Patent US 4,038,541

Hard magnetic bubble domains are propagated in displaced orbits in response to the product of two cyclically varying propagation control fields. The control fields modulate the hard bubble domain diameter and a driving field gradient. Repulsive boundaries establish a restricted propagating channel in a layer of bubble domain material to maintain the net displacement of orbital movements of the bubble domain along a predetermined axis. The axis of the bubble domain net displacement is perpendicular to the direction of the driving field gradient and preferably along a neutral axis of the driving field gradient. The net displacement of the hard bubble domains provide an improved analog multiplication of two alternating current computational input signals controlling the propagation control fields.