EAGER: Tuning granular phononic crystals through pattern transformations

Investigators: J. Shim, M.A. Karami

Funding Source: NSF-MOMS (Sep. 2016 - Feb. 2018)

Abstract: Phononic band-gap materials are composite materials characterized by phononic band-gaps, i.e., frequency ranges in which the propagation of mechanical waves is prohibited. Phononic band-gap materials made of conventional structural materials possess typically fixed narrow phononic band-gaps in some high-frequency ranges (i.e., normally in the range of MHz or higher). However, unwanted vibrations and noises disturbing human body are characterized by broadband frequency contents in rather low-frequency ranges (commonly only up to a few kHz or less). Thus, due to this knowledge gap, their practical products has not appeared yet. This award supports fundamental research to provide knowledge for a pattern-transformable granular phononic crystal, which may have tunable low-frequency band-gaps. This new approach will open the possibility of practical phononic band-gap materials. Therefore, if this project succeeds, results from this research will benefit the U.S. manufacturing industry. Furthermore, the PI will design hands-on activities relating to pattern transformations for diverse audiences including under-represented minorities and female students. With these activities, the goal is to stimulate students to pursue a career in engineering.

The objective of this project is to explore the proof-of-concept of a pattern-transformable 2-D granular crystals, which is characterized by its low-frequency tunable phononic band-gaps. The proposed objective is based on the central hypothesis that instability is closely relating to the pattern-transformation-induced bandgap tunability. The hypothesis will be demonstrated by performing the following specific tasks: (1) identification of pattern transform mechanism, (2) experimental validation of the identified mechanism, (3) numerical phononic dispersion relations, and (4) experimental validation of the numerical phononic dispersion relations. The proposed work attempts to take a transformative approach that links conventional instability theory to an uncharted area of granular phononic crystals. Instability phenomenon is nearly length-scale independent. Therefore, the successful completion of this research could have a significant impact in the field of phononic band-gap materials, because the proposed instability-induced mechanism can be adopted for the design of tunable granular phononic crystals using various actuations in a wide range of length scales.

Pattern transformation of a 2-D deformable granular phononic crystal showing its drastically changed band-gap structure under uniaxial compression. Particle arrangements and the corresponding dispersion relations for (A) undeformed and (B) deformed configurations. Pictures from Journal of the Acoustical Society of America, 131(6)EL475, 2012 and Soft Matter, 7(6)2321, 2011