Exploring heterogeneity and disorder In tunable elastic metamaterials

Abstract

The dominant paradigm in the design of elastic metamaterials revolves around periodic arrays of identical resonating elements, which are known to allow subwavelength locally-resonant bandgaps. In this work, we deliberately explore the wave manipulation capabilities of metamaterial configurations that are characterized by significant heterogeneity and disorder. Heterogeneity is here intended as the coexistence of multiple types of resonators tuned to resonate at distinct frequencies. Disorder refers to the arrangement of the resonators, which is randomized in space. The metamaterials of choice are thin elastic sheets endowed with heterogeneous populations of tunable telescopic pillars whose resonant characteristics can be agilely tuned through simple manual operations. The configurability of our experimental platform allows to seamlessly fabricate and compare a multitude of specimens, thus allowing to extract some empirical yet general rules. We first document how heterogeneity can lead to broadband mechanical filtering. More specifically, we illustrate how randomized spatial arrangements consistently outperform their functionally graded counterparts in terms of maximum achievable bandgap width. Our investigation shows that the design space of mechanical metamaterials can be stretched beyond the limits imposed by order and homogeneity, thus highlighting the engineering significance of the emerging concepts of organized disorder and design modularity.