Optimized Design of a Novel Permanent Magnet-Free Giant Magnetostrictive Ultrasonic Transducer
Wu Zhenjian1, Shi Wenze1, Lu Chao1, Cai Ying2, Wang Jianxin2, Xu Zisheng1
1. Key Laboratory of Nondestructive Testing Ministry of Education Nanchang Hangkong University Nanchang 330063 China; 2. Inner Mongolia North Heavy Industry Group Co. Ltd Baotou 014033 China
Abstract：The magnetostrictive patch transducer is an ultrasonic transducer based on the magnetostrictive effect, capable of generating and detecting ultrasonic waves in both ferromagnetic and non-ferromagnetic materials. The conventional permanent magnet type magnetostrictive patch transducer has problems such as easy adsorption of ferromagnetic particles, non-adjustable magnetic field strength and magnetic degradation after long-term use, which leads to a decrease in the magnetostrictive excitation efficiency. To solve these problems, this study proposes a permanent magnet-free giant magnetostrictive patch transducer and its detection circuit. Firstly, we designed the detection circuit for permanent magnet-free giant magnetostrictive ultrasonic transducer. The circuit dynamically adjusted the on-time sequence of the IGBT and MOSFET elements to generate strong, prolonged current (pulse widths greater than 200 μs) and a short 1 MHz pulse current in the coil, resulting in the formation of a composite field of bias and high-frequency alternating magnetic fields in the coil. Under the combined action of these superimposed magnetic fields, the patch generated magnetostrictive stress. The stress coupled through the patch-specimen interface and ultimately excited ultrasonic wave propagation to the specimen's bottom. Secondly, a finite element model for the permanent magnet-free giant magnetostrictive patch transducer was established based on the linear constitutive equations of the magnetostrictive effect. This model successfully excited bulk waves dominated by shear wave components within the aluminum alloy specimen. To enhance transduction efficiency, the effects of voltage parameters, coil geometric parameters, and patch dimensions on received signal amplitude were analyzed. Finally, a permanent magnet-free giant magnetostrictive patch transducer testing system was designed and constructed, and the effects of key parameters such as voltage amplitude, coil geometry and patch dimensions on the received signal amplitude were experimentally verified. The experimental results showed that the proposed ultrasonic transducer had a non-linear response with DC voltage and a linear response with alternating voltage. When the DC voltage increased from 18 V to 24 V, shear wave amplitude increased by 228%. With a further increase to 26 V, longitudinal wave amplitude rose by 344%,while the shear wave exhibited a declining trend. It is shown that adjusting the voltage parameter can optimise the operating state of the Terfenol-D patch to improve the direct wave amplitude. The direct wave amplitude decreased with the increase in the number of turns of the coil and increased with the increase in the diameter of the coil wire. The optimum signal amplitude for the transducer was obtained when the thickness of the Terfenol-D patch was close to the height of the nano-core air gap. The following conclusions can be drawn from the analysis: (1) There exists an optimal operating point for the permanent magnet-free giant magnetostrictive patch transducer, where the peak response amplitude can be excited when the excitation voltages (DC voltage and alternating voltage) are in the optimal interval. (2) Reducing the number of coil turns and increasing the wire diameter improves transducer efficiency. The optimal thickness of the Terfenol-D patch should match the air gap height of the nanocrystalline magnetic core to balance magnetic field utilization and mechanical impedance, while the patch length must satisfy uniform bias magnetic field distribution requirements.
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2026, Vol. 41 
