Tonal noise propagating in ducts and radiating from their outlets is a common problem in situations where a fan or a blower is used to drive exhaust gases through the exhaust duct out to the environment. It is also a problem in the exhausts of large diesel engines such as those used to power large marine vessels. One way of attenuating tonal noise propagating in ducts is to use one or more side branch resonators, each of which is specifically designed for optimal performance at a particular frequency. One of the major problems associated with the use of side branch resonators is that any slight change in excitation frequency decreases the effectiveness of the resonators. The change in excitation frequency can be caused by a change in the speed of the engine, fan or blower, or change in temperature in the duct, which changes the speed of sound, and hence the wavelength of the noise. Resonators incorporating a provision for altering their geometry in real - time in order to adapt to environmental or operating condition changes is one approach that has been used by previous researchers. In particular, adaptive Helmholtz resonators have received considerable attention in the literature. Previous work has involved the use of one or more pressure sensors located in the duct downstream of the resonator to provide a cost function to be minimised by an electronic control system which alters the geometry of the resonator. However, in many cases, especially where the duct serves as a passage for exhaust gases to be driven out to the environment, it is not desirable to mount microphones in the duct. Also, microphones located remote from the resonator introduce wiring problems as well as the need to mount the microphones at the correct location in the duct, which will change as the wavelength of the tonal noise in the duct changes as a result of changes in operating or environmental conditions. It is highly desirable to have a completely self - contained Helmholtz resonator ( HR ) which can be attached to the duct and for which the only external wiring needed is the power supply. The work described in this thesis is concerned with the development of a self - contained adaptive HR which can be optimally tuned by using signals from two microphones located in the cavity and neck of the resonator, respectively. The primary focus of the work is the development of a novel cost function, which can be used by an electronic controller to optimally tune the HR. The scope of the analysis has been restricted here to the ' no mean flow ' condition. The theoretical and numerical analysis of the duct - HR system is first conducted using the well known transfer matrix method and finite element analysis ( FEA ) software package ANSYS, respectively. The net acoustic power transmission in the duct downstream of the HR is estimated by using the two - microphone method. Analysing the duct - HR system with the transfer matrix method mandates the incorporation of three end - correction factors which are related to the unflanged open end of the duct, neck - cavity interface and neck - duct interface. However, because of the complexity in estimating the end - correction factor of the neck at the neck - duct interface due to the generation of a complex sound field in the vicinity of the neck opening, the transfer matrix method only approximates the in - duct net acoustic power transmission. This implies that changing the value of the neck - duct interface end - correction factor changes the calculated frequency at which the maximum reduction of in - duct net acoustic power transmission downstream of the HR occurs. On the other hand, ANSYS does not require the inclusion of any kind of end - correction factors apart from the actual physical dimensions of the system, and is thus much more accurate than the transfer matrix method. To minimise the in - duct net acoustic power transmission downstream of the HR, a number of different cost functions that were related to the net acoustic power transmission were investigated theoretically, numerically and experimentally. These all involved either the acoustic pressure at the top of the closed end of the cavity of the HR or at the neck wall of the HR close to the neck - duct interface or the amplitude of the pressure transfer function between two microphones located in the resonator. The two potential cost functions which were initially considered to be maximised for indicating the minimisation of the in - duct net acoustic power transmission downstream of the resonator were : ( a ) the pressure at the top of the closed end of the cavity, and ( b ) the amplitude of the pressure transfer function between the pressure at the top of the closed end of the cavity and the pressure at the neck wall close to the neck - duct interface. It was found that the location of the microphone in the neck was extremely important, with the best location being at the centre of the duct adjacent to the neck opening. However, this location was not considered practical because a microphone in the duct can obstruct the mean flow of gas in the duct. The best location for mounting the microphone in the neck was found to be at the neck wall as close as possible to the neck - duct interface. The results are shown in two different ways : ( 1 ) broadband analysis, whereby the in - duct net acoustic power transmission downstream of the HR, the pressure at the top of the closed end of the cavity and the pressure transfer function between the pressure at the top of the closed end of the cavity and at the neck wall close to the neckduct interface are plotted as a function of frequency, and ( 2 ) single frequency analysis, whereby all the aforementioned results are plotted as a function of the cylindrical cavity length ( for a fixed cavity diameter ) for a single, tonal frequency. For broadband analysis, the numerical ( ANSYS ) results showed that the frequency at which the maximum reduction of in - duct net acoustic power transmission downstream of the HR occurs differs from the frequencies which correspond to the maximum responses of cost functions ( a ) and ( b ) described above. For single frequency analysis, when trying to optimise the performance of a duct - mounted HR at a particular frequency by altering its volume, the optimal dimensions of the HR required to attain the maximum reduction of in - duct net acoustic power transmission at that frequency differ from the dimensions of the HR which correspond to the maximised responses of the cost functions ( a ) and ( b ). These results were validated experimentally using a 3 m long circular duct of 0.1555 m diameter with an attached cylindrical HR. During the experimental work, only plane waves were propagating down the duct and there was no mean flow in the duct. Instead of only focusing on the amplitude of the pressure transfer function between the pressures at the top of the closed end of the cavity and the pressure at the neck wall close to the neck - duct interface, the phase difference between the same locations in the HR was also considered. It was found that the phase difference depends on the quality factor ( or damping ) of the entire acoustic system. Experiments were conducted with varying dimensions of the HR and two novel cost functions were empirically derived. Both cost functions, which does not include any kind of measurement remote from the HR, are based on the damping ( or the quality factor ) of the duct - HR system and the phase difference between the pressure at the top of the closed end of the cavity and the pressure at the neck wall close to the neck - duct interface. The effectiveness and performance of both cost functions were found to be excellent for minimising the in - duct net acoustic power transmission downstream of the HR. However, the second cost function is preferred because the procedure involved for measuring the system damping is more convenient from the practical point of view than the procedure for the first one. The quality factor of the duct - mounted HR, at the frequency at which noise needs to be attenuated, was determined by tuning the length of the cavity of the HR so as to maximise the amplitude of the pressure transfer function of the HR. This estimated quality factor was found to be directly related to the transfer function phase which corresponds to the minimum in - duct net acoustic power transmission at the tonal frequency. Once this optimum transfer function phase is known, an active control system can be used to drive a motor to adjust the cavity length of the HR to achieve the optimum phase. / Thesis (M.Eng.Sc.)--School of Mechanical Engineering, 2006.

