# Resonant Ultrasound Spectroscopy Detection Using a Non-Contact Ultrasound Microphone

## TL;DR

This paper introduces a non-contact method to detect high-frequency vibrations in small objects using an optomechanical microphone and piezoelectric shaker.

## Contribution

The novel approach enables MHz-range ultrasound detection without physical contact, suitable for industrial quality control.

## Key findings

- Vibrational eigenmodes were detected in glass and sapphire lenses over a 0–8 MHz range.
- Eigenfrequencies matched numerical predictions closely.
- The method works with 1–10 mm spacing between object and microphone.

## Abstract

We observed vibrational eigenmodes for a variety of millimeter-scale objects, including glass and sapphire lenses, by placing them on a piezoelectric ‘shaker’ driven by a broadband noise or frequency sweep signal, and using an optomechanical microphone to pick up their vibrational signatures emitted into the surrounding air. High-quality vibrational modes were detected over the ~0–8 MHz range for a typical object–microphone spacing of 1–10 mm. The observed eigenfrequencies are shown to be in excellent agreement with numerical predictions. Non-contact detection of resonant vibrational eigenmodes in the MHz ultrasound range could find application in the quality control of numerous industrial parts, such as ball bearings and lenses.