跑道型线圈EMAT等效阻抗影响因素分析

Analysis of influencing factors of EMAT equivalent impedance of racetrack coil

电磁超声换能器(EMAT)是一种不需要耦合剂就能对被测试件进行超声检测的传感器,在常规超声难以检测的领域发挥着重要的作用。但是电磁超声换能器换能效率低、信噪比差的问题,制约着电磁超声换能器的发展。该文主要从等效阻抗的角度研究传感器的阻抗特性,分析影响传感器阻抗特性的影响因素,根据传感器的阻抗特性对传感器进行优化设计,并对不同工况下的传感器进行阻抗匹配,研究不同工况下阻抗匹配网络对于传感器信号幅值和信噪比的影响。研究结果表明,磁铁到线圈间距和提离距离对传感器等效阻抗的影响较为显著,按照提离距离为0.5 mm和磁铁到线圈间距为1 mm设计的传感器能够满足对不同性质的被检材料检测时信号幅值达到最优的目的,在不同被检材料下随提离距离的变化信号幅值的衰减规律不同,阻抗匹配网络的加入有利于提高大提离下信号的信噪比。

Electromagnetic ultrasonic transducer(EMAT)is a transducer that can ultrasonically detect the test piece without the need for a coupling agent,and plays an important role in areas that are difficult to detect with conventional ultrasound.However,the problems of low transduction efficiency and poor signal-to-noise ratio of electromagnetic ultrasonic transducers are restricting the development of electromagnetic ultrasonic transducers.This paper mainly studies the impedance characteristics of the sensor from the perspective of equivalent impedance,analyzes the influencing factors affecting the impedance characteristics of the sensor,optimizes the design of the sensor according to the impedance characteristics of the sensor,and impedance matches the sensor under different operating conditions,and investigates the impact of the impedance matching network on the amplitude of the sensor signal and the signal-to-noise ratio under different operating conditions.The results show that the magnet-to-coil spacing and lift-off distance have a significant effect on the equivalent impedance of the sensor,and the sensor designed according to the lift-off distance of 0.5 mm and magnet-tocoil spacing of 1 mm can meet the purpose of detecting the optimal signal amplitude of the detected materials of different properties,and the attenuation of signal amplitude with the change of the lift-off distance is different in different materials,and the addition of impedance matching network is conducive to the improvement of signal-to-noise ratio under large lift-off.