Dispersion of deterministic sound wave into stochastic noise by a linear acoustic layer with time-varying and quantized material properties

TL;DR

This paper presents a novel randomized acoustic meta-layer that linearly shifts sound waves into stochastic noise using a time-varying, quantized material property, enabling new applications like noise generation and secure communication.

Contribution

Introduction of a new class of temporal modulation material with a high modulation ratio that converts monochromatic sound into white noise through a randomized acoustic meta-layer.

Findings

The device effectively converts sound into white noise.

The meta-layer operates with a pseudo-random modulation of impedance.

Potential applications include psychoacoustic enhancement and encrypted communication.

Abstract

Wave is crucial to acquiring information from the world and its interaction with matter is determined by the wavelength, or frequency. Search for the ability to shift frequency often points to material nonlinearity, which is significant only when the excitation level is very high. Temporal modulated material is expected to shift sound frequency in a linear manner, but is so far not effectively realized due to inadequate modulation ratio. This study introduces a new class of temporal modulation material with a giant modulation ratio. When the modulation is given in a random time sequence, a monochromatic sound wave is converted to a white noise of a continuous frequency band. The demonstrated device is called a randomized acoustic meta-layer, consisting of a suspended diaphragm shunted by an analog circuit. The circuit alters the acoustic impedance of the layer which operates in two quantized states when the shunt is connected and disconnected by a MOSFET with a pseudo-random time sequence. The device has unprecedented potential applications such as converting annoying tones to white-noise-like hum to improve psychoacoustic quality, allowing encrypted underwater communication, and super-resolution imaging.