Abnormal topological refraction into free medium at subwavelength scale in valley phononic crystal plates

Robust Fano resonance between mechanical first- and second-order topological states

“…We assume that each oscillator has only one degree of freedom, the vertical displacement parallel to the z axis. The time-harmonic vibration of the resonators interacts with the elastic plate through the connecting springs, which gives the reaction force as [39] J o u r n a l P r e -p r o o f…”

“…Additionally, structural imperfections such as defects or disorder may shift the Fano resonant frequency, or even completely damage the Fano line shape. The developments of topological insulators (TIs) [16,17] and their classical analog in optical [18][19][20][21], acoustical [22][23][24][25][26][27][28] and mechanical [29][30][31][32][33][34][35][36][37][38][39][40] systems may provide an elegant solution to this problem. TIs support unique edge states protected by the intrinsic bulk bands topology, regardless of the local perturbations such as defects or disorders.…”

Acoustic suppressed topological refraction in valley sonic crystals

“…Accompanied by the breaking of mirror [7][8][9][10][11][12][13] or inversion [15][16][17][18] symmetry, researchers have observed acoustic valley Hall (AVH) phase transitions, and demonstrated that there exist topological edge states [7][8][9][10][11][12][13][14][15][16][17][18][19][20] of sound in the domain walls between two valley sonic crystals (VSCs) with opposite valley Chern numbers. Beyond that, based on typical features of valley-momentum locking, the edge states have been demonstrated to support robust valley transports against various defects around the domain wall with negligible intervalley scatterings, which provides the feasibility of designing sound devices with versatile applications, such as valley selective sound transmitters [8], acoustic delay lines [11], energy concentrators [12], valley-chirality locked sound splitters [14], directional antennas [21], mode-conversion emitters [22], and dual-band valley-locked discriminators [23].…”

“…In addition to its robust valley transports, topological refractions of valley edge states from an impedance-mismatched zigzag interface between the VSCs and external medium have also become a hot topic in acoustics [21][22][23][24][25][26][27], which has a unique advantage of reflection-free sound refraction owing to the suppression of intervalley scattering. In previously demonstrated topological refractions, when the output wave vector of topological refractions is in the range of the 1st Brillouin zone of the VSCs, a single-beam topological refraction is generally obtained in topological waveguides composed of two VSCs, providing the feasibility of designing a directional acoustic antenna [21,22,24,25]. However, when the working band of the edge state moves into the high-frequency region gradually, the output wave vectors of the topological refraction are beyond the range of the 1st Brillouin zone of the VSCs.…”

Tunable Topological Refractions in Valley Sonic Crystals With Triple Valley Hall Phase Transitions (Invited Paper)

“…Recently, the research on valley degree of freedom has become a hot topic due to its potential as an excellent candidate of information carrier and important applications in information communication and processing [1][2][3][4][5][6]. Inspired by the valleytronics, researchers have introduced this concept into several subfields of physics, such as photonics [7][8][9][10][11][12][13][14][15][16][17][18][19], mechanics [20][21][22][23][24][25][26], and acoustics [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41]. In acoustics, by breaking mirror [28-31, 35, 38-40] or inversion [33,36,37] symmetry, various types of valley topological transports with negligible inter-valley scatterings have been demonstrated by designing a pair of valley sonic crystals (VSCs) with opposite valley Hall phases.…”