Comparison of the L-Network and Simplified Network's Impedance Matching of Electromagnetic Acoustic Transducers

Electromagnetic Acoustic Transducers (EMATs) can generate several types of ultrasonic waves without requiring contact with the sample under test. However, EMATs are usually less power-efficient than piezoelectric transducers. In other to mitigate this, an impedance matching technique can be used. The L-network is one of the most common techniques and is composed of two reactive elements. In this paper, two simplified variations of the L-network are proposed and theoretically evaluated, namely, the one-parallel-element (OPE) and one-series-element (OSE) networks. These simplified networks have advantages such as, simpler construction, which leads to lower real-world lower losses and they are easier to tune and adjust. OPE, OSE, full L-Network (FLN), and the unmatched circuit are theoretically exploited with three EMATs, and their performances are compared. The performance depends on the EMATs and frequency: OPE provides better results at higher frequencies, and the OSE at lower frequencies. For the EMATs and frequencies analyzed here, a combination of simplified networks, considering whichever works best in any particular case, can achieve from 78 to 99% of the performance of the full L-network.