Qida Zhao

FBG-type sensor for simultaneous measurement of force (or displacement) and temperature based on bilateral cantilever beam

An improved FBG-type sensor for simultaneous measurement of force (or displacement) and temperature based on the bilateral cantilever beam (BCB) is proposed and demonstrated. The two parts of the beam are subject to opposite forces (or displacements) leading to a red shift for the part of the FBG subject to stretch and to a blue shift for the other one. An FBG bonded to the surface of the middle of the BCB is experimentally demonstrated to have a force sensitivity of /spl sim/1.046 nm/N, a sensitivity of the displacement-based strain of /spl sim/0.317 nm/mm, and a temperature sensitivity of /spl sim/0.190 nm//spl deg/C between 0/spl deg/C and 70/spl deg/C, respectively.

Temperature-insensitive fiber Bragg grating liquid-level sensor based on bending cantilever beam

A temperature insensitive fiber Bragg grating (FBG) liquid level sensor based on bending cantilever beam (BCB) is proposed and demonstrated. The BCB induces axial strain gradient along the sensing FBG, resulting in a Bragg bandwidth modulation. The broadening of FBG spectrum bandwidth and the reflection optical power change with the liquid level and they are insensitive to spatially uniform temperature variations. For a liquid level variation of 500 mm and a temperature range from 0/spl deg/C to 80/spl deg/C, the measured liquid level fluctuates less than 2% without any temperature compensation. By optical power detection via a pin photodiode, the liquid-level sensor avoids complex demodulation process and potentially costs low.

Relative Humidity Sensor Based on Tilted Fiber Bragg Grating With Polyvinyl Alcohol Coating

A relative humidity (RH) sensor based on tilted fiber Bragg grating (TFBG) is proposed by utilizing polyvinyl alcohol (PVA) as the sensitive cladding film. RH increasing in the PVA coating will result in reduction of refractive index. Due to the TFBGs sensitivity to ambient refractive index, the spectral properties of PVA-coated TFBG are modified under exposure to different ambient humidity levels ranging from 20% to 98% RH. The transmission power of TFBG has different linear behaviors for two different humidity ranges (20%-74% RH and 74%-98% RH), and the sensitivity for each humidity range reaches as high as 2.52 and 14.947 dBm/%RH, respectively. Combining the advantages of optical fiber grating and PVA as a smart material, this design involves simple configuration, low cost, compactness, a small degree of hysteresis, stability, and wide dynamic sensing range as well. Therefore, the sensor could be applied in real-time RH monitoring for normal as well as extremely humid environments.

Simultaneous measurement of temperature and pressure by a single fiber Bragg grating with a broadened reflection spectrum

Simultaneous measurement of temperature and pressure with a single fiber Bragg grating (FBG) based on a broadened reflection spectrum is proposed and experimentally demonstrated. A novel double-hole structure of a cantilever beam is designed, and a FBG is affixed on the nonuniform strain area of the cantilever beam. The Bragg reflection bandwidth is sensitive to the spatially gradient strain but is free from the spatially uniform temperature. The wavelength peak shift and the bandwidth broadening of the FBG with a change of temperature and pressure allow for simultaneous discrimination between the temperature and the pressure effects. Standard deviation errors of 1.4 degrees C and 1.8 kPa were obtained with temperature and pressure ranges of 20 degrees C-100 degrees C and 0-80 kPa, respectively. This novel and low-cost sensor approach has considerable potential applications for temperature-insensitive strain measurement.

Temperature-insensitive fiber Bragg grating force sensor via a bandwidth modulation and optical-power detection technique

A technique for temperature-insensitive force measurement using a single fiber Bragg grating (FBG) based on strain-gradient-induced reflection spectrum-bandwidth modulation and optical-power detection is demonstrated. A specially designed bending cantilever beam (BCB) is used to induce axial-strain gradient along the sensing FBG, resulting in a Bragg bandwidth modulation. The broadening of the FBG spectrum bandwidth and reflection optical power linearly change with the applied force, and both of them are insensitive to spatially uniform temperature variations. For a temperature range from 20 degC to 80 degC, a linear response of force measurement up to 20 N with fluctuation less than 0.8% full-scale is achieved without any temperature compensation. The demodulation process is simplified by optical-power detection via a p-i-n photodiode, and the sensing system is potentially cost-effective

Dynamic Temperature Compensating Interrogation Technique for Strain Sensors With Tilted Fiber Bragg Gratings

In this letter, we propose a novel method of edge filter linear demodulation using tilted fiber Bragg gratings (TFBGs) in a fiber sensor system. Based on the filter characteristics of TFBGs and the same temperature characteristics as the FBG, the strain sensor demodulation system with dynamic temperature compensation can be achieved. An experimental system is built up to achieve one or multichannels of sensor demodulation. The experimental results were analyzed in detail. Using this method based on intensity, linear demodulation with a bandwidth of 6 nm can be achieved. The advantages of this system are an all-fiber design, quasi-static and dynamic operation, and potential high-speed demodulation.

Temperature-insensitive fiber Bragg grating dynamic pressure sensing system

Temperature-insensitive dynamic pressure measurement using a single fiber Bragg grating (FBG) based on reflection spectrum bandwidth modulation and optical power detection is proposed. A specifically designed double-hole cantilever beam is used to provide a pressure-induced axial strain gradient along the sensing FBG and is also used to modulate the reflection bandwidth of the grating. The bandwidth modulation is immune to spatially uniform temperature effects, and the pressure can be unambiguously determined by measuring the reflected optical power, avoiding the complex wavelength interrogation system. The system acquisition time is up to 85 Hz for dynamic pressure measurement, and the thermal fluctuation is kept less than 1.2% full-scale for a temperature range of -10 degrees C to 80 degrees C.

Simultaneous measurement of stress and temperature with a fiber Bragg grating based on a loop thin-wall section beam.

We designed and demonstrated what we believe to be a novel sensor for simultaneous measurement of stress and temperature. A fiber Bragg grating is flatly adhered to the surface of a loop thin-wall section beam. The theoretical analyses and the experimental results show that both the central wavelength shift and the chirped bandwidth of the grating reflection spectrum have a linear relationship with the stress and the temperature, respectively, and the slopes of them are different. Therefore, the temperature and stress can be discriminated by interrogating the chirped fiber grating. Moreover, we also investigated the strain of the loop thin-wall section beam, and the results show that the strain is cosine proportional to the double positional angle.

Time-Division Multiplexing Fiber Grating Sensor With a Tunable Pulsed Laser

A novel time-division-multiplexing fiber Bragg grating (FBG) sensor with a tunable pulsed laser is proposed and demonstrated. A tunable pulsed fiber laser based on a matched FBG is applied. The wavelengths of the sensing FBGs are obtained by detecting maximum voltages with a photodiode, which avoids a complex demodulation process. The advantages of the sensor include simple structure, high signal-to-noise ratio, and the sensing signals obtained by detecting the maximum voltages

Force sensing with temperature self-compensated based on a loop thin-wall section beam

A novel method about force sensing with temperature self-compensated based on a loop thin-wall section beam is proposed and demonstrated. Two identical fiber Bragg gratings are rigidly affixed on the outer surface of the beam with the positional angle difference between the two gratings of 90/spl deg/. The wavelength space between the two reflected peaks of the gratings is proportional to the force and insensitive to temperature when the direction of the force and one of the two gratings are located along a diameter; therefore, the force sensing with temperature self-compensated can be achieved.