New method for natural frequency extraction

A new method is described for extracting natural frequencies from measured late-time transient responses. In this method, nonlinear soft-thresholding based on the orthogonal base of compactly supported wavelets in frequency d omain is firstly used to the measured response so that the white noise is s uppressed almost entirely without spoiling the signal, then the rational mi nimax approximation is performed by the Fourier transformation of the even extension of the denoised response, finally, the natural frequencies direct ly is obtained from the zeros of the denominator polynomial of the optimum rational function. The effectiveness of this method is verified by a synthe tic transient response and a measured response of a conducting sphere.