Materials Science Forum Vol. 1107

Abstract: Recently, ultracompact electric vehicles (EVs) have begun to be sold, instead of general vehicles equipped with gasoline engines, for transportation. However, because the outer plate of an ultracompact EV has low rigidity, the road noise generated by rotation and the wind noise generated from the vehicle's projection shape are transmitted to the inside of the EV. This interior noise reduces the ride comfort for passengers. Therefore, an active noise control (ANC) system was proposed for controlling noise transmitted from the outside of the EV. The proposed ANC system was configured to control the sound generated using a giant magnetostrictive actuator on the wall surface in the cabin of the EV, instead of a vehicle installation speaker.In this study, Tb, Dy, and Fe powders, which are giant magnetostrictive materials, were mixed and mechanically alloyed to produce multiple giant magnetostrictive materials to be used in the proposed ANC system. The displacement of each alloyed giant magnetostrictive material was measured. In addition, each alloyed material was analyzed using X-ray diffraction and their crystal orientation was confirmed.

Abstract: As an analogy of topological insulators and superconductors, “topological phononics”, which applies the concept of band topology to acoustic dispersion, has attracted increasing attention in recent years. We present design of topological acoustic/elastic waveguides in phononic crystals. Topological waveguides are designed from the phonon dispersion analyses by finding edge modes appearing at interfaces between phononic crystals with different band topologies. As a prototype model, we first designed the topological waveguides in kHz regimes. Experimental validation of the designed waveguide has been performed in the frequency region via laser-doppler measurements. The robustness of the waveguide propagation against defects, corners, and structural inaccuracy in the waveguide has been quantitatively evaluated. We also introduced a structural transition of local symmetry inversion in the phononic crystal to implement a reconfigurability into the waveguide .Further development toward GHz regime will pave the way to the development of next-generation information devices using the proposed structures as an alternative or complimentary approach.