Current induced on single and crossed electrically short and thin tubular cylinders by a normally incident plane electromagnetic wave

The currents induced in electrically thin conducting tubes are evaluated from the general solution of the coupled integral equations derived by C. C. Kao [5] in the form of transverse Fourier components. It is shown that on a single cylinder of length and radius in a normally incident -polarized field with wavenumber , the rotationally symmetric zero-order term dominates for and increases in magnitude as is reduced, but only when . Under these conditions, supplemented with the inequality , thin-cylinder theory is valid. The relatively small first-order term produces small departures from rotational symmetry that increase or decrease the current on the illuminated side depending on the condition of axial resonance and the location of the cross section in the standing-wave pattern. As is reduced so that , the rotationaily symmetric part of the axial current decreases and becomes negligible compared to the first-order current which is proportional to . Thin-cylinder theory is then no longer useful. When two electrically thin tubes intersect, thin-wire theory and junction conditions determine only the rotationally symmetric part of the axial currents in the arms. These dominate only when the arms of the cross are not electrically short. The fast-order nonrotationally symmetric components of the axial current and the transverse currents can be determined from the incident magnetic field. They dominate when the arms of the cross are electrically short. The significance of the surface currents and charges on aircraft illuminated by an electromagnetic wave or pulse at low frequencies is pointed out.