An optic fiber-based sensor design is presented, suitable for use at high temperatures (up to 750 C) for measurement of the frequency of dynamic strain having wide magnitude range. The design and optimization of the location of the fiber sensor on a diaphragm structure, in two interferometer configurations is analyzed. The complete signal extraction and evaluation with signal processing electronics and DSP algorithm is realized in low power (under 15 mW). The challenge in the implementation of this technology is the need to perform under difficult industrial conditions namely, very large temperature range, high pressure dynamics, good chemical corrosion resistance, high measuring range, high sensitivity, vibration immunity, and low-power operation.Index Terms-Dynamic strain frequency measurement, flat diaphragm, linear phase demodulation, low-power signal processing, optic fiber interferometer, pseudo-heterodyne demodulation.
In this study, an innovative method is presented for preparing optical fibers for application in fiber optic sensors operating in harsh environments. It is shown, how to attach a metalcoated fiber electrolytically to a metal sensing element, as well as an electroless method for depositing a nickel protective layer on optical fibers. Additionally, the results of the reliability tests of these methods are presented. It is also shown, that by depositing an additional nickel protective layer, it is possible to slow down the oxidation process of the copper coating. Analysis of the conducted experiments allows us to predict, that the connection method investigated and the method of protecting the fiber are robust and may find application in industrial optical sensors.Index Terms-Metal-coated fibers, optical fiber applications, optical fibers, optical fiber sensors, reliability test of fibers, specialty optical fibers.
In this work we present an innovative method of connecting metal coated optical fibers with metal surfaces. The process is based on electrolytic reaction between copper and allows to obtain a robustand inflexible connection. Furthermore reliability tests of such fiber to metal joints have been performed, with the results of mechanical strength and temperature resistance tests presented. Additionally, as accelerated oxidation of copper at elevated temperatures is a major concern in long term temperature stability of the connection, we propose a method of slowing down the oxidation process with chemical nickel coating. Analysis of the obtained results allows us to predict that the investigated connection may find applications in various industrial optical sensors with special focus on harsh environments.
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