Educação matemática pela arte
Gusmão, Lucimar Donizete
2013-08-28
Search results
30 records were found.
Two complimentary optical fiber strain sensors employing lock-in techniques are presented. The first system interrogates an array of long gauge length sensors, defined by broadband optical reflectors and employs multiplexing in the time domain. The second system operates over shorter gauge lengths using multiple narrowband reflectors and wavelength-division-multiplexing. The first system tracks minima in the amplitude response produced from the superposition of two sinusoidal subcarrier waves. The second uses an acousto-optic-tunable-filter (AOTF) to track the peak reflective wavelength of an array of Bragg gratings. Both systems are constructed using telecommunications components. Together, the systems may be used to examine both line-integrated strain (or temperature) over long gauge lengths and local strain at a number of selected d...
We report on recent progress on developing a complimentary pair of optical-fibre-based sensor methods for structural monitoring, for potential application in aerospace composites or civil engineering structures. Particular emphasis is placed on a method for addressing arrays of grating sensors using an acousto-optic tunable filter (AOTF), and on a longer-gauge-length system based on optical-time-domain reflectometry (OTDR). The AOTF possesses the desired frequency-agile capability for random multiplexed access and has a wide tuning range. It is suitable for both dynamic and quasi-static strain sensing. The scheme involves frequency-shift-keying of the RF drive to an AOTF to track the wavelength changes of gratings. We are currently constructing a compact interrogation system based on the concept.
For many sensing applications, it i...
The paper discusses two complimentary optical fibre sensing techniques which have been researched for structural monitoring applications. The short-gauge-length sensor system is based on fibre gratings and has achieved a strain resolution below 1 microstrain. The long-gauge-length sensor system has achieved 100 micron spatial resolution using a new OTDR technique. Results are presented for surface-mounted and embedded sensors. Both sensors systems can be multiplexed to make more efficient use of the interrogating unit. Their system designs should be capable of being developed to meet real engineering applications
We have demonstrated a new frequency-agile system for the interrogation of in-fibre Bragg grating sensors. The scheme involves frequency shift keying (FSK) of the RF drive to an acousto-optic tunable filter (AOTF) to track the wavelength shifts of a Bragg grating. Theoretical studies to derive the optimum frequency deviation for achieving maximum sensitivity are given, and experimental results are presented for temperature measurement. This technique is capable of rapid, random access and very wide tuning range, showing the potential for interrogating multiplexed arrays of Bragg-grating-based sensors
A new method for the simultaneous interrogation of conventional two-beam interferometers and Bragg grating sensors is proposed and demonstrated. An unbalanced Mach-Zehnder interferometer illuminated by a low coherence source is used to act as a wavelength tunable source for the grating and as a path matched filter for a Fizeau cavity. The technique gives high phase resolution. The grating sensor gave a dynamic strain resolution of approximately equals 0.05με/√Hz at 20Hz and the interferometric resolution was better than 1 mrad/√Hz at 20Hz, corresponding to an rms mirror displacement of 0.08nm
A novel approach for the interrogation of multiplexed fiber optic Bragg grating sensors is described. Signal recovery is achieved by matching a receiving grating to a corresponding sensor grating. As a demonstration, the technique is applied to strain sensing
As part of a project to optimise hybrid laminates for resistance to fatigue failure, arrays of fibre Bragg gratings are being used to monitor small-scale strain perturbations in composite materials. A remote multiplexed sensing system with 40 remote sensing sites using fibre optic technology, has been developed to monitor the strain field developed across the composite lamina of a hybrid laminate in the vicinity of a fatigue crack. Developed primarily for fatigue-critical aerospace applications, i.e. fuselage and lower wing skins, the hybrid laminates are orthotropic materials having lower density and higher strength than a simple alloy monolith without reinforcement. Fatigue crack growth in hybrid laminates is a complex process that involves a combination of delamination and fibre bridging. The fibre optic system has been applied to t...
Distributed optical fibre temperature sensing (DTS) provides an elegant way of monitoring the temperature at many points without necessitating the accurate positioning of individual discrete sensors. This paper demonstrates recent advances in distributed temperature sensing based on spontaneous Brillouin scattering. A high spatial and temperature resolution is achieved by exploiting a novel low cost detection system. The experimental configuration consists of two key components; a Q-switched laser source to generate the backscattered signal and the low cost detection system which comprises an in-fibre double pass Mach-Zehnder interferometer and a sensitive InGaAs APD connected to a computer based averaging system. It is the relative low cost of these components which has made the Brillouin based temperature sensor so attractive for com...
Monitoring the concentration of gaseous O(2), CO(2) and CH(4) is needed for many environmental, medical and industrial applications. We model the COSM method of correlation spectroscopy, where two broadband light sources are intensity modulated in antiphase, the first being directed via the measurement cell after first passing through the reference sample, the second being more directly-coupled. The subsequent difference in fractional attenuation in the measurement cell indicates the concentration of target gas in this cell. Using data from the HITRAN database, comprehensive analyses are presented to predict the optical modulation index and the signal to noise ratio at the detector, as a function of optical filter properties, and for various gas temperatures and pressures (concentrations). The predicted detection sensitivities are pres...
We describe a compact, pulsed, broadband source for sensing using ASE from Er gas detection.
