Microbending Effect Research Articles

Research and application of an improved internal thrust force measurement system for rock and soil mass based on OFDR

Internal thrust force of unstable rock and soil mass is an essential parameter for prediction of many geological hazard. Currently, fiber bragg grating (FBG) and optical time-domain reflectometer (OTDR) are widely used to measure internal stress of unstable rock and soil mass. However, these methods have disadvantages such as low spatial resolution and the paucity of distributed measurements. This paper develops a quasi-distributed thrust measurement system based on an optical frequency domain reflectometer (OFDR). Firstly, we design an optical fiber stress sensor head using the characteristics of the optical fiber microbending effect. And then, the cubic spline interpolation method is used to compensate for the nonlinear effects of the OFDR. Finally, we implement a laboratory experiment of lateral stress to make error calibration. As a result, the OFDR sensing system achieved a spatial resolution of 20 cm by using a 500 m test fiber, maximum measurement pressure reached 1.059 MPa and relative error is 8.9%. We implemented OFDR in the Chenjiagou landslide located at the Three-Gorge of Chongqing in China. The results showed that this system can accurately locate six fiber stress sensors within the landslide over a range of 0 ∼ 420 m, obtaining the lateral thrusts as well.

A bio-signal monitoring sensor based on the microbending effect of fiber

In this paper, the focus of the study is the bio-signal monitoring sensor based on microbending effects and bending loss in fiber, the physical natures of the microbending effects and bending loss of multimode fiber are expounded through the microbending principle of fiber, and the effect of displacement on the microbending loss of fiber is explored and analyzed by deriving the microbending loss formula under the optical fiber theory. After putting the sensor on the back of a chair and letting the subject sit on the chair with the back on the sensor, the degree of microbend or radius of the fiber change as the change in chest volume during breathing results in the change in the external force, i.e., the force applied to the sensing part of the fiber. The physical change in the fiber induce changes in the amount of light energy transmitted in the fiber, causing optical loss. The respiratory rate is obtained by measuring the optical loss. The results show that the waveform displayed on the computer has good traceability performance, on which the frequencies of respiratory signals including normal breath, deep breath, and rapid breath can be distinguished. Experiments show that the sensor has good traceability feature and can automatically recognize the breathing conditions, with a signal-to-noise ratio of over 28dB

Analysis of mechanical vibrations applied on a LPGFS smart composite polymer material

The response of a Long Period Grating Fibre Sensor embedded into polymer matrix of a smart composite material to applied mechanical vibrations is analysed by observing the spectral shifts, broadenings and splitting of the resonance absorption bands appearing into resulting transmission spectrum. The developed model aims to improve the engineering of smart composite material fabrication and the design of its applications in aeronautics, industry, medicine and defence. The Long Period Grating Fibre Sensor simulation model is developed considering the role of optical fibre micro-bending effects caused by mechanical vibrations applied to polymer matrix. The sensor is operated as the smart composite material feedback loop which provides the input signal for automation systems and/or for smart material monitoring. The results of the performed simulations are compared to experimental results reported in literature observing a good agreement.

Textile Fiber Optic Microbend Sensor Used for Heartbeat and Respiration Monitoring

This paper reports on a textile fiber optic microbend sensor for heartbeat and respiration monitoring. A section of multimode optical fiber sandwiched between parallel strips acting as a microbender is being integrated onto an elastic substrate. Its design is based on fiber microbending effects. The textile sensor can be used to measure heartbeat and respiration rate simultaneously during standing and sitting position. The detected heart rates from our sensor are in good agreement with that from the commercial SpO2, whereas the respiration rate is verified by counting the breathing manually. We characterize the frequency response of the sensor with a simulation setup and find that the sensitivity of the sensor is large enough at 105 r/min although it decreases with the increase of the motor speed. The textile fiber optic sensor is very comfortable to wear due to the elastic nature of the substrate.

Intensity-Modulated Microbend Fiber Optic Sensor for Respiratory Monitoring and Gating During MRI

This paper describes a novel microbend fiber optic sensor system for respiratory monitoring and respiratory gating in the MRI environment. The system enables the noninvasive real-time monitoring and measurement of breathing rate and respiratory/body movement pattern of healthy subjects inside the MRI gantry, and has potential application in respiratory-gated image acquisition based on respiratory cues. The working principle behind this sensor is based on the microbending effect of an optical fiber on light transmission. The sensor system comprises of a 1.0-mm-thin graded-index multimode optical fiber-embedded plastic sensor mat, a photoelectronic transceiver, and a computer with a digital signal processing algorithm. In vitro testing showed that our sensor has a typical signal-to-noise ratio better than 28 dB. Clinical MRI trials conducted on 20 healthy human subjects showed good and comparable breathing rate detection (with an accuracy of ±2 bpm) and respiratory-gated image quality produced using the sensor system, with reference to current predicate hospital device/system. The MRI safe, ease of operation characteristics, low fabrication cost, and extra patient comfort offered by this system suggest its good potential in replacing predicate device/system and serve as a dual function in real-time respiratory monitoring and respiratory-gated image acquisition at the same time during MRI.

