The ability to reduce flexural vibrations of lightweight structures has been a goal for many researchers. A type of transducer-controller system that accomplishes this is a piezoelectric patch connected to an electrical impedance, or shunt. The piezoelectric patch converts the vibrational strain energy of the structure to which it is bonded into electrical energy. This converted electrical energy is then modified by the shunt to influence to mechanical response. There are many types of shunt circuits which have demonstrated effective control of flexural systems. Of interest in this work is the negative capacitance shunt, which has been shown to produce significant reduction in vibration over a broad frequency range. A negative capacitance circuit produces a current that is 180̊ out of phase from a traditional, passive capacitor. In other words, the voltage of the capacitor decreases as charge is added. The negative capacitance shunt consists of a resistor and an active negative capacitance element. By adding a resistor and negative capacitor to the electrical domain, the shunt acts as a damper and negative spring in the mechanical domain. The performance of the negative capacitance shunt can be increased through proper selection of the shunt's electrical components. Three aspects of component selection are investigated: shunt efficiency, maximum suppression, and stability. First, through electrical modeling of the shunt-patch system, the components can be chosen to increase the efficiency of the shunt for a given impedance. Second, a method is developed that could be utilized to adaptively tune the magnitude of resistance and negative capacitance for maximum control at a given frequency. Third, with regard to stability, as the control gain of the circuit is increased, by adjusting the circuit parameters, there is a point when the shunt will become unstable. A method to predict the stability of the shunt is developed to aid in suppression prediction. The negative capacitance shunt is also combined with a periodic piezoelectric patch array to modify the propagating wave behavior of a vibrating structure. A finite element method is utilized to create models to predict both the propagation constant, which characterizes the reduction in propagating waves, and the velocity frequency response of a full system. Analytical predictions are verified with experimental results for both a 1- and 2-D periodic array. Results show significant attenuation can be achieved with a negative capacitance shunt applied to a piezoelectric patch array. Three electromechanical aspects are developed: design for maximum suppression, more accurate stability prediction, and increased power-output efficiency. First, a method is developed that may be used to adaptively tune the magnitude of resistance and negative capacitance for maximum suppression. Second, with regard to stability, a method is developed to predict the circuit components at which the circuit will obtain a stable output. Third, through electrical modeling of the shunt-patch system, the components are chosen to increase the power output efficiency of the shunt circuit for a given impedance. The negative capacitance shunt is also combined with a periodic piezoelectric patch array to modify the propagating wave behavior of a vibrating structure. Analytical predictions are verified with experimental results for both a 1- and 2-D periodic array. Results show significant attenuation can be achieved with a negative capacitance shunt applied to a piezoelectric patch array.

Contrast-enhanced mammography (CEM) relies on visualizing the growth of new blood vessels (i.e. tumor angiogenesis) to provide sufficient materials for cell proliferation during the development of cancer. Since cancers will accumulate an injected contrast agent more than other tissues, it is possible to use one of several methods to enhance the area of lesions in the x-ray image and remove the contrast of normal tissue. Large area flat panel detectors may be used for CEM wherein the subtraction of two acquired images is used to create the resulting enhanced image. There exist several methods to acquire the images to be subtracted, which include temporal subtraction (pre- and post-contrast images) and dual-energy subtraction (low- and high-energy images), however these methods suffer from artifacts due to patient motion between image acquisitions. In this research the use of a multilayer flat panel detector is examined for CEM that is designed to acquire both (low- and high-energy) images simultaneously, thus avoiding motion artifacts in the resulting subtracted image. For comparison, a dual-energy technique prone to motion artifacts that uses a single-layer detector is also investigated. Both detectors are evaluated and optimized using amorphous selenium as the x-ray to charge conversion material, however the theoretical analysis could be extended to other conversion materials. Experimental results of single pixel prototypes of both multilayer and single-layer detectors are also discussed and compared to theoretical results. For a more comprehensive analysis, the motion artifacts present in dual-exposure techniques are modeled and the performance degradation due to motion artifacts is estimated. The effects of noise reduction techniques are also evaluated to determine potential image quality improvements in CEM images.

