Imdad Imam

Active control of noise and vibrations in magnetic resonance imaging systems using vibrational inputs

An active noise and vibration control system which minimizes noise output by creating a secondary, cancelling noise and/or vibration field using vibrational inputs. The system includes one or more piezoceramic actuators mounted to the inner surface of a magnetic resonance imaging device. The actuators can be either mounted directly to the device or to one or more noise cancelling members which are resiliently mounted to the device. Transducers are also provided for sensing the noise or vibrations generated by the device and producing an error signal corresponding to the level of noise or vibrations sensed. A controller sends a control signal to the actuators in response to the error signal, thereby causing the actuators to vibrate and generate a noise or vibration field which minimizes the total noise emanating from the device. Alternatively, the system can use noise and vibration feedback simultaneously.

Compressor noise attenuation using branch type resonator

A Helmholtz resonator is used in communication with the compression chamber of a rotary compressor in order to attenuate noise. The resonator concentrates the attenuation of noise in a frequency band around 4 kHz corresponding to the concentration of noise produced by a particular rotary compressor, this band also corresponding to the frequencies which the human ears are most sensitive to. The resonator branches off from the discharge port in an end wall of the compressor. The resonantor uses an easily machined cylindrical resonance cavity on the surface of the end wall, the resonance cavity also being bounded on one side by a cylindrical wall of the rotary compressor. The resonator significantly reduces the noise in a rotary compressor of a specific type commonly used for compressing refrigerant gases in a refrigerator.