Optically-trapped microspheres are high-bandwidth acoustic transducers

TL;DR

This paper demonstrates that optically-trapped microspheres can serve as high-bandwidth acoustic transducers, achieving a 1 MHz bandwidth and outperforming previous microsphere-based flow measurement methods.

Contribution

The authors develop a quantitative model and calibration method for using optically-trapped microspheres as acoustic sensors, significantly enhancing bandwidth capabilities.

Findings

Achieved 1 MHz bandwidth in acoustic measurements.

Validated technique in air with comparison to commercial sensors.

Demonstrated improved bandwidth over previous microsphere-based methods.

Abstract

We report on the use of an optically-trapped microsphere as an acoustic transducer. A model for the hydrodynamic coupling between the microsphere and the surrounding acoustic fluid flow is combined with thermo-mechanical calibration of the microsphere's position detection to enable quantitative acoustic measurements. We describe our technique in detail, including the self-noise, sensitivity, and minimum detectable signals, using a model appropriate for both liquid and gas environments. We then test our approach in an air-based experiment and compare our measurements with two state-of-the-art commercially-available acoustic sensors. Piezoelectrically-driven bursts of pure tones and laser ablation provide two classes of test sounds. We find accurate measurements with a bandwidth of 1 MHz are possible using our technique, improving by several orders of magnitude the bandwidth of previous flow measurements based on optically-trapped microspheres.