Detta examensarbete omfattar akustiska undersökningar utav en desinficerande diskmaskin av typ Getinge 8666/8668 och har utförts på Getinge Desinfection AB i Växjö. Vi har undersökt hur man med enkla medel kan sänka ljudtrycksnivån i maskinens närhet. Mätningar har utförts på diskmaskinens torkprogram, där torkfläktarna är de mest dominerande ljudkällorna och ljudet främst är luftburet. En systematisk analysmetod bestående av införandet av successiva dämpningsåtgärder visade att de dominerande ljudvägarna går via taket, golvet samt till viss del spalter i maskinens väggar. Genom att isolera både tak, golv och spalter kunde ljudtrycksnivån sänkas med totalt hela 5,9 dB. Med enkla produktionsanpassade lösningar, i form utav en isolerad golvsockel och en bättre kåpa runt fläktarna, kan man sänka nivån med så mycket som 3,6 dB. Rapporten ska även kunna användas som ett underlag för vidare akustiska undersökningar på Getinge Desinfection AB. / This dissertation examines acoustic research of a disinfecting dishwasher type Getinge 8666/8668. The research has been performed in collaboration with Getinge Desinfection AB, a world wide known manufacturer of disinfecting equipment for healthcare, located in Växjö, Sweden. We have examined how to reduce noise from the dishwasher with simple measures. Measurements have been performed during the drying program of the machine. The drying fans are the dominating sources of sound, and the sound is air bourn. A systematic method by reducing the sound step by step shows that the major ways of sound is through the ceiling and through the floor. There is also a minor noise leakage through the gaps in the walls of the dishwasher. By isolating the ceiling, the floor and the gaps in the walls, it is possible to reduce the noise with totally 5.9 dB. With more production adapted solutions, in shape of an isolated floor base and a more efficient fan cover, it is possible to reduce the noise with as much as 3.6 dB. This dissertation is thought to be used as a basis for further acoustic research at Getinge Desinfection AB.

Uppsatsen behandlar bullerdämpning vid kap på ProfilGruppen Extrusions AB i Åseda. Problemen med ljudnivån beror bland annat på stomljudet som alstras av kapen i de långa profilerna. För att sänka ljudnivån har fastklampningskonstruktioner tagits fram som dämpar stomljudet och förslag på vidare åtgärder rapporterats. Försök och jämförande mätningar av ljudnivån har utförts för att få ett bra underlag att utvärdera. Resultaten av försöken med viskoelastisk plast som dämpelement visar en viss dämpning. Dämpningen kan med all sannolikhet bli större med användning av tjockare dämpelement. / This project is about noise reduction of a cross cut saw at ProfilGruppen Extrusions AB, Åseda. The problems with the sound level depend on the structure-borne sound that generates in the long profiles. To lower the sound level have press clamp constructions been developed which reduce and further attends have been suggested. Attempts and comperative measurings of the sound level have been evaluated. The results of the comperative measurings with viscoelastic plastic as damping element display certain damping. The damping can in all probability become larger using a thicker damping element.

Achieving a low noise level is of great interest to the forest machine industry. Traditionally this is obtained by using passive noise reduction, i.e. by using materials for sound isolation and sound absorption. Especially designs to attenuate low frequency noise tend to be bulky and impractical from an installation point of view. An alternative solution to the problem is to use active noise control (ANC). The basic principle of ANC is to generate an anti-noise signal designed to destructively interfere with the unwanted noise. In this thesis two algorithms (Feedback FxLMS and Feedforward FxLMS) are implemented and evaluated for use in the ANC-system. The ANC-system is tuned to the specific environment in the driver’s cabin of a Komatsu forest machine. The algorithms are first tested in a simulated environment and then in real-time inside a forest machine. Simulations are made both in Matlab and in C using both generated signals and recorded signals. The C code is implemented on the Analog Devices Blackfin DSP card BF526. The result showed a significantly reduction of the sound pressure level (SPL) in the driver’s cabin. The noise attenuation obtained using the Feedback FxLMS was approximately 14 dB for a tonal 100 Hz signal and 11 dB using recorded engine noise from a forest machine at 850 rpm.

