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We present a study on the existence of synthetic Weyl points with various planar symmetries in phononic crystals. We design a set of phononic crystals to display Weyl points at high-symmetry points with different symmetries in both square and honeycomb lattices. We demonstrate that, in a square lattice, double Weyl points are protected by C4 rotation symmetry, while in a honeycomb lattice, they are protected by C3 rotation symmetry. Additionally, we investigated the effects of symmetry on double Weyl points. The results indicate that double Weyl points would split into two single Weyl points along high-symmetry lines if we break the corresponding symmetries. The distributions of Weyl points in various symmetries are presented systematically. Finally, gapless surface states and the robust one-way acoustic transport in a square lattice are demonstrated in a double Weyl system. [ABSTRACT FROM AUTHOR]

Topological valley states, emerging as an exciting field in condensed matter physics, are attracting attention because of their potential as a new type of information carrier with orbital angular momentum. In this paper, we exhibit that the acoustic valley states can achieve trapping of microparticles due to the acoustic radiation force induced by the acoustic vortex. In addition, we can achieve the separation of microparticles based on different acoustic contrast factors. Our study shows a demonstration of acoustic valley states in the field of particle contactless manipulation. Potential applications can be predicted by the exotic interaction of acoustic vortices with microparticles, such as cell separation, drug delivery, and other biomedical applications. [ABSTRACT FROM AUTHOR]

This article reports a realization of subwavelength acoustic topological edge states realized by a triangular array of hexagonal columns with Helmholtz resonators. Using the strategy of zone folding, Dirac cones can be folded into double Dirac cones to construct pseudo-spin states. By adjusting the length of both the center and corner units, topological phase transition as well as the common bulk bandgap can be achieved. The calculated results show that the acoustic metamaterials with different boundaries exhibit different bulk transmission properties. Topological acoustic metamaterials can be combined with different boundaries to construct nine different interfaces, and the simulation results show that nine different interfaces can exhibit robust, weak, and even disappearing topological edge states. We manufacture the samples and carry out experiments to test the transmission spectra of nine different interfaces. Experimental results demonstrate that a sound wave can transmit well along the topological interface 1 path compared with the other eight interface paths. This study provides a simple approach to create acoustic topological edge states at the subwavelength scale and experimentally confirms the influence of boundaries selection on acoustic topological insulators. [ABSTRACT FROM AUTHOR]

Enhanced acoustic sensing is a topic of interest in a variety of research fields. Here, we propose a gradient coiling up metamaterial (GCM), combining gradient and coiled structures, so as to realize enhanced broadband acoustic sensing. Compared with metamaterials without coiled structures, the GCM shows a far superior performance in terms of acoustic enhancement, enabling the acoustic signals to be magnified up to approximately 80 times, over a wide frequency range. Moreover, by virtue of coupling the coiled structures, trapped and enhanced frequencies in the GCM can be reduced by nearly 43%. In addition, we numerically and experimentally demonstrate the property of frequency-selective enhancement over a wide frequency range, which can be used to approximate unknown signals by changing their measured positions. Moreover, harmonic signals with useful information can be effectively recognized and recovered from strong background noise, using GCM. Our results indicate that GCMs can be regarded as a functional material or an enhanced acoustic sensing device to improve the acoustic sensing performance of signal detection in practical engineering applications. [ABSTRACT FROM AUTHOR]