Real-time Denoising of Ae Signals by Short Time Fourier Transform and Wavelet Transform

Laser AE method is a non-contact AE detection technique, which utilizes laser interferometer as sensor. This method is less subjected to environmental difficulties and can be adaptive for wider target than conventional PZT sensors. However, laser AE method has to improve its sensitivity because the noise level of laser interferometer is higher than PZT sensors. In this study, a method to reduce the noise component of output signal of laser interferometer is investigated. Output signals from laser interferometer were recorded continuously with 10-MHz sampling frequency and transformed into spectrogram (time-frequency-magnitude data) by time-frequency analysis method. After noise component in this spectrogram is cut, inverse transform is applied to obtain clear AE signals in time domain. Whole signal processing can be done in real time. Simulated AE detection test was conducted to confirm the effectiveness of this noise reduction scheme. In the result, weak AE signals buried in noise could be recovered and the improvement of sensitivity of laser AE system was demonstrated. Current real-time processing can extract about 100 events/s.