Iulian Rosu, YO3DAC / VA3IUL, http://www.qsl.net/va3iul The term Impedance is a general term which can be applied to any electrical ethnicity which impedes (obstruct) the flow of the current. Oliver Heaviside (1850-1925) coined Impedance definition, as well as many other terms of art in electromagnetic theory: Inductance, Admittance, Conductance, Permeability, Permittance (Susceptance), Reluctance, Electret. Oliver Heaviside also reformulated Maxwell's field equations in terms of electric and magnetic forces and energy flux, and independently co-formulated Vector Analysis, which is needed to express the impedance in coordinates. Impedance Matching was originally developed for electrical power, but can be applied to any other field where a form of energy (not necessarily electrical) is transferred between a source and a load. • The first Impedance Matching concept in RF domain was related to Antenna Matching. Designing an antenna can be seen as matching the free space to a transmitter or to a receiver. Impedance Matching is always performed between two specified terminations • The main purpose of Impedance Matching is to match two different terminations (Rsource and RLoad) through a specific pass-band, without having control over stop-band frequencies. We may assume that component losses are negligible but parasitic effects need to be considered. Reactance and LC Resonance • Reactance X is a measure of the opposition to the current of Capacitance C and Inductance L. Reactance is measured in ohms and varies with the frequency of the AC signal. • Reactance takes two forms: Inductive (XL), and Capacitive (XC). XL = ω L = 2 π f L XC = 1 / (ω C) = 1 / (2 π f C) Where: ω is angular frequency, f is frequency, L is inductance, and C is capacitance. • When the magnitudes of L reactance and C reactance are equal, the L-C pair resonates. • At resonance the net reactance of a series-connected L-C circuit is zero (a short circuit), and the net reactance of a parallel-connected L-C circuit is infinite (an open circuit). • The resonant frequency is getting by equating the magnitudes of the L and C reactances (XL = XC) Quality-Factor The Quality Factor Q serves as a measure of a reactance's purity (how close it is to being a pure reactance, and not a resistance), and is defined as the ratio of the energy stored in a component to the energy dissipated by the component. • Q is a dimensionless unit and is expressed function of reactance X and resistance R as: Q = X / R • It should be stated that Q of the L-C circuit is defined at circuit resonance. • If the circuit reactance is plotted as a function of frequency, the slope of the reactance at resonance is a measure of Q. Resonant frequency is given by:
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International Journal of Engineering
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The Arab Journal of Scientific Research
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Impedance spectroscopy (IS) is a measurement technique which can be applied to any physical and electrochemical system modelled by an equivalent circuit consisting of resistor (R), capacitor (C) and inductor (L). In general, impedance of a physical system refers to all frequency dependent and independent resistivity effects opposed to the flow of current. In this work, theoretical real and complex impedance data are obtained by using Origin 7.0 programme for typical ac equivalent circuit models proposed for pn and pin junction type diodes in the frequency range in between 5 Hz -13 MHz. The dif-ferent steps of impedance data analysis are described with the help of Cole-Cole (Nyquist) and Bode graphical methods.
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