Circumferential Radially Magnetized Electromagnetic Acoustic Transducer for Nondestructive Monitoring in High-Temperature (≥600 °C) Environments

In the petrochemical industry, plants must be shut down regularly for maintenance to safeguard human lives and property from catastrophic explosions. The introduction of nondestructive monitoring technologies has made this process more efficient and economical. However, nondestructive monitoring in extreme heat environments ( ${\ge } 600~^{\circ }$ C) remains a challenge. Electromagnetic ultrasound technology has notable advantages in monitoring high-temperature equipment due to the absence of coupling agents and the allowance of lift-off distances. However, weak signal amplitudes and low operating temperatures of electromagnetic acoustic transducers (EMATs) severely limit their application in harsh high-temperature scenarios. To improve the signal amplitude and solve the problem of monitoring extreme heat equipment, we propose a circumferential radially magnetized EMAT (CRM-EMAT). It consists of eight circumferential radially magnetized (CRM) sector-shaped permanent magnets, wrapped around a cylindrical core, and a permalloy patch attached to the lower surface of this magnetic combination. Three-dimensional numerical simulations and laboratory experiments were carried out to obtain the optimal dimensions of each part and to demonstrate that the probe improves the signal amplitude by a factor of over 6 and can operate stably up to $600~^{\circ }$ C. The CRM-EMAT represents a breakthrough in the operation temperature of EMATs and realizes superior signals with lower power consumption, thus accelerating the industrial application of electromagnetic ultrasound technology.