中文摘要：

针对电磁超声换能器（electromagnetic acoustic transducer，EMAT）转换效率低、信号微弱、信噪比低的问题，设计开发了包括电磁超声换能器在内的，由低噪前置放大器、宽带接收器以及基于虚拟仪器的正交锁相放大等构成的电磁超声检测系统。对比了传统EMAT结构与新的EMAT结构磁通密度的不同，通过提高偏置磁场的强度提高EMAT的换能效率；分析了前置放大器、宽带接收器、电磁超声换能器的频率响应特性；研究了相敏检波器中低通滤波器的阶数、滤波器类型以及截止频率对电磁超声回波信号检测的影响，并对铝板进行了缺陷检测实验。实验结果表明：该系统能够实现电磁超声信号的实时采集、分析和存储，同时能够提高信号的信噪比和分辨率。

英文摘要：

To solve the problem of low transduction efficiency, weak signal and low signal-to-noise ratio （SNR） in electromagnetic acoustic transducer （EMAT） system, the detection system was designed, including EMAT, low noise preamplifier, broadband receiver and the orthogonal phase-locked amplifier based on the LabVIEW. The difference between the traditional EMAT structure and the new EMAT structure flux density was compared, by increasing the intensity of the bias magnetic field can improve the efficiency of EMAT; The frequency response characteristic of preamplifier, broadband receiver and EMAT were analyzed. The impact of the order, filter type and cut-off frequency of the low pass filter, to detect the ultrasonic echo signal was studied. Results indicate that the system can achieve the goal of real-time acquisition, storage and analysis of electromagnetic ultrasonic echo signal and improve the SNR and resolution of signals.