In a groundbreaking development, researchers have extended the principles of effective medium theory (EMT) to encompass time-modulated, frequency-dispersive acoustic metamaterials with multiple resonances, opening new avenues for innovative acoustic device design. This advancement, led by Xinghong Zhu, Hong-Wei Wu, and Jensen Li, addresses the limitations of previous studies that focused solely on non-dispersive or single-resonance systems.
The team’s research delves into the intricate interplay between resonant and modulation frequencies, deriving explicit averaging rules that account for this dynamic interaction. They found that when resonant frequencies are significantly lower than the modulation frequency, modulating the resonant strength yields the temporal average of monopolar susceptibility, while modulating the resonant frequency results in the average of the inverse of monopolar susceptibility, applied per resonance mode. This nuanced understanding allows for precise control and manipulation of acoustic properties in programmable materials.
For scenarios where high-frequency resonances exist alongside lower-frequency ones, the researchers propose a hybrid approach. High-frequency resonances, when relative to the modulation frequency, can be renormalized as a non-dispersive background. This allows the remaining lower-frequency resonances to be averaged, providing a comprehensive framework for designing complex acoustic devices.
The practical implications of this research are profound. The generalized temporal EMT offers a unified framework for creating compact, topologically robust, and non-Hermitian acoustic devices. These devices could revolutionize various fields, including audio engineering, noise control, and medical imaging. By leveraging the programmability of time-dependent material parameters, future acoustic devices could achieve unprecedented levels of precision and functionality, paving the way for innovative applications in music and audio production, architectural acoustics, and beyond. Read the original research paper here.
