A Fiber Optic Seismic Sensor for Unattended Ground Sensing Applications

Abstract : 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 -40 deg C and +50 deg C 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.