In this paper, a method for interrogation of Fibre Bragg Grating (FBG) and single mode-multimode-single mode (SMS) fiber for simultaneous measurement of temperature and strain using is proposed and demonstrated. A half etched FBG is deployed in the optical circuitry for sensitivity enhancement. The sensor exhibits the temperature and strain sensitivity of 20.2 pm/°C and 1.91 pm/με over the range of 20-200 °C and 100-2020 με respectively. The resolution for temperature and strain measurement is ±0.5 °C and ±12 με. The experimental results show that the sensor is able to measure strain and temperature simultaneously by sensitivity matrix with additional advantages such as simple structure, compact size, ease of fabrication, and low cost.
This paper proposes a chemo-mechanical-optical sensing approach for the detection of carcinogenic chromium (VI) metal ion using an etched fiber Bragg grating (FBG) coated with stimulus responsive hydrogel. Hydrogel synthesized from the blends of (3-acrylamidopropyl)—trimethylammonium chloride, which is highly responsive to chromium ions suffers a volume change when placed in Cr solution. When the proposed sensor system is exposed to various concentrations of Cr (VI) ion solution, FBG peak shifts due to the mechanical strain induced by the swelling of the hydrogel. The peak shift is correlated with the concentration of the Cr (VI) metal ion. Due to the reduction in the cladding diameter of FBG, wastage of swelling force due to hydrogel on FBG is lowered and utilized for more wavelength peak shift of FBG resulting in the increase in the sensitivity. The resolution of the sensor system is found to be 0.072 ppb. Trace amounts of chromium (VI) ion as low as 10 ppb can be sensed by this method. The sensor has shown good sensitivity, selectivity, and repeatability. The salient features of the sensors are its compact size, light weight, and adoptability for remote monitoring.
This paper describes a fiber optics based pH sensor by using wavelength modulated techniques. Fiber Bragg grating (FBG) is functionalized with a stimulus responsive hydrogel which induces a strain on FBG due to mechanical expansion of the gel in response to ambient pH changes. The gel is synthesized from the blends of Poly (vinyl alcohol)/Poly (acrylic acid). The induced strain results in a shift of FBG reflected peak which is monitored by an interrogator. The sensor system shows a good linearity in acidic pH range of 3 to 7 with a sensitivity of 12.16pm/pH. Besides that it shows good repeatability which proves it to be fit for pH sensing applications.
We present a fiber-optic wavelength-modulated sensor for pH applications. Fiber Bragg grating (FBG) is functionalized with a stimulus-responsive hydrogel that induces a strain on FBG due to mechanical expansion of the gel in response to ambient pH changes. The gel is synthesized from the blends of poly (vinyl alcohol)/poly (acrylic acid). The induced strain results in a shift of FBG reflected peak that is monitored by an interrogator. The sensor system shows good linearity in the acidic pH range of 3 to 7 with a sensitivity of 12.16 pm/pH. In addition, it shows good repeatability and oscillator behavior, which proves it to be fit for pH sensing applications.
An intensity modulated Fiber optic prism based liquid concentration sensor is proposed. The sensing principle is based on total internal reflection (TIR) inside the prism which gets modulated in the vicinity of liquid as a function of refractive index. The precise movement of sensor head in liquids, gives rise to a hysteresis curve which is considered as a measure of liquid concentration. Different liquid concentrations of Sucrose, Saline solution (NaCl) and Glycerin are taken for the study. The sensor exhibits sensitivity of 371.16, 2133.25 and 1501.89 Sucrose, Saline water and Glycerin solutions respectively.
The present article reports a hydrogel coated Fiber Bragg Grating (FBG) based sensor for chromium metal ion detection. The presence of chromium metal ion in environmental water causes many toxic effects both on humans and animals. The inability of sensing traces of chromium ions is still remains a challenging problem for decades, as the Chromium exists in the environment in different oxidation states. This Paper discusses a chemo-mechanical-optical sensing approach for sensing harmful Chromium ions in environmental water. Fiber Bragg Grating is functionalized with a stimulus responsive hydrogel which swells or deswells depending on ambient chromium ion concentrations. This volume change of the hydrogels causes a bragg shift of the FBG peak. Different peak shifting’s, corresponding to different concentrations of the Cr ion concentrations, can be considered as a measure for quantifying traces of chromium ions. Hydrogel network cross-linked with (3-Acrylamidopropyl)-trimethylammonium chloride (ATAC) was synthesized and coated on FBG by dip coating method. Chromium ion concentrations up to ppm (parts per million) can be sensed by this technique.
