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An exhaust manifold of a truck engine is subjected to tough conditions. As the truck is started, operated and shut down, it becomes subjected to thermal cycling up to around 800°C. At such high temperatures, corrosion, fatigue and creep are active degradation mechanisms. As can be imagined, the interplay between the three complicates materials selection. It is desired to have a versatile grade of high durability which is not too expensive. At the moment, a ferritic, ductile cast iron designated SiMo51 is used for the application. However, due to the rough conditions, it is considered to be on the verge of its operational limit. As a consequence, there is an ongoing search for candidate materials. In this study, the ductile cast irons SiMo51, SiMo1000, D5S and the cast steel HK30 have been included. In the past, there have been several studies describing corrosion and fatigue of the cast materials used for exhaust manifolds. However, on the subject of creep of cast materials, little is known. The present study aims to reveal creep tendencies of cast materials and to do it in several ways. More precisely, three creep-testing methods were employed: the conventional constant-load creep-test, the “Sequential tensile test (STT)” and “Stress relaxations with thermal cycling (SRTC)”. The first one is the traditional one. It is tedious, usually lasting months or years. The second one is a tensile test in which the strain rate is changed in sequences as specimen deformation proceeds. Here, the idea is that a slow tensile test is not different from a conventional creep test. In the third one, stress relaxations are provoked as a specimen is thermally cycled in a locked state. Since stress relaxations are a consequence of creep deformation, the relaxation data gathered from isothermal holds can be directly compared to results from the isothermal constant-load creep-test and STT. When thermally cycled in a locked state, the materials display a loop character in σ, ε and T which provides extensive information about the mechanical properties over the selected temperature interval. In a logarithmic Norton plot, the creep strain rate is plotted as a function of stress. By plotting STT-data in such Norton plots, it was shown that the creep behaviour of the included materials is well represented by Norton’s law. Furthermore, it was found that the creep strain rates and stress relaxations, measured during isothermal holds in SRTC, in several cases show perfect coincidence with tensile test data obtained through STT. At 700°C, data from all three tests were inserted in the same Norton plot. At higher stress levels, the SRTC-curve follows the STT-curve and at lower stresses, when the creep regime is entered, it bends down and unites with data obtained by the constant-load creep tests. Additionally, it was seen that a relatively high degree of pre-deformation can give a critical stress below which creep deformation stops completely. / <p>The Financier is Scania CV. </p>

<p>The phenomenon of image blurring on laser-printed or electro-photocopied paper has been discovered since the 1980s. In the 1990s, the problem was confirmed to be associated with the undesired surface conduction along the unique photoconductive polymer surface during the photoconduction process. Other than this, little progress has been made in investigating this phenomenon, due to the limited experimental techniques.</p> <p>In this thesis, the electrical properties of a commercially available photoconductor as a result of Corona charging were studied. Various techniques including vacuum deposition and step-function impedance spectroscopy were employed, to overcome the nature of the photoconductor that prevented the use of conventional techniques such as AC impedance spectroscopy. Negative dielectric constant (NDC) has been prevalently discovered at a broad range of frequencies (below 1Hz and up to 1 MHz) and it was questioned in the form of a physically-impossible inductor. This precipitous sign switch of dielectric constant is found in various areas ranging from physics, chemistry, biology to electronics. The magnitude of the NDC decreased drastically with the decrease of electric field frequency. The system obeyed the proposed free-carrier plasma model with a resonance frequency at MHz level.</p> <p>Commercially available polymeric photoconducting materials showing NDC at extremely low frequency are expected to provide unusual scattering to electromagnetic waves and therefore demonstrate profound implications with reduced cost. It has paved the way for many applications such as inductors in integrated chips without bulky coils and provides an insight into a possible revolution in electronics and photonics.</p> / Doctor of Philosophy (PhD)

