Flux Reversal in Three-Rung Laddics

When the flux in the driven branch of a multipath core is reversed most of it will return via the shortest return path in the core. A small fraction will return by the next shortest. The ratio of the flux change in the shortest path to that in the next shortest is called the branching ratio r. Experimental branching ratios are much larger than they reasonably should be. In this paper a magnetic circuit analysis which neglects leakage and reversible flux but includes the dependence of branch reluctance on flux is applied to the three-rung laddic. The calculations predict a branching ratio at infinite drive which is about a factor of two greater than might be naively expected. Except in special cases they predict that it should decrease monotonically with drive. Experimentally it may either increase, decrease, or saturate shortly after threshold. The experimental values are uniformly greater than the theoretical. It appears likely that the disparity between theory and experiment can be attributed to flux leakage during switching. This leakage may be minimized by silver plating the core. A remeasurement of the branching ratio as a function of drive and geometry seems to be indicated at the present time.