Drugi optično vlakenski senzorji
Monitoring and analysis of pendant droplets evaporation using bare and monolayer-coated optical fiber facets

The monitoring of sub nano-liter pendant liquid droplets, during their evaporation from the cleaved facet of a standard optical fiber, is proposed and demonstrated. The combined reflections of incident light from the two boundaries, between fiber and liquid and between liquid and air, give rise to interference fringes as the fluid evaporates. The analysis of the fringe pattern allows for the reconstruction of the instantaneous size and evaporation rate of the droplets. These, in turn, provide information regarding the properties of the liquid itself, and the surface to which it is applied. The sensor readout is validated against direct video observation of evaporating droplets. Several examples illustrate the potential of the proposed sensor. Evaporation dynamics measurements identify the ethanol contents in binary ethanol-water mixtures with 2% certainty. The evaporation dynamics are modified by the application of a hydrophobic self-assembled monolayer coating to the tip of the fiber. Ten different organic solvents are accurately classified by clustering analysis of their evaporation data, collected using bare and coated fibers. Potential applications of the sensors could include quality control of water, beverages and oils, recognition of flexible fuel blends and fuel dilutions, mobile point-of-care diagnostics, and laboratory analysis of surface treatments.

Focused ion beam post-processing of optical fiber Fabry-Perot cavities for sensing applications

Focused ion beam technology is combined with chemical etching of specifically designed fibers to create Fabry-Perot interferometers. Hydrofluoric acid is used to etch special fibers and create microwires with diameters of 15 ?m. These microwires are then milled with a focused ion beam to create two different structures: an indented Fabry-Perot structure and a cantilever Fabry-Perot structure that are characterized in terms of temperature. The cantilever structure is also sensitive to vibrations and is capable of measuring frequencies in the range 1 Hz 40 kHz.

Cost-efficient speckle interferometry with plastic optical fiber for unobtrusive monitoring of human vital signs

A cost-efficient plastic optical fiber (POF) system for unobtrusive monitoring of human vital signs is presented. The system is based on speckle interferometry. A laser diode is butt-coupled to the POF whose exit face projects speckle patterns onto a linear optical sensor array. Sequences of acquired speckle images are transformed into one-dimensional signals by using the phase-shifting method. The signals are analyzed by band-pass filtering and a Morlet-wavelet-based multiresolutional approach for the detection of cardiac and respiratory activities, respectively. The system is tested with 10 healthy nonhospitalized persons, lying supine on a mattress with the embedded POF. Experimental results are assessed statistically: precisions of 98.8%1.5% and 97.9%2.3%, sensitivities of 99.4%0.6% and 95.3%3%, and mean delays between interferometric detections and corresponding referential signals of 116.655.5 and 1299.2437.3??ms for the heartbeat and respiration are obtained, respectively.

Monitoring the Evaporation of Fluids from Fiber-Optic Micro-Cell Cavities

Fiber-optic sensors provide remote access, are readily embedded within structures, and can operate in harsh environments. Nevertheless, fiber-optic sensing of liquids has been largely restricted to measurements of refractive index and absorption spectroscopy. The temporal dynamics of fluid evaporation have potential applications in monitoring the quality of water, identification of fuel dilutions, mobile point-of-care diagnostics, climatography and more. In this work, the fiber-optic monitoring of fluids evaporation is proposed and demonstrated. Sub-nano-liter volumes of a liquid are applied to inline fiber-optic micro-cavities. As the liquid evaporates, light is refracted out of the cavity at the receding index boundary between the fluid and the ambient surroundings. A sharp transient attenuation in the transmission of light through the cavity, by as much as 50 dB and on a sub-second time scale, is observed. Numerical models for the transmission dynamics in terms of ray-tracing and wavefront propagation are provided. Experiments show that the temporal transmission profile can distinguish between different liquids.

A Plastic Optical Fiber Microbend sensor Used as a Low-Cost Anti-Squeeze Detector

This paper presents a low-cost fiber optic anti-squeeze sensor, suitable for use in high-volume cost driven applications. The sensor, used as a car window anti-squeeze detector, complies with EC 2000/4/EC and U.S. Federal Motor Vehicle Safety Standard No. 118. The proposed design relies on microbend, loss induced in plastic optical fiber (POF). The sensor assembly employs only low-cost optoelectronic components readily in use by automotive and consumer markets. The lifetime tests have been performed on prototype sensors. The results show that the proposed design can easily reach and exceed 100 000 operational cycles even though it relies on flexible and all-polymer design. The proposed sensor design can be easily extended to other nonautomotive applications, such as protection devices in automatic door openers.

A simple fiber-optic vehicle axle detector for roadways

This paper presents a fiber-optic vehicle axle detector for roadways. It is based on a fiber-optic Michelson interferometer that is mounted directly into the road surface. The fully dielectric design allows for remote operation of the sensor via a long section of optical fiber. A simple signal-processing scheme of the output signals has been adopted that allows for reliable detection of commercial and personal vehicles.

System for precise balancing and controlled unbalancing of fiber-optic interferometers

A system for accurate balancing and controlled unbalancing of the optical path difference in all-fiber optical interferometers is described. Interferometers with various arm lengths (130 m) and with initial optical path differences of as much as 1 cm have been successfully balanced within a 5-m range. In addition, the proposed system allows for controlled unbalancing of arbitrary all-fiber optical interferometers with a precision better than 5 m.

Optical fiber Fabry-Prot sensor fabrication based on focused ion beam post-processing

A combination of focused ion beam milling and chemical etching is proposed for the creation of Fabry-Prot cavities in microwires. Both simple cavities and cantilevers are created on 15 ?m-diameter microwires and characterized in temperature. The cantilever structure shows sensitivity to vibration and is capable of measuring frequencies in the range 1 Hz 40 kHz.