There is ever-increasing demand in telecommunication system, data server and computer equipment for low voltage, high current power supply. LLC resonant converter is a good topology on primary side of the converter because it has soft switching and resonant conversion. However, the passive rectifier in the secondary side has high power dissipation. Synchronous rectifier is a popular method to reduce this rectification loss. Although there are many types of synchronous rectifier for PWM converter, most of them do not function well in LLC resonant converters. It is because the wave form of LLC resonant converter is different from PWM. The objective of this research is to reduce the power dissipation and physical size at the same time. In this thesis, a novel current driven synchronous rectifier with saturable current transformer and dynamic gate voltage control for LLC resonant Converter is presented. This novel circuit reduces the rectification loss and size of the current transformer in the synchronous rectifier. This synchronous rectifier has several outstanding characteristics compared with generic voltage driven and current driven synchronous rectifier. The saturable feature reduces the current transformer turns. Inherent dynamic gate voltage controlled by saturable current transformer reduces gate loss in the MOSFET. A novel driving circuit is proposed for accurate turn off time. It reduces loss significantly. This synchronous rectifier is completely self-contained which can replace the rectifier diode as a drop in replacement. It is insensitive to parasitic inductance. In order to explain the current transformer saturable, a model of saturable current transformer is proposed. A prototype demonstrates the advantages of the proposed current driven synchronous rectifier. Furthermore, a novel integrated synchronous rectifier is presented which provides a more compact system. The synchronous rectifier current transformer is integrated with the main transformer which reduces the number of circuit joints in power path. Each soldering joint generates significance loss in power converter. A pair of 0.5mΩ soldering joint in 25A current path produces 0.62W loss. The placement of the integrated current transformer is important. A criterion for the placement of the current transformer within the main transformer is to avoid interference to the current transformer from the magnetic flux of the main transformer. Thus, a placement method to integrate the current transformer into the main transformer is proposed. An integrated current transformer model is suggested to explain the operation of the integrated synchronous rectifier. A prototype demonstrates the advantages of the integrated synchronous rectifier. / published_or_final_version / Electrical and Electronic Engineering / Master / Master of Philosophy