This paper reports a simple technique for hydraulic pressure measurement with enhanced resolution using a fiber Bragg grating (FBG) and a metal spring which acts as transducer. The sensor works by means of measuring the Bragg wavelength shift of FBG caused by the longitudinal elongation of optical fiber due to applied pressure. Experimental results show that the sensor possesses good linearity and repeatability in pressure measurement ranging over 0 to 55 bar, with a sensitivity of 57.7 pm/bar. A wavelength-intensity interrogation scheme using single-multiple-single-mode fiber structure is designed for FBG sensor, which enabled the system to be compact, lightweight, inexpensive, and high resolution.
A simple and low-cost fiber optic refractometer has been designed and demonstrated. The sensor is configured by etching a short region of a standard single-mode circularly bent fiber. Circularly bent three fiber loops are etched in equal lengths and arranged parallel to each other. The working principle of the sensor is by detecting the evanescent field modulation with respect to the change in ambient refractive index. In the present study glycerin solution with various concentrations, possessing different refractive indices is chosen as the ambient.
Bent and etched optical fiber sensors have increased sensing capabilities but they are very much prone to fracture and breakage. The proposed sensor is stable showing very less tendency towards any breakage or fracture. The sensitivity of the sensor is tested for glycerin with different concentrations. It is evident from the experimental results that with the increase of glycerin concentration the output intensity of the sensor is decreased linearly. The proposed sensor may find applications in detecting various chemical species and biochemical applications.
A novel sensor for high-temperature measurement using Fiber Bragg grating (FBG) has been designed and simulated. The sensor works based on measurement of the shift in Bragg wavelength that corresponds to the temperature induced strain by making use of a mechanical transducer. The transducing element provides temperature dependent strain on FBG by means of differential linear thermal expansion of two different ceramic materials: Alumina and Silicon Carbide. The designed sensor can measure the temperatures from 20°C to 1500°C.
A fiber Bragg grating (FBG)–based high-temperature sensor accompanied by a low-cost interrogation scheme with liquid-crystal display (LCD) has been designed, developed, and tested. The sensor probe is configured by encapsulating a femtosecond laser drawn FBG with an aluminum nitride capillary tube, and is used to measure the temperature from 20°C to 650°C. The interrogation system consists of a long period fiber grating, two photodiodes, a 2-channel transimpedance amplifier, and a field-programmable gate array with an LCD. It displays the temperature directly in °C with a resolution of 1°C. The sensor output is found to be linear with coefficient of 0.999, and independent of source power fluctuations. The results showed that the sensor has good accuracy with a negligible error bar of ±1.23%.
This article demonstrates use of a fiber Bragg grating (FBG) sensor for in situ monitoring of vacuum process with high sensitivity. The sensor head consists of a commercial syringe barrel with plunger, metal spring, pressure chamber, FBG and safeguarding outer tube. The sensor is configured by firmly fixing the FBG between the plunger and the rigid support provided to the safeguarding tube. Under vacuum process the metal spring facilitates the FBG to get strained in axial direction which results in shift of Bragg wavelength of FBG. The Bragg wavelength shift of FBG is found to be linear with respect to vacuum pressure with a linear coefficient of 0.9988. Pressure sensitivity of the sensor is found to be 27 pm/cm Hg. The sensor design is simple, low-cost and has the advantage of all fiber optic sensors.