<p>In compressive sensing, the fundamental problem is to reconstruct sparse signal from its nonadaptive insufficient linear measurement. Besides sparse signal reconstruction algorithms, measurement matrix or measurement dictionary plays an important part in sparse signal recovery. Orthogonal Matching Pursuit (OMP) algorithm, which is widely used in compressive sensing, is especially affected by measurement dictionary. Measurement dictionary with small restricted isometry constant or coherence could improve the performance of OMP algorithm. Based on measurement dictionary, sensing dictionary can be constructed and can be incorporated into OMP algorithm. In this thesis, two methods are proposed to design sensing dictionary. In the first method, sensing dictionary design problem is formulated as a linear programming problem. The solution is unique and can be obtained by standard linear programming method such as primal-dual interior point method. The major drawback of linear programming based method is its high computational complexity. The second method is termed sensing dictionary designing algorithm. In this algorithm, each atom of sensing dictionary is designed independently to reduce the maximal magnitude of its inner product with measurement dictionary. Compared with linear programming based method, the proposed sensing dictionary design algorithm is of low computational complexity and the performance is similar. Simulation results indicate that both of linear programming based method and the proposed sensing dictionary designing algorithm can design sensing dictionary with small mutual coherence and cumulative coherence. When the designed sensing dictionary is applied to OMP algorithm, the performance of OMP algorithm improves.</p> / Master of Science in Electrical and Computer Engineering (MSECE)

Supramolecular host-guest chemistry is a topic of great current interest. However, the further development of host-guest chemistry is still limited by the number of available host-guest recognition motifs. This makes it necessary and valuable to find new host-guest recognition motifs and apply known host-guest recognition motifs in the preparation of novel supramolecular systems. By comparing the crystal structures of the host and its taco complex, we proved that folding is a necessary step during the formation of taco complexes. Based on the known bis(m-phenylene)-32-crown-10/paraquat recognition motif, the first solid-state supramolecular poly(taco complex) was prepared. We demonstrate not only that bis(m-phenylene)-32-crown-10-based cryptands are powerful hosts for paraquat derivatives compared with the simple crown ether, but also that cooperative complexation can be obtained with the cryptand structure. It was shown that the significant improvement in complexation was the result of the combination of the preorganization of the cryptand hosts and the introduction of additional and optimized binding sites. Furthermore, it was demonstrated that improved complexation of bis(secondary ammonium) and bisparaquat salts could also be achieved by the formation of the pseudocryptand structure. We also prepared two dimers of inclusion cryptand/paraquat complexes driven by dipole-dipole and face-to-face p-stacking interactions. An interesting complex based on dibenzo-24-crown-10 and diquat was prepared. In its crystal structure the diquat guest lies in the concave cavity provided by two dibenzo-24-crown-8 hosts. Monopyridinium-based [2]- and [3]-pseudorotaxanes were prepared based on the newly discovered bis(m-phenylene)-32-crown-10/monopyridinium salt and cryptand/monopyridinium salt recognition motifs. Inspired by the formation of solid-state taco complexes between bis(m-phenylene)-32-crown-10 and paraquat derivatives, we designed and synthesized the first cylindrical bis(crown ether) host for paraquat derivatives and studied its complexation with paraquat. We prepared three slow-exchange C3-symmetric inclusion complexes based on a newly discovered cryptand/trispyridinium recognition motif, in which 1,3,5-trispyridiniumbenzene salts act as guests. Finally the application of several new and known recognition motifs in the preparation of a supramolecular poly[3]pseudrotaxane, and the first pseudorotaxane-type supramolecular star-shaped polymer, and the first supramolecular hyperbranched polymer was discussed. / Ph. D.

