A novel electric current sensor based on a high-birefringence fiber loop mirror(HBFLM) and a kind of magnetostrictive material rod(MMR) is demonstrated theoretically and experimentally. Part of the high-birefringence fiber(HBF) is pasted onto the MMR which is placed in the central part of a solenoid. The HBFLM is used as the sensor head and the linear filter simultaneously. Part of the high-birefringence fiber(HBF) is pasted onto the MMR which is placed in the central part of a solenoid. The rod will have elastic lengthening along the direction of the magnetic field when the uniform magnetic field changes, which will lead to a change of transmission intensity of the HBFLM filter, thus the variation of the electric current can be determined via the laser wavelength within the quasi-linear transmission range of the HBFLM filter. The sensitivity reaches 0.0153/100mA, the resolution reaches 10mA. Comparing with the previous fiber-optic electric current sensor, it has nothing with the linear birefringence based on Faraday effects in the previous fiber-optic electric current sensor. Comparing with the expensive and complex FBG electric current, the sensing signal can be directly detected by a photodiode(PD) and complicated demodulation devices are avoidable. The advantages of the electric current include optical power detection, simple and smart structure, high sensitivity, low cost, and good repeatability, etc.
A technique for temperature-insensitive displacement measurement using a single fiber Bragg grating (FBG) based on
strain-gradient-induced reflection spectrum bandwidth modulation and optical power detection is demonstrated. Linear
displacement measurement up to 20mm with displacement resolution of 0.054 mm and thermal stability of < 0.8 % F.S.
for temperature range from 20 °C to 80 °C are respectively achieved without any temperature compensation.i
Temperature-insensitive pressure measurement using a single fiber Bragg grating (FBG) based on reflection spectrum
bandwidth modulation and optical power detection is proposed. A specially designed double-hole cantilever beam
(DHCB) is used to provide pressure induced axial strain gradient along the sensing FBG and further modulate the
reflection bandwidth of the grating. The bandwidth modulation immunes to spatially uniform temperature effect and the
pressure can be unambiguous determined by reflected optical power measurement, avoiding the complex wavelength
interrogation system. The thermal fluctuate of the system is less than 1.2 % F.S. for temperature range from -10°C to 80
°C without any temperature compensation.
Temperature-independent micro-displacement measurement using a single fiber Bragg grating based on broadened reflection spectrum is proposed and experimentally demonstrated. The structure of specially designed bending cantilever beam (BCB) is proposed. The BCB induces axial strain gradient along the sensing FBG, resulting in a Bragg bandwidth modulation. The broadening of FBG spectrum bandwidth and the reflected optical power correspond to micro-displacement changes, insensitive to spatially uniform temperature variations. For a displacement variation of 20mm and a temperature change from 20°C to 100°C, the micro-displacement measurement deviation error is ±0.12mm without any temperature compensation. Through optical power detecting by a pin photodiode (PD), the micro-displacement sensor avoids complex demodulation process and potentially costs little.
Simultaneous measurement of temperature and force using a single fiber Bragg grating based on broadened reflection spectrum is proposed and demonstrated. The wavelength peak shift and the bandwidth broadening with the change of temperature and force allow discrimination between the temperature and force effects. Standard deviation errors of 1.8°C and 0.16N have been obtained with temperature and force ranges of up to 20~100°C and 0~8N, respectively.
Design and construction of temperature-insensitive fiber Bragg grating (FBG) liquid level sensor based on bending cantilever beam (BCB) is proposed and demonstrated. The BCB induces spatially gradient strain on the unique sensing FBG, resulting in a Bragg bandwidth modulation. The broadening of FBG spectrum bandwidth and the reflected optical power are corresponded to liquid level changes, insensitive to spatially uniform temperature variations. In the liquid-level range of 500 mm and temperature change from 20oC to 80oC, the liquid level measurement fluctuates less than 2% without any temperature compensation. By a pin-photodiode (PD) optical power detecting, the liquid-level sensor avoids expensive and complex demodulation techniques and potentially costs low.
An innovative algorithm based on the evolutionary programming (EP) method is developed for recovering distributions of axial strain along a fiber grating from its reflection spectral response. The proposed method exhibits a number of attractive features that prove to be effective for solving the inverse problems. The basics of EP are reviewed and the detailed programming procedures of the proposed algorithm are presented. By combining EP and the matrix method for calculating the reflection spectrum of a FBG, we obtain a new method for the distributed sensing. The numerical simulations show good agreements between the original and the reconstructed strain profiles.
In this paper, a filter which is cascaded n-stage high-birefringence fiber loop mirrors is presented. The related theory is analyzed and an expression cascaded with n-stage high-birefringence fiber loop mirrors of output intensity is given. Since experiment results are consistent with simulation outcomes, our theory is proved. Compared with a single stage high-birefringence filter, the cascaded filter shows more complex transmission Characteristics. Therefore, this kind of filter is flexible transmission spectrum and low cost for manufacture.
We propose a novel temperature compensation method that HBF is mounted on a piece of organic glass. It can lessen its temperature sensitivity to 0.059 nm/K, which are two orders of magnitude lower than that of an uncompensated HBF loop mirror. It is feasible that HBF loop mirror packaged with a large thermal-expansion material is insensitive to ambient temperature perturbation. This technique is beneficial to the practicality of loop mirror filter based fiber sensors.
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