The fiber optic sensors have grown to a promising technology in the application of oil and gas prospecting. Our group
has embarked on the experimental design of fiber optic seismic geophone based on fiber-Bragg-grating (FBG)
technology recently. This paper provides the detailed investigation and analysis of the sensor field test result in the
seismic reflection survey of the oilfield exploration as a continuing effort to our previous research. Several revisions of
previous sensor head design have been implemented which include the carbon fiber composite material based cantilever,
auxiliary beam mechanical design, and the moving coil electro-magnetic damping design for an improved seismic signal
sensitivity in the field test. The field tests of the redesigned sensing system show that: (1) the FBG seismic geophone has
a higher sensitivity than the commercial geophone between 10-70 Hz and equal sensitivity to commercial geophone
between 80-140 Hz (2) compared to the conventional geophone, the FBG seismic geophone is significantly immune
from the electro-magnetic interference (3) the FBG geophone has a less nonlinear distortion than the conventional
geophone and it is totally compatible with various commercial seismic recorders.
Traditionally, the broadband amplified spontaneous emission (ASE) source is considered to be used as
the light source for the fiber Bragg grating (FBG) sensing technology. However, this kind of light source has some
disadvantages − the huge volume and the high power consumption. These shortages will hamper the development of
FBG sensing technology in some kind of applications such as unattended sensor and space environment. In this
paper, the authors will present a new approach, the usage of the light emitted diode (LED) as the light source. The
LED source is very compact, easy to integrate, and significantly reduced the cost and power consumption. But the
light density of LED is so weak that the useful signal is almost buried by noise. A solution proposed by our group is
to enhance SNR by digital signal processing (DSP) technology, including high frequency modulation, phase-lock
amplifier, encoding on LED and decoding on the synchronistic detection. The experimental results show our effort
could significantly increases the signal noise ratio (SNR) and make FBG sensor practical on application.
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.
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.
In this paper a new type of fiber Bragg grating (FBG) sensor based geophone is introduced. This FBG geophone is mainly used in the seismic reflection survey of oilfield exploration to detect the motion of the earth. The basic detection principle of the seismic survey and the fiber Bragg grating sensing technique is explained in brief. An eight channel FBG sensor based geophone system is developed and demonstrated in both laboratory tests and field tests. The experimental results show the sensor system frequency response bandwidth at 10-100Hz in shallow layer and 10-140Hz in medium and deep layer separately. A high dynamic range and good signal to noise ratio are also observed in the experiment.
Based on matched fiber grating interrogation scheme, a fiber grating strain sensors system has been proposed and experimentally demonstrated on an equivalent-strength cantilever beam model, which can be deployed for civil structural strain and mechanical vibration simultaneous detection. Through special designing of sensor head, the temperature cross-sensitivity in strain sensing has been automatically removed. A common-path reference measurement structure has been used, so measurement errors caused by fluctuation of losses in the system or the light source power has been effectively eliminated, and the long-term stability of sensor system has been improved.
Optical fiber sensors based on Fiber Bragg Grating (FBG) technology have found many applications in the area of civil structural monitoring systems, such as in bridge monitoring and maintenance. FBG sensors can measure the deformation, overload and cracks on bridge with a high sensitivity. In this paper we report on our recent work a structural monitoring system using FBG sensors. Basic theoretical background and design of the system is described here, including the light source, FBG sensors, demodulator sensors, signal detection and processing schemes. The system will be installed on a major arch bridge currently under construction in Shanghai, China for long-term <i>in situ</i> health monitoring. The system schematic arrangement on the bridge is introduced in brief. Simulation experiments in the laboratory were carried out to test the performance of FBG strain sensors. The sensor response shows excellent linearity against the strain imposed on it. Traffic and overload monitoring on bridge using FBG sensors is also discussed and planned for the near future.