arXiv subjects

Brian L. Kim

Publications and source records attributed to Brian L. Kim.

3 recordsLinked to original sources

arXiv2023

Experimental Evidence of Amplitude-Dependent Surface Wave Dispersion via Nonlinear Contact Resonances

In this letter, we provide an experimental demonstration of amplitude-dependent dispersion tuning of surface acoustic waves interacting with nonlinear resonators. Leveraging the similarity between the dispersion properties of plate edge waves and surface waves propagating in a semi-infinite medium, we use a setup consisting of a plate with a periodic arrangement of bead-magnet resonators along one of its edges. Nonlinear contact between the ferromagnetic beads and magnets is exploited to realize nonlinear local resonance effects. First, we experimentally demonstrate the nonlinear softening nature and amplitude-dependent dynamics of a single bead-magnet resonator on both rigid and compliant substrates. Next, the dispersion properties of the system in the linear regime are investigated. Finally, we demonstrate how the interplay of nonlinear local resonances with plate edge waves gives rise to amplitude-dependent dispersion properties. The findings will inform the design of more versatile surface acoustic wave devices that can passively adapt to loading conditions.

physics.app-ph↗

arXiv2022

Dynamics of Time-Modulated, Nonlinear Phononic Lattices

The propagation of acoustic and elastic waves in time-varying, spatially homogeneous media can exhibit different phenomena when compared to traditional spatially-varying, temporally-homogeneous media. In the present work, the response of a one-dimensional phononic lattice with time-periodic elastic properties is studied with experimental, numerical and theoretical approaches. The system consists of repelling magnetic masses with grounding stiffness controlled by electrical coils driven with electrical signals that vary periodically in time. For small amplitude excitation, in agreement with theoretical predictions, wavenumber bandgaps emerge. The underlying instabilities associated to the wavenumber bandgaps are investigated with Floquet theory and the resulting parametric amplification is observed in both theory and experiments. In contrast to genuinely linear systems, large amplitude responses are stabilized via the nonlinear nature of the magnetic interactions of the system. In particular, the parametric amplification induced by the wavenumber bandgap can lead to bounded and stable responses that are temporally quasi-periodic. Controlling the propagation of acoustic and elastic waves by balancing nonlinearity and external modulation offers a new dimension in the realization of advanced signal processing and telecommunication devices. For example, it could enable time-varying, cross-frequency operation, mode- and frequency-conversion, and signal-to-noise ratio enhancements.

physics.app-ph↗

arXiv2016

Band Gap Engineering with Ultralarge Biaxial Strains in Suspended Monolayer MoS2

We demonstrate the continuous and reversible tuning of the optical band gap of suspended monolayer MoS2 membranes by as much as 500 meV by applying very large biaxial strains. By using chemical vapor deposition (CVD) to grow crystals that are highly impermeable to gas, we are able to apply a pressure difference across suspended membranes to induce biaxial strains. We observe the effect of strain on the energy and intensity of the peaks in the photoluminescence (PL) spectrum, and find a linear tuning rate of the optical band gap of 99 meV/%. This method is then used to study the PL spectra of bilayer and trilayer devices under strain, and to find the shift rates and Grüneisen parameters of two Raman modes in monolayer MoS2. Finally, we use this result to show that we can apply biaxial strains as large as 5.6% across micron sized areas, and report evidence for the strain tuning of higher level optical transitions.

cond-mat.mes-hall↗