Magnetostrictive grating with an optimal yoke for generating high-output frequency-tuned SH waves in a plate

If the notion of gratings is used to make a frequency-tuned magnetostrictive ultrasonic SH (shear-horizontal) wave transducer for plates, one can easily adjust the tuning frequency by the interval of a grating. On the other hand, the presence of the gap among grating strips inevitably obstructs magnetic flow. Because magnetic field is the main physical quantity to actuate and sense ultrasonic waves, the transducer performance is most significantly influenced by the magnetic field distribution in the strips. Thus, wave transduction efficiency can be substantially improved if better magnetic flow is formed in the strips. The objective of this study is to find an optimal magnetic yoke configuration maximizing the magnetic flux density and improving flux uniformity in the strips, which will increase the transducer signal output. The topology optimization method was employed to find the optimal yoke configuration in this investigation. A series of experiments on an aluminum plate were conducted using a grating with and without the designed yoke; when the yoke was used, the signal outputs increased up to 60%.