The future voltage regulator module (VRM) challenges of high bandwidth control with fast transient response, high current output, simple implementation, and efficient 48V solution are tackled in this dissertation. With the push for control bandwidth to meet design specifications for microprocessor VRM with larger and faster load transients, control can be saturated and lost for a significant period of time during transient. During this time, undesirable transient responses such as large undershoot and ringback occurs. Due to the loss of control, the existing tools to study the dynamic behavior of the system, such as small signal model, are insufficient to analyze the behavior of the system during this time. In order to have a better understanding of the system dynamic performance, the operation the VRM is analyzed in the state-plane for a clear visual understanding of the steady-state and transient behaviors. Using the state-plane, a simplified state-plane trajectory control is proposed for constant on-time (COT) control to achieve the best transient possible for applications with adaptive voltage positioning (AVP). When the COT control is lost during a load step-up transient, the state-plane trajectory control will extend on-time to provide the a near optimal transient response. By observing the COT control law in the state-plane, a simplified state-plane trajectory control with analog implementation is proposed to achieve the best transient possible with smooth transitions in and out of the steady-state COT control. The concept of the simplified state-plane trajectory control is then extended to multiphase COT. For multiphase operation, additional operating behavior, such as phase overlapping during transient and interleaving during steady-state, need to be taken into consideration to design the desired state-plane trajectory control. A simple state-plane trajectory control with improved Ton extension is proposed and verified using multiphase COT control. After tackling the state-plane trajectory control for current mode COT, the idea is then extended to V2 COT. V2 COT is a more advanced current mode control which requires a more advanced state-plane trajectory control to COT. By calculating the intersection of the extended on-stage trajectory during transient and the ideal off trajectory in the form of a current limiting wall, a near optimal transient response can be achieved. For V2 COT with state-plane trajectory control, implementations using inductor vs. capacitor current, effect of component tolerance, and effect of IC delay are studied. The proposed state-plane trajectory control is then extended to enhanced V2 COT. Aside from tackling existing VRM challenges, the future datacenter 48V VRM challenge of a high efficiency, high power density solution to meet the VRM specifications is studied. The sigma converter is proposed for the 48V VRM solution due to exhibition of high efficiency and high-power density from hardware evaluation. An accurate model for the sigma converter is derived using the new modeling approach of modularizing the small signal components. Using the proposed model, the sigma converter is shown to naturally have very low output impedance, making the sigma converter suitable for microprocessor applications. The sigma converter is designed and optimized to achieve AVP and very fast transient response using both voltage-mode and current-mode controls. / Doctor of Philosophy / Microprocessors, such as central processing unit (CPU) and graphics processing unit (GPU) are the basis of today's electronics. In the recent decades, the demand for more powerful and faster data processing lead to a significant increase in power consumption by these microprocessors. Even with the introduction of multi-core processors and adaptive voltage positioning (AVP) to reduce the average power provided by the power supplies, the microprocessor can still draw a large amount of instantaneous power in a short period of time. With the microprocessors demanding high amount of current at fast slew-rate, the challenges for the next generation of microprocessor power supply, or voltage regulator modules (VRM), are fast response speed to ensure proper operation of the microprocessors, and high efficiency VRM to minimize the overall system power consumption. The challenge of a VRM with fast response speed is tackled first. To meet the AVP and transient requirements of microprocessor, the VR need to utilize high-bandwidth control methods. Of the control methods used by the industry, high control bandwidth can be easily achieved using constant on-time (COT) control. With the ever-increasing output current level and transient slew-rate requirements, COT control can saturate and lose its steady-state control for a period of time during load step-up transient. During this time, the system will operate with a fixed frequency control until COT control is recovered. Although the method is widely used in the industry, the method is too slow to meet the transient requirements. Many state-of-art methods have been proposed to resolve the load step-up transient issue of COT. However, of the methods proposed, it is difficult to optimize the transient improvement while having a simple analog implementation to ensure a fast response for the wide operating range and aggressive transient conditions observed in microprocessor VRM application. In this dissertation, COT control is studied using the state-plane to provide a clear visual understanding of the transient behavior of the control. Using the state-plane, a state-plane trajectory control is proposed to achieve near optimal load step-up transient response. The concept is then extended to multiphase VRM, which is typically used for high current applications. The state-plane trajectory control concept is then further extended to V2 COT control for VRM without AVP, such as those used by GPU and smartphone CPU. For the proposed state-plane trajectory controls, hardware implementation, evaluation, and experimental results are provided. After tackling the challenge of a VRM with fast response speed, the challenge of an efficient VRM is then tackled. In recent years, a significant amount of research has been put into studying VRM for a power delivery architecture which uses a 48V bus instead of the 12V bus. By using the 48V bus, less redundancy in the power delivery path can greatly increase the overall system efficiency if the VRM stage retains its efficiency. However, the increase in input voltage for the VRM provides an additional challenge to maintain high efficiency for the VRM stage itself. To maintain good efficiency, it is difficult to increase converter switching frequency beyond 300kHz. This limitation on switching frequency will limit the ability to achieve high bandwidth design and fast transient requirements. A 48V VRM using a different topology, the sigma converter, has demonstrated high-efficiency and high-power density, but the converter behavior and control methodology for VRM application is unclear. In this dissertation, the modeling and control of the sigma converter are studied using the proposed small-signal model. By evaluating the proposed small-signal model, the sigma converter can naturally have very low output impedance, making it an ideal candidate for 48V VRM. Then, the design guideline of the sigma converter with current-mode control is provided. With the work discussed in this dissertation, further study of the sigma converter with COT and state-plane trajectory control can be conducted in the future.

