The invention provides a method for measuring thickness of coatings through the ultrasonic
signal spectrum filter technology in a nondestructive mode, and belongs to the technical field of ultrasonic non-
destructive testing. The method includes the steps that normalization
processing is conducted on reflective
sound pressure P[reflection] (x1) by ultrasonic incident
sound pressure P[incidence] (x0), and then normalization
sound pressure reflection coefficients R (x1-x0) of the coatings are acquired, and the R (x1-x0) is expanded to plural Fourier series through the
spectrum analysis technology and divided into an independent real part function Real (f) and an independent imaginary part Imag (f); Fourier transformation is conducted on a real part function V[real] (f) in an
effective frequency band acquired through windowing
processing to acquire a power spectrum M (tau) of the real part function V real (f), FFT filtering bandwidths are selected according to the occurrence positions of maximum values of the power spectrum, the V[real] (f) is sequentially filtered to acquire a series of cosine functions, the periods of the cosine functions are read, propagation sound time ti of ultrasonic
waves in the coatings is calculated, and then the thickness of the coatings is represented by the cooperation of
longitudinal wave sound velocity of the coatings. The method is not affected by material attributes and the process environment, the problems that in a conventional ultrasonic method,
aliasing occurs in time domains, and resonant frequency of the spectrum is difficult to recognize are solved, and the problem of
ultrasonic thickness measurement of the multiple coatings is solved.