Alumina-copper woodpile-kind locally resonant phononic crystal

Locally resonant phononic crystals (LRPCs) have zero group speeds along a few directions and possess bandgaps at frequencies corresponding to an order of wavelength lower than the corresponding phononic crystals of the same characteristic size. We report on a scalable, quick fabrication of metal-ceramic LRPC and its acoustic characterization using experiments and computation. Copper wires were coated with alumina by dip-coating method and assembled as a three-dimensional woodpile-kind LRPC by soldering. First, the elastic properties of alumina were estimated using a resonant ultrasound spectrometer. The properties were used to compute the bandgaps and transmission loss (TL) using the finite-element method. Ultrasonic TL measurements revealed the presence of bandgaps in the 0.6-1.2-MHz regime, which agreed with the computationally estimated TL. The computed band diagrams indicated bandgaps around 0.05 MHz, an order lower than the bandgap of an equivalent PhC of the LRPC. Furthermore, we found several directions along which the group speed was zero. This work demonstrates the use of simple, traditional fabrication methods to achieve ceramic LRPCs.