A simplified automatic impedance matching network for electromagnetic acoustic transducers

Electromagnetic acoustic transducers (EMATs) generate ultrasonic waves without requiring physical contact with the medium under test. Nevertheless, they present a main disadvantage of less efficiency, when compared to commonly used piezoelectric transducers, which leads to a lower signal-to-noise ratio. L-network impedance matching network is often used in order to overcome this drawback and ensure higher power transfer to the EMAT. Manually impedance matching is a laborious and time-consuming task and must be repeated whenever the transducer, specimen material, or operating frequency changes. In this paper, an automatic one-element impedance matching network was designed and its benefit in increasing the EMAT efficiency was evaluated. The theoretical optimal value for the one-element matching network was derived. Simulations confirmed its efficiency and showed that, in the analyzed scenario, it provided 90% of full, two-element, impedance matching L-network’s benefit. An automatic one-element matching network was fabricated and experimentally evaluated. The automatic system was able to determine the best configuration for the one-element matching network and provided up to 5.6 dB gain, similar to a manual solution, more than two-fold faster.