An extrinsic Fabry–Perot interferometer (EFPI) acoustic sensor based on a gold diaphragm with an about 100 nm thickness has been proposed and demonstrated. The Fabry–Perot (F-P) cavity consists of a gold diaphragm and a fiber endface. Experimental results illustrate a static pressure sensitivity of about 19.5 nm / kPa in the range from 0 to 100 kPa with linearity of about 0.99. Meanwhile, the flat acoustic frequency response of about 35.0 mV / Pa between 0.2 and 2.0 kHz is achieved, and the largest acoustic pressure sensitivity is about 80.6 mV / Pa at 2.6 kHz. The noise-limited minimum detectable pressure is 1.3 mPa / Hz1/2 @ 2.6 kHz. The proposed EFPI acoustic sensor may have potential application in security and surveillance systems.
Due to the lack of an economic midinfrared laser, especially wavelength around 3 μm, light sources are critical to trace gas sensing for the gases without absorption in the near-infrared zone. We present a trace ethane photoacoustic (PA) sensor using a midinfrared light-emitting diode (MIR LED). MIR LEDs are very attractive sources for PA technology since they are relatively high power spectral density, easy modulation, low power consumption, and low cost. The proposed PA system with a 3.36-μm MIR LED shows good linearity to ethane concentration and reaches a detection limit of 10 parts per million by volume easily. Ideas of further enhancement of the sensitivity are discussed.
Detection of Hg2+ with high sensitivity is of great significance in the biochemical sensing field. Quantitative of Hg2+ was realized based on the influence of Hg2+ on the UV–vis absorption performance of Au–Pt–Au core-shell nanoraspberry (APA)–rhodamine-6G (R6G) structure. First, APA sol was added into R6G indicator solution and the UV–vis absorption signal intensity of R6G was evidently promoted. The signal intensity monotonously increased as more APA sol was added. However, when HgCl2 solution was introduced, the signal intensity declined. A linear relationship between Hg2+ concentration and signal intensity at 527 nm was revealed, based on which quantitative determination of Hg2+ could be realized. Hg2+ detection sensitivity was measured to be 0.031 a.u./M with a limit of detection of 10-7 M and the response time was 20 s. A high Hg2+ detection selectivity over Cu2+, Na+, Li+, and K+ was demonstrated. Due to its simplicity and high sensitivity, the proposed method could find an extensive application prospect in the Hg2+ detection field.
Traditional electrical sensor or traditional fiber Bragg grating sensing technology is not applicable to the measurement of nonuniform strain in composite material. Therefore, the distributed nonuniform strain in the lap plate position of composite interlining material is measured using a single fiber with optical frequency domain reflection technology in this study. The experimental results show consistency with the experiment phenomena, and the measurement accuracy could be increased to the submillimeter level.
A fiber Bragg grating (FBG) sensing network with a bus chain typology structure based on time-division multiplexing (TDM) technology has been developed. Each FBG sensor was placed in an isolated branching circuit separated by an optical splitter. By doing this, multiple reflection and spectrum shadow, which are common in a traditional TDM network, were eliminated since incident light reflected by each sensor did not go through the other sensors. Interference among different FBGs was also avoided. The system was experimentally verified by constructing such a network with 17 FBGs involved. Wavelength and position interrogation were successfully realized. Temperature experiment was carried out on four of the FBGs and the sensitivity was 9.87, 9.92, 9.91, and 9.97 pm/°C, respectively. The durability, reliability, and measuring accuracy of the sensing network were effectively improved due to the bus chain typology structure.
A novel optic fiber hydrogen sensor is proposed in this paper. Two Bragg gratings with different reflectivity were written in single mode fiber with phase mask method by 248 nm excimer laser. The end-face of singe mode fiber was deposited with WO3-Pd-Pt multilayer films as sensing element. The peak intensity of low reflectivity FBG is employed for hydrogen characterization, while that of high reflectivity FBG is used as reference. The experimental results show the hydrogen sensor still has good repeatability when the optic intensity in the fiber is only 1/3 of its initial value. The hydrogen sensor has great potential in measurement of hydrogen concentration.
Fabricating microstructures into the cladding of fiber Bragg grating, the FBG sensors will have wider applications in magnetic field measurement or gas sensing. In present paper, we regulate the physical feature of FBG by ablating single or cross spiral micro-trench with femtosecond laser. The influences of different processing parameters on M-FBG (microstructured FBG) have been investigated. The waveform variations and its controlling method have been discussed. It is shown that, the central wavelength shift enlarged with increasing of the laser energy, or decreasing of scanning speed. Finally, a cross spiral type M-FBG magnetic field probe and a temperature probe are also demonstrated.
A metal packed fiber Bragg gratings accelerometer has been proposed. Copper was adopted to cover the surface of
optical fiber by magnetron sputtering and electroplating technology, and then tin soldering was used to fix the metalized
fiber on mass and foundation. Because of copper coating and soldering, the elastic coefficient and ductility of FBGs have
been increased, and the problems of aging and creep arising from polymer or adhesive packaged have been avoided.
Experiment result demonstrated that the accelerometer possess of a resonant frequency of 2800Hz, a wide linear
measurement range from 0.5g to 5.3g and a sensitivity of 84mv/g.