A Fiber Optic Seismic Sensor for Unattended Ground Sensing Applications

Fiber optic seismic sensors have been increasingly recognized as promising technologies for many applications, such as intruder detection and perimeter defense systems. Among these, a military seismic sensor is especially challenging because it requires a robust, compact, reliable, easily installable and operated product. This article reports on our recent experimental investigations of a military fiber optic seismic sensor. In particular, an improved sensor design and new signal processing techniques are illustrated in this article, which include: (a) a scanning laser wavelength-based demodulation system; (b) a digital lock-in amplifier and field programmable gate array techniques for weak signal detection and processing; and (c) overall improved seismic sensitivity based on carbon fiber composite cantilever and fiber-Bragg-grating sensing technology. The experimental results show that the fiber-Bragg-grating seismic sensor frequency response band is between 10 and 300 Hz and that it has a higher sensitivity than the conventional electromagnetic geophone within the frequency response band most important for battlefield monitoring. The fiber-Bragg-grating seismic sensor is totally immune to electromagnetic interference and has a working temperature between 240uC and +50uC for military harsh environments. Comparisons are also presented of the fiber-Bragg-grating seismic sensor with the commercial REMBASS sensor in a series of field tests.