密集型矩形阵列参数对激光Lamb波成像的影响分析

Analysis on the influence of compact rectangular array parameters on laser-based Lamb wave imaging

激光超声技术具有非接触、检测效率高等优点,在无损检测领域受到广泛关注;充分利用激光超声技术的高空间分辨率特性,结合密集型矩形阵列和激光Lamb波技术进行板中缺陷检测。采用连续小波变换对频带宽、时域分辨率低的激光Lamb波信号进行提取,得到特定频率下具有高时域分辨率的窄带信号;利用线性映射补偿技术消除所提取窄带信号中的频散,消除频散的信号用于缺陷成像;最后,结合幅值成像技术和符号相干因子成像技术对频散补偿后的信号进行处理,实现铝板中缺陷的成像和定位。在此基础上,进一步对不同的阵元数量和阵元间距对密集型矩形阵列指向性和缺陷成像质量的影响进行分析。当阵元数量为16,阵元间距为一个Lamb波波长时,主瓣宽度较窄且没有栅瓣出现,缺陷成像质量得到有效提高。

The laser ultrasonic technology has the advantages of non-contact and high inspection efficiency. It has been widely concerned in the field of nondestructive testing. Fully utilizing the characteristic of high spatial resolution of the laser ultrasound technology, a defect detection method for plate structures was put forward by the combined use of the compact rectangular array and laser-based Lamb wave technology. The continuous wavelet transform was used to process the wide-band Lamb wave signal with low time-domain resolution so as to obtain a narrow-band signal with high time-domain resolution at a given frequency. The linear mapping compensation technology was used to eliminate the dispersion in the narrow-band signal. The obtained signals after dispersion compensation were used for defect imaging. The dispersion compensated signals were processed by integrating the amplitude imaging technique and the sign coherence factor imaging technique, and then the defect imaging and location for an aluminum plate were achieved. Based on this, the effects of element spacing and number on the beam steering and the quality of defect imaging of the compact rectangular array were analyzed. When the number of array elements is 16 and the array element spacing is one wavelength of Lamb wave mode, the width of the main lobe is narrow and there are no grating lobes, the defect imaging quality is improved effectively.