Field Access Bubble Propagation Circuits

Abstract

The theoretical model proposed by Archer et al for analysis of field access magnetic bubble propagation circuits is extended to include rotating drive fields. This extension allows the study of bubble propagation along T‐Bar patterns. Computer simulations are made to determine energy profiles for a bubble interacting with the drive circuit. The motion of the bubble along the propagation circuit is determined as a function of external drive field by assuming that the bubble follows the energy minima. Bubble velocity profiles can be calculated from the bubble position as a function of drive field orientation. This allows, for the first time, the comparison of Archer's theoretical model with the experimental observations. A study of the spacing between circuit elements of a T‐Bar pattern reveals that the optimum value of this spacing should be a quarter of a bubble diameter. The factors which are primarily responsible for limiting propagation speed are determined and modifications to existing field access circuits are suggested to improve propagation at high frequencies. Extending the principles evolved from this computer simulation, a field access circuit of substantially different character from previously fabricated circuits was designed. This circuit shown below was built and tested, and showed an essentially uniform bubble velocity profile, one of the primary requirements of a high speed, wide margin propagation circuit. Results of experiments with this circuit are presented and relevant circuit parameters discussed.