Single uniform FBG for simultaneous measurement of liquid level and temperature

In this paper, we propose and demonstrate a novel scheme for simultaneous measurement of liquid level and temperature based on a simple uniform fiber Bragg grating (FBG) by monitoring both the short-wavelength-loss peaks and its Bragg resonance. The liquid level can be measured from the amplitude changes of the short-wavelength-loss peaks, while temperature can be measured from the wavelength shift of the Bragg resonance. Both theoretical simulation results and experimental results are presented. Such a scheme has some advantages including robustness, simplicity, flexibility in choosing sensitivity and simultaneous temperature measurement capability.

Single uniform FBG for simultaneous measurement of liquid level and temperature

In this paper, we propose and demonstrate a novel scheme for simultaneous measurement of liquid level and temperature based on a simple uniform fiber Bragg grating (FBG) by monitoring both the short-wavelength-loss peaks and its Bragg resonance. The liquid level can be measured from the amplitude changes of the short-wavelength-loss peaks, while temperature can be measured from the wavelength shift of the Bragg resonance. Both theoretical simulation results and experimental results are presented. Such a scheme has some advantages including robustness, simplicity, flexibility in choosing sensitivity and simultaneous temperature measurement capability.

Microchanneled chirped fiber Bragg grating formed by femto-second laser aided chemical etching for refractive index and temperature measurements

In this work, a microchanneled chirped fiber Bragg grating (MCFBG) is proposed and fabricated through the femtosecond laser-assisted chemical etching. The microchannel (~550 µm) gives access to the external index liquid, thus inducing refractive index (RI) sensitivity to the structure. In the experiment, the transmission bands induced by the reduced effective index in the microchannel region were used to sense the surrounding RI and temperature changes. The experimental results show good agreement with the theoretical analysis. The proposed MCFBG offers enhanced RI sensitivity without degrading the robustness of the device showing good application potential as bio-chemical sensors.

Spatially-multiplexed fibre-optic Bragg grating strain and temperature sensor system based on interferometric wavelength-shift detection

A prototype fibre-optic system using interferometric wavelength-shift detection, capable of multiplexing up to 32 fibre-optic Bragg grating strain and temperature sensors with identical characteristics, has been demonstrated. This system is based on a spatially multiplexed scheme for use with fibre-based low-coherence interferometric sensors, reported previously. Four fibre-optic Bragg grating channels using the same fibre grating have been demonstrated for measuring quasi-static strain and temperature.

Simultaneous refractive index and temperature measurement using cascaded long-period grating in double-cladding fibre

A compact scheme for simultaneous temperature and surrounding refractive index (SRI) measurement using two long-period gratings (LPGs) of different periods inscribed side-by-side in a single piece of a double-cladding fibre is presented. One of the LPGs is sensitive to both SRI and temperature, whilst the second is sensitive to temperature only.

Ultrasonic field and temperature sensor based on short in-fibre Bragg gratings

The authors demonstrate that in-fibre Bragg gratings may be successfully used to measure megahertz acoustic fields if the grating length is sufficiently short and the optical fibre is appropriately desensitised. A noise-limited pressure resolution of 4.5 × 10 –3 atm vHz was found. The capability to simultaneously act as a temperature sensor is also demonstrated.

Discrimination between strain and temperature effects using first and second-order diffraction from a long period grating

We study the effects of temperature and strain on the spectra of the first and second-order diffraction attenuation bands of a single long-period grating (LPG) in step-index fibre. The primary and second-order attenuation bands had comparable strength with the second-order bands appearing in the visible and near-infra red parts of the spectrum. Using first and second-order diffraction to the eighth cladding mode a sensitivity matrix was obtained with limiting accuracy given by cross-sensitivity of ~1.19% of the measurement. The sensing scheme presented as a limiting temperature and strain resolution of ±0.7 °C and ~±25 µ.

Combined ultrasound and temperature sensor using a fibre Bragg grating

We demonstrate the feasibility of using in-fibre Bragg gratings to measure MHz acoustic fields and temperature simultaneously. We achieved a noise-limited pressure resolution of ˜4.5×10-4 Atm/vHz and a temperature resolution of 0.2°C.

Strain and temperature sensitivity of a single mode polymer optical fiber

We have measured the optical phase sensitivity of fiber based on poly(methyl methacrylate) under near-single-mode conditions at 632.8 nm wavelength. The elongation sensitivity is 131±3×105 rad m-1 and the temperature sensitivity is -212±26 rad m-1 K-1. These values are somewhat larger than those for silica fiber and are consistent with the values expected on the basis of the bulk polymer properties.