<p>Detta examensarbete omfattar akustiska undersökningar utav en desinficerande diskmaskin av typ Getinge 8666/8668 och har utförts på Getinge Desinfection AB i Växjö. Vi har undersökt hur man med enkla medel kan sänka ljudtrycksnivån i maskinens närhet. Mätningar har utförts på diskmaskinens torkprogram, där torkfläktarna är de mest dominerande ljudkällorna och ljudet främst är luftburet. En systematisk analysmetod bestående av införandet av successiva dämpningsåtgärder visade att de dominerande ljudvägarna går via taket, golvet samt till viss del spalter i maskinens väggar. Genom att isolera både tak, golv och spalter kunde ljudtrycksnivån sänkas med totalt hela 5,9 dB. Med enkla produktionsanpassade lösningar, i form utav en isolerad golvsockel och en bättre kåpa runt fläktarna, kan man sänka nivån med så mycket som 3,6 dB. Rapporten ska även kunna användas som ett underlag för vidare akustiska undersökningar på Getinge Desinfection AB.</p> / <p>This dissertation examines acoustic research of a disinfecting dishwasher type Getinge 8666/8668. The research has been performed in collaboration with Getinge Desinfection AB, a world wide known manufacturer of disinfecting equipment for healthcare, located in Växjö, Sweden. We have examined how to reduce noise from the dishwasher with simple measures. Measurements have been performed during the drying program of the machine. The drying fans are the dominating sources of sound, and the sound is air bourn. A systematic method by reducing the sound step by step shows that the major ways of sound is through the ceiling and through the floor. There is also a minor noise leakage through the gaps in the walls of the dishwasher. By isolating the ceiling, the floor and the gaps in the walls, it is possible to reduce the noise with totally 5.9 dB. With more production adapted solutions, in shape of an isolated floor base and a more efficient fan cover, it is possible to reduce the noise with as much as 3.6 dB. This dissertation is thought to be used as a basis for further acoustic research at Getinge Desinfection AB.</p>

<p>Uppsatsen behandlar bullerdämpning vid kap på ProfilGruppen Extrusions AB i Åseda. Problemen med ljudnivån beror bland annat på stomljudet som alstras av kapen i de långa profilerna. För att sänka ljudnivån har fastklampningskonstruktioner tagits fram som dämpar stomljudet och förslag på vidare åtgärder rapporterats.</p><p>Försök och jämförande mätningar av ljudnivån har utförts för att få ett bra underlag att utvärdera. Resultaten av försöken med viskoelastisk plast som dämpelement visar en viss dämpning. Dämpningen kan med all sannolikhet bli större med användning av tjockare dämpelement.</p> / <p>This project is about noise reduction of a cross cut saw at ProfilGruppen Extrusions AB, Åseda. The problems with the sound level depend on the structure-borne sound that generates in the long profiles. To lower the sound level have press clamp constructions been developed which reduce and further attends have been suggested.</p><p>Attempts and comperative measurings of the sound level have been evaluated. The results of the comperative measurings with viscoelastic plastic as damping element display certain damping. The damping can in all probability become larger using a thicker damping element.</p>

Contrast-enhanced mammography (CEM) relies on visualizing the growth of new blood vessels (i.e. tumor angiogenesis) to provide sufficient materials for cell proliferation during the development of cancer. Since cancers will accumulate an injected contrast agent more than other tissues, it is possible to use one of several methods to enhance the area of lesions in the x-ray image and remove the contrast of normal tissue. Large area flat panel detectors may be used for CEM wherein the subtraction of two acquired images is used to create the resulting enhanced image. There exist several methods to acquire the images to be subtracted, which include temporal subtraction (pre- and post-contrast images) and dual-energy subtraction (low- and high-energy images), however these methods suffer from artifacts due to patient motion between image acquisitions. In this research the use of a multilayer flat panel detector is examined for CEM that is designed to acquire both (low- and high-energy) images simultaneously, thus avoiding motion artifacts in the resulting subtracted image. For comparison, a dual-energy technique prone to motion artifacts that uses a single-layer detector is also investigated. Both detectors are evaluated and optimized using amorphous selenium as the x-ray to charge conversion material, however the theoretical analysis could be extended to other conversion materials. Experimental results of single pixel prototypes of both multilayer and single-layer detectors are also discussed and compared to theoretical results. For a more comprehensive analysis, the motion artifacts present in dual-exposure techniques are modeled and the performance degradation due to motion artifacts is estimated. The effects of noise reduction techniques are also evaluated to determine potential image quality improvements in CEM images.

