Internal impedance of a circular cylindrical wire under external, submillimeter wave illumination

Abstract A complete, non‐approximate expression of the internal impedance for an open‐ended circular cylindrical wire being subject to externally incident radiation is derived. A comparison is made with the well‐known formula given by Stratton and later given by Ramo. The modes in which the electromagnetic field oscillates are due to the incoming wave, and the corresponding boundary conditions do not lead to the homogeneous system of linear equations that produce the usual and relatively complex spectrum of damped modes discussed by Stratton. The approximations made to obtain Stratton and Ramo's formula are applicable again to the expression found here and produce the same result. Such approximations are adequate for good conductors at frequencies in the microwave region. However, it is shown that the new formulation, which includes the displacement current and the real part of the permittivity of the wire, is needed for the case of submillimeter radiation. In effect, the values of the impedance computed by using the new expression are considerably different from those resulting from Stratton or Ramo's formula in the Terahertz domain. In particular, these values show now a larger resistive part and a smaller reactive part in this domain.