Optical monitoring of gas supply systems in metropolitan area

A novel fiber optic sensor system to monitor the gas pipeline network designed for PGNiG, Polish oil and gas exploration and production company is presented. The system is based on standard telecommunication fibers and devices, except for user-oriented and specially designed intensity-based optical sensors that utilize fiber macro- and microbending effects. Laboratory tests showed that the system is simple, easy to install, reliable, and fulfils the user requirements. Full Text: PDF References L. Zou, G. Ferrier, S. Afshar, Q. Yu, L. Chen, X. Bao,"Distributed Brillouin Scattering Sensor for Discrimination of Wall-Thinning Defects in Steel Pipe under Internal Pressure", App. Opt. 43, 1583 (2004) [CrossRef] L. Zou, X. Bao, S. Yang, L. Chen, F. Ravet,"Effect of Brillouin slow light on distributed Brillouin fiber sensors", Opt. Lett. 31, 2698 (2006) [CrossRef] D. Marcuse,"Microdeformation losses of single-mode fibers", Appl. Opt. 23, 1082 (1984) [CrossRef] R. Olshansky,"Distortion losses in cabled optical fibers", Appl. Opt. 14, 20 (1975) A.W. Domański, T. Poczęsny, K. Prokopczuk, P. Makowski,"An optical fiber loop sensor for vibration monitoring", Phot. Lett. Poland 2(2), 58 (2010) T. Poczęsny, K. Prokopczuk, P. Makowski, A.W. Domański,"Optical fiber macro-bend seismic sensor for real-time vibration monitoring in harsh industrial environment", Proc. SPIE 8082, 80823L (2011) [CrossRef] K. Prokopczuk, T. Poczęsny, A.W. Domański,"Multi-point vibration sensor using a fiber optic telecommunication cable", Proc. SPIE 8010, 80100E (2011) [CrossRef]

Analysis of a fiber specklegram sensor by using coupled-mode theory

The performance of the fiber specklegram sensor (FSS) by use of the waveguide coupled-mode theory is analyzed. The analyses are based on the microbending effect on the sensing fiber, in which we have found that the sensitivity of the FSS is affected by the core diameter and the bending geometry. Experimental confirmations of the analyses are also provided in which we have shown that experimental data are consistent with the analyses.

Photoacoustic spectrometry using a fiber-optic pressure sensor

A photoacoustic sensor is constructed by using an optical fiber. Tie signal is measured as a light transmission loss caused by a microbending effect. The pressure sensor, consisting of a coiled optical fiber, is installed in a sample cell for absorption measurement by photoacoustic spectroscopy (PAS). A frequency-doubled Xd:YAG laser is introduced into the sample cell, and a photoacoustic signal is measured as an intensity decrease of a He-Xe laser beam passed through an optical fiber. The detection limit for a chelate compound of iron II -4,7-diphenyl-1,10-phenanthrolinedisulfonic acid is 1.2×10 -6 M

Characterization of single-mode coated fibers at low temperatures using periodic distortion of the fiber axis

Microbending effects on cabled single-mode optical fibers are analyzed both theoretically and experimentally over the temperature range -30°C-25°C. The loss in single-mode fiber is attributed to the coupling between the guided and radiative modes caused by micro-bending effects. The primary coupling between the guided LP 01 and the radiative LP 11 modes is studied by imposing periodically controlled perturbations on the fiber axis at different temperatures.

Microbending effects on monomode light propagation in multimode fibers

The effects of periodic axis deformations on propagation in multimode optical fibers with single-mode excitation are investigated numerically and experimentally. The numerical study, based on ray theory, deals with helical rays in the presence of sinusoidal axis deformations for various shapes of index profile. The corresponding experimental observations and results, carried out on tubular modes, confirm the existence of resonance effects between the helical ray period and the fiber axis deformation. This technique permits the observation of mode-to-mode power transfer and provides a sensitive tool to investigate the mode-coupling mechanism in optical fibers.

Polarisation holding in coiled high-birefringence fibres

The polarisation holding ability of high birefringence fibres wound into small coils is investigated. For coil diameters below 3 cm–4 cm, the polarisation holding degrades very quickly with decreasing diameter. The crosscoupling is thought to be due to microbending effects.