Une onde acoustique plane propagée dans un guide couplée à des parois vibrantes, siège d'ondes transversale ou de flexion, donne un ensemble d'ondes dans le fluide et dans la structure. Les ondes dans le fluide sont évanescentes, propagatives, ou encore propagatives avec un amortissement. Il n'est pas besoin que l'ensemble soit dissipatif pour en arriver là car les résultats proviennent d'interférences destructives on constructives. Un amortissement dans la structure donne un système cette fois-ci dissipatif et ajoute ses effets à la dissipation mais pas de façon classique puisqu'il s'agit ici d'ondes couplées acoustique/structure. En présence d'un flux stationnaire et uniforme la capacité d'une paroi vibrante à produire de l'atténuation acoustique se réduit. Les opérateurs en jeu, les méthodes pour les résoudre dont celle des éléments finis donnent accès à des prédictions. Elles sont confrontées à des résultats expérimentaux. Sans écoulement, les prédictions font sens. En revanche, avec écoulement, il n'en est pas de même et le mémoire tentera d'analyser les raisons. En conclusion technologique, une atténuation d'une quinzaine de décibels en moyenne sur une gamme de fréquences de quelques centaines de Hz centrées dans les médiums (500Hz) est envisageable avec une paroi mince qui n'encombre pas le guide. / A plane acoustic wave propagated in a duct some walls of which are vibrating due to transversal or flexural waves gives rise to a set of various waves within the fluid and the structure. Within the fluid, the waves are evanescent, propagatives or propagatives with decreasing amplitudes. There is no need for the global operator to be dissipative for such a result since it is arising from destructive or constructive interferences. When the structural damping exists, as in the real life, it adds its effect to the coupling but not in a classical way as coupled acoustic/structure waves are at play rather than pure acoustic or structural waves. Now in presence of a convection of the fluid that bears the acoustic wave (a stationary and uniform flow), the attenuation is reduced sligtly at the very low Mach numbers, and significantly at higher Mach numbers. As far as technological conclusions are sought, an averaged acoustic attenuation of around fifteen dB in a frequency range of some hundreds Hz centered at 500Hz can be obtained with this system very light and needing almost no room.

Noise induced hearing loss has been extensively researched and commented on, yet it remains prevalent among industrial workers. The real-world attenuation properties of the Noise Clipper® custom-made hearing protection device and the comfort levels it afford are unknown. Furthermore, research in hearing conservation is seldom focused on the critical/biological thresholds for temporary threshold shift. Field studies on hearing protection devices have demonstrated that laboratory derived measures bear little relation to attenuation achieved in workers. Research has consistently demonstrated that noise reduction ratings that are derived from the laboratory real-ear-at-threshold method do not accurately represent the attenuation of noise that these devices actually provide and the matter remains unclear. Too many important variables are neglected in current real-ear-atthreshold evaluation protocols. This study used an alternative method, the microphone-inreal- ear approach where a dual-element microphone probe was inserted into the Noise Clipper® to measure noise reduction by recording the difference in noise levels outside and behind the device. The sub aims of the study were to record ambient noise levels and frequency spectra; to determine the attenuation characteristics; and to compare the attenuation thresholds to biological thresholds for temporary threshold shift. Using this protocol, measurements were made on 20 subjects in real world situations in order to match the attenuation characteristics of the Noise Clipper® to the actual noise exposure. The microphone-in-real-ear derived attenuation thresholds were compared to the real-earat- threshold values provided by the manufacturer of the Noise Clipper®. Additional subaims were to determine the comfort levels of the Noise Clipper® and record the selfreported wearing time of the device. Wearing comfort was evaluated using a bipolar rating scale. The researcher interviewed 240 mine workers at a platinum mine. Several comfort related sub-scales were used to quantify reported comfort levels. Simultaneously, usage time of the device was self-reported by each worker. Results of the microphone-in-real-ear measurements indicated that ambient noise levels fluctuated from day to day. The attenuation results indicated that most of the measurements suggested protection against noise induced hearing loss through the use of the Noise Clipper®. It was found that the REAT results over estimated the attenuation ability of the Noise Clipper® when compared to the results of the F-MIRE measurements. Eighty seven percent of the measurements indicated protection from thresholds below the biological threshold for temporary threshold shift. Seventy five percent of the workers indicated that the Noise Clipper® was comfortable to wear and 79% indicated that they used it for a full eight hour shift. The results provide an opportunity to assess the use of a protection device and its effectiveness among mineworkers combined with information regarding noise exposure levels. The findings highlight the importance of evaluating variability in terms of individual-specific protection. / Dissertation (MCommunication Pathology)--University of Pretoria, 2013. / Speech-Language Pathology and Audiology / unrestricted