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
In this paper, the plane wave expansion model is introduced to analyze the effect of a metamaterial with an uneven groove depth distribution on the radiation performance of a sound source, such as on directivity and transmission efficiency. The optimal groove depth distributions for two applications that need to maximize and minimize the transmission efficiency are obtained on the basis of this method. Further, the proposed plane wave expansion model can be degenerated to the acoustic grating model and the effective medium model with certain constraints.
A method for the automated alignment of optical waveguides and fibers based on a multiobjective evolutionary algorithm is proposed. This algorithm reduces the number of parallel operations considerably compared to previous automation schemes. The automated alignment of a single-core input fiber with a channel waveguide and a single-core output fiber is completed using this system in less than 3 min. The alignment of a single-core input fiber with a 1x8 splitter coupler and an eight-core output fiber array is completed in less than 10 min. These results demonstrate the effectiveness of the proposed scheme for automated waveguide alignment, substantially outperforming previous automatic alignment methods.
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