arXiv subjects

Yeongtae Jang

Publications and source records attributed to Yeongtae Jang.

4 recordsLinked to original sources

arXiv2024

Bound States-to-Bands in the Continuum in Cylindrical Granular Crystals

We theoretically investigate and experimentally demonstrate that genuine bound states in the continuum (BICs) -- polarization-protected BICs -- can be completely localized within finite-size solid resonators. This bound mode is realized in a highly tunable mechanical system made of cylindrical granular crystals, where tunning the contact boundaries enables the in situ transition from the BICs to quasi-BICs in a controllable manner. Since a single-particle resonator can support BICs itself, these bound states can extend to form bound bands within periodic structures composed of such resonators. We experimentally demonstrate the emergence of a quasi-bound (flat) band in a finite chain with broken resonator symmetry, using a laser Doppler vibrometer. Remarkably, we show that all cylindrical resonators within the entire chain exhibit high-Q and dispersionless resonance.

physics.app-ph↗

arXiv2024

Singular Topological Edge States in Locally Resonant Metamaterials

Band topology has emerged as a novel tool for material design across various domains, including photonic and phononic systems, and metamaterials. A prominent model for band topology is the Su-Schrieffer-Heeger (SSH) chain, which reveals topological in-gap states within Bragg-type gaps (BG) formed by periodic modification. Apart from classical BGs, another mechanism for bandgap formation in metamaterials involves strong coupling between local resonances and propagating waves, resulting in a local resonance-induced bandgap (LRG). Previous studies have shown the challenge of topological edge state emergence within the LRG. Here, we reveal that topological edge states can emerge within an LRG by achieving both topological phase and bandgap transitions simultaneously. We describe this using a model of inversion-symmetric extended SSH chains for locally resonant metamaterials. Notably, this topological state can lead to highly localized modes, comparable to a subwavelength unit cell, when it emerges within the LRG. We experimentally demonstrate distinct differences in topologically protected modes -- highlighted by wave localization -- between the BG and the LRG using locally resonant granule-based metamaterials. Our findings suggest the scope of topological metamaterials may be extended via their bandgap nature.

cond-mat.other↗

arXiv2024

Demonstrating a Bi-directional Asymmetric Frequency Conversion in Nonlinear Phononic Crystals

Beyond the constraints of conservative systems, altering wave propagation frequency emerges as a crucial factor across diverse physical domains. This Letter demonstrates bi-directional asymmetric frequency conversion -- either upward or downward -- depending on the excitation direction in the elastic domain, moving beyond uni-directional approaches. We numerically and experimentally demonstrate its practical realization in a model system of cylindrical beam crystals, a type of granular crystal characterized by intrinsic local resonance. This novel wave transport mechanism operates through the interplay of nonlinear contact, spatial asymmetry, and the coupling of local resonance. Thanks to the proposed highly tunable architecture, we demonstrate various ways to manipulate wave transport, including tunable frequency conversion. Given that the local resonance we employ exemplifies avoided crossings (i.e., a strong coupling effect), our work may inspire investigations into diverse physical nonlinear domains that support material/structural resonance.

physics.app-ph↗

arXiv2023

Physics-informed discrete element modeling for the bandgap engineering of cylinder chains

We propose an efficient method to build a simple discrete element model (DEM) that accurately simulates the oscillation of a continuum beam. The DEM is based on the Timoshenko beam theory of slender cylindrical members and their corresponding wave dynamics in assembly. This physics-informed DEM accounts for multiple vibration modes of the constituting beam elements in wide frequency ranges. We construct various DEMs mimicking cylinder chains and compare their wave dynamics with those measured in experiments to validate the proposed method. Furthermore, we construct a graded woodpile chain of slender cylinders. We experimentally and numerically investigate the frequency bandgaps of the system and demonstrate the possibility of constructing a wide bandgap by consecutively superposing multiple stop bands generated from cylinders of various lengths. This system is highly efficient in blocking propagating waves by leveraging the vibration isolation effect stemming from the local resonance of the cylinders. The proposed DEM method can be useful for investigating and designing complex vibration systems in an efficient and accurate manner. Moreover, the design approach of manipulating the frequency bandgap can be exploited for developing vibration filters and impact mitigation devices.

cond-mat.other↗