Design method of unidirectional wideband SH guided wave phased array magnetostrictive patch transducer

The existing meander coil type SH guided wave electromagnetic acoustic transducer (EMAT) has a fixed center frequency and narrow bandwidth, which cannot quantify the defect size by continuous frequency scanning. Therefore, this study proposes an array of wideband unidirectional SH guided wave magnetostrictive patch transducer and its control method for excitation of unidirectional SH guided waves at random frequencies over a wide frequency range. A narrow magnetostrictive patch and a linear coil are used for each array element to increase the bandwidth of a single element. By controlling the excitation delay and initial phase of each array element separately, the direction of the SH guided wave can be controlled, and its wavelength can be changed without replacing the coil. In addition, a mathematical model of the array sources of finite width is developed to excite unidirectional SH guided waves at different frequencies. Based on this model, the effects of the number, width and distance of the array element on the frequency response characteristics of the transducer array are analyzed. The experiments show that: The proposed transducer array can excite unidirectional SH guided waves of random frequency over a wide frequency range. The amplitude of the guided wave signal on the suppressed side is almost 0, while the signal on the non-suppressed side is significantly increased, leading to a significant improvement in the energy conversion efficiency. The frequency range can be selected by designing the width and distance of array elements, and the experimentally measured frequency response characteristics of the transducer array are highly consistent with the trend of the mathematical model results.