No description available.

The ZEBRA battery based on Na/NiCb chemistry shows promise for powering electric vehicles and load leveling systems. The ZEBRA cell consists of a liquid sodium negative electrode separated from the positive electrode by a W'-alumina solid electrolyte. The current state of development of this battery makes use of glass sealing and thermo compression sealing as an integral part of the cell assembly. One objective of the present research was to reduce the thickness of the W'alumina electrolyte thickness as a means to improve perfomance, by lowering the internal cell resistance. The second objective was to develop a ceramic seal with matching thermal expansion coefficient (TEC) to increase battery durability. An added benefit realized with the new ceramic seal was its use for high temperature applications such as emf measurements ordinary systems to determine thermodynamic properties. Dense electrolyte tubes with reduced thickness of less than 100 J..Lm and supported on a porous substrate were successfully produced by slip casting. The slip casting parameters, sintering conditions and materials were optimized and electrolyte resistance was measured by a DC method. A ceramic seal was developed from a eutectic mixture of Na20 and Al203 and tested in galvanic cells. The reproducibility of the emf data shows that the seal is fully impervious and can sustain a high alkali pressure atmosphere up to 1 000°C without cracking or degradation. The seal microstructure revealed liquid phase formation of the seal and diffusion bonding with the lid and tube. The thermodynamic properties and phase relations of the Na-Si binary system were studied by the emf method using Na|β-alumina|Si-Na galvanic cells over the whole composition range below 600°C. There is very limited solubility of Si in molten Na. Properties of the sodium silicon compounds were determined from the emf measurements. / Thesis / Doctor of Philosophy (PhD)

The dissertation solved some critical issues in thermoelectric energy harvesting and tried to broaden the thermoelectric application for energy recovery and sensor powering. The scientific innovations of this dissertation were based on the new advance on thermoelectric material, device optimization, fabrication methods, and system integration to increase energy conversion efficiency and reliability of the thermoelectric energy harvester. The dissertation reviewed the most promising materials that owned a high figure of merit (ZT) value or had the potential to increase ZT through compositional manipulation or nano-structuring. Some of the state-of-art methods to enhance the ZT value as well as the principles underneath were also reviewed. The nanostructured bulk thermoelectric materials were identified as the most promising candidate for future thermoelectric applications as they provided enormous opportunities for material manipulation. The optimizations of the thermoelectric generator (TEG) depended on the accuracy of the mathematical model. In this dissertation, a general and comprehensive thermodynamic model for a commercial thermoelectric generator was established. Some of the unnecessary assumptions in the conventional models were removed to improve the accuracy of the model. This model can quantize the effects of the Thomson effect, contact thermal and electrical resistance, and heat leakage, on the performance of a thermoelectric generator. The heat sink can be another issue for the design of high-performance TEG. An innovative heat sink design integrated with self-oscillating impinging jet generated by the fluidic oscillator arrays were adopted to enhance the heat convection. The performance of the heat sink was characterized by large eddy simulation. The compatibility mismatch had been a practical problem that hindered the further improvement of energy conversion efficiency of thermoelectrics. In this dissertation, a novel method to optimize the geometry of the thermo-elements was developed. By varying the thickness and cross-sectional area of each thermoelectric segment along the length of the thermo-element, the compatibility mismatch problem in the segmented TEG construction was eliminated. The optimized segmented TEG can make the best of the existing thermoelectric materials and achieve the maximum energy conversion efficiency in a wide temperature range. A segmented TEG with an unprecedented efficiency of 23.72% was established using this method. The complex geometry structure of the established thermo-elements would introduce extra difficulty in fabrication. Thus selective laser melting, a high-temperature additive manufacture method, was proposed for the fabrication. A model was built based on the continuous equations to guide the selective-laser-melting manufacturing of thermoelectric material with other nanoparticles mixed for high thermoelectric performance. Thermoelectric energy harvesting played a critical role in the self-powered wireless sensors, as it was compact and quiet. In this dissertation, various thermoelectric energy harvesters were established for self-powered sensors to in-situ monitor the working condition in the gas turbine and the interior conditions in nuclear canisters. The sensors, taking advantage of the thermal energy existing in the local environment, can work continuously and provide tremendous data for system monitor and diagnosis without external energy supply. / Doctor of Philosophy / The dissertation addressed some critical issues in thermoelectric energy harvesting and broadened its application for energy recovery and sensor powering. Some of the most advanced technologies were developed to improve the energy conversion efficiency and reliability of the thermoelectric energy harvesters. In this dissertation, a general and comprehensive thermodynamic model for a commercial thermoelectric generator (TEG) was established. The model can be used to optimize the design of the existing commercial TEG modules. High performance heat sink design was critical to maximize the temperature drop in the TEG module, thus increase the power output and energy conversion efficiency of the TEG. An innovative heat sink design integrated with self-oscillating impinging jet generated by the fluidic oscillator arrays were designed to cool the cold end of the TEG, thus enhance the performance of the TEG. The performance of the heat sink was characterized by large eddy simulation. A single thermoelectric material only had high thermoelectric performance in a narrow temperature range. A segmented TEG could achieve a high energy conversion efficiency over a wide temperature range by adopting different materials which had high thermoelectric performance at low, moderate, and hight temperature ranges. However, the material compatibility mismatch had been a practical problem that hindered the further improvement of energy conversion efficiency of the segmented TEG. In this dissertation, a novel method was developed to eliminate the compatibility mismatch problem via optimizing the geometry of the thermo-elements. A segmented TEG with an unprecedented efficiency of 23.72% was constructed using the method proposed in this dissertation. The complex geometry structure of the established thermo-elements would introduce extra difficulty in fabrication. Thus selective laser melting, a high-temperature additive manufacture method, was proposed for the fabrication. A physical model based on the v conservation equations was built to guide the selective-laser-melting manufacturing of the optimized segmented TEG mentioned above. In this dissertation, two thermoelectric energy harvesters were built for self-powered sensors to in-situ monitor the interior conditions in nuclear canisters. The sensors, taking advantage of the thermal energy existing in the local environment, can work continuously and provide tremendous data for system monitor and diagnosis without external energy supply. Also, a compact thermoelectric energy harvester was developed to power the gas sensor for combustion monitoring and control.