A temperature independent high sensitive pressure sensing system using fiber Bragg grating (FBG) and ‘C’ shaped Bourdon tube (CBT) is demonstrated. The sensor is configured by firmly fixing the FBG (FBG1) between free and fixed ends of the CBT. Additional FBG (FBG2) in line to the FBG1 is introduced which is shielded from the external pressure, tend to measure only the ambient temperature fluctuations. The CBT has an elliptical cross section where its free end is sealed and the fixed end is open for subjecting the liquid or gas pressure to be measured. With the application of pressure, the free end of CBT tends to straighten out results in an axial strain in FBG1 causes red shift in Bragg wavelength. The pressure can be determined by measuring the shift of the Bragg wavelength. The experimental pressure sensitivity is found to be 66.9 pm/psi over a range of 0 to 100 psi. The test results show that the Bragg wavelength shift is linear corresponds to change in applied pressure and well agreed with the simulated results. This simple and high sensitive design is capable of measuring static/dynamic pressure and temperature simultaneously which suits for industrial applications.
A fiber-optic sensor scheme, capable of the simultaneous measurement of pressure and temperature using two in-line Fiber Bragg Gratings (FBGs) is reported. Sensor head is configured by embedding the two FBGs with metal bellows, such that FBG1 is sensitive to both pressure and temperature, whereas FBG2 is only sensitive to temperature. High pressure sensitivity is achieved because of the lower spring rate in longitudinal direction to that of the large elastic modulus in transverse direction of the metal bellows. Pressure and temperature measurement is made by monitoring the shift of Bragg wavelengths of the FBGs corresponds to variation in pressure and temperature. From the test results, the obtained pressure and temperature sensitivities are 86 pm/psi and 9.17 pm/°C, over a dynamic range of 0-40 psi pressure, and 25-110°C temperature measurements respectively. The experimental results well agreed with the theoretical results and show good linearity. This simple design, economical and all fiber optic sensors can be used for liquid and gas pressure measurements, and under-water applications.
A high sensitive pressure sensor based on Fiber Bragg grating (FBG) integrated with a thin metal diaphragm was
designed and demonstrated. To enhance the pressure sensitivity FBG is firmly glued across the diameter of the
diaphragm. Under pressure, the diaphragm deforms and produces an induced strain along the length of the fiber causes
shift in Bragg wavelength of the FBG. Pressure measurement is made by measuring the Bragg wavelength shift against
change in pressure. The sensor was tested up to the maximum pressure of 140 psi and the corresponding pressure
sensitivity was found to be 0.0204 nm/psi, which is approximately 970 times higher than that can be achieved with a
bare FBG. The experimental results show good agreement with the theoretical results and possess good linearity and
repeatability. This sensor can be used for the measurement of medium pressure, liquid level and depth of underwater.
The performances of two liquid level sensors based on Fiber Bragg grating are studied. The Fiber Bragg gratings (FBG) are sensitive to strain and temperature. We investigate on enhancement of strain sensitivity of the FBG for liquid level measurement. Two different sensor heads arrangement are fabricated to exploit the strain sensitivity of FBG and use it for the liquid level measurement. The measurement sensitivity of a FBG based fiber optic liquid level sensor can be improved by controlling the parameter such as diameter of the FBG.
An intensity based fiber optic liquid level sensor for continuous measurement is described. The sensing principle is based on intensity of reflected light which is disturbed by the change in proximity of the fiber probe and the reflector. A Mechanical CAM is used in the sensing arrangement. It converts the rotatory motion into a linear displacement. As the liquid level raises, rotation of the CAM takes place and the CAM follower connected to it moves linearly. A reflector which is attached to the end of the CAM follower reflect the incident light. As the displacement of reflector occur the intensity of reflected light also changes and is a measure of change in liquid level. The prototype designed sensor can sense liquid level upto 17cm. The proposed sensor can find potential applications in transportation and process industries.
In this work half the length of the single FBG is chemically etched and the un-etched half is glued on a cantilever. The response of the grating is investigated as a function for buoyancy force on the cantilever due to liquid level and temperature. Simultaneous measurement of liquid level and temperature is achieved from the coefficients of liquid level and temperature sensitivities obtained from the experimental results.
