Frequency tuning by magnetic field in Josephson-junction fluxon oscillators

The effect of an applied magnetic field on the frequency of oscillation of long Josephson tunnel junctions current-biased on zero-field steps is studied by numerical simulation and by a mechanical analog. The frequency increases with field for larger values of the bias and decreases for smaller values, corresponding to a rotation about some midpoint of the zero-field step in the sense of higher differential resistance.