# Tailoring one-dimensional layered metamaterials to achieve unidirectional transmission and reflection

## TL;DR

This paper explores how multilayered elastic metamaterials can be designed to achieve unidirectional wave transmission and reflection by exploiting wave conversion and spatial dispersion, with potential applications in seismic protection and sensing.

## Contribution

It demonstrates the control of wave directionality in multilayered elastic metamaterials through wave conversion and structural design, including gain/loss elements and defects.

## Key findings

- Wave conversion leads to non-reciprocal transmission at certain frequencies.
- Directionality can be enhanced with gain/loss elements.
- Defects cause variability useful for sensing applications.

## Abstract

We investigate elastic-wave propagation in a spatially-dispersive multilayered, totally passive metamaterial system. At oblique incidence a longitudinal (acoustic) wave can convert to transverse in the solid material comprising the layers, but when the incident wave enters the multilayer from a solid as opposed to a liquid medium, the incident transverse component supported by the solid medium indirectly causes the longitudinal transmission response to be greatly modified and similarly for the transverse wave exiting the multilayer into a solid medium in response to an incident longitudinal wave. The conversion between longitudinal and transverse waves is found to lead to the emulation of a characteristic non-reciprocal phenomenon at some frequencies: a directionality in the transmission response, sometimes simultaneously with the reflection response. The directionality can be exploited for example in the construction of antiseismic structures or breakwater structures. The inclusion of gain/loss elements can strongly enhance the directionality. Periodicity-breaking defects can cause a great variability in the response, enabling the use of devices based on this phenomenon as sensors.