Study of one-dimensional multifunctional acoustic metamaterials

Kota Mikoshiba, Purdue University

Abstract

A metamaterial is a material that gains its properties from its microstructures rather than from its constituent material phases. One type of metamaterial takes the form of a composite that contains manmade microstructures embedded in a matrix material. If the periodically placed microstructures display a local resonant frequency, the metacomposite as a whole forms a metamaterial with frequency-dependent effective mass density. Also the acoustic metamaterial exhibits unusual dynamic responses such as negative effective mass densities in certain frequency range (the bandgap). It is demonstrated that, in a one-dimensional acoustic metamaterial with resonator microstructures, the amplitude of harmonic waves with frequencies near the local resonance frequency of the resonator attenuates significantly. In other words, these waves are stopped by the metacomposite. Another unusual behavior of this metacomposite is that when excited with frequencies near the local resonance frequency, the internal mass in the microstructure can absorb a large amount of energy from the external excitation. If this type of microstructure is used to make a composite with a matrix material then we will have a metacomposite which can block unwanted dynamic disturbances to propagate into the material and harvest kinetic energy with internal masses. In this study, the function of the resonator is extended to perform energy harvesting by converting its kinetic energy into electric energy making the metamaterial multifunctional. The proposed design of the local resonator consists of a permanent magnet (to be doubly used as an internal mass) supported by springs and enclosed with a capped tube. Coils are wrapped around the tube for electricity generation. The metamaterial contains many of these unit cells whose local resonance frequency can be easily selected according to the environment. As the magnet oscillates, electricity is generated. The desired conditions for electricity generation and wave attenuation for finite length of the metamaterial are determined by finite element analysis. A preliminary simulation showed that one unit cell could produce AC current with the local resonance frequency. The experiment demonstrates that this acoustic metamaterial which contain seven unit cells can generate electricity and the voltage of the generated electricity is dependent on the driving frequency. Thus, when the metamaterial is subjected to dynamic disturbances with these bandgap frequencies, energy is stored in the resonators leaving the metamaterial to appear quiet. The stored energy in the internal masses is then converted to electricity.

Degree

M.S.E.

Advisors

Sun, Purdue University.

Subject Area

Aerospace engineering|Electrical engineering

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