The device uses optomechanical ultrasound sensing – combining optical and mechanical resonances – to sense noise-equivalent pressures of 8 to 300 micropascal per Hz^1/2 at kilohertz to megahertz frequencies. This is done with a silicon-based MEMS sensor that demonstrates more than 120dB dynamic range. The sensitivity surpasses previous air-coupled ultrasound sensors by several orders of magnitude.
The noise floor derives from molecular collisions within the coupling gas and the technique could be used to detect metabolism-induced vibrations of single biological cells. Other applications could include biomedical diagnostics, trace gas sensing and autonomous navigation, the researchers suggest.
The sensor works by a cavity that responds to an external acoustically-coupled source, changing its optical resonance and allowing very precise measurement of the stimulus.
The researchers have designed and fabricated a suspended spoked silica microdisk optomechanical system in which light is confined in a high-quality whispering-gallery mode around the periphery of the disk. The disk has outer and inner radii of 148-micron and 82-micron, respectively, and a thickness of approximately 1.8-micron resulting in a mass of approximately 230ng.
"We'll soon have the ability to listen to the sound emitted by living bacteria and cells," said lead author Sahar Basiri-Esfahani, in a statement. "This is a particularly attractive application, as it could fundamentally improve our understanding of how these small biological systems function."
The research has been published in Nature Communications .
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