A bandgap switchable elastic metamaterial using shape memory alloys

Abstract

Adaptive elastic metamaterials are generally tunable but not switchable. Here, the word “switchable” means switching between different bandgap mechanisms, such as from the local resonance bandgaps to the Bragg scattering bandgaps and vice versa. In this work, to achieve switchable bandgaps, we report a new class of elastic metamaterials whose transmission properties can be significantly tuned by curved two-way shape memory alloy (SMA) resonators. The proposed switchable metamaterial possesses bandgaps capable of being switched back and forth between the Bragg scattering and localized resonance ones. Without thermally activating the curved SMA resonators, the metamaterial beam behaves as a phononic crystal beam whose bandgaps are formed by a periodic array of concentrated masses. By heating the SMAs, the SMAs recover their original curved shape and lift the concentrated masses to form the local resonance bandgaps. The reversible dramatic variation in shape and the stiffness of the SMA resonators allows the bandgaps to be switchable and of course tunable. In addition, the equivalent spring stiffness of a curved beam at two possible directions for the first two modes is derived based on Castigliano's second theorem and is experimentally validated. Compared to SMA springs, the curved shape SMAs allow the generation of high-order local resonance bandgaps. If thermally activated at different temperatures, the negative effective mass density can further be tunable. To the author's knowledge, this work is the first theoretical and careful experimental investigation realizing switchable metamaterials using the two-way shape memory alloys.

A brief review of metamaterials for opening low-frequency band gaps

“…7(a)) [30,92] , and the temperature (see Fig. 7(b)) [93][94] are primary controllable variables. The piezoelectric actuator and the electromagnet are two main electronic components for the stiffness tuning based on the electrical elements.…”

Metamaterials and their applications: An overview

“…Because of the inability to switch different bandgap mechanisms in the conventional metamaterials, Chuang et al 57 introduced a new set of metamaterials in which it was possible to switch the bandgap by using two-way curved shape memory alloys. The proposed metamaterials allowed twoway switching of bandgap between the local resonance and the Bragg scattering mechanisms.…”

“…The experimental setup for measuring the transmission spectrum is displayed in Figure 60. 57 They considered monopolar, dipolar, and quadrupolar resonances in composites with spheres coated in a solid matrix to design composites with negative bulk modulus, negative shear modulus, and effective negative mass. Homogenization theory was used to estimate the effective dynamic properties of the composite.…”

Tunable elastic metamaterials using rotatable coupled dual-beam resonators

“…Recently, tunable or switchable metamaterials with SMA springs and tip masses (as tunable spring-mass resonators) have been theoretically studied and experimentally demonstrated by employing cantilever straight/straight beams (i.e., with varying stiffness) or straight/curved beams (i.e., with varying geometry and stiffness). [9][10][11][12] However, only two extreme states of the elastic modulus or geometry of the SMA beam-type resonators were experimentally realized in these studies, and thus the bandgap tuning was not a continuous process. In the present work, we design beam-type resonators, as shown in Fig.…”

“…[1][2][3][4] In order to enable tunable bandgaps, smart materials such as piezoceramics or shape memory alloys (SMAs) are usually incorporated in the design of local resonators. [5][6][7][8][9][10][11][12] Although smart materials can actively tune the bandgaps, the tuning range and performance of the bandgaps might be practically limited due to the size (e.g., the thickness of the SMAs), characteristics (e.g., heat transfer duration for the SMAs or circuit stability for the piezoceramics), geometry (e.g., straight or curved SMAs), among other parameters of these materials.…”