Influence of Nearby Conductors on Thin Film Switching

Abstract

The usual concept of a thin film or other open flux path magnetic element consists of the material itself closely encircled by drive and sense conductors. Strips of conductor of width approximately that of the element are attractive for several reasons, i.e., low resistance, low skin effect, and low line impedance. However, these strips, being closely coupled to the element, can severely influence its dynamic properties by means of induced eddy currents. These conductors manifest themselves in three ways: 1. A slowing of the switching due to the air return flux path of the element passing through a conductor and being damped. 2. A dynamic distortion of the air return flux due to shielding effects. 3. A dynamic distortion of an applied field due to shielding effects. All of these effects can be detrimental to the operation of the element. In this paper, approximate calculations are presented to show the extent of these effects. The geometry considered is that of a "conventional" flat thin film element, driven and sensed by strip transmission lines. Several drive and sense configurations are considered, and experimental evidence is presented in support of these calculations. Although the cases considered are somewhat arbitrary, the methods and many of the results are applicable to other cases of utilization of open flux path elements. © 1960 The American Institute of Physics.