High power conversion efficiency is desirable in power supplies. Design optimization of on-line power converter is presented in this thesis. High efficiencies over a wide load range, for example 20%, 50% and 100% load, are often required. It is a challenge for on-line pulse-width modulation (PWM) converters to maintain good efficiencies with light load as well as full load. A two-stage multi-objective optimization procedure is proposed to optimization power converter efficiencies at 20%, 50% and 100% load. Two-FET forward prototype converters are built to verify the optimization results. The LLC (abbreviation of two resonant inductor L and one resonant capacitor C ) series resonant converter can provide high power conversion efficiency because of the resonant nature and soft switching. The design of LLC resonant converter is more difficult than that of PWM converters since the LLC resonant converter has many resonant modes. Furthermore, the LLC resonant converter does not have analytical solution for its resonant operation. In this thesis, a systematic optimization procedure is proposed to optimize LLC series resonant converter efficiency. A mode solver technique is developed to solve LLC resonant converter operations. The proposed mode solver employs non-linear programming techniques to solve a set of LLC state equations and determine the resonant modes. Loss models are provided which serve as the objective-function to optimize converter efficiency. Optimization results show outstanding efficiency performance and experimental agreement with optimization. The optimization work extends to the LLC resonant converter with power factor correction (PFC) circuits where the effect of LLC converter input voltage variation cased by the PFC circuit is considered. Detail comparisons of PWM converter and LLC resonant converter loss profiles are also presented. The reasons that LLC resonant converter has higher efficiency are given and supported by quantitative data. Converter lifetime is highly related to component losses and temperature. The lifetime analysis is presented. The analysis reveals that the LLC resonant converter output capacitor is the weakest component concerning life. / published_or_final_version / Electrical and Electronic Engineering / Doctoral / Doctor of Philosophy

Thesis (M.Eng.Sc.) -- University of Adelaide, School of Mechanical Engineering, 2007. / Includes author's previously published papers. "Dissertation submitted for the award of the degree of Master of Engineering Science on the 25th of September, 2006. Qualified on the 28th November, 2006" Includes bibliography (p. 191-199) Also available in print form.

Thesis (Ph. D.)--University of Oregon, 2006. / Typescript. Includes vita and abstract. Includes bibliographical references (leaves 204-213). Also available for download via the World Wide Web; free to University of Oregon users.

Two new power conversion techniques, the constant-frequency zero-voltage-switching multiresonant-converter (CF ZVS-MRC) technique and the zero-voltage-switching technique that uses the magnetizing inductance of the power transformer as a resonant element {ZVS {L_M)) are proposed. analyzed, and evaluated for high-frequency applications. In addition, a novel design optimization approach for resonant type converters is introduced. Complete dc analysis of CF forward and half-bridge {HB) ZVS-MRCs are given, and the dc voltage-conversion-ratio characteristics for each of these two converters are derived. Graphic design procedures that maximize the efficiency and minimize current and voltage stresses are established. The design guidelines are verified on a 50 W CF forward ZVS-MRC operating with a switching frequency above 2 MHz, and on a 100 W HB ZVS-MRc operating with a switching frequency of 750 kHz. The ZVS (LM) technique is developed to eliminate the need for a large, inefficient external resonant inductor in ZVS resonant converters. This new family of isolated converters can operate with zero-voltage-switching of the primary active switches only (quasi-resonant (QR) operation) or with soft-switching of all semiconductor devices (multi-resonant (MR) operation). Furthermore, variable and constant frequency operation of all topologies in this new family of dc/dc converters are possible. A complete dc analysis of the HB ZVS-MRC (L_M) is given, and the dc voltage-conversion-ratio characteristics are derived. Design guidelines are defined using the same graphic method employed in the design of CF ZVS-MRCs. Constant frequency implementation of the HB ZVS-MRC (L_M) using controllable saturable inductors is also proposed. Finally, a novel approach to evaluate and design resonant converters based on the minimization of reactive power is developed. / Ph. D.

