| Immittance | |
|---|---|
 Combined measure of impedance, admittance, or both. Immittance is crucial to several practices, such astympanometry. | |
Common symbols | W,Za,Ya,[1]C,F,t,∈,ℝ,jt,ϵ,χ,M[2] |
| SI unit | N/A |
Immittance is a term used withinelectrical engineering andacoustics, specificallybioacoustics and theinner ear, to describe the combined measure ofelectrical oracoustic admittance andelectrical oracoustic impedance. Immittance was initially coined byH. W. Bode in 1945, and was first used to describe the electrical admittance or impedance of either anodal or amesh network. Bode also suggested the name "adpedence", however the current name was more widely adopted. In bioacoustics, immittance is typically used to help define the characteristics of noise reverberation within the middle ear and assist withdifferential diagnosis of middle-ear disease.[1] Immittance is typically acomplex number which can represent either or both the impedance and the admittance (ratio ofvoltage tocurrent or vice versa in electrical circuits, or volume velocity tosound pressure or vice versa in acoustical systems) of a system.[3]
Immittance does not have an associated unit because it applies to both impedance, which is measured inohms (Ω) oracoustic ohms, and admittance, which is commonly measured insiemens (S) and historically has also been measured inmhos (℧), thereciprocal of ohms.
Inaudiology,tympanometry is sometimes referred to asimmittance testing. Tympanometry is especially effective when both the impedance and admittance of the inner ear are accounted for. Immittance allows for the analysis of both, and therefore is crucial to multiple-component, multiple-frequency tympanometry. Clinically, few cases require the use of this technique for accurate diagnosis; but for the fewer than 20% of cases which do require it, the technique is a necessity. Multiple-component, multiple-frequency tympanometry is invaluable for the differential diagnosis of fixation of the lateralossicular chain from fixation of thestapes, profoundmixed hearing losses, clinicalotosclerosis from disruption of the ossicular chain,hypermobility of theincudostapedial joint, and congenital ossicular fixation in children.[4]
In electronics, an immittanceSmith chart can be created by overlaying both the impedance and admittance grids, which is useful for cascading series-connected with parallel-connected electric circuits. This allows for the visualization of changes in impedance or admittance in the system caused by components of either the series or parallel circuit.[5]
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