High-sensitivity sensor of low relative humidity based on overlay on side-polished fibersABSTRACT: In this article, a miniaturized rectangular printed antenna that meets the ultrawideband (UWB) characteristics in terms of bandwidth and reflection coefficient is proposed. The designed antenna with dimension of 25316 mm 2 (L 3 W) was fabricated on FR-4 epoxy dielectric with relative permittivity of 4.4. SMA female connector is used for feeding with characteristic impedance of 50 X. The antenna exhibits good UWB characteristics and has the capability of operating between 3.92 to 11.32 GHz. The proposed antenna has omnidirectional radiation pattern on most of the operating band. The measured reflection coefficient of the proposed antenna is compared with the simulated one; good agreement is observed. Also, radiation pattern and gain of the antenna are presented. All simulations are carried out using the EM commercial simulators, HFSS, and CST.
A long period grating (LPG) coated with hydrogel has been developed for monitoring the relative humidity (RH) levels. The response wavelength of the LPG varies with the changes of the relative humidity. The four-layered step index waveguide model is presented to explain this observation, which is based on the effect of the hydrogel thin film, the index of which increases with the increasing RH. Experiment shows that the hydrogel-coated LPG sensor is highly sensitive between 38.9% and 100% RH, and behaves linearly with humidity with an accuracy of ±2.3% RH. The small-size and low-cost LPG fibre sensor will have extensive applications in various areas, such as remotely measuring RH, building health monitoring, medical facilities and goods' preservation.
This paper research an ultra long distance distributed fiber-optic intrusion detects system. Laser source is amplified and modulated before input to the dual Mach-Zehnder interferometers. This ensures the system can detect longer distance with less loss and nonlinearity than continuous laser input. The cross correlation algorithm is considered to locate the vibration event after the polarization controlled of the optical source, and the locate precision is also discussed. Finally, an experiment result is given as the sensing fiber length is 112km with the location precision about 160m.
We demonstrated a down-hole seismic survey system that can be applied in three dimensions vertical seismic profile (VSP) detection in petroleum exploration. The results of experiments show that the system has a dynamic measurement range of 80db (ratio of maximum to minimum value) and the total delay for signal collection, process and communication is less than 200ms @ 2k bit sample rates. An array consisting of six fiber-optic accelerometers (receivers) is applied in this system. Each receiver is comprised of three fiber-optic Michelson interferometers. In order to meet the requirements of high precision and real-time measurement, the high-speed DSP chips are employed to realize the algorithms of signal filters and Phase Generated Carrier (PGC) demodulation to obtain the seismic information. Multi-ARM CPUs are introduced into the system to design the fiber-optic accelerometer array controller and the receiver array local bus that are used for real-time data communication between the multi-level receivers and controller. The system interface for traditional ELIS Down-hole Instrument Bus (EDIB) is designed by the use of FPGA so that our system can attach to EDIB and cooperate with other instruments. The design and experiments of the system are given in this paper in detail.
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