Abstract: The present invention is noise attenuation system and related method for suppressing noise generated by a noise source, such as a jet engine, contained in a housing. An impedance device is positioned in the housing to attenuate the amplitude of sound waves generated by the noise source propagating in one direction and to create a reflected sound wave. The reflected sound wave is out of phase with the sound waves propagating from the noise source away from the impedance device. The reflected sound wave destructively interferes with this sound wave to attenuate the amplitude.

Abstract: The system disclosed herein controls the vibratory energy radiated from a structure subject to excitation from an outside disturbance by enforcing a preselected mechanical impedance upon at least one point in the structure using an electromechanical transducer connected to the structure at that point. The transducer is energized in response to the output of an adjustable or adaptable filter. Sensors provide signals representing the force applied by the transducer and the resultant velocity. The force and velocity signals are applied as inputs to the adaptable filter through circuit means including a component providing an electrical analog of the preselected mechanical impedance. The adaptable filter is then controlled to reduce the amplitude of the input signal applied to the filter, i.e. the error between the measured mechanical impedance and the desired impedance.

Abstract: A magnetic bearing control system for a rotating shaft, for example, includes a plurality of electromagnets disposed around and in close proximity to the surface of the shaft. The control system provides a bias current to the electromagnets to maintain the shaft in a null position. Levitation of the shaft is controlled by a levitation controller, and disturbance rejection is effected by a disturbance rejection controller. Flux sensors, suitably located near the electromagnets, determine the magnitude and polarity of the flux resident in the gap between each electromagnet and the shaft. The controller determines the size of the gap based on the flux and generates a corresponding control signal to maintain the position of the shaft within the bearing.