admittanz

Admittanz, in electrical engineering and physics, is a complex quantity that describes how readily an electrical network allows current to flow when driven by a voltage. It is the reciprocal of impedance, expressed as Y = 1/Z. The unit is the siemens (S). In most circuit analyses, admittance is written as Y = G + jB, where G is conductance (the real part) and B is susceptance (the imaginary part). G represents resistive conduction, while B captures the net effect of capacitive or inductive elements. Positive B indicates net capacitive behavior, while negative B indicates net inductive behavior. For a purely capacitive element, Y = jωC (B = ωC). For a purely inductive element, Y = -j/(ωL) (B = -1/(ωL)).

In circuit theory, admittance is particularly convenient because it adds for elements connected in parallel. The total admittance of a network is the sum of the individual admittances. This enables straightforward use of nodal analysis and the construction of admittance matrices in solving for node voltages and branch currents. The concept is also essential in frequency-domain analysis, impedance spectroscopy, and RF circuit design.

Common examples include a resistor and capacitor in parallel, which yields Y = 1/R + jωC. More generally, any two-terminal network has a complex Y that depends on frequency. The magnitude and phase of Y describe how the current responds to an applied voltage at a given frequency.

Origin and usage: Admittanz is the standard term in German-language literature for this concept, while English texts typically use “admittance.” The concept stands alongside impedance as a fundamental descriptor of AC circuits.