Broadband electrical impedance matching of sandwiched piezoelectric ultrasonic transducers for structural health monitoring of the rail in-service

Abstract

To achieve high power transmission efficiency and high signal-to-noise ratio of sandwiched piezoelectric ultrasonic transducers (SPUTs) over a wide bandwidth, broadband electrical impedance matching (EIM) is investigated in-depth. Firstly, L type, T type, III type, IV type and V type EIM networks are designed and the corresponding component parameters are determined by the Smith chart with a quality factor Q constraint. Secondly, the above EIM networks are compared by reflection coefficient S11, transducer power gain (TPG) and active power. It is shown that they can effectively improve the TPG, and active power by two times and greatly reduce S11. Then the emitted voltage and received voltage under different excitation frequencies and EIM networks are analyzed. It is shown that the III type network presents optimal performance, which can make the aforementioned voltage values increase by two times over entire frequency range of interest. Finally, the effect of III type and IV type networks on electromechanical characteristics is studied by using the PSpice model of SPUTs. Compared to non-matching, the electro-acoustical gain ratio is improved almost two times, while the electro-acoustical power ratio is greatly reduced.