Time-frequency analysis of multiple fringe and nonsinusoidal signals obtained from a fiber-optic vibration sensor using an extrinsic Fabry-Perot interferometer

In the case of multiple fringes and complex frequency measurements, the frequency of the output signal changes rapidly when the vibration changes and frequency breakdown takes place at the turning point. For a particular vibration signature containing many frequency components at different time intervals, it is often difficult to trace the direction of the vibration as well as individual frequency peaks. In such cases, advanced signal-processing scheme is necessary to decode the vibration signature. This paper investigates the data interrogation technique for multifrequency and complex signals of surface Vibration obtained from an extrinsic Fabry-Perot interferometric sensor. In this paper, wavelet transform (WT)-based signal processing methodology has been employed to count of optical fringes with special reference to signals having subfringes. A WT-based tool has also been developed for unambiguous identification of frequency components from a nonsinusoidal vibration. The results of such WT-based analyses are presented, and merits as well as demerits of the proposed methods are discussed

Detection of Ammonia Gas Molecules in Aqueous Medium by Using Nanostructured Ag-Doped ZnO Thin Layer Deposited on Modified Clad Optical Fiber

The synthesis of Ag-doped ZnO nanorod employing hydrothermal process over modified cladd optical fiber is reported. The developed material is characterized using X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FESEM), and Brunauer-Emmett-Teller (BET)analysis to evaluate the morphology and the nature of nanorod formed. The initial performance of the coated modified clad optical fiber toward detection of ammonia gas in aqueous solution is also presented. The sensing performance revealed that the developed material possess improved sensitivity toward ammonia gas at room temperature compared to Ag doped nanowires containing optical fiber sensor

Impact of targeted interventions on heterosexual transmission of HIV in India

<p>Abstract</p> <p>Background</p> <p>Targeted interventions (TIs) have been a major strategy for HIV prevention in India. We evaluated the impact of TIs on HIV prevalence in high HIV prevalence southern states (Tamil Nadu, Karnataka, Andhra Pradesh and Maharashtra).</p> <p>Methods</p> <p>A quasi-experimental approach was used to retrospectively compare changes in HIV prevalence according to the intensity of targeted intervention implementation. Condom gap (number of condoms required minus condoms supplied by TIs) was used as an indicator of TI intensity. Annual average number of commercial sex acts per female sex worker (FSW) reported in Behavioral Surveillance Survey was multiplied by the estimated number of FSWs in each district to calculate annual requirement of condoms in the district. Data of condoms supplied by TIs from 1995 to 2008 was obtained from program records. Districts in each state were ranked into quartiles based on the TI intensity. Primary data of HIV Sentinel Surveillance was analyzed to calculate HIV prevalence reductions in each successive year taking 2001 as reference year according to the quartiles of TI intensity districts using generalized linear model with logit link and binomial distribution after adjusting for age, education, and place of residence (urban or rural).</p> <p>Results</p> <p>In the high HIV prevalence southern states, the number of TI projects for FSWs increased from 5 to 310 between 1995 and 2008. In high TI intensity quartile districts (n = 30), 186 condoms per FSW/year were distributed through TIs as compared to 45 condoms/FSW/year in the low TI intensity districts (n = 29). Behavioral surveillance indicated significant rise in condom use from 2001 to 2009. Among FSWs consistent condom use with last paying clients increased from 58.6% to 83.7% (p < 0.001), and among men of reproductive age, the condom use during sex with non-regular partner increased from 51.7% to 68.6% (p < 0.001). A significant decline in HIV and syphilis prevalence has occurred in high prevalence southern states among FSWs and young antenatal women. Among young (15-24 years) antenatal clinic attendees significant decline was observed in HIV prevalence from 2001 to 2008 (OR = 0.42, 95% CI 0.28-0.62) in high TI intensity districts whereas in low TI intensity districts the change was not significant (OR = 1.01, 95% CI 0.67-1.5).</p> <p>Conclusion</p> <p>Targeted interventions are associated with HIV prevalence decline.</p

Prospects for Fibre Bragg Gratings and fabry-perot interferometers in fibre-optic vibration sensing

Vibration monitoring of machinery is reducing the overall operating costs of industrial plants. Conventional vibration sensors, based on capacitive or piezoelectric principles, are limited in application due to the problem of electrical isolation. Fibre-optic based instrumentation is thus an attractive alternative method of vibration measurement in the vicinity of electrical substation. This paper discusses several techniques of vibration sensing using optical fibre technology and assesses their potential for use on electromechanical equipment. Firstly an overview of sensor based on In-Fibre Bragg Gratings is presented, and its potential for the measurement of strain and vibration is assessed. Secondly, vibration sensing using fibre-optic intensity-based measurement is presented and then Fabry-Perot Interferometer (FPI) for vibration sensing is critically reviewed. Of these, the FPI is the most attractive since it can easily be configured within a reflective fibre-optic probe. However, reported FPI sensors have been highly sensitive to measurement errors caused by mechanical vibration, temperature, and acoustic waves. This paper reviews technological developments of FPI to vibration sensing in extreme electromechanical environments and also for non-contact measurement. Finally this paper presents an overview of dual-wavelength technique for assessment of vibration signature. (C) 2004 Elsevier B.V All rights reserved

