Ultrasonic guided waves have been successfully applied in nondestructive evaluation (NDE) and structural health monitoring (SHM) of pressure vessels and pipelines due to their advantages, such as long detection range and high inspection efficiency. Compared with other ultrasonic guided wave actuators, magnetostrictive transducers are more cost-effective, involve simpler fabrication process, and have higher possible transduction efficiency. The normal mode expansion (NME) method is adopted to analyze the forced response and perturbation analysis of elastic hollow cylinders with respect to magnetostrictive loadings, including partial loading, axial array loading, and circular array loading. The phase velocity and frequency spectra of axisymmetric/non-axisymmetric guided waves excited by magnetostrictive transducers are analyzed. The theoretically predicted trends are verified by finite element numerical simulations and experiments.
In this work, we show how to modify radiation amplitude with a leaky wave antenna to improve the quality of sound radiation. The designed gradient amplitude leaky wave antenna consists of a straight pipe with periodically loaded membranes, open channels and Helmholtz resonators. An equivalent acoustic composite right/left-hand transmission line that considers the effects of viscous-thermal and viscous-elastic losses is utilized to steer the radiation angle continually from backward to forward as a function of the incident frequency. The numerical results show that by appropriately selecting the structural parameters of the channel and Helmholtz resonator cavity, the quality of the directional radiation is improved based on the gradient distribution of the radiation amplitude and the near unitary phase. Compared with traditional antennas, the proposed gradient amplitude antenna incorporates a frequency scanning capability with gradient amplitude, which improves the directivity quality of the acoustic waves among the operated frequency band, and provides a new design method for acoustic leaky wave antennas.New J. Phys. 21 (2019) 103023 J Lan et al
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