Smart cameras operate mostly in sleep mode, which is light load for power supplies. Typical buck converter applications have low efficiency under the light load condition, primarily from their power stage and control being optimized for heavy load. The battery life of a smart camera can be extended through improvement of the light load efficiency of the buck converter. This thesis research investigated the first stage converter of a car black box to provide power to a microprocessor, camera, and several other peripherals. The input voltage of the converter is 12 V, and the output voltage is 5 V with the load range being 20 mA (100 mW) to 1000 mA (5000 mW). The primary design objective of the converter is to improve light load efficiency. A 3-level buck converter and its control scheme proposed by Reusch were adopted for the converter in this thesis. A 3-level buck converter has two more MOSFETs and one more capacitor than a synchronous buck converter. Q1 and Q2 are considered the top MOSFETs, while Q3 and Q4 are the synchronous ones. The extra capacitor is used as a second power source to supply the load, which is connected between the source of Q1 and the drain of Q2 and the source of Q3 and the drain of Q4. The methods considered to improve light load efficiency are: PFM (pulse frequency modulation) control scheme with DCM (discontinuous conduction mode) and use of Schottky diodes in lieu of the synchronous MOSFETs, Q3 and Q4. The 3-level buck converter operates in CCM for heavy load above 330 mA and DCM for light load below 330 mA. The first method uses a COT (constant on-time) valley current mode controller that has a built in inductor current zero-crossing detector. COT is used to implement PFM, while the zero-crossing detector allows for DCM. The increase in efficiency comes from reducing the switching frequency as the load decreases by minimizing switching and gate driving loss. The second method uses an external current sense amplifier and a comparator to detect when to shut down the gate drivers for Q3 and Q4. Schottky diodes in parallel with Q3 and Q4 carry the load current when the MOSFETs are off. This increases the efficiency through a reduction in switching loss, gate driving loss, and gate driver power consumption. The proposed converter is prototyped using discrete components. LTC3833 is used as the COT valley current mode controller, which is the center of the control scheme. The efficiency of the 3-level buck converter was measured and ranges from 82% to 95% at 100 mW and 5000 mW, respectively. The transient response of the converter shows no overshoot due to a 500 mA load step up or down, and the output voltage ripple is 30 mV. The majority of the loss comes from the external components, which include a D FF (D flip-flop), AND gate, OR gate, current sense chip, comparator, and four gate drivers. The proposed converter was compared to two off-the-shelf synchronous buck converters. The proposed converter has good efficiency and performance when compared to the other converters, despite the fact that the converter is realized using discrete components. / Master of Science

Master of Science

The research presented in this thesis focused on pseudorotaxanes and supramolecular polymers based on a new recognition motif, the dibenzo-24-crown-8/paraquat recognition motif. Main kinds of pseudorotaxanes and rotaxanes and various protocols used for the study of them were discussed first. By preparation and characterization of a series of pesudorotaxanes based on DB24C8 and paraquat derivatives, it was found that these complexes were stabilized by N+...O interactions, C-H...O hydrogen bonding, and face-to-face p-stacking interactions. Because methyl protons of paraquat are involved in hydrogen bonding to the host, the substitution of any methyl hydrogen on paraquat causes apparent association constant of the pseudorotaxane to decrease. The concentration dependence of apparent association constants, Ka,exp, of fast exchange host-guest systems was studied for the first time by using complexes based on viologens and crown ethers as examples. While the bis(hexafluorophosphate) salts of paraquat derivatives are predominantly ion paired in acetone (and other low dielectric constant solvents presumably) the complex based on dibenzo-24-crown-8 and paraquat is not ion paired in solution, resulting in concentration