A versatile smart transformation optics device with auxetic elasto-electromagnetic metamaterials

Abstract

Synergistic integration of electromagnetic (EM) and mechanical properties of metamaterials, a concept known as smart metamaterials, promises new applications across the spectrum, from flexible waveguides to shape-conforming cloaks. These applications became possible thanks to smart transformation optics (STO), a design methodology that utilizes coordinate transformations to control both EM wave propagation and mechanical deformation of the device. Here, we demonstrate several STO devices based on extremely auxetic (Poisson ratio −1) elasto-electromagnetic metamaterials, both of which exhibit enormous flexibility and sustain efficient operation upon a wide range of deformations. Spatial maps of microwave electric fields across these devices confirm our ability to deform carpet cloaks, bent waveguides, and potentially other quasi-conformal TO-based devices operating at 7 ~ 8 GHz. These devices are each fabricated from a single sheet of initially uniform (double-periodic) square-lattice metamaterial, which acquires the necessary distribution of effective permittivity entirely from the mechanical deformation of its boundary. By integrating transformation optics and continuum mechanics theory, we provide analytical derivations for the design of STO devices. Additionally, we clarify an important point relating to two-dimensional STO devices: the difference between plane stress and plane strain assumptions, which lead to elastic metamaterials with Poisson ratio −1 and −∞, respectively.

Mechanical Metamaterials with Thermoresponsive Switching between Positive and Negative Poisson's Ratios

“…Similar properties have also been found in human coronary arteries, and in graphene under specific conditions . A number of 2D and 3D structures with an NPR have been extensively studied because of their potential applications; some examples are shock absorbers, photonic metamaterials, and smart mechanical metamaterials …”

An electric concentrator and thermal cloaking device

“…Laplace's equation is used to provide a bridge between physical and virtual domains. It helps in the calculation of materials parameter of TO devices using suitable boundary conditions [29]. Here we use the Laplace equation in spherical coordinates to observe the flow of electrical and thermal conditions.…”

Auxetic structures with regularly configured rigid sliding units

“…Since auxetic materials are rare in nature, researchers proposed various artificial auxetic materials with deformable honeycomb structures , networks of rotating rigid or semi‐rigid units , chiral structures , and dilational materials involving friction . Auxetic materials have various potential applications in sound and vibration absorption , biomedicine , sports application , smart transformation optics .…”