Four microphones track a flying drone
Four microphones track a flying drone lead image
Quadcopter drones are getting cheaper and more ubiquitous by the day, and along with their rise in popularity come various privacy and security issues. Regulations often struggle to keep up, as do the practicality challenges when it comes to enforcing them, such as the basic ability to detect and track them across the sky.
Wu et al. developed a device for detecting nearby drones, consisting of metal diaphragm-based omnidirectional fiber-optic acoustic sensors, and a cross-shaped fiber-optic sensor array with four microphones.
The special microphone was developed to work in a temperature range from -20 to 60 C, with a sensitivity of more than 800 mV/Pa and a sensitivity fluctuation of less than 3 dB for the frequency range between 0.1 to 6 kHz. Besides the individual mics, the great stability and phase consistency among the four mics is also crucial in enabling the overall device to detect and localize the sound source.
The authors tested their prototype with a drone and compared the device’s accuracy to the GPS log onboard the drone. Compared to a conventional electret condenser microphone, the device was able to detect the acoustic signature of the drone from up to 300 m away, with a less than 10-degree deviation in its detected azimuth angle.
“With the proven advantages of high stability, broad-band response, great phase consistency, compact size and cost-effectiveness, the proposed fiber-optic acoustic sensor is not only suitable for sound source localization system, but has great potential in photoacoustic spectroscopy and photoacoustic imaging,” said author Gaomi Wu.
Combined with image identification and machine learning, the device may find use in industrial and security operations, such as sound source photographing and object classification.
Source: “Development of highly sensitive fiber-optic acoustic sensor and its preliminary application for sound source localization,” by Gaomi Wu, Linsen Xiong, Zhifei Dong, Xin Liu, Chen Cai, and Zhi-mei Qi, Journal of Applied Physics (2021). The article can be accessed at https://doi.org/10.1063/5.0044997 .
