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Full-Text Articles in Physical Sciences and Mathematics
Making Mri Scans Quieter Through Time-Reversal Acoustics And Active Noise Control, Trent Furlong, Brian Anderson
Making Mri Scans Quieter Through Time-Reversal Acoustics And Active Noise Control, Trent Furlong, Brian Anderson
Journal of Undergraduate Research
Noise from magnetic resonance imaging (MRI) equipment puts patients at risk for hearing damage.i Active noise control (ANC) systems have been implemented inside the MRI’s bore to reduce perceived noise, but the equipment used cannot have magnetic material or the ANC system will interfere with the MRI machine’s imaging quality. These systems are also limited in size because of the MRI machine’s small bore. Our project was to determine the feasibility of using time-reversal (TR) acoustics to remotely focus a noise-canceling signal to a desired point in space (e.g. a patient’s ear inside an MRI machine) and see if significant …
Active Control Of Cylindrical Shells Using The Weighted Sum Of Spatial Gradients (Wssg) Control Metric, Pegah Aslani
Active Control Of Cylindrical Shells Using The Weighted Sum Of Spatial Gradients (Wssg) Control Metric, Pegah Aslani
Theses and Dissertations
Cylindrical shells are common structures that are often used in industry, such as pipes, ducts, aircraft fuselages, rockets, submarine pressure hulls, electric motors and generators. In many applications it is desired to attenuate the sound radiated from the vibrating structure. There are both active and passive methods to achieve this purpose. However, at low frequencies passive methods are less effective and often an excessive amount of material is needed to achieve acceptable results. There have been a number of works regarding active control methods for this type of structure. In most cases a considerable number of error sensors and secondary …
Analog Feedback Control Of Broadband Fan Noise, Cole Victor Duke
Analog Feedback Control Of Broadband Fan Noise, Cole Victor Duke
Theses and Dissertations
Active noise control (ANC) has been implemented using analog filters to reduce broadband noise from a small axial cooling fan. Previous work successfully attenuated narrow-band, tonal portions of the noise using a digital controller. The practical performance limits of this system were reached and it was desirable to attenuate the noise further. Additional research, therefore, sought to attenuate broadband noise from the fan using a digital controller, but performance was limited by the group delay inherent in the digital signal processor (DSP). Current research attempts to further attenuate broadband noise and improve performance of the system by combining the tonal …
Active Noise Control Of A Centrifugal Fan Mounted In A Mock Laptop Enclosure, John J. Esplin
Active Noise Control Of A Centrifugal Fan Mounted In A Mock Laptop Enclosure, John J. Esplin
Theses and Dissertations
Noise from information technology (IT) equipment is a significant problem in today's modern society. Active Noise Control (ANC) has shown promise in reducing the effect of IT fan noise on users. Though ANC has been applied to axial fans (such as those found in desktop computers), it has not been applied to centrifugal fans, such as those found in laptop computers. This work applies an ANC method to a centrifugal fan mounted in a mock laptop enclosure. This method is applied in four steps. First, secondary sources are placed in the vicinity of the fan. Second, an accurate model of …
Generalized Acoustic Energy Density And Its Applications, Buye Xu
Generalized Acoustic Energy Density And Its Applications, Buye Xu
Theses and Dissertations
The properties of acoustic kinetic energy density and total energy density of sound fields in lightly damped enclosures have been explored thoroughly in the literature. Their increased spatial uniformity makes them more favorable measurement quantities for various applications than acoustic potential energy density (or squared pressure), which is most often used. In this dissertation, a new acoustic energy quantity, the generalized acoustic energy density (GED), will be introduced. It is defined by introducing weighting factors, α and 1 − α, in the formulation of total acoustic energy density. With the additional degree of freedom, the GED can conform to the …
Error Sensor Strategies For Active Noise Control And Active Acoustic Equalization In A Free Field, Ryan T. Chester
Error Sensor Strategies For Active Noise Control And Active Acoustic Equalization In A Free Field, Ryan T. Chester
Theses and Dissertations
Several measurements may be used as error signals to determine how to appropriately control a sound field. These include pressure, particle velocity, energy density and intensity. In this thesis, numerical models are used to show which signals perform best in is free-field active noise control (ANC) using error sensors located in the near field of the sound sources. The second is equalization in a free field and a semi-free field. Minimized energy density total power output (MEDToPO) plots are developed; these indicate the maximum achievable attenuation for a chosen error sensor as a function of location. A global listening area …
Error Sensor Placement For Active Control Of An Axial Cooling Fan, Benjamin M. Shafer
Error Sensor Placement For Active Control Of An Axial Cooling Fan, Benjamin M. Shafer
Theses and Dissertations
Recent experimental achievements in active noise control (ANC) for cooling fans have used near-field error sensors whose locations are determined according to a theoretical condition of minimized sound power. A theoretical point source model, based on the condition previously stated, reveals the location of near-field pressure nulls that may be used to optimize error sensor placement. The actual locations of these near-field pressure nulls for both an axial cooling fan and a monopole loudspeaker were measured over a two-dimensional grid with a linear array of microphones. The achieved global attenuation for each case is measured over a hemisphere located in …
Feedback Applications In Active Noise Control For Small Axial Cooling Fans, Matthew J. Green
Feedback Applications In Active Noise Control For Small Axial Cooling Fans, Matthew J. Green
Theses and Dissertations
Feedback active noise control (ANC) has been applied as a means of attenuating broadband noise from a small axial cooling fan. Such fans are used to maintain thermal stability inside of computers, projectors, and other office equipment and home appliances. The type of low-level noise radiated from axial cooling fans has been classified as harmful to productivity and human well being. Previous research has successfully implemented feed-forward ANC, targeting specific narrow-band fan noise content related to the blade passage frequency (BPF) of the fan. The reference signal required for a feed-forward algorithm limits its ability to attenuate much of the …
Optimization Of Active Noise Control For Small Axial Cooling Fans, Brian B. Monson
Optimization Of Active Noise Control For Small Axial Cooling Fans, Brian B. Monson
Theses and Dissertations
Previous work has shown that active noise control is a feasible solution to attenuate tonal noise radiated by small axial cooling fans, such as those found in desktop computers. One such control system reduced noise levels of a baffled 80-mm fan in the free field with four small loudspeakers surrounding the fan. Due to industry specified spatial constraints, a smaller fan and speaker configuration was desirable. The smaller configuration maintains similar control performance, further facilitating practical implementation of the control system. The smaller control system employs a smaller fan running at a higher speed. Different loudspeaker configurations for control exist …
Active Minimization Of Acoustic Energy Density In A Mock Tractor Cab, Benjamin Mahonri Faber
Active Minimization Of Acoustic Energy Density In A Mock Tractor Cab, Benjamin Mahonri Faber
Theses and Dissertations
An active noise control (ANC) system has been applied to the problem of attenuating low-frequency tonal noise inside small enclosures. The intended target application of the system was the reduction of the engine firing frequency inside heavy equipment cabins. The ANC system was based on a version of the filtered-x LMS adaptive algorithm, modified for the minimization of acoustic energy density (ED), rather than the more traditional minimization of squared acoustic pressure (SP). Three loudspeakers produced control signals within a mock cabin composed of a steel frame with plywood sides and a Plexiglas® front. An energy density sensor, capable of …