电磁超声兰姆波的无损探伤技术

摘要

针对金属薄板的缺陷检测问题,进行了电磁超声兰姆波无损探伤技术的研究.基于兰姆波的频散特性,推导出了兰姆波各模式相(群)速度关于线圈间距、频厚积及激励频率的表达式,确定了电磁超声换能器的结构参数.设计了一种DDS与FPGA相结合,产生串码、频率可调的脉冲激励信号串发生电路,利用H桥放大电路对激励信号进行了升压处理,并对激励线圈进行了阻抗匹配.试验结论表明:永磁铁与激励线圈的不同组合形式可以分别在铁磁性和非铁磁性金属薄板中激发出兰姆波.研制的功率放大电路及信号处理电路能够在金属薄板中激发出高性能的兰姆波并实现稳定接收,具有较高的信噪比,能够实现对金属薄板的无损探伤.%For the sheet metal defect detection problem, advanced the electromagnetic ultrasonic Lamb wave nondestructive testing technology research. Based on the dispersion characteristics of Lamb waves, derived out the model of the Lamb wave phase ( group) velocity of the coil spacing, frequency and excitation frequency thickness product expression and determine the electromagnetic ultrasonic transducer structure parameters. Design a DDS and FPGA combined generating circuit, which can generate string of code, adjustable pulse frequency excitation signal string, Used the H-bridge amplifier circuit excitation signal for the boost treatment and then impedance matched the excitation coil. Experiment concluded shown, different form of permanent magnet and excitation coils combination can respectively stimulate Lamb in the ferromagnetic and non-ferromagnetic metal sheet. Developed power amplifier circuit and signal processing circuit can stimulate high-performance in sheet metal and realize stable reception, has a high signal to noise ratio and can execute Non-destructive testing of metal sheet.