654 research outputs found
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Integrating communication with sensing micro-bending of multi-mode optical fibre
No full textEnvironment perturbations on a multi-mode fibre lead to changes in intensity at the output due to bending induced losses. A carrier signal has been modulated in a form such that, the amplitude of the light signal is not affected, which is left for sensing light intensity variations due to micro-bending. Pulse frequency modulation has been suggested for this purpose using a voltage-to-frequency converter. This information is again decoded at the receiver end using frequency-to-voltage conversion. In this manner, a fibre link, which is acting as a perturbation sensor, also acts as a communication link without affecting the sensing capability as long as the link is not damaged due to perturbation. It is known that, the multi-mode fibre can be used to sense any form of environment perturbation, such as strain, pressure, force, position, acceleration, temperature etc1-3. The proposed approach is applicable in all these situations with integrated communication capability
Measurement of temperature and temperature fluctuation of a gaseous flame using double and single exposure speckle photography
No full textMeasurement of accurate spatial distribution of temperature and temperature fluctuation in a flame is important to study the combustion process in detail. In this paper first we have presented measurement of temperature profile of a gaseous flame of a two-dimensional slot burner. The errors due to halo effect in the measurements of temperature are minimized by correcting the width of the fringes. Further single exposure speckle photography is used to study temperature fluctuation inside the flame. The 3-D plot of temperature fluctuation for different fuel flow rates of air and acetylene at different vertical heights above the mouth of the burner with distance from the one end of the burner is also presented
Highly Sensitive Pulsed Digital Holography for Built-in-defect analysis with a laser excitation.
No full textA highly sensitive method is presented for noninvasive defect analysis on thin structures with a Q-switched double-pulsed ruby laser with frequency doubling (347 nm). In our research we feature an all-optical arrangement, where a focused laser pulse derived from the same ruby laser (694 nm) acts as a built-in synchronous excitation source for digital holographic interferometry. The recordings are made with a CCD camera for capturing two holograms (two states of the specimen) corresponding to the two UV laser pulses with a short time separation (10–50 μs). Subtraction of the phase distribution in two digital holograms gives a fringe phase map that shows the change in deformation of the specimen between the recordings. The advantage of the proposed method is two fold. First, the use of a shorter wavelength results in a higher sensitivity. Second, owing to the induced synchronous built-in optical excitation, the specimen is not subjected to any external physical excitation devices. Experimental results are presented on identification and evaluation of defects in thin metal sheets
Optimization of grinding process parameters using enumeration method
No full textThe selection of grinding parameters if done on hit and miss method not only wastes time but also leads to an inefficient process. The parameters should be so selected so as to result in an optimal solution. In this paper the “enumeration” method is discussed. By using this approach the user can select input parameters to achieve an optimal cutting condition
Measurement of Parallelism of Suriaces of a Transparent Sample.
No full textAn interferometric method for the measurement of parallelism of the end faces of a transparent material is described. It is based on the measurement of fringe displacement caused by the wedge angle of the material by using the Lau effect
Experimental Feasibility Study of Fiber Optic Extrinsic Fabry-Perot Interferometric Sensor for Civil Structures and other Applications
No full textAn experimental bench set up of a fibre optic Extrinsic Fabry-Perot Interferometer (EFPI) sensor was realised and its feasibility demonstrated in an open configuration. The basic interferometric coupling between the sensing and reference reflections from a Fabry Perot (FP) air cavity realised between two fibre ends was so achieved that the sensor exhibits extreme sensitivity to external disturbances. The study reports about the salient features, scope, operating principle, and details of the experimental set-up of a fibre optic EFPI. The results of qualitative studies undertaken for sensing vibrations due to external disturbances under different situations and its further refinement/modifications for applications in health monitoring of structures are also discussed
Comparative Study of Various Endoscopes for Pulsed Digital Holographic Interferometry
No full textA comparison of several endoscopes as object image carriers in pulsed digital holography is presented. Three multicore flexible fiber endoscopes of different spatial resolution and one rigid endoscope are investigated. The four endoscopes are integrated in a setup for the recording of digital holograms on a CCD camera. A double-pulsed ruby laser is used as the light source. A spatial carrier is introduced by an off-axis reference beam, which permits quantitative evaluation of the phase difference between two holograms recorded with a short time separation (5–600 μs). From reported studies it may be inferred that the quality of the phase maps so derived from digital holographic interferometry has a strong correlation to the spatial resolution of the multicore fiber used in these endoscopes. With the endoscopic technique combined with pulsed digital holography a number of useful applications (in areas such as medical endoscopy, micromechanics, and microelectronics) are envisaged for which access to the objects of interest is otherwise difficult
Global description of edge patterns using moments
No full textShape recognition has traditionally been accomplished using well bounded segmented regions or their closed contours. In this way, the internal edge details of the objects are ignored. There are cases such as in character recognition and in object recognition when patterns are not closed contours. In this paper, such patterns are defined as edgepatterns and Edge Standard Moments (ESM) are developed which are invariant to location, scale and rotation. Results of patterns matching with character recognition and polyhedral object recognition are presented
Edge-moment-based three-dimensional object recognition
No full textA novel global shape description technique based on edge
segments is applied for recognition of 3-D objects. This approach extends the boundary-based representation to generalized edge patterns that may have segments that are straight, curved, crossing, or open. A novel representation of edge moments is used for shape description, with a novel normalization. The invariant features may be formed by using standard (invariant) moments. This has led to the development of edge standard moments. The power of the method is demonstrated for the recognition of 3-D polyhedral objects
RECOGNITION OF LINE PATTERNS USING MOMENTS
No full textMost reliable features that can be readily extracted from intensity images comprising of line segments: both straight and curved. Most applications rely on the recognition of such line patterns. Fourier Descriptors, which are widely used, require the patterns to be closed and binary. Other techniques which are based on the chain codes or vectorisation have quantisation errors and therefore need additional preprocessing. Furthermore, almost all the
description methods for line patterns inherently have an element of "tracing" involved in them and their generalisation to grey scale or multi-coloured patterns is limited.
A novel global shape description technique based on edge segments is used for recognition of line patterns. This
approach extends the boundary based representation to generalised edge patterns that may have segments which
are straight, curved, crossing or open. A novel representation of Edge Moments (EM) is used for shape description with a novel normalisation. The invariant features may be formed by using standard (invariant) moments. This has led to development of Edge standard moments (ESM). The power of the method is demonstrated for
recognition of 3-D polyhedral objects