An Experimental Analysis of an Active Elastic Metamaterial

Abstract

Abstract Elastic and acoustic metamaterials provide an approach to creating materials which possess properties which are not found in natural or conventional materials. This notably includes dynamic effective material properties, i.e. density and modulus, which can become negative in prescribed frequency bands. Elastic and acoustic metamaterials provide alternative solutions to existing problems in acoustics and provide a route to realizing novel new concepts. Novel concepts associated with metamaterials include acoustic invisibility and sub-wavelength imaging. Elastic metamaterials with negative effective parameters can be realized using arrays of local resonators. However the performance of these devices suffers due to a fixed and usually narrow frequency band in which the effective parameters are negative. Active metamaterials provide an alternative approach in which control forces applied to a transmission medium emulate the desired response. Such devices have the benefit of being able to realize a response which is both tunable and not possible with passive components alone. This paper focuses on the development of an experimental demonstration of active elastic metamaterials with negative mass or stiffness across desired frequency bands. The active elastic metamaterial is a one-dimensional structure composed of a series of constrained lumped masses to which control forces are applied through a feedback control. The dynamic effective parameters are extracted from the measured data using a least squares approach to fit the data to an effective system. Comparison of the measured effective parameters to the simulated results verifies the effective response of the active elastic metamaterial in experimentation.