A single mode fiber optic vibration senor is designed and demonstrated to monitor the vibration of a simply
supported beam. A rectangular beam (length 30.8 cm, width 2.5cm and thickness 0.5mm) made of spring-steel is
arranged as simply supported beam and is made to vibrate periodically. To sense the vibrations a telecommunication
fiber is chemically etched such that its diameter reaches 50μm and is glued using an epoxy at the centre of the beam. A
broadband light (1550nm) is launched into Fiber Bragg Grating (FBG) through a circulator. The light reflected by the
FBG (1540.32nm) is coupled into the centre etched fibre through the circulator and is detected by photodiode connected
to a transimpedance amplifier. The electrical signal is logged into the computer through NI-6016 DAQ. The sensor
works on transmission power loss due to the mode volume mismatch and flexural strain (field strength) of the fiber due
to the bending in the fiber with respect to the bending of the spring-steel beam. The beam is made to vibrate and the
corresponding intensity of light is recorded. Fast Fourier transform (FFT) technique is used to measure the frequencies of
vibration. The results show that this sensor can sense vibration of low frequency accurately and repeatability is high. The
sensor has high linear response to axial displacement of about 0.8 mm with sensitivity of 32mV/10μm strain. This lowcost
sensor may find a place in industry to monitor the vibrations of the beam structures and bridges.
This study focused on the development of high sensitivity pressure sensor based on reduced clad FBG encapsulated
in a stainless steel cylinder, partially filled with silicon rubber. The sensor works by means of transferring radial or
lateral pressure into an axially stretched- strain along the length of the FBG. The experiment is carried out using two
different FBG's have core/clad diameters of 9/125μm (FBG1) and 4/80μm (FBG2). FBG2 is chemically etched to reduce
the cladding diameter which significantly enhances the pressure sensitivity. The shift of the Bragg wavelength in
response to applied pressure is monitored with an optical spectrum analyser (OSA). The measured pressure sensitivity of
FBG2 and FBG1 are found to be 5.85 x 10-2 MPa-1 and 2.07 x 10-2 MPa-1, which are approximately 18870 and 6677
times respectively higher than that can be sensed with a bare FBG. A very good linearity is observed between Bragg
wavelength shift and pressure. This compact, low cost and robust design of the sensor can find applications in the areas
of low and medium pressure measurement.
A small and simple hydrostatic pressure sensor using fiber Bragg grating sensor for liquid level sensing is reported. The working principle of the sensor head design is based on transferring hydrostatic radial pressure to axial strain to the FBG. An FBG written in a fiber of diameter 50μm has been used for the measurement. The experimental result shows that sensitivity of the sensor can reach 23pm/cm of liquid column. The sensor can be useful in applications that involved with less hydrostatic pressure, like a tank with inflammable liquid in a fuel gas station.
A fiber optic vibration sensor is demonstrated using bifurcated bundle fiber based on the principle of extrinsic
displacement sensor. An IR source is used along with glass fibers to avoid the effect of stray light in sensing. The
encapsulation of the sensor enables easy alignment, flexible handling and usage in harsh environments. The sensor is
capable of measuring the frequencies up to 650Hz with vibration amplitude resolution of 10μm, enough to monitor the
vibrations generated in heavy machines. The sensor is tested in the field to monitor the health condition of the diesel engine.
A temperature compensated liquid level sensor using FBGs and a bourdon tube that works on hydrostatic pressure is
presented. An FBG (FBG1) is fixed between free end and a fixed end of the bourdon tube. When hydrostatic pressure
applied to the bourdon tube FBG1 experience an axial strain due to the movement of free end. Experimental result
shows, a good linearity in shift in Bragg wavelength with the applied pressure. The performance of this arrangement
is tested for 21metre water column pressure. Another FBG (FBG2) is included for temperature compensation. The
design of the sensor head is simple and easy mountable external to any tank for liquid level measurements.
A simple and effective method of encapsulation of a fiber Bragg grating (FBG) sensor for use at elevated temperatures and harsh and corrosive environments using a rigid probe technique is presented in this paper. A thorough characterization has been carried out on the encapsulated, as well as bare, FBGs. The experimental studies reveal that encapsulated FBGs are superior in their responsivity, linearity, sensitivity, and repeatability when compared with unencapsulated ones.
An encapsulated fiber optic sensor head for the detection of level of fuel in a tank is presented. The design is
based on a concentric cam used along with a float and extrinsic intensity modulation of light. The sensor has been tested
for its performance to measure a fuel level range of 35cm and a sensitivity of 0.2316 volts/cm was observed during rise
in fuel level. The sensitivity and range of level sensing can be varied by varying the length of the connecting rod.
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