中文摘要：

空气耦合超声检测信噪比低、脉冲余振长,需要采用合适的信号处理技术增强接收信号的信噪比。根据空气耦合超声检测过程中影响接收信号的因素,提出先采用相敏检波技术对接收信号进行处理,获取相位信号,然后计算得到超声检测信息。介绍了超声检测中的超外差接收、相敏检波原理,并阐述了在超声检测应用中需注意的问题。根据分析研究结果,构建了相敏检波空气耦合超声检测系统,在常规超声检测系统的基础上进行了相应改造,实现了超声成像检测。碳纤维增强复合材料板的成像检测结果表明：相敏检波可以有效提高系统信噪比和检测效果。

英文摘要：

The signal to noise ratio（SNR） of air-coupled ultrasonic testing is very poor and there is long time pulse residue,so it needs to adopt appropriate signal processing method to enhance the SNR of received signals.Factors which affected the received signals in ultrasonic testing process were analyzed.Phase sensitivity detection technology was presented to process the received signals,and ultrasonic testing information could be acquired by the calculation of phase signals.The principles of super-heterodyne receiver and phase sensitivity detector were introduced,some problems which should be payed attention in ultrasonic testing process were explained.Based on the research results,air-coupled ultrasonic testing system with phase sensitivity detector is constituted.Experimenal results of image testing on carbon fiber reinforced plastic plate indicate that,phase sensitivity detection technology can improved SNR of system and testing effects in evidence.