dependence of Ka,exp. However, four complexes of two different bis(m-phenylene)-32-crown-10 (BMP32C10) derivatives and bis(p-phenylene)-34-crown-10 (BPP3C10) with viologens are ion paired in solution, as shown by the fact that Ka,exp is not concentration dependent for these systems involving hosts with freer access to bound guests. X-ray crystal structures support these soluton-based assessments in that there is clearly ion pairing of the cationic guest and its PF6- counterions in the solid states of the latter four examples, but not in the former. The complexes based on the new dibenzo-24-crown-8/paraquat recognition motif are thus different from the complexes based on two old recognition motifs: the BPP34C10/BMP32C10-paraquat and DB24C8-ammonium motives. In order to compare these recognition motives further, the selectivity between two hosts, DB24C8 and BPP34C10, and two guests, dimethyl paraquat and dibenzyl ammnonium salt, was discussed. By individual and competitive complexation studies, it was demonstrated that DB24C8 is a better host than BPP34C10 for paraquat, and that paraquat is a better guest than dibenzyl ammonium salt for DB24C8. Finally the DB24C8-paraquat recognition motif was successfully applied in the preparation the first star-shaped supramolecular polymer based on a tetraparaquat guest and a DB24C8 functionalized polystyrene oligomer. A model system based on this guest and DB24C8 was also studied for comparison. It was found that the complexation in these two systems is cooperative, as are most biological complexations of multitopic species. Due to the ready availability of DB24C8 and paraquat derivatives, the new recognition motif should prove to be very valuable for self-assembly of other more sophisticated supramolecular systems. / Master of Science

Recently, as a promising lighting source, light-emitting diodes (LEDs) have become more and more attractive and have great opportunity to replace traditional lighting sources - incandescent, fluorescent and HID because of the advantages such as high luminous efficacy, long lifetime, quick on/off time, wide color gamut, eco-friendly etc. Based on the research from U.S. Department of Energy, over 30% of total electric consumption in U.S. each year is for lighting, 75% of which are for indoor lighting (including both residential and commercial buildings). In the indoor LED lighting application, to provide multiple current source outputs for multiple LED strings, traditional solutions usually adopt a two-stage structure, which is complicated and cost-ineffective. How to design a simple, low-cost and efficient LED driver with multiple current source outputs is in great demand and really challenging. In this thesis, a single-stage multi-channel constant current (MC3) LED driver structure has been proposed. Multiple transformer structure is utilized to provide multiple current source outputs. The current control scheme is also simple - only one LED string current is sensed and controlled; other strings' currents are cross regulated. Firstly, a PWM half bridge topology is chosen to implement the proposed single-stage MC3 LED driver concept. In order to analyze the current cross regulation, a general model is derived. The circuit has been simulated under various LED load conditions to verify its good current sharing capability. In order to further improve efficiency, simplify the driver's complexity and reduce cost, a LLC resonant topology is also investigated. LLC current gain characteristic has been derived by considering LED's i-v character and a design procedure is developed. A 100 kHz, 200 W, 4-string MC3 LLC LED driver is designed and tested. The experimental results show that the driver can maintain constant current output within the whole input and output variations, achieve good efficiency and realize current sharing under both balanced and unbalanced LED conditions. The dimming function can also be realized through frequency modulation method and burst mode control method. As a conclusion, a single-stage MC3 LED driver concept is proposed and implemented with two topologies. The proposed idea provides a simple, low-cost and efficient solution for indoor LED lighting application with multiple LED string configuration. It also has good current sharing capability and robustness to LED forward voltage variations or short failures. / Master of Science