Non-contact vibration measurement based on an extrinsic Fabry–Perot interferometer implemented using arrays of single-mode fibres

This paper presents a novel non-contact vibration-monitoring technique based on transient measurements from a Fabry–Perot interferometric displacement sensor implemented using single-mode fibre. Two different extrinsic sensor configurations are demonstrated using one-fibre and two-fibre arrays of 4/125 μm single-mode fibre butted with a gradient-index lens. The design concept, mathematical modelling and results are demonstrated. The sensor configurations exploit fringe discrimination over multiple orders. A working range up to 14 μm is demonstrated for the measurement of vibration amplitude at 1 kHz excitation using the one-fibre configuration. Similar tests using the two-fibre configuration indicated a displacement measurement up to 65 μm and vibration measurement up to 7 μm at 2.5 kHz. The two-fibre configuration is also assessed in conjunction with an absolute scheme for the measurement of vibration using dual-wavelength signal processing. In this scheme, two wavelength signals are captured from the sensing interferometer to provide unambiguous measurement of vibration direction

Prospects for speckle-pattern based vibration sensing in electromechanical equipment

Condition monitoring of heavy electromechanical equipment such as electrical switchgear is increasingly reliant on vibration sensing technology. Of applicable optical methods, electronic speckle-pattern interferometry (ESPI) is established as a sensitive whole-field technique for monitoring surface vibration. Such systems incorporate video signal processing to offer automated real-time measurement of vibrational amplitude and phase. Speckle fluctuations, often a source of noise, may also be utilized within multimode fibres for fast one-dimensional sensing. This paper discusses the optoelectronic processing behind such speckle metrologies, and reviews technological developments suited to vibration monitoring in extreme electromechanical environments. Advances in the technology, particularly in the areas of transient and multiple-frequency response, will be driven by the application and the ability to fabricate industry-compatible system prototypes

Prospects of photonic crystal fiber for analyte sensing applications: an overview

The detection and monitoring of physical, chemical and biomedical parameters are increasingly reliant on fiber-optic sensing technology. Of applicable optical methods, photonic crystal fiber (PCF) sensors show its potential as a sensitive technique in environmental, industrial, food preservation and medical applications. Such a system incorporates the fabrication of a particular PCF, the interaction of wave propagation with the measured field, signal processing to offer automated real-time measurement in terms of the amplitude, phase, polarization and wavelength of spectrum. This article is an endeavour towards giving a brief overview of the development of analyte sensors using PCFs in the last few years. Different kinds of PCF analyte sensors are discussed based on the measuring entity and reported works. This discussion integrates a variety in the nature of the core, metal coating on the PCF and liquid infiltration in the holes. It is also considered to present the phenomena of its internal structure and interference techniques for several applications. Advances in this technology, particularly in the areas of gas sensing, chemical spices and bio analytes, will be discussed in this article with some applications

Prospects of Photonic Crystal Fiber as Physical Sensor: An Overview

Photonic crystal fiber sensors have potential application in environmental monitoring, industry, biomedicine, food preservation, and many more. These sensors work based on advanced and flexible phototonic crystal fiber (PCF) structures, controlled light propagation for the measurement of amplitude, phase, polarization and wavelength of spectrum, and PCF-incorporated interferometry techniques. In this article various PCF-based physical sensors are summarized with the advancement of time based on reported works. Some physical PCF sensors are discussed based on solid core as well as hollow core structures, dual core fibers, liquid infiltrated structures, metal coated fibers, grating incorporated fibers. With the advancement of sensing technology the possibilities of temperature, pressure, strain, twist, curvature, electromagnetic field, and refractive index sensing are discussed. Also, limitations as well as possible solutions and future hopes are outlined

Prospects of Photonic Crystal Fiber as Physical Sensor: An Overview

Photonic crystal fiber sensors have potential application in environmental monitoring, industry, biomedicine, food preservation, and many more. These sensors work based on advanced and flexible phototonic crystal fiber (PCF) structures, controlled light propagation for the measurement of amplitude, phase, polarization and wavelength of spectrum, and PCF-incorporated interferometry techniques. In this article various PCF-based physical sensors are summarized with the advancement of time based on reported works. Some physical PCF sensors are discussed based on solid core as well as hollow core structures, dual core fibers, liquid infiltrated structures, metal coated fibers, grating incorporated fibers. With the advancement of sensing technology the possibilities of temperature, pressure, strain, twist, curvature, electromagnetic field, and refractive index sensing are discussed. Also, limitations as well as possible solutions and future hopes are outlined