Phononic crystal with free-form waveguiding and broadband attenuation

Waveguiding is highly desirable for multiple applications but is challenging to achieve in wide continuous frequency ranges. In this work, we developed a three-dimensional phononic crystal with broadband waveguiding functionality. Waveguiding is achieved by combining two types of unit cells with different wave scattering features to create an arbitrary-curved defect path. The unit cell design is governed by contradictory requirements to induce narrow- and broad-band wave attenuation along the path and within the phononic medium, respectively. This is achieved by modulating structural parameters to activate Bragg's scattering, local resonances and inertial amplification mechanism and interplay between them. We demonstrated numerically and experimentally the waveguiding with strong wave localization and confinement in additively manufactured three-dimensional structures along straight, angle- and arbitrary-curved paths. This work opens new perspectives for the practical utilization of phononic crystals in ultrasonic sensors, medical devices, and acoustic energy harvesters.