Office of Technology Transfer – University of Michigan

Low Noise Magnetron and Crossed-field Amplifier by Azimuthally Varying Axial Magnetic Field

Technology #2512p1

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Ronald M. Gilgenbach
Managed By
Keith Hughes
Assistant Director, Physical Sciences & Engineering 734-764-9429

UM File # 2512p1

The noise generation mechanisms of linear electron beam devices are well-known. Generally, fluctuations of cathode electron emission excite space charge waves, which propagate along the electron beam. Calculations and computations of noise figures in linear devices agree with experiments. Methods of noise suppression in linear tubes are at a very advanced stage. On the other hand, noise generation mechanisms in cross-field devices are not presently understood and predictive computational calculations do not exist. Methods of noise suppression in crossed-field devices have not previously been practically realized.
Technology Description
University of Michigan researchers have developed a cost-effective, low-noise, crossed-field device, such as a microwave magnetron, a microwave oven utilizing same, and crossed-field amplifier utilize an azimuthally varying, axial magnetic field. The magnetic configuration reduces and eliminates microwave and radio frequency noise. This microwave noise is present near the carrier frequency and as sidebands, far separated from the carrier. The device utilizes azimuthally-varying, axial, magnetic field perturbations. At least one permanent perturbing magnet having an azimuthally-varying magnetic field impressed thereupon causes the axial magnetic field to vary azimuthally in the magnetron and completely eliminates the microwave noise and unwanted frequencies. Preferably, the number of axial magnetic field perturbations is based on the number of cavities of the magnetron. Please see UM File No. 2512.
Applications • Reduction of interference with telephoneand computer communications by microwavemagnetrons in microwave ovens • Lighting and industrial heating, wherenoise-free magnetrons can be used • Applications in which precise microwavefrequency is desired • Reduction of noise in crossed-fieldamplifiers
Advantages • Completely eliminates the microwave noise and unwanted frequencies