Fig. 3: Experimental observation of type-II nodal rings.
From: Topological phononics arising from fluid-solid interactions
a Schematic of experimental setup for near-field scanning. A hydrophone is employed to image the ultrasound signal at facet 2. Piezoelectric actuators are used to actuate the phononic crystal. When detecting bulk bands, the actuator attached on facet 1 is excited, while detecting the surface states, the actuator attached on facet 2 is excited. b Photograph of the sample and experimental setup. White scale bar: 40 mm. c Spatial Fourier spectra of experimentally imaged fields at corresponding frequencies. The bright stripes correspond to modes of the 1st and 2nd bands excited and observed in experiments. Gray-shaded regions: the sound cone projected on the kx-ky plane. d Experimental Fourier spectra along high-symmetry directions. Gray shaded region: the projected sound cone. Black circles: calculated band structure projected along kz. The bright stripes correspond to excited modes, which generally overlap with black circles from full-wave simulations. The colored dots represent the nodal rings of the same color denoted in Fig. 1.
