# Acoustic Fabry–Perot Resonance Detector for Passive Acoustic Thermometry and Sound Source Localization

## TL;DR

This paper introduces a new acoustic sensor that can measure temperature and locate sound sources using resonance effects and an array design.

## Contribution

A novel acoustic Fabry-Perot resonance detector with dual capabilities for passive thermometry and sound source localization is developed and experimentally validated.

## Key findings

- The AFPRD achieved a temperature measurement accuracy of 0.4 °C in an anechoic room.
- The AFPRD array demonstrated sound source localization with an error of less than 1.2° in outdoor conditions.
- The device uses weak ambient noise and real-time sound speed to enhance its performance.

## Abstract

Acoustic temperature measurement (ATM) and sound source localization (SSL) are two important applications of acoustic sensors. The development of novel acoustic sensors capable of both ATM and SSL is an innovative research topic with great interest. In this work, an acoustic Fabry-Perot resonance detector (AFPRD) and its cross-shaped array were designed and fabricated, and the passive ATM function of the AFPRD and the SSL capability of the AFPRD array were simulated and experimentally verified. The AFPRD consists of an acoustic waveguide and a microphone with its head inserted into the waveguide, which can significantly enhance the microphone’s sensitivity via the FP resonance effect. As a result, the frequency response curve of AFPRD can be easily measured using weak ambient white noise. Based on the measured frequency response curve, the linear relationship between the resonant frequency and the resonant mode order of the AFPRD can be determined, the slope of which can be used to calculate the ambient sound velocity and air temperature. The AFPRD array was prepared by using four bent acoustic waveguides to expand the array aperture, which combined with the multiple signal classification (MUSIC) algorithm can be used for distant multi-target localization. The SSL accuracy can be improved by substituting the sound speed measured in real time into the MUSIC algorithm. The AFPRD’s passive ATM function was verified in an anechoic room with white noise as low as 17 dB, and the ATM accuracy reached 0.4 °C. The SSL function of the AFPRD array was demonstrated in the outdoor environment, and the SSL error of the acoustic target with a sound pressure of 35 mPa was less than 1.2°. The findings open up a new avenue for the development of multifunctional acoustic detection devices and systems.