admittance [ədˈmɪt^əns]

1. the right or authority to enter

2. the act of giving entrance (Electronics) (Physics / General Physics)

3. (Engineering / Electrical Engineering) Electrical engineering the reciprocal of impedance, usually measured in siemens. It can be expressed as a complex quantity, the real part of which is the conductance and the imaginary part the susceptance Symbol y

http://whatis.techtarget.com/definition/admittance-Y

admittance (Y)

Part of the Electronics glossary:

Admittance (symbolized Y ) is an expression of the ease with which alternating current ( AC) flows through a complex circuit or system. Admittance is a vector quantity comprised of two independent scalar phenomena: conductance and susceptance .

Conductance, denoted G , is a measure of the ease with which charge carriers can pass through a component or substance. The more easily the charge carriers move in response to a given applied electric potential, the higher the conductance, which is expressed in positive real-number siemens . Conductance is observed with AC and also with direct current ( DC ).

Susceptance, denoted B , is an expression of the readiness with which an electronic component, circuit, or system releases stored energy as the current and voltage fluctuate. Susceptance is expressed in imaginary number siemens. It is observed for AC, but not for DC. When AC passes through a component that contains susceptance, energy might be stored and released in the form of a magnetic field, in which case the susceptance is inductive (denoted - jB _L ), or energy might be stored and released in the form of an electric field, in which case the susceptance is capacitive (denoted + jB _C ).

Admittance is the vector sum of conductance and susceptance. Susceptance is conventionally multiplied by the positive square root of -1, the unit imaginary number called symbolized by j , to express Y as a complex quantity G - jB _L (when the net susceptance is inductive) or G + jB _C (when the net susceptance is capacitive).

In parallel circuits, conductance and susceptance add together independently to yield the composite admittance. In series circuits, conductance and susceptance combine in a more complicated manner. In these situations, it is easier to convert conductance to resistance, susceptance to reactance, and then calculate the composite impedance.

Also see conductance , reactance , resistance , impedance , ohm , siemens , henry , andfarad .

http://en.wikipedia.org/wiki/Admittance

Admittance

From Wikipedia, the free encyclopedia

In electrical engineering, the admittance (Y) is a measure of how easily a circuit or device will allow a current to flow. It is defined as the inverse of the impedance (Z). The SI unit of admittance is the siemens (symbol S). Oliver Heaviside coined the term in December 1887.^[1]

$Y = Z^{-1} = 1/Z \,$

where

Y is the admittance, measured in siemens

Z is the impedance, measured in ohms

Note that the synonymous unit mho, and the symbol ℧ (an upside-down uppercase omega Ω), are also in common use.

Resistance is a measure of the opposition of a circuit to the flow of a steady current, while impedance takes into account not only the resistance but also dynamic effects (known as reactance). Likewise, admittance is not only a measure of the ease with which a steady current can flow, but also the dynamic effects of the material's susceptance to polarization:

$Y = G + j B \,$

where

$Y$ is the admittance, measured in siemens (a.k.a. mho, the inverse of ohm).
$G$ is the conductance, measured in siemens.
$B$ is the susceptance, measured in siemens.
$j^2 = -1$

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[edit]Conversion from impedance to admittance

Parts of this article or section rely on the reader's knowledge of the complex impedance representation of capacitors andinductors and on knowledge of the frequency domain representation of signals.

The impedance, Z, is composed of real and imaginary parts,

$Z = R + jX \,$

where

R is the resistance, measured in ohms

X is the reactance, measured in ohms

$Y = Z^{-1}= \frac{1}{R+jX} = \left( \frac{R}{R^2+X^2} \right) + j\left(\frac{-X}{R^2+X^2}\right)$

Admittance, just like impedance, is a complex number, made up of a real part (the conductance, G), and an imaginary part (the susceptance, B), thus:

$Y = G + jB \,\!$ ,

where G (conductance) and B (susceptance) are given by:

$G = \Re(Y) = \left( \frac{R}{R^2+X^2} \right)$

$B = \Im(Y) = \left( \frac{-X}{R^2+X^2}\right)$

The magnitude and phase of the admittance are given by:

$\left | Y \right | = \sqrt {G^2 + B^2} = \frac {1} {\sqrt {R^2 + X^2} } \,$

$\angle Y = \arctan \left( {\frac{B}{G}} \right)= \arctan \left( {\frac{-X}{R}} \right)$

where

G is the conductance, measured in siemens

B is the susceptance, also measured in siemens

Note that (as shown above) the signs of reactances become reversed in the admittance domain, i.e. capacitive susceptance is positive and inductive suceptance is negative.

[edit]Admittance in mechanics

In mechanical systems (particularly in the field of haptics), an admittance is a dynamic mapping from force to motion. In other words, an equation (or virtual environment) describing an admittance would have inputs of force and would have outputs such as position or velocity. So, an admittance device would sense the input force and "admit" a certain amount of motion.

Similar to the electrical meanings of admittance and impedance, an impedance in the mechanical sense can be thought of as the "inverse" of admittance. That is, it is a dynamic mapping from motion to force. An impedance device would sense the input motion and "impede" the motion with some force.

An example of these concepts is a virtual spring. The equation describing a spring is Hooke's Law,

$F = -kx \,$

If the input to the virtual spring is the spring displacement, x, and the output is the force that the virtual spring applies, F, then the virtual spring would be classified as an impedance. If the input to the virtual spring is the force applied to the spring, F, and the output is the spring displacement, x, then the virtual spring would be classified as an admittance.

[edit]Admittance in geophysics

The geophysical conception of admittance is similar to that described above for mechanical systems. The concept is primarily used for describing the small effects of atmospheric pressure on earth gravity. Studies have also been carried out regarding the gravity of Venus.^[2] Admittance in geophysics takes atmospheric pressure as the input and measures small changes in the gravitational field as the output. Geophysics admittance is commonly measured in μGal/mbar. These units convert according to 1 Gal = 0.01 m/s²and 1 bar = 100 kPa, so in SI units the measurement would be in units of;

$\frac{\mathrm{m}/\mathrm{s}^2}{\mathrm{Pa}}$ or $\frac{\mathrm{m}/\mathrm{s}^2}{\mathrm{N}/\mathrm{m}^2}$ or $\frac{\mathrm{m}^3}{\mathrm{N}\cdot \mathrm{s}^2}$ or, in primary units $\frac{\mathrm{m}^2}{\mathrm{kg}}$

However, the relationship is not a straightforward one of proportionality. Rather, an admittance function is described which is time and frequency dependent in a complex way.^[3]

[edit]Admittance in Building Fabric

This is the buildings response to a swing in temperature over 24 hours, i.e. Watts absorbed per unit area (meters) per temperature change (K).

Jana

Saturday 5 January 2013

Admittance

admittance (Y)

Admittance

Contents

[edit]Conversion from impedance to admittance

[edit]Admittance in mechanics

[edit]Admittance in geophysics

[edit]Admittance in Building Fabric

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