Thermally reconfigurable helical shape memory alloy–based metamaterial

Abstract

This paper presents our investigation and experimental validation of a thermally reconfigurable shape memory alloy (SMA)-based metamaterial with the offered degree of freedom of SMA mechanical features. The metamaterial unit cell consists of a two-way helical SMA acting as the resonator element and a cartridge heater for controlling the excitation temperature of the helical SMA. Experimental results of electrical control of the cartridge heater's excitation temperature show that as the temperature increases from room temperature (25°C) to approximately 92°C-corresponding to input DC voltages of 0 and 4 V, respectivelythe metamaterial structure acts as a switchable absorber with an absorptivity of 97.2% and a reflector with a reflectivity of 89.4% at 7.13 GHz. Additionally, it deforms to its initial state as the temperature decreases to room temperature.

Metamaterial Absorbers: From Tunable Surface to Structural Transformation

“…Compared to the planar arrays in MAs, the employment of SMAs facilitates 3D, structurally reconfigurable and tunable MAs, capable of tuning the absorption in a relatively larger range. [ 77,78,80 ] Phon et al. demonstrated a reconfigurable MM comprising of helical SMA.…”

“…[77,78,80] Phon et al demonstrated a reconfigurable MM comprising of helical SMA. [78] The experimental results showed that the function of MM could be switched from an MA with nearly perfect absorption (97.2%) to a reflector with high reflectivity (89.4%) at 7.13 GHz when temperature of the SMA increased from 25 to 92 °C. The mechanism was ascribed to the extended length of the helical SMA under high temperature.…”

“…Compared to the planar arrays in MAs, the employment of SMAs facilitates 3D, structurally reconfigurable and tunable MAs, capable of tuning the absorption in a relatively larger range. [77,78,80] Phon et al demonstrated a reconfigurable MM comprising of helical SMA. [78] The experimental results showed that the function of MM could be switched from an MA with nearly perfect absorption (97.2%) to a reflector with high reflectivity (89.4%) at 7.13 GHz when temperature of the SMA increased from 25 to 92 °C.…”

“…[4,62,64] In addition, broadband absorption can also be achieved by incorporating these lumped elements, followed by selecting optimized values of these elements. [65][66][67] In addition to lumped elements, active materials including phase-change materials (PCMs), [27,30,41,[68][69][70][71] 2D materials, [18,[72][73][74][75][76] shape-memory materials (SMMs), [77][78][79][80] and liquid metals, [81][82][83] have also been explored in the design of tunable/reconfigurable MAs due to their change in electrical properties under external stimuli including heat, electric field, and light. The integration of active materials to MAs design has been found to be effective in controlling EM properties of MAs (Figure 2g) operating at frequencies from gigahertzes (GHz), terahertz (THz), infrared (IR) and even to optical regimes.…”