Isotropic Negative Thermal Expansion Metamaterials

TL;DR

This paper introduces a metamaterial design combining bi-material strips and anti-chiral structures to achieve large, tunable isotropic negative thermal expansion, with experimental validation.

Contribution

It presents a novel metamaterial approach for isotropic negative thermal expansion using combined structural elements, achieving significant expansion coefficients.

Findings

Measured negative thermal expansion coefficient of -68.1×10⁻⁶ 1/K

Demonstrated isotropic negative thermal expansion over 303.15 K to 773.15 K

Showed tunability of expansion coefficient via structural parameters

Abstract

Negative thermal expansion materials are important and desirable in science and engineering applications. However, natural materials with isotropic negative thermal expansion are rare and usually unsatisfied in performance. Here, we propose a novel method to achieve negative thermal expansion via a metamaterial approach. The metamaterial is constructed with unit cells that combine bi-material strips and anti-chiral structures. Both experimental and simulation results display isotropic negative thermal expansion properties. The coefficient of negative thermal expansion of the metamaterials is demonstrated to be dependent on the difference between the thermal expansion coefficients of two component materials in the bi-material strips, as well as on the circular node radius and the ligament length in the anti-chiral structures. The measured value of the linear negative thermal expansion coefficient reaches -68.1X10-6 1/K in an operating temperature range from 303.15 K to 773.15 K, which is among the largest achieved in experiments to date. Our findings provide a novel and practical approach to obtaining materials with tunable isotropic negative thermal expansion on any scale.