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2002
Fast precise moisture measurement in mineral process plants, has long been a difficult problem. In this master thesis a foundation for a new way of measurement using transmission line theory, is laid out. Macroscopic electro-magnetic properties of the measured sample can be linked to those of the individual constituents of the sample. Thus one is believed to be able to do a precise estimate of the amount of moisture in a sample. In our case the samples are moist magnetite concentrate. The characterization of sample macroscopic electro-magnetic properties is done by using a coaxial cell, performing frequency spectra measurement. In this master thesis, the electrical behavior that links the measured data to the macroscopic electro-magnetic properties is examined. It exists two setups, one inductive and one capacitive. The DC resistivity of the moist magnetite concentrate is determined and some interesting phenomena, suggested to be self potential were discovered. This phenomenon is in general known from geochemistry of mineral rich clays. This made the measurements of resistivity tricky to perform, some measurements were achieved and a new relation between moisture of the moist magnetite concentrate and resistivity is presented. Studies have been performed on the history of attempts of solving this problem, as well as current relevant research. Reference samples have been prepared in a geotechnical laboratory. Impedance frequency behavior of the measurement equipment is measured and presented, with different curves for different moisture content. From these measurements it is obvious that the moisture affects the impedance of the measurement equipment and thus it is possible to use this method to measure moisture content, if one can determine the electrical model which describes the measurement system. A few equivalent circuits of transmission lines have been discussed, and one was chosen to represent the purely coaxial part of the coaxial cell. Other parts have been modeled with other elements of AC theory. A new electrical model for the coaxial probe is proposed, based on LC resonances. Some Comsol FEM simulations have been performed on the coaxial cell, as well as on electric property sensors. Ideas to designs of electrical sensors are discussed. It is mainly the geometry which has been investigated. First it was proposed that a phenomenon of resonance occurs at the interface of the bottom and coaxial part of the cell, LC resonance. The resonance effect has later been investigated and identified as quarter wavelength resonance, due to the length of the measurement cell and change of wave velocity due to wave propagation in MUT. Simulations of proposed circuit equivalents in Orcad with PSpice have given some correlation with measured data for dry and non-conducting samples. There is still work to be done, to complete an accurate mathematical model of the system.
Soil Science Society of America Journal
Calibration of Hydra Impedance Probes using Electric Circuit Theory2009 •
2014 •
This paper describes a sensor dedicated to measuring the vertical profile of the complex permittivity and the temperature of any medium in which sensor electrodes are inserted. Potential applications are the estimate of the humidity and salinity in a porous medium, such as a soil. It consists of vertically-stacked capacitors along two conductive parallel cylinders of 5 cm in diameter and at a 10-cm distance to scan a significant volume of the medium (∼1 L). It measures their admittances owing to a self-balanced impedance bridge operating at a frequency in the range of 1–20 MHz, possibly 30 MHz. Thanks to accurate design and electronic circuit theory-based modeling, the determination of the admittances takes into account all distortions due to lead and bridge electromagnetic effects inside the sensor when working at high frequencies. Calibration procedures and uncertainties are presented. The article also describes developments to make the present sensor autonomous on digital acquisition, basic data treatment and energy, as well as able to transfer stored data by a radio link. These steps in progress are prerequisites for a wireless network of sensors.
2011 •
Este artículo presenta una implementación del método de línea de transmisión/reflexión para determinar las propiedades electromagnéticas intrínsecas de materiales desconocidos con permeabilidad magnética relativa distinto de uno. Con un analizador vectorial de redes (AVR), los coeficientes de dispersion de la energía transmitida y reflejada se miden simultáneamente para extraer la permitividad eléctrica relativa y la permeabilidad magnética relativa. La tecnica de extracción clásica de Nicolson-Ross-Weir en el dominio de la frecuencia es explicada extensamente y presentada tal que las ecuaciones pueden ser fácilmente implementadas mediante el Software libre GNU OCTAVE. El desfasaje en los planos de referencia y las mediciones de calibración del conector, son realizadas por un AVR de bajo costo sin la funcion de incorporación. Una línea de transmisión coaxil con conectores N hembra es usada por su bajo costo, con el porta muestras de fácil construcción. El procedimiento de medición e...
IEEE Transactions on Microwave Theory and Techniques
Noninvasive electrical characterization of materials at microwave frequencies using an open-ended coaxial line: test of an improved calibration technique1990 •
Soil Science Society of America Journal
Calibration of Capacitance Probe Sensors in a Saline Silty Clay Soil2004 •
ALMA AI, via Galliera 3, Bologna Sala Kelsen, II piano
London - John Murray - Albemarle Street + James Wallton - Gower Streer
The ancient history of the East. From the earliest times to the conquest by Alexander thte Great. Including Egypt, Assyria, Babylonia, Media, Persia, Cappadocia , Armenia, Asia Minor, Syria, Israel Phœnicia - Philip Smith -an Exhaustive book with each Ch. pg. Header listing 100 Subjects ! 571 PagesAltamira XC
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Using concept maps to assess change in teachers’ understandings of algebra: a respectful approach2007 •
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