Inverse-designed flexural wave metamaterial beams with thermally induced tunability

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Elastic metamaterials (EMMs) have been developed for more than two decades, but their practical applications have been scarcely reported due to their narrow bandgaps, relatively high working frequency ranges, poor load-bearing capabilities, and other implementation-related issues. As an attempt to solve some of these problems, in this work, a novel kind of tunable metamaterial beams is proposed to mitigate or isolate low-frequency and broadband flexural waves, where the integrated tunable elements made of a 3D-printed thermally sensitive material are inversely designed. The tunability is further achieved through the thermal-driving on the tunable elements. The optimized tunable elements are fabricated independently and have pretty good load-bearing capabilities under quasi-static uniaxial compression tests. They are directly glued on the host beams to form simple structured metamaterial beams without destruct the host beams. The experimentally measured transmission spectra under different thermal loadings demonstrate that the third pass-bands of the optimized three metamaterial beams at room temperature (RT) are changed to bandgaps or stop-bands as the temperature increases to about 60 °C, and vice versa. In addition, this temperature change induced bandgap is concatenated to the optimization obtained bandgap to form a wider bandgap. The good thermal reversibility is also validated by experimental tests under several thermal-loading cycles. Our present work suggests a dual-technique combined method to design low-frequency and broadband EMMs.