available measured data and no information of the resonance/anti-resonance. The method feasibility and antiinterference capability are analyzed and testified by the numerical simulation for the two cases of an ultra-thin layer and the narrow-band spectra, respectively.