Microfiber Bragg grating-based acoustic sensor offers reduced size and electromagnetic immunity

Acoustic sensors used for sound source localization (SSL) generally employ microphone arrays for detection, using sound pressure measurements to determine source direction. Many such devices have found inspiration in biology, with designs based on the aural organs of insects or lizards.

Other SSL devices measure acoustic particle velocity through temperature difference, indicated by resistance change in an electronic signal. These don’t suffer from the relatively large sizes typical of sensors that use pressure differentials, but they are subject to electromagnetic interference. Gao et al. now demonstrates a new all-fiber vector acoustic sensor less than 1.5 nanometers in size, capable of two-dimensional sound source localization and impervious to electromagnetic (EM) interference.

The sensor features two orthogonally crossed microfiber Bragg gratings, using parallel, micro-Co²⁺-doped optical fibers, which allow detection in a figure 8 pattern with 1.57 millivolts per degree orientation sensitivity. Experiments using a pump laser and the application of an acoustic wave tested the new device. The self-heating and asymmetric temperature changes in the Co²⁺-doped optical fibers provided direct measurements of acoustic particle velocity in the frequency range from 500 to 5,000 Hz.

The authors note that the greatly decreased size of this SSL sensor compared to microphone arrays and bio-inspired devices, along with its EM immunity, may make it suitable for broad applications including acoustic communication, pipeline monitoring, navigation, and other uses requiring small size and improved sensitivity.

Source: “Miniature all-fibre microflown directional acoustic sensor based on crossed self-heated micro-Co²⁺-doped optical fibre Bragg gratings,” by Ran Gao, Mengying Zhang, and Zhi-mei Qi, Applied Physics Letters (2018). The article can be accessed at https://doi.org/10.1063/1.5043519 .