Spectral characteristics of tapered LPG device as a sensing element for refractive index and temperature

The fabrication and characterization of long-period gratings (LPGs) in fiber tapers is presented alongside supporting theory. The devices possess a high sensitivity to the index of aqueous solutions due to an observed spectral bifurcation effect, yielding a limiting index resolution of ±8.5×10-5 for solutions with an index in the range 1.330-1.335.

Targets and self monitoring in hypertension: randomised controlled trial and cost effectiveness analysis

OBJECTIVES: To assess whether blood pressure control in primary care could be improved with the use of patient held targets and self monitoring in a practice setting, and to assess the impact of these on health behaviours, anxiety, prescribed antihypertensive drugs, patients' preferences, and costs. DESIGN: Randomised controlled trial. SETTING: Eight general practices in south Birmingham. PARTICIPANTS: 441 people receiving treatment in primary care for hypertension but not controlled below the target of < 140/85 mm Hg. INTERVENTIONS: Patients in the intervention group received treatment targets along with facilities to measure their own blood pressure at their general practice; they were also asked to visit their general practitioner or practice nurse if their blood pressure was repeatedly above the target level. Patients in the control group received usual care (blood pressure monitoring by their practice). MAIN OUTCOME MEASURES: Primary outcome: change in systolic blood pressure at six months and one year in both intervention and control groups. Secondary outcomes: change in health behaviours, anxiety, prescribed antihypertensive drugs, patients' preferences of method of blood pressure monitoring, and costs. RESULTS: 400 (91%) patients attended follow up at one year. Systolic blood pressure in the intervention group had significantly reduced after six months (mean difference 4.3 mm Hg (95% confidence interval 0.8 mm Hg to 7.9 mm Hg)) but not after one year (mean difference 2.7 mm Hg (- 1.2 mm Hg to 6.6 mm Hg)). No overall difference was found in diastolic blood pressure, anxiety, health behaviours, or number of prescribed drugs. Patients who self monitored lost more weight than controls (as evidenced by a drop in body mass index), rated self monitoring above monitoring by a doctor or nurse, and consulted less often. Overall, self monitoring did not cost significantly more than usual care (251 pounds sterling (437 dollars; 364 euros) (95% confidence interval 233 pounds sterling to 275 pounds sterling) versus 240 pounds sterling (217 pounds sterling to 263 pounds sterling). CONCLUSIONS: Practice based self monitoring resulted in small but significant improvements of blood pressure at six months, which were not sustained after a year. Self monitoring was well received by patients, anxiety did not increase, and there was no appreciable additional cost. Practice based self monitoring is feasible and results in blood pressure control that is similar to that in usual care.

Bragg grating in polymer optical fibre for strain, bend and temperature sensing

We report on a Bragg grating written in an eccentric-cored polymer optical fibre for measurement of strain, bend and temperature. The strain sensitivity achieves 1.13 pm µe -1. The temperature response shows a negative sign with the thermal sensitivity of -50.1 pm ?C-1. For bend sensing, this device exhibits a strong fibre orientational dependence, wide bend curvature range of ±22.7 m-1 and a high bend sensitivity of 63.3 pm/m-1.

Simultaneous refractive index and temperature measurement using a cascaded long-period grating device

We present a compact scheme for simultaneous temperature and surrounding refractive index (SRI) measurement using two long period gratings (LPGs) of different periods inscribed side-by-side in a single piece of a double-cladding fibre. One of the LPGs is sensitive to both SRI and temperature changes whilst the second is SRI-insensitive but shows spectral shift with temperature changes. In addition, we show that a resonance peak of the SRI-insensitive LPG can be designed to appear in the EDFA wavelength region with potential use for gain flattening applications.

Measurements of polarimetric sensitivity to hydrostatic pressure, strain and temperature in birefringent dual-core microstructured polymer fiber

We experimentally characterized a birefringent microstructured polymer fiber of specific construction, which allows for single mode propagation in two cores separated by a pair of large holes. The fiber exhibits high birefringence in each of the cores as well as relatively weak coupling between the cores. Spectral dependence of the group and the phase modal birefringence was measured using an interferometric method. We have also measured the sensing characteristics of the fiber such as polarimetric sensitivity to hydrostatic pressure, strain and temperature. Moreover, we have studied the effect of hydrostatic pressure and strain on coupling between the cores.