Continuous-wave amplitude control via the interference phenomenon in acoustic structures

TL;DR

This paper introduces a passive acoustic structure that enables continuous and reconfigurable control of wave amplitude through interference of mode-conversion paths, using geometric phases in meta-atoms.

Contribution

It presents a novel scheme utilizing geometric-phase meta-atoms to achieve 100% amplitude modulation in acoustic waves, verified by both theory and experiments.

Findings

Achieves full amplitude modulation via interference in acoustic structures.

Demonstrates reconfigurable amplitude control with passive meta-devices.

Validates the scheme through theoretical analysis and experimental results.

Abstract

We propose a strategy to continuously tune the amplitude of acoustic waves based on the interference among two mode-conversion paths in passive acoustic structures. The interference phenomenon is attributed to two conjugate acoustic geometric phases obtained with two mode-conversion processes in hybrid-type geometric-phase meta-atom (HGPM) pair. Notably, 100% modulation depth of the wave amplitude is achievable by simply varying the local orientation angle of meta-atom. We utilize the acoustic structure made of two cylindrical resonators to construct deep-subwavelength secondary source with designated initial phase delay, and HGPM supporting desired mode-conversion functionality is accordingly fabricated with four secondary sources. Both theory and experiment consistently verify the continuous amplitude modulation function of HGPM pair, which showcases a general scheme for reconfigurable amplitude-type acoustic meta-devices, i.e., those that require grayscale amplitude modulation for acoustic field engineering.