The dynamic impedance matching method for high temperature electromagnetic acoustic transducer

Temperature fluctuation and lift-off form the sample had caused the resonant frequency shift and impedance variation of electromagnetic acoustic transducer (EMAT). They result in low power efficiency and unstable echo amplitude. To solve this problem, a dynamic impedance matching system has been developed to accurately achieve impedance match for high temperature EMAT at the broadband. It based on the linear model of an EMAT. The main advantage of the method is use the switch combination to changing parameter values of the LC network at the temperature fluctuation. The reasonable signal-to-noise ratios were to be achieved based on the most useful LC matching network for ultrasonic transducer. Furthermore, there is no need controller due to this method based on take turns to query coded values and which find the suitable switch combination of LC network. In this paper, the main influence of coil impedance is high temperature, and the change trends of coil parameters is analyzed in different temperature. The experimental results show that the dynamic impedance matching method can effectively improve the ultrasonic conversion efficiency of the transducer at the temperature fluctuation, and it verified the effectiveness of this method.