穿透式空气耦合超声检测中，由于较低声波透射率、激励接收系统噪声及声波在介质中的散射噪声导致接收信号信噪比较低，小波阈值滤噪技术在解决上述问题时面临小波基、分解层数及阈值函数的选取难题。基于小波分析的基本原理，以单因素分析方法开展小波阈值滤噪试验研究。选择不同小波族(Daubechies，Symlet和Coiflet)中的小波基、小波分解层数(4～8层)及阈值函数(软阈值及改进阈值函数)对实际含噪超声信号进行小波阈值滤噪处理，并通过对比滤噪信号的信噪比及频谱特性得出不同参数对滤噪效果的影响。结果表明，选择Coiflet小波族中的小波基能获得具有更高信噪比及透射信号幅值的滤噪信号；分解层数越高，滤噪信号的信噪比越高，但增长趋势渐趋稳定；阈值函数对滤噪性能的影响并不十分显著，一般采用软阈值函数或改进阈值函数就能获得良好滤噪效果。

In air-coupled ultrasonic testing, the received ultrasonic signal has poor signal to noise ratio(SNR) due to low transmission ratio, noises introduced by transmitting and receiving system, and scattering noises during the propagation of ultrasound in the media. The use of wavelet threshold denoising technique to deal with handicaps above is faced with problems of parameter selection including wavelet base, decomposition level, and threshold function. The wavelet threshold denoising experiments are carried out using the single factor analysis method based on the basic principles of wavelet theory. Different wavelet bases from different wavelet family(Daubechies, Symlet, and Coiflet), decomposition level(4-8 levels ), and threshold function(soft threshold function or improved threshold function based on hard and soft threshold) are used to wavelet threshold denoising process for the realistic noisy ultrasonic signal. The impacts of different parameters on noise filtering are analyzed from the comparison of SNR and frequency spectrum of the denoised signal. From the results, denoised signal possesses higher SNR and signal amplitude using wavelet base from coiflet family. The higher the decomposition level, the higher the SNR of the denoised signal, but growth trend gradually stabilized. The impact of threshold function on the performance of denoising is not very significant, and acceptable filtering results can be acquired from soft threshold or improved threshold function.