# Gradient-index granular crystals: From boomerang motion to asymmetric transmission of waves

## TL;DR

This paper introduces a gradient-index granular crystal capable of tunably controlling elastic wave propagation, demonstrating boomerang-like wave motion and asymmetric transmission through numerical and experimental methods, with potential applications in advanced wave control.

## Contribution

It presents a novel gradient-index granular crystal that enables tunable control of elastic waves, including linear and nonlinear effects, through both numerical simulations and experiments.

## Key findings

- Demonstrated boomerang-like wave motion in the crystal
- Achieved asymmetric wave transmission at different crystal ends
- Validated tunable wave control through experiments and simulations

## Abstract

We present a gradient-index crystal that offers extreme tunability in terms of manipulating the propagation of elastic waves. For small-amplitude excitations, we achieve control over wave transmission depth into the crystal. We numerically and experimentally demonstrate a boomerang-like motion of wave packet injected into the crystal. For large-amplitude excitations on the same crystal, we invoke nonlinear effects. We numerically and experimentally demonstrate asymmetric wave transmission from two opposite ends of the crystal. Such tunable systems can thus inspire a novel class of designed materials to control linear and nonlinear elastic wave propagation in multi-scales.