An unattended seismic sensor based on optical fiber Bragg grating (FBG) sensing technology is presented in this paper. One of the applications is its deployment in the battlefield remote monitoring system to detect the presence of personnel, wheeled vehicles, and tracked vehicles. The customized FBG sensor prototype is demonstrated which consists of two FBG sensor/demodulation grating pair attached on a spring-mass mechanical system. The sensor performance is evaluated in laboratory and the field tests were carried out in the shooting range using the conventional military Rembass-IIS/A sensor (remotely monitored battlefield sensor system II seismic acoustic sensor) as the benchmark. Personnel and a series of vehicles were used as targets. The experimental data of the field test show that the FBG sensor averaged a 30.20 % greater detection range than the Rembass-IIS/A sensor. It is hoped that the FBG sensor system will be a promising tool for real time monitoring system in the battlefield applications.
Because methane is an inflammable and explosive gas, it is indispensable to monitor methane. It is very useful to develop a portable methane detector in order for the application multiple purpose, such as coal mine safety monitoring. This paper gives a prototype design of a portable methane gas sensor with 1.65μm LED. Sensor is made by a 1.65μm LED and high responsivity photo receiver. The experimental result shows nearly linear at low methane concentration. And a prototype portable gas sensor has been demonstrated.
In this paper we will demonstrate our fiber Bragg grating (FBG) accelerometer system in seismic wave detection applications. Optical fiber sensors using fiber Bragg grating have a number of advantages such as immune to electromagnetic interference, lightweight, and low power consumption. Most important, the FBG sensor has high sensitivity to dynamic strain signals and the strain sensitivity can approach sub micro-strain. The basic principle of the FBG seismic sensing system is that it transforms the acceleration of ground motion into the strain signal of the FBG sensor through mechanical design, and after the optical demodulation generates the analog voltage output proportional to the strain changes. The customized FBG seismic sensor prototype is described, which includes the electro-optical design, mechanical design and the hardware and software interface of the sensor system. The laboratory evaluation of the system is performed systematically on a commercial vibration stage. Studies of the sensor properties show that the sensor has a high sensitivity (2500 mV/g at 90 Hz) to the acceleration signal, a large dynamic range (80 dB), the good linearity and stability after device integration and packaging.
In this paper, a particular equipment, one-channel optical-fiber-based methane gas real-time monitoring system, will be demonstrated. The system is designed especially for the mining complexes and residential area. A long-distance silica fiber link with a self-design optical gas sensor head have been employed in conjunction with a wavelength-tunable InGaAsP DFB laser diode at 1.64μm (around R(6) absorption peak of methane)1 to realize highly sensitive remote interrogation of CH4. By wavelength modulation with the DFB laser diode and a self-design processing circuit, sensitivities of less than 0.1 % (volume) have been achieved with the response time of less than 5 seconds.
A new type of fiber Bragg grating (FBG) sensor–based seismic geophone is presented. The major application of this FBG geophone is in the seismic reflection survey of oilfield exploration to detect the seismic waves from the Earth. The customized FBG geophone prototype that is demonstrated consists of two FBG sensor/demodulation grating pairs attached on a spring-mass mechanical system. The sensor performance is characterized in the laboratory in comparison with the conventional geophone. The FBG sensor is resistant to electromagnetic interference and has higher frequency response bandwidth and sensitivity than a conventional moving-coil electromagnetic geophone. The field tests results taken in the oil field show the sensor system frequency response bandwidth at 10 to 100 Hz in Shallow layer and 10 to 140 Hz in medium and deep layer separately.
This paper will demonstrate a particular one-channel optical-fiber- based CH<sub>4</sub> gas real-time monitoring system in the mining complexes and residential area. A long-distance silica fiber link with self-design gas sensor heads has been employed in conjunction with a wavelength-tunable InGaAsP DFB laser diode at 1.64μm (around R (6) absorption peak of methane) to realize highly sensitive remote interrogation of CH<sub>4</sub>. By wavelength modulation with the DFB laser diode and a self-design processing circuit, sensitivities of less than 0.1% (volume) have been achieved.
In this paper we have demonstrated an unattended seismic wave sensor based on the optical fiber Bragg grating (FBG) sensing technology. The basic principle of seismic wave detection and the fiber Bragg grating sensing technique is introduced in brief. Our FBG seismic sensor system consists of the broadband light source, FBG sensors coupled with spring / mass configuration, 3-dB optical couplers, demodulator FBG gratings, signal detection and processing hardware. Systematic experiments were carried out in Fort Dix at New Jersey. Target source includes personnel, military HMMWV and wheeled truck. The FFT analysis shows that the frequency response of the seismic signal is 20-40 Hz. The comparison data also show that the FBG sensor is more sensitive than the conventional seismic sensor both in personnel and vehicle detection. The ultimate object of this imbedded fiber optic sensor system is to recognize the presence of troop or vehicle movement through their induced seismic activity as a helpful tool in battlefield monitoring and perimeter defense system.
The work presented in this paper demonstrates a sensing technology for unattended seismic sensors based on the optical fiber Bragg grating. This kind of sensor can perform accurate measurements of the seismic activity due to their high sensitivity to dynamic strains caused by small ground vibrations. One of the applications is its deployment in the battlefield remote monitoring system to track and geo-locate the presence of personnel, wheeled vehicles, and tracked vehicles. The experimental data of the field test are shown as well as the comparable result with commercial seismic sensors.
An optical-fiber-based gas sensor for CH<sub>4</sub> gas real-time monitoring has been developed and tested. A long-distance
silica fiber link with compact single-path or multi-path gas cells has been employed in conjunction with a wavelength-tunable.
InGaAsP DFB laser diode at 1.64μm (at the R(6) absorption peak of methane) to achieve highly sensitive remote interrogation of CH<sub>4</sub> with potential application in the mining complexes and residential areas. By wavelength modulation with the DFB laser diode, multi-path gas cell and a self-design processing circuit, sensitivities of less than 1% of lower explosive limit (LEL) had been achieved in the laboratory.