The authors propose and demonstrate the time-stretched short-time Fourier transform (TS-STFT) technique to overcome the limitation of an analog-digital converter (ADC) in the time-frequency analysis of ultrafast signals. Experimentally, the time-frequency analysis of highly chirped RF signals, with a chirp rate as high as 350 GHz/ns, is demonstrated. An effective real-time sampling rate of 320 GSa/s is achieved. Time stretching enhances the analog bandwidth and the effective sampling rate of the ADC and enables measurement of the instantaneous behavior of highly nonstationary ultrawideband signals.
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"In such cases it is preferable to decompose the signal into elementary building blocks that are well localized in both time and frequency. This alternative can be achieved by using the Short Time Fourier transform (STFT)  and the Wavelet transform (WT) . In this way, it is possible to define the local irregularity of a signal as special signature as input to an machine learning algorithm. "
[Show abstract][Hide abstract] ABSTRACT: This study concerns with the diagnosis of aerospace structure defects by applying a HPC parallel implementation of a novel learning algorithm, named U-BRAIN. The Soft Computing approach allows advanced multi-parameter data processing in composite materials testing. The HPC parallel implementation overcomes the limits due to the great amount of data and the complexity of data processing. Our experimental results illustrate the effectiveness of the U-BRAIN parallel implementation as defect classifier in aerospace structures. The resulting system is implemented on a Linux-based cluster with multi-core architecture.
"Mais la résolution fréquentielle obtenue est alors inversement proportionnellè a la plage d'analyse temporelle, limitant l'intérêt de cette méthode pour l'analyse de signaux fortement non-stationnaires. Cette limitation peutêtre contournée en utilisant une transformée de Fourierà court termé etirée temporellement , reposant sur l'utilisation d'une modulation optique quí etire le signal analogique avant sa conversion numérique; le matériel nécessaire est actuellement trop volumineux. La plupart des autres RTFs proviennent de la RTF de Wigner-Ville : "