An electrically tunable terahertz plasmonic device based on shape memory alloys and liquid metals

TL;DR

This paper presents a novel electrically tunable terahertz plasmonic device utilizing liquid metals and shape memory alloys, enabling reversible and controllable spectral shifts through thermal cycling and applied voltage.

Contribution

It introduces a new design combining liquid metal microfluidics and shape memory alloy wires for dynamic control of terahertz transmission properties.

Findings

Reversible tuning of transmission resonances over 500 thermal cycles.

Observation of unexpected dual resonances and increased transmission amplitude.

Numerical simulations explain the unique spectral features.

Abstract

An electrically tunable terahertz (THz) plasmonic device is designed and fabricated using liquid metals (eutectic gallium indium EGaIn) and shape memory alloy wires (Flexinol). The liquid metal is injected into the voids of a poly(dimethyl) siloxane (PDMS) microfluidic mold forming a periodic array of subwavelength apertures, while the wires are inserted into the elastomer below the metal plane. When a DC voltage is applied to the wires, they contract via Joule heating, reducing the aperture periodicity and blue-shifting the transmission resonances of the device. When the voltage is removed, the wires cool and elongate back to their original length, allowing the transmission spectrum to return to its original state. The magnitude of this change depends upon the applied voltage. The device is shown to thermally cycle between the relaxed state and the fully contracted state reproducibly over at least 500 thermal cycles. The asymmetric geometry of the device and the contraction process yield transmission properties that are unexpected: two closely spaced resonances, where both resonances correspond to the same scattering indices, and an increase in the transmission amplitude of the lowest order resonance upon contraction. We use numerical simulations to understand these features.