Dragan Z. Stupar

Wearable Low-Cost System for Human Joint Movements Monitoring Based on Fiber-Optic Curvature Sensor

In this paper, a measurement system for human joint movements monitoring based on a simple and low-cost intensity modulated fiber-optic curvature sensor is presented. The implemented curvature sensor is made up of a plastic optical fiber, which is optimized for small curvature measurements, and has a high sensitivity in a wide measuring range. The sensor sensitivity and resolution, in the measurement range, are 20 mV/° and 1°, respectively. The fabrication process of proposed curvature sensor is also given. The implemented sensor is wearable, noninvasive, nonintrusive, and completely harmless. In this paper, the characteristics of the sensor measured in laboratory conditions as well as measurements of the human knee joint movements are given. Wireless electronics based on ZigBee are also presented. Therefore, the sensor has the possibility of wireless measurement. The main advantages of this sensor are simplicity, lightness, and flexibility. This sensor is also electrically safe and immune to electromagnetic interference. The application, which provides a possibility of remote human joints monitoring over the internet is implemented in the LabVIEW software package.

A simple fibre optic inclination sensor based on the refraction of light

This paper presents a relatively simple and low-cost plastic fibre optic inclination sensor based on refraction of light through a medium. The sensor is cylindrically shaped and made of plastic with water in it as a movable mass and two plastic optical fibres. The sensor housing is filled with water to half of the height of the cylinder. The sensor is based on refraction on the boundary surface of two media inside the sensor. As the inclination increases, the angle of the water–air boundary surface changes with respect to the fibres. This causes a change in intensity of the received light depending on the angle. In this paper, the characteristic of the sensor measured in steps of 5° is also given. The measured characteristic is symmetric with respect to 180°. It has four linear regions and each linear region extends along 30°. A tilt angle sensitivity of 84 mV per degree for the 20°–50° range and 72 mV per degree for the 210–240° range with an accuracy of 0.5° and a resolution of 0.12° has been obtained.

The possibility of using a plastic optical fibre as a sensing element in civil structural health monitoring

In this paper we propose a low-cost fibre-optic sensor, primarily intended for application in civil structural health monitoring. The sensor is based on a plastic optical fibre as a sensing element. The sensing optical fibre is optimized for measuring small curvature displacements. The behaviour of the sensor is first measured on flexible structures to achieve the characteristic of the sensor. In this paper, we perform the curvature gauge characterization and discuss the results. The characterized sensor is then mounted on a fragile material construction to investigate its potential for crack detection.

A simple low-coherence interferometric sensor for absolute position measurement based on central fringe maximum identification

In this paper, a simple low-coherence interferometric sensor for absolute position measurement based on central fringe maximum identification is presented. The channeled spectrum, captured by a commercial spectrometer, is analyzed by using an algorithm based on the fitting of the calculated autocorrelation function of the captured optical power spectrum with the sum of two Gaussian functions. The position of the central fringe is obtained directly from the separation between two fitted Gaussian functions. In order to boost the precision of such a built sensing system, the position of the maximum of the central fringe is identified by a simple algorithm. The system currently provides unambiguous measurement over a range of 200 μm with a mid-range error less than 1.4 nm. In addition to this, the sensor is characterized by a very small sensing head (bare single-mode fiber with a diameter of 125 μm) and by very high resistance to environmental influences, thus enabling the possibility of using a very long down-lead sensing fiber.

Temperature Dependence of Mode Coupling in low-NA Plastic Optical Fibers

Using the power flow equation and experimental measurements, investigated in this paper is the state of mode coupling in low NA (0.3) step-index (SI) plastic optical fibers under varied temperature. Numerical results obtained using the power flow equation agree well with experimental measurements. It is found that elevated temperatures of low-NA SI plastic optical fibers strengthened mode coupling. These properties remained after a year, with the fiber being subjected to environmental temperature variations of >35 K. These thermally induced changes of the fiber properties are attributed to the increased intrinsic perturbation effects in the PMMA material at higher temperatures. This results in an increase of the measured bandwidth with increasing fiber temperature as well as earlier the bandwidth switch from the functional dependence of 1/z to 1/z1/2 (slower bandwidth decrease).

An intensiometric contactless vibration sensor with bundle optical fiber for real time vibration monitoring

In this paper a low-cost fiber-optic intensity based vibration sensor is presented. As sensing element a bundle optical fiber was used. The sensor is based on changes of the reflected light intensity in bundle fiber which is placed near the vibrating element. As the vibrating element loudspeaker cone was used. The sensor was tested in the range of frequencies from 10 Hz to 1 kHz. The minimum detectable amplitude of vibration achieved is 1 μm. An application for real time vibration monitoring in LabVIEW software package was developed. The advantages of the proposed sensor are its simplicity, low-cost, immunity to electromagnetic interference, and the possibility of distributed and long term vibration monitoring over a single optical fiber link.

High-speed and high-sensitivity displacement measurement with phase-locked low-coherence interferometry.

A novel high-speed and high-sensitivity displacement measurement sensing system, based on the phase-locked low-coherence interferometry, is presented. The sensing system is realized by comprising the Michelson fiber-optic interferometer. In order to obtain quadrature signals at the interferometer outputs, a 3×3 fused silica fiber-optic directional coupler is used. Therefore, the usage of the interferometer phase modulation as well as the usage of the lock-in amplification has been avoided. In this way, the speed of such a realized sensing system is significantly increased in comparison with the standard phase-locked interferometric systems that can be found elsewhere in the literature. The bandwidth of the realized sensing system is limited by the first resonance frequency of the used piezo actuator to 4.6 kHz. The estimated noise floor in the displacement measurement is approximately 180  pm/√Hz.

A Novel Fiber-Optic Mass Flow Sensor

In this paper a novel fiber-optic mass flow sensor based on coriolis force is presented. As sensing elements two fiber-optic curvature sensors mounted on elastic rubber tube are used. Rubber tube with sensing elements is excited by stepper motor. Produced system has the option of varying angle and speed of excitation. The bending of the fibers at the sensitive zone on curvature sensor changes the intensity of light traveling through the optical fiber. Curvature sensors are attached to the rubber tube so that they can measure phase difference produced by coriolis force. Mass flow rate is obtained by digital signal processing technique for phase difference detection.

Experimental and simulation analysis of fiber-optic refractive index sensor based on numerical aperture

In this paper a very simple refractive index sensor made up of plastic optical fibers is presented. Produced fiber-optic sensor is based on intensity change due to refractive index change. The proposed sensor has linear characteristic in the range of refractive indices of tested liquids (1.33-1.47). The results obtained by simulation are well consistent with the results obtained by measurements and analytically. The proposed sensor is characterized with simple and low-cost design, and high immunity to electromagnetic interference.

Resolution limit of the white-light interferometric sensor for absolute position measurement based on central fringe maximum identification

In this paper a simple theoretical analysis together with an experimental verification of the analysis that provides an estimation of the resolution limit of the white-light interferometric sensor for absolute position measurement based on central fringe maximum identification is presented. The resolution better than 10 pm is obtained in the white-light interferometric sensing system where the signal-to-noise ratio was greater than 80 dB.