The primary purpose of this paper is the improved detection of a nonstationary target signal embedded in a nonstationary background. Accordingly, the first part of the paper is devoted to a detailed exposition of how to deal with the issue of nonstationarity. The material presented here starts with Loève’s probabilistic theory of nonstationary processes. From this principled discussion, three i...

Time-frequency distributions (TFDs) are powerful tools to represent the energy content of time-varying signal in both time and frequency domains simultaneously but they suffer from interference due to cross-terms. Various methods have been described to remove these cross-terms and they are typically signal-dependent. Thus, there is no single TFD with a fixed window or kernel that can produce ac...

New method of observation and diagnosis of inverter-fed induction motor drives is developed and tested. Unsymmetrical conditions concerning the machine impedances or valves operation are reflected in the spectrum of the current space-phasor. The spectrum of the space-phasor was estimated with the help of the Wigner-Ville distribution (WVD) and its time-frequency representation with excellent ti...

It has been shown that detailed information from non-stationary signals such as speech are better represented by an acoustic image, a two dimensional feature representation [10]. Several time frequency representations such as the spectrogram, Wigner-ville and choi-williams distribution have been proposed [6] while the acoustic images based on the two dimensional root cepstrum analysis (TDRC) is...

This paper is focused on the problem of mode identification of Lamb waves in ultrasonic testing, and the principle and process of two time-frequency transform method, smooth pseudo Wigner–Ville distribution and two-dimensional Fourier transform, were discussed. The experimental work were carried out in aluminium plates, and the single and multimode Lamb waves were excited by 5MHz oblique incide...

Most of signals in engineering are nonstationary and time-varying. The Fourier transform as a traditional approach can only provide the feature information in frequency domain. The time-frequency techniques may give a comprehensive description of signals in time-frequency planes. Based on some typical nonstationary signals, five time-frequency analysis methods, i.e., the short-time Fourier tran...