Precision ultrasound sensing on a chip

TL;DR

This paper presents a novel silicon-chip-based ultrasound sensor that uses cavity optomechanics to achieve unprecedented sensitivity and dynamic range, surpassing previous sensors and enabling diverse scientific and technological applications.

Contribution

Introduction of cavity optomechanical ultrasound sensing on a chip, significantly enhancing sensitivity and dynamic range over existing optical resonance-based sensors.

Findings

Achieved noise equivalent pressures of 8--300 μPa/√Hz across kilohertz to megahertz frequencies.

Sensor sensitivity exceeds similar optical resonance sensors and surpasses previous air-coupled sensors by orders of magnitude.

First noise floor dominated by molecular collisions in the surrounding gas.

Abstract

Ultrasound sensors have wide applications across science and technology. However, improved sensitivity is required for both miniaturisation and increased spatial resolution. Here, we introduce cavity optomechanical ultrasound sensing, where dual optical and mechanical resonances enhance the ultrasound signal. We achieve noise equivalent pressures of 8--300 $\mu$Pa/$\sqrt{\rm Hz}$ at kilohertz to megahertz frequencies in a microscale silicon-chip-based sensor with $>$120 dB dynamic range. The sensitivity far exceeds similar sensors that use optical resonance alone and, normalised to sensing area, surpasses previous air-coupled ultrasound sensors by several orders of magnitude. The noise floor is, for the first time, dominated by collisions from molecules in the gas within which the acoustic wave propagates. This new approach to acoustic sensing could find applications ranging from biomedical diagnostics, to autonomous navigation, trace gas sensing, and scientific exploration of the life-induced-vibrations of single cells.