Abstract
When chirp pulse compression technology (PCT) is applied in Electromagnetic Acoustic Transducers (EMATs), the frequency response characteristic of the EMAT testing system may be inconsistent with the chirp signal bandwidth. Furthermore, it causes a loss in the frequency spectrum and distortion of the ultrasonic echo waveform, leading to a decrease in the signal-to-noise ratio (SNR) and range resolution of the pulse compressed signal. To solve this problem which has not been further researched in the previous publications, we proposed a new circuit-field coupling finite element model for ultrasonic wave generation of the spiral coil EMAT for enhancing the pulse compression effect, and the excitation circuit for the EMAT is also considered in this model. Furthermore, the effects of the diameter of the spiral coil wire, matching method of the impedance matching network, and parameter of the matching components on the peak and width of the main lobe after pulse compression were analysed through simulations and experiments. Subsequently, the optimal combination of the EMAT coil conductor diameter, impedance matching method, and matching component parameters were determined and verified by experiments. The results show that the SNR and range resolution of the pulse compressed ultrasonic signal can be largely enhanced when the diameter of the spiral coil wire, impedance matching method, and the parameter of the matching components are chosen carefully. When the aforementioned parameters are appropriately selected, the amplitude of the main lobe can be increased 3.16 times, and the width of the main lobe is reduced by 31.7%.
Published Version
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