- Kinetic inductance
Kinetic inductance is the manifestation of the inertial mass of mobile
charge carriers in alternating electric fields as an equivalent seriesinductance . Kinetic inductance is observed in high carrier mobility conductors (e.g.superconductors ), and at high frequencies.Explanation
A change in
electromotive force (emf) will be opposed by theinertia of the charge carriers since, like all objects with mass, they prefer to be travelling at constant velocity and it therefore takes a finite time to accelerate the particle. This is similar to how a change in emf is opposed by the finite rate of change of magnetic flux in an inductor. The resulting phase lag in voltage is identical for both energy storage mechanisms, making them indistinguishable in a normal circuit.Kinetic inductance arises naturally in the
Drude model ofelectrical conduction when the relaxation time (collision time) au is taken to be non-zero. This model defines acomplex conductivity in a time-varying electric field of frequency omega given by sigma(omega) = sigma_{1} - isigma_{2 - the imaginary part arising due to kinetic inductance. This complex conductivity can be expanded into its real and imaginary components:sigma = frac{ne^2 au}{m(1+iomega au)} = frac{ne^2 au}{m(1+omega^2 au^2)}-ifrac{ne^2omega au^2}{m(1+omega^2 au^2)}
where m is the mass of the charge carrier (i.e.; effective
electron mass in metallic conductors) and n is the carrier number density. In normal metals the collision time is normally approx 10^{-14} s, so for frequencies < 100 GHz the term omega^2 au^2} is very small and can be ignored. Kinetic inductance is therefore only really noticeable at optical frequencies and in superconductors when au ightarrow infty}.Applications
Kinetic inductance in superconductors is exploited to make efficient
microwave delay lines as it increases the inductance per unit length of superconductingtransmission lines . Kinetic inductance can also be used for sensitivephoton detection, as the change in the superconducting carrier (Cooper pair ) density brought about by an incident photon produces a measurable change in kinetic inductance.See also
*
Drude model
*Electrical conduction
*Electron mobility
*Inductance
*Superconductivity
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