Professor John Gregg

Abstract:

We describe a general mechanism of controllable energy exchange between waves propagating in a dynamic artificial crystal. We show that if a spatial periodicity is temporarily imposed on the transmission properties of a wave-carrying medium while a wave is inside, this wave is coupled to a secondary counterpropagating wave and energy oscillates between the two. The oscillation frequency is determined by the width of the spectral band gap created by the periodicity and the frequency difference between the coupled waves. The effect is demonstrated with spin waves in a dynamic magnonic crystal.

Abstract:

Electric generator (100), comprising: a turbine (1); a rotor (5), operable by the turbine (1); a stator having stator coils (6); a controller (9); and an electrical circuit (150), connected to the stator coils (6) and having a same load impedance; in which the actual component of the load

Abstract:

Spin-wave active rings - positive-feedback systems incorporating spin-wave waveguides - provide important insight into fundamental magnetics, enable experimental investigations into nonlinear wave phenomena, and potentially find application in microwave electronics. Such rings break into spontaneous, monomode oscillation at a certain threshold value of feedback gain. In general, the wavenumber of this initially excited, threshold mode is impossible to predict precisely. Here we discuss how, by exploiting resonant spin-wave reflections from a magnonic crystal, an active ring system having a threshold mode with a well-defined and precisely predictable wavenumber may be realized. Our work suggests that study and development of active ring systems incorporating magnonic crystals may deliver useful insight into spin-wave transmission in structured magnetic films as well as devices with technological applicability.