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The electrical impedance of the speaker varies with the back EMF and thus with the applied frequency. The impedance is at its maximum at F s, shown as Z max in the graph. For frequencies just below resonance, the impedance rises rapidly as the frequency increases towards F s and is inductive in nature.
In electrical engineering, impedance is the opposition to alternating current presented by the combined effect of resistance and reactance in a circuit. [1]Quantitatively, the impedance of a two-terminal circuit element is the ratio of the complex representation of the sinusoidal voltage between its terminals, to the complex representation of the current flowing through it. [2]
The visual frequency orientation (clockwise vs. counter-clockwise) enables one to differentiate between a negative / capacitance and positive / inductive whose reflection coefficients are the same when plotted on a 2D Smith chart, but whose orientations diverge as frequency increases.
In general the elements of the Z-parameter matrix are complex numbers and functions of frequency. For a one-port network, the Z-matrix reduces to a single element, being the ordinary impedance measured between the two terminals. The Z-parameters are also known as the open circuit parameters because they are measured or calculated by applying ...
Practical impedance-matching devices will generally provide best results over a specified frequency band. The concept of impedance matching is widespread in electrical engineering, but is relevant in other applications in which a form of energy, not necessarily electrical, is transferred between a source and a load, such as in acoustics or optics.
Most impedance analyzers come with a reactance chart [5] which shows the reactance values for capacitive reactance X C and inductive reactance X L for a given frequency. The accuracy of the instrument is transposed on the chart to allow the user to quickly see what accuracy they can expect for a given frequency and reactance.
The characteristic impedance () of an infinite transmission line at a given angular frequency is the ratio of the voltage and current of a pure sinusoidal wave of the same frequency travelling along the line. This relation is also the case for finite transmission lines until the wave reaches the end of the line.
SWR is used as a measure of impedance matching of a load to the characteristic impedance of a transmission line carrying radio frequency (RF) signals. This especially applies to transmission lines connecting radio transmitters and receivers with their antennas, as well as similar uses of RF cables such as cable television connections to TV receivers and distribution amplifiers.