Hysteresis phenomena of the parametric oscillations

Parametric amplifiers have been described which are based on the magnetoelastic interaction of the oscillation of a torsional pendulum and an electrical circuit. When the inverting amplifier is driven overcritically, selfexcitation of the pendulum occurs. Because of the nonlinear magnetoelastic damping, it may happen that the pendulum oscillates only in a certain range of amplitudes. Varying the intensity of the magnetic pumping field, hysteresis effects of the oscillation appear which can be explained by damping measurements. Oscillation measurements of other authors can now be understood.The author thanks Prof. Dr. G.Dietz for many valuable remarks to this paper and Prof. Dr. H.Happ in whose institute the experiments were performed.