DIGITAL FILTER IN FREQUENCY DOMAIN AND ITS APPLICATION TO COMPUTERIZED ELECTROMAGNETIC NONDESTRUCTIVE TESTING
He Ling · Nondestructive Testing · 2003
The signals of electromagnetic testing are directly related to faults or flaws in space domain. It is difficult to filter those spatial signals in the time domain with analog signal processing. So a method of frequency digital filter has been proposed in which a symmetrical frequency structure for producing the linear phase response of the filter and a digital Butterworth filter for producing the maximum flat frequency pass band are used. The rapid digital filtering algorithm is based on FFT(fast Fourier transform). The long term noise caused by the swing of sensor and the short term noise caused by electromagnetic waves can be removed successfully by the method.