Driving frequency dependent wave modes of point-focusing electromagnetic acoustic transducers

This article presents a driving frequency dependent wave mode of point-focusing electromagnetic acoustic transducers (PF-EMATs), which is composed of a cylindrical permanent magnet and a concentric meander line (CML) coil with a varying spacing interval for concentring the ultrasound waves to a point. A finite element model is established to simulate the incentive and propagation process of ultrasonic waves so that the focusing characteristic, such as displacement, amplitude profile, and focal offset, can be obtained, allowing for investigation into the driving frequency dependence of wave modes. In addition, the universality of driving frequency dependent wave modes is well demonstrated. Furthermore, the relationship between the focusing performance of the developed PF-EMAT and the coil parameters, inner radius R and number of turns N of the CML coil, is explored. Finally, the experimental results show good agreement with the simulated results and indicate that the presented driving frequency dependent wave modes of PF-EMATs employing CML coils could manipulate the wave modes by carefully controlling the driving frequency.