Research on EMAT Transmitting Circuit Based on Self-Induction Effect

Electromagnetic Acoustic (EMAT) transducers offer significant advantages for non-destructive testing in harsh environments, including high temperatures and on moving components. However, their application is limited by the inherently weak ultrasonic signal intensity. To address this critical challenge, this study introduces a novel self-inductive transmitting circuit leveraging the transducer’s own inductive properties. The proposed transmitting circuit is verified by means of simulations and experiments. Firstly, the equivalent circuit of the EMAT transducer was analyzed, and it was determined that the transducer exhibits inductive load characteristics at the detection frequency. Next, further investigation of the non-tuning transmitting circuit principle indicates that during the turn-off transient of the MOSFET, the magnetic field energy stored (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E_L</i>) in the transducer’s equivalent inductance is dissipated as heat through the resistive path. Subsequent analysis revealed that only 1.15% of the total energy was utilized for sound wave generation, whereas <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E_L</i> accounted for 82.7%. Furthermore, based on the self-induction effect of the EMAT transducer, a miniaturized self-induction transmitting circuit is developed, which realizes the miniaturization of 36 mm × 66 mm × 15 mm (35.64 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup>). The circuit makes use of the self-inductance effect and can continue to use <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E_L</i> to generate an ultrasonic signal after MOSFET is turned off. This represents a 60.4% volume reduction compared to conventional full-bridge solutions. Performance testing demonstrated an output voltage of 1800 V and a peak power of 33.1 kW. When integrated into an ultrasonic system, the circuit yielded a 5.2 dB improvement in echo signal-to-noise ratio (SNR) over non-tuning circuits. The continuous 72-hour operation test demonstrates significant long-term operational stability of the circuit. This optimized approach provides a new pathway for the miniaturized design of high-performance EMAT inspection equipment.