Active Noise and Vibration Control
Introduction
Generally, there are two major categories of noise control techniques; namely passive and active control. The purpose of passive control is to control the target noise by either modifying the structure, such as by adding mass, tuning stiffness, or increasing system damping, or by creating a means for the vibratory energy to be reflected or absorbed. Normally the passive control approach is appropriate for middle and high frequency ranges, and is typically weighty and less effective for low frequency disturbances. The idea of active acoustic noise control is based on introducing secondary sound pressure waves that are out-of-phase from the original sound pressure waves such that the resultant perceived sound is canceled out or significantly diminished. Compared to passive control, active control is more suitable for low frequency ranges.
Basic Concept of Active control
Active control configuration
Capability of adaptive algorithms:
- Time-domain filtered-x LMS algorithm
- Frequency-domain filtered-x FLMS algorithm
- Sample-based update frequency-domain FxLMS algorithm
- Sub-band adaptive filtering algorithm
- Virtual secondary path algorithm
Capability of adaptive algorithms:
- Time-domain filtered-x LMS algorithm
- Frequency-domain filtered-x FLMS algorithm
- Sample-based update frequency-domain FxLMS algorithm
- Sub-band adaptive filtering algorithm
- Virtual secondary path algorithm
Typical Active Noise and Vibration Control Projects
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Active noise and vibration control in Vehicle systems
- Active Control of road and powertrain noise
- Active vibration control of gearbox
- Active control of MRI noise
Active Noise and Vibration Control in Vehicle Systems
- The vehicle noise and vibrations are dominant in the low and middle frequency range.
- Active control is much more effective in controlling low and middle frequency range than traditional passive control.
- Active noise control has potential to reshape the noise in order to achieve better interior sound quality.
- Active control will lead to a lighter-weight, fuel efficient vehicles by avoiding bulky passive control applications.
Active Control of Road and Powertrain noise
Active Vibration Control of Gearbox
Active Control of MRI Noise
Magnetic Resonance Imaging (MRI) is a powerful imaging tool used in clinical diagnosis and biomedical research. One of the undesirable characteristics of the process is the loud noise generated during a scan. A major source of this noise is the result of switching electrical current in gradient coils within the static magnetic field. The sound pressure levels (SPLs) the patient is subjected to not only produce discomfort, but are potentially harmful as well. The research is focused on the development of a physical simulation of active noise control of MRI due to high cost of real-time scan in the MRI machine.Once the active control strategy is established in the physical simulation, the experimental prototype is then validated through in-situ measurements at the Center for Imaging Research, University of Cincinnati. The results of the in-situ measurements have been promising and the prototype is in the commercial implementation stage
