Wyniki 1-4 spośród 4 dla zapytania: authorDesc:"Jan NEDOMA"

Measurement of electric current using optical fibers: A Review DOI:10.15199/48.2017.11.30

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The fiber-optic sensor is based on the use of Faraday's magneto-optical effect (year of discovery is 1845), in which there is a magnetic rotation of plain of the polarized light, see Figure 1. However, the use of this phenomenon for the measurement of electrical quantities has only occurred thanks to the development of fiber optic technology. The rate of twisting of the polarization plane is directly proportional to the path d, after which the light in the given environment spreads and size of the components of the vector of magnetic induction B in the direction of light propagation. The orientation of the vector determines the meaning of the polarization plane. The size of the angle of rotation β, by which the polarization plane is rotated (see Fig. 1) can easily be calculated by a simple relationship (1): (1) 􀟚 􀵌 V ∗ B ∗ d, where: V - Verdet constant, B - density of magnetic induction, d - length of path The Verdet constant depends on the wavelength of the light and it is an optical "constant" that describes the strength of the Faraday-effect for a particular material. Fig.1. Basic scheme of the Faraday-effect. Fiber-optic current sensors are referred to as FOCS (Fiber-Optic Current Sensor). Figure 2 shows the principle of the fiber-optic current sensor FOCS. FOCS benefits are high accuracy, high bandwidth: detection of current ripple and transients, wide temperature range, full digital processing, uni- or bi-directional current measurement, analogue and digital outputs, easy to install, adaptable shape of sensing head, small size and weight, no magnetic centering necessary, no magnetic overload problem, immunity to electromagnetic interference and many others. Fig. 2. Principle of the fiber-optic current sensor FOCS An important application area of FOCS is the metallurgical industry, where an electrolytic process is used to obtain precious metals. Typical electrolyzers work with DC (D[...]

Tram Type Influence on the Frequency Spectrum Character of the Subsoil Dynamic Response DOI:10.15199/48.2018.11.22

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Standard seismic stations equipped with speed or acceleration sensors are commonly used to measure the natural, induced and technical seismicity [1, 2, 3, 4]. Such a station, for example, monitors the dynamic response of buildings or the dynamic response of rock masses due to various sources [5, 6, 7] and, on the basis of such measurements, the possible damage to buildings or the influence of vibrations on humans is assessed according to the technical standards or the attenuation parameters of the rock environment are determined [8, 9, 10]. The obtained results of such seismic measurements are in the form of wave images and frequency spectra wherein maximum values or maximum frequency values are monitored in the wave images at a certain time interval, and the predominant frequency of the dynamic load source is determined from the frequency spectra [11]. The frequencies themselves then play a very significant role in the possible structural damage to buildings, especially if the resonance of the building's own frequency and the dynamic load source frequency occur. Long-term effects of vibrations to buildings may result in cracks in the plaster, masonry and, possibly, other faults, e.g. in vibration-sensitive equipment [12, 13, 14]. One of the most common sources of vibrations in the intravilan of large cities are the passing trams [15, 16, 17]. The intensity of these vibrations is mainly dependent on the type and age of the passing trams, but also on the structure and condition of the trackbed and the local geological structure [18, 19]. The range of maximum amplitudes of velocity, acceleration and frequency of the measured values for the rail transport in general are defined, for example, in International Standard ISO 4866:2010 [20]:  the maximum range of the vibration velocity amplitude: 0.2-50 mm.s-1  the maximum range of the acceleration amplitude: 0.02-1 m.s-2  the frequency range: 1-80Hz Th[...]

Thermal analysis of PDMS light bulbs with a luminophore DOI:10.15199/48.2018.12.02

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1. Introduction Polydimethylsiloxane (hereinafter referred to as PDMS) has been primarily designed to encapsulate photovoltaic cells, printed circuit boards, transformers, current sources, thermally stressed cables, optical connectors, etc. [1-3]. Later, it also began to be used for other purposes because it conveniently combines mechanical, electrical and optical properties. In the 3D printing technology using the method of DPL (Digital Light Processing), it is used for the production of a printing base and is also widely used for fine lithography techniques, especially for the creation of microfluidic and microengineering systems - MEMS (Micro Electro Mechanical Systems). For example, the authors of the publication [4] describe an optical biopsy microsystem technology that has smaller dimensions (11.2 x 18.6 mm) compared to other systems and reduced power consumption. The microsystem includes an image magnification optical microsystem (IMOM) and light emitting diodes (LED). Microlenses made from PDMS are integrated into the IMOM subsystem to achieve image magnification and to improve LED illumination. Other interesting solutions in the field of MEMS systems are described by authors of publications [5-10]. Publication [11] describes a new construction of a hybrid multichannel optical sensor system designed to monitor patient's vital functions. The noninvasive measuring probe is based on two FBGs encapsulated in the polymer; the authors selected the PDMS polymer because it is inert. There was no deformation of the FBG sensors in the vulcanization process; after the vulcanization, a fourfold increase in temperature sensitivity was observed compared to the nonencapsulated FBG. The probe and the associated multichannel system offer the ability to monitor the basic vital functions (body temperature, heart rate and respiratory rate) in up to 128 patients. The same issue is addressed by the authors of publications [12-15]. Ot[...]

Micro-bending sensor made from polydimethylsiloxane DOI:10.15199/48.2019.06.02

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Polydimethylsiloxane (PDMS) is a polymeric material on the basis of silicone, which is used in many scientific fields for various applications. One of the key characteristics is the excellent heat resistance of the material, under long term heat exposure PDMS resists temperatures of 200 °C and for short term exposure temperatures up to 350 °C. This is why it is very often used in electronics for pouring plates of wide connectors, transformers, power sources and so on. The authors of publication [1] concentrate on one concrete type of polydimethylsiloxane identified as Sylgard 184 and check its mechanical characteristics at various hardening temperatures (25 - 200 °C). The results show that the hardening temperature can change certain mechanical characteristics of PDMS. Samples prepared at a hardening temperature of 25 °C showed a hardness value of 43.8 Shore A, whereas samples prepared at a temperature of 200 °C showed a hardness value of 54 Shore A. In the construction of sensors (particularly pressure sensors) this information is very important because the hardness of the material undoubtedly affects the resulting behaviour of the sensor. Publication [2] describes a magnetic pole sensor which is constructed from two types of PDMS and a multimodal optical fibre with iron nano-particles. The cover of the sensor is formed by hard polydimethylsiloxane and the internal part of the sensor is filled with a soft silicon gel based on PDMS, so that it is possible using a magnetic field to deflect the first optical fibre with the iron nano-particles. The deviation of the optical fibre has an output of lowering the optical performance. A sensor set up like this can detect a magnetic field up to 0.3 T. A slightly altered sensor can also for instance detect vibrations up to 100 Hz, as is shown in publication [3]. A simple form of pressure sensor made from PDMS is shown in publication [4]. When manufacturing the sensor it is very impo[...]

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