This thesis describes a method for using stripline resonators to characterize the electrical properties of materials used in the construction of planar geometry transmission lines and circuits. The method characterizes both dielectric and conductor materials. It can be used to find the relative dielectric constant and to separate the conductor and dielectric losses. The separation of the loss terms is achieved by fitting measurements of stripline losses to a well known model. This model identifies the loss terms separately based on variation of the losses with stripline dimensions. This thesis presents the complete stripline resonator model used. The model has been incorporated into a computer simulation which predicts the resonator response. This simulation is useful in many ways, including the design of various resonators needed in experiments. Also presented are the results of an experiment which demonstrates the feasibility of this method when applied to real samples. These results show that this method works well for low loss materials. Further development may produce 6 model which will allow this method to be used on higher loss materials. A similar theoretical derivation may be used to develop a model for using this method with other transmission line structures such as coaxial lines. This method is advantageous because it does not assume that material properties are independent of frequency and can be designed to produce results at a specific frequency. Stripline resonators are easily manufactured and a network analyzer is the only test equipment required. For these reasons, this method can be used to provide accurate results at a low cost. / Master of Science

Narrowband spectral filters find important applications in optical fiber communication systems, particularly in wavelength demultiplexers and single-frequency semiconductor lasers. Conventional Fabry-Perot resonators provide a narrow spectral width but lack the capability of mode discrimination. A new coupled-waveguide Fabry-Perot resonator made of two parallel waveguides with reflecting mirrors at the ends is proposed for application as narrowband tuned spectral filter in single-mode diode lasers and wavelength demultiplexers. The interference of counter propagating waves from reflection by end mirrors and the coupling of waves between the two parallel guides contribute to the operation of this resonator structure. Thus, the device exhibits the attributes of both Fabry-Perot resonator and directional coupler. The coupled-mode theory of parallel waveguides is employed to analyze the proposed structure. Spectral characteristics are derived from the governing coupled-mode equations and related boundary conditions. Two geometries consisting of identical waveguides, as well as nonidentical waveguides, are examined. The spectral characteristics of the proposed resonator demonstrate that significant improvement in mode discrimination capability and longitudinal mode spacing over the conventional Fabry-Perot resonator is achieved. Numerical results for several example cases are presented and the influence of various parameters on spectral properties are investigated. / Master of Science

This dissertation reports, for the first time, on the electrical coupling of microelectromechanical (MEM) resonators for high order bandpass filter synthesis. Electrical coupling of MEM resonators has a strong potential for extension of the operating frequency of MEM bandpass filters into the ultra high frequency (UHF) range and provides higher tunability and design flexibility compared to the mechanical coupling approach. Various schemes of electrical coupling are presented in this dissertation. Electromechanical models of clamped-clamped beam resonators, and various types of electrically coupled filters are presented. Lower frequency prototypes of electrically coupled filters with operating frequencies in the hundreds of kHz are implemented using micromechanical single crystal silicon clamped-clamped beam resonators. Measurement results are in good agreement with the developed electrical equivalent models of the filters. It is demonstrated that the characteristics of electrically coupled filters can be widely tuned by changing the DC polarization voltages.

Thesis (Ph. D.)--Ohio State University, 2005. / Title from first page of PDF file. Includes bibliographical references (p. 115-120).