Department of Electronic Engineering, Fudan University, Shanghai 200433, China.
J Acoust Soc Am. 2012 Apr;131(4):2714-22. doi: 10.1121/1.3685482.
Ultrasonic Lamb modes typically propagate as a combination of multiple dispersive wave packets. Frequency components of each mode distribute widely in time domain due to dispersion and it is very challenging to separate individual modes by traditional signal processing methods. In the present study, a method of dispersion compensation is proposed for the purpose of mode separation. This numerical method compensates, i.e., compresses, the individual dispersive waveforms into temporal pulses, which thereby become nearly un-overlapped in time and frequency and can thus be extracted individually by rectangular time windows. It was further illustrated that the dispersion compensation also provided a method for predicting the plate thickness. Finally, based on reversibility of the numerical compensation method, an artificial dispersion technique was used to restore the original waveform of each mode from the separated compensated pulse. Performances of the compensation separation techniques were evaluated by processing synthetic and experimental signals which consisted of multiple Lamb modes with high dispersion. Individual modes were extracted with good accordance with the original waveforms and theoretical predictions.
超声波兰姆模通常以多个频散波包的组合形式传播。由于频散的原因，各模式的频率分量在时域中分布广泛，传统的信号处理方法很难将它们分离。在本研究中，提出了一种用于模式分离的频散补偿方法。该数值方法补偿，即压缩，各离散波形成时间脉冲，从而在时间和频率上几乎没有重叠，因此可以通过矩形时间窗单独提取。进一步说明，频散补偿还提供了一种预测板厚的方法。最后，基于数值补偿方法的可逆性，从分离的补偿脉冲中，使用人工频散技术来恢复各模式的原始波形。通过处理由多个具有高色散的兰姆模式组成的合成和实验信号，评估了补偿分离技术的性能。与原始波形和理论预测具有良好的一致性，提取出了各个模式。
