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...

Conventional vibration signals processing techniques are most suitable for stationary processes. However, most mechanical faults in machinery reveal themselves through transient events in vibration signals. That is, the vibration generated by industrial machines always contains nonlinear and nonstationary signals. It is expected that a desired time-frequency analysis method should have good com...

Characterizing signals jointly in the time and frequency domains through time-frequency representations (TFRs) such as the Wigner-Ville Distribution (WVD) is a natural extension of Fourier analysis and gives a more complete representation of signal behavior, particularly in the case of non-stationary signals. In the presence of additive impulsive noise, TFRs quickly break down and any informati...

A slant removal algorithm is presented based on the use of the vertical projection pro"le of word images and the Wigner}Ville distribution. The slant correction does not a!ect the connectivity of the word and the resulting words are natural. The evaluation of our algorithm was equally made by subjective and objective means. The algorithm has been tested in English andModern Greek samples of mor...

In this paper, A flexibility-based method for damage identification of cantilever-type structures is proposed. Using the linear relation between flexibility matrix element and structure parameter, the damage equation involving modal parameter and damage coefficient of each structure element is established firstly. Then, using the free vibration response signal of structure and the time-frequenc...

S-transform is a new time-frequency analysis method, which is deduced from short-time Fourier transform and continue Wavelet transform. It has much better performance than traditional time-frequency method. Therefore, in this paper, the basic principle of is briefly introduced and the relationships between is analyzed by theoretical derivation. According to the simulation experiments, the time-...

Free-space propagation can be described as a shearing of the Wigner distribution function in the spatial coordinate; this shearing is linear in paraxial approximation but assumes a more complex shape for wide-angle propagation. Integration in the frequency domain allows the determination of near-field diffraction, leading to the well known Fresnel diffraction when small angles are considered an...