Dresden 2006 – wissenschaftliches Programm

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TT: Tiefe Temperaturen

TT 11: Superconductivity: Heterostructures, Andreev Scattering, Proximity Effect, Coexistence

TT 11.11: Vortrag

Dienstag, 28. März 2006, 12:15–12:30, HSZ 301

Impedance and field profiles of thin ohmic or superconducting strips with applied ac current — •Ernst Helmut Brandt — Max-Planck-Institut für Metallforschung, Stuttgart

A long wire carrying an applied ac current is a standard problem in electrodynamics when the wire is cylindric. The circular symmetric solutions far away from the current contacts are easily obtained for an ohmic wire with resistivity ρ and for a superconducting wire with London depth λ. When the wire has a non-circular cross section the problem becomes much more complex. Apparently, no analytic or transparent numerical solutions are available, not even for the complex impedance of thin strips that is needed, e.g., in the theory of SQUID systems. This contribution presents the inductance, resistance, and magnetic field and current distributions of thin long ohmic or superconducting strips and their dependences on λ, ρ, ac frequency, and strip length l. Approximate analytic expressions are given for the inductance and resistance. Interestingly, the inductance per unit length of the strip depends on its length while the field and current distributions and the susceptibility and resistance are independent of l. As compared to cylindrical wires, the skin effect in thin ohmic strips is much weaker (logarithmic).