# Dictionary Definition

admittance

### Noun

2 the act of admitting someone to enter; "the
surgery was performed on his second admission to the clinic" [syn:
admission]

# User Contributed Dictionary

## English

### Pronunciation

IPA: WEAE /ædˈmɪt.n̩s/### Noun

- The act of admitting.
- Permission to enter; the power or right of entrance; also, actual entrance; reception.
- The act of giving possession of a copyhold estate.
- The reciprocal of impedance

#### Translations

reciprocal of impedance

- Croatian: admitancija
- Danish: admittans

### Synonyms

# Extensive Definition

In electrical
engineering, the admittance (Y) is the inverse
of the impedance
(Z). The SI unit
of admittance is the siemens.
Oliver
Heaviside coined the term in December 1887.

- Y = Z^ = 1/Z \,

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

Admittance is a measure of how easily a circuit
or device will allow a current to flow. Resistance is a measure of
the opposition of a circuit to the flow of a steady current, while
impedance takes in to account not only the resistance but dynamic
effects (known as reactance) as well. Likewise,
admittance is not only a measure of the ease with which a steady
current can flow (conductance,
the inverse of resistance),
but also takes in to account the dynamic effects of susceptance (the inverse of
reactance).

## Conversion from impedance to admittance

The impedance, Z, is composed of real and imaginary parts,- Z = R + jX \,

- R is the resistance, measured in ohms
- X is the reactance, measured in ohms

- Y = Z^= \frac = \left( \frac \right) \cdot \left( \frac \right) = \left( \frac \right) + j\left(\frac\right)

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

- Y = G + j B \,

- Y = G + jB = \left( \frac \right) + j \left( \frac \right)

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

- G = \Re(Y) = \left( \frac \right)

- B = \Im(Y) = \left( \frac\right)

The magnitude and phase of the admittance are
given by:

- \left | Y \right | = \sqrt = \frac \,

- \angle Y = \arctan \left( \right)= \arctan \left( \right)

where

- G is the conductance, measured in siemens
- B is the susceptance, measured in siemens

## 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.

## 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. 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 1m/s2 = 100 gal and 1 bar 100kPa (kN/m2) so in SI units the measurement would be in units of;\frac or
\frac or, in primary units
\frac

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.

## See also

SI electromagnetism unitsadmittance in Catalan: Admitància

admittance in Czech: Admitance

admittance in Danish: Elektrisk admittans

admittance in German: Admittanz

admittance in Spanish: Admitancia

admittance in French: Admittance

admittance in Korean: 어드미턴스

admittance in Italian: Ammettenza

admittance in Hebrew: אדמיטנס

admittance in Dutch: Admittantie

admittance in Japanese: アドミタンス

admittance in Norwegian: Admittans

admittance in Polish: Admitancja

admittance in Portuguese: Admitância

admittance in Russian: Адмиттанс

admittance in Slovak: Admitancia

admittance in Slovenian: Admitanca

admittance in Finnish: Admittanssi

admittance in Chinese: 导纳