Yeongtae Jang

August 3, 2026• Physics 19, 109 Two experiments demonstrate a promising platform for trapping, sorting, and directing vibrational energy. Figure 1: An elastic wave (black) enters a square lattice of slightly misaligned triangular elements (gray). Synthetic magnetic and electric fields (not shown) cause different frequencies of the wave to localize at different positions in the material’s bulk. The result is a so-called elastic rainbow (colored regions).

We theoretically investigate and experimentally demonstrate that genuine bound states in the continuum (BICs)—polarization-protected BICs—can be completely localized within compact solid resonators. This bound mode is realized in a highly tunable mechanical system made of cylindrical granular crystals, where tuning the contact boundaries enables the in situ transition from the BICs to quasi-BICs in a controllable manner.