This study presents a plastic optical fiber (POF) sensor for measuring the driver's gripping force applied to a steering wheel. This sensor consists of a POF wound around the steering wheel covered with a soft material. The sensing method is based on the bending radiation loss of the POF induced by the driver's gripping force applied to the steering wheel. The bending radiation loss is proportional to the gripping force, and the response time of the POF sensor is about 2 s. The experimental results show that a POF sensor can be effective for monitoring the driver gripping force, and hence driver fatigue.
A reflection-type side-polished optical fiber submersion sensor with an optical fiber mirror in a manhole is proposed.
When this sensor is submerged into distilled water in a manhole and the measurement is made at about 1km from the
sensor, the throughput power gain is changed by about 2.04dB at 1540nm and the resonance wavelength shifts from
1540nm to 1541.6nm.
A bending-sensitive fiber (BSF) is fabricated and analyzed to create a microbend fiber sensor (MFS) with a simple structure. The BSF exhibits a gradual rather than sudden change in the microbend loss, according to a variation in the microbend applied to the BSF. According to the measured refractive index profile of the fabricated BSF, the proposed BSF consists of three different regions: the first core equal to the core of a SMF; the second core that is located around the first core, and whose refractive index is lower than the first core and higher than the cladding; and the cladding. The 3-D finite difference beam propagation method (3-D FD-BPM) is utilized to analyze the characteristics of the BSF. Based on the numerical results using 3-D FD-BPM and the fabricated BSF, a simple MFS with a BSF is created and compared to the MFS with a SMF. In particular, the MFS with the BSF showed a microbend loss from –1 to –20 dB at 1550 nm when the pressure given to the optical fiber is varied from 0 to 0.05 MPa; meanwhile, the MFS with the SMF showed no optical power attenuation.
The miniature fiber optic Fabry-Perot pressure sensor with a silicon diaphragm was developed for medical applications. The configuration of this sensor was a 1-mm long fiber optic Fabry-Perot interferometer bonded to an 80 micrometers -thick diaphragm. The length of the sensor was about 1.5 mm and the area of the diaphragm was 1 mm x 1 mm. The phase shift of the interferometric sensor was proportional to the applied pressure. The relationship between the applied pressure and the phase change was nonlinear.
Intensity based fiber optic pressure sensor has been fabricated using micromachining technology. The sensor consists of a multimode fiber bundle and a 100nm-Au/30nm- NiCr/150nm-Si3N4/300nm-SiO2/150nm- Si3N4 diaphragms supported by a micromachined frame-shape silicon substrate. The distance between the fiber bundle and the diaphragm of the pressure sensor is 900 micrometers . Three fiber optic pressure sensor having different size diaphragms were fabricated and used in experiments. The pressure sensitivities were 20.69 nW/kPa, 26.70 nW/kPa, and 39.33 nW/kPa for the pressure sensor with diaphragms of 3 X 3 mm2 area, 4 X 4 mm2 area, and 5 X 5 mm2 area.
The optical fiber intrusion sensor is investigated in the configuration of an optical time domain reflectometer using coherent interference of Rayleigh backscattering in a single mode fiber. When the modulation pulse width was 4 usec, the spatial resolution of this intrusion sensor was about 400m, the signal to noise ratio was about 3.3 and the bandwidth was about 30.5Hz.
We have developed the high sensitivity fiber optic Fabry- Perot pressure sensor with a Si3N4/SiO2/Si3N4(N/O/N) diaphragm fabricated using micromachining technology in the anisotropic etchant KOH solution. The configuration of this sensor was a 2 cm length fiber optic Fabry-Perot interferometer bonded to a 0.6 micrometers thick diaphragm. When the area of the N/O/N diaphragm used in the experiments was 2 X 2 mm2, the pressure sensitivity was 0.11 radian/kPa, and when the area was 8 X 8 mm2, the pressure sensitivity was increased to 1.57 radian/kPa. The phase change was dependent upon the applied pressure linearly.
The feasibility of producing a practical buried fiber optic sensor with high sensitivity for detecting intruders is demonstrated. Experiments were carried out on such an all fiber Michelson interferometer in which the sensing arm was buried in sand. When a 42 inch sensing arm was buried 8 inches deep in sand, the weight required for a half fringe shift in the sensor output was 22 pounds and the sensitivity was about 10 degrees/pound. The relation between the applied pressure and the phase change was linear. Experimental results indicated that the sensitivity of an optical fiber sensor was sufficient to detect people on foot and vehicles passing over the buried fiber.
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