The capability of CFD is assessed by utilizing CFDShip-Iowa V4.5 for the prediction of the 6DOF motion responses, forces, moments and the local flow field of the 2.7m KCS model in various weather/operating conditions. The discretized propeller is preferred and the rudder is designed to be active up to ±35 degrees. Grid triplets are generated with the refinement ratio √2 and verification is achieved for the resistance and propeller open water tests while for the other tests is only partially fulfilled. The verification shows unsmooth convergence, however, the errors from grid triplets are small. The propeller open water test validates the performance of the discretized propeller successfully. The free decay tests could predict reasonable heave/pitch/roll natural frequencies. The resistance test verifies the nominal wake distribution. The self-propulsion test using discretized propeller shows 18% higher propeller inflow and 0.1 thrust deduction factor compared to resistance test. A propeller blade that sweeps the starboard experienced higher thrust inducing non-axisymmetric propeller wake and thus affecting the angle of attack of the rudder. Neutral rudder angle diminishes effective angle of attack and keeps the course straight. Maneuvering simulations could predict qualitatively good agreement for validation variables while the trajectory needs more improvement. Using the discretized propeller for the head/oblique wave course-keeping simulations achieved validation successfully. The RAO of added thrust, torque and propeller rotational speed resembles the RAO of added-resistance except showing larger values during long waves. The mean propeller efficiency is at the minimum when the ship experiences a resonance. The first harmonic amplitude of the propeller efficiency increases followed by the increase of the wavelength.

abstract: Bioimpedance measurements have been long used for monitoring tissue ischemia and blood flow. This research employs implantable microelectronic devices to measure impedance chronically as a potential way to monitor the progress of peripheral vascular disease (PVD). Ultrasonically powered implantable microdevices previously developed for the purposes of neuroelectric vasodilation for therapeutic treatment of PVD were found to also allow a secondary function of tissue bioimpedance monitoring. Having no structural differences between devices used for neurostimulation and impedance measurements, there is a potential for double functionality and closed loop control of the neurostimulation performed by these types of microimplants. The proposed technique involves actuation of the implantable microdevices using a frequency-swept amplitude modulated continuous waveform ultrasound and remote monitoring of induced tissue current. The design has been investigated using simulations, ex vivo testing, and preliminary animal experiments. Obtained results have demonstrated the ability of ultrasonically powered neurostimulators to be sensitive to the impedance changes of tissue surrounding the device and wirelessly report impedance spectra. Present work suggests the potential feasibility of wireless tissue impedance measurements for PVD applications as a complement to neurostimulation. / Dissertation/Thesis / Masters Thesis Bioengineering 2015

Re-powering solar PV plants is an upcoming discussion on the global stage. Although the respective component warranties indicate the time to change the system machinery, the methodology and justification for carrying this out are two aspects that need further study. The rooftop solar PV system on top of Dalarna University was re-positioned in 2014. Prior to installing the system in its new position, the system arrays were reconfigured and new inverters were installed. This thesis aimed to compare and analyze two sections of the solar power plant to understand which amongst them performs better. Graphs depicting energy, current, voltage and other parameters were formulated to ascertain the efficacy of the array configurations for this Nordic latitude. Thereafter, PVsyst and SAM were used to compare the simulated results with the actual output from the system. It was found that the measured energy output from one section of the solar power plant was higher than that of the other during 2014. On an annual basis, this difference was 21.5 kWh or 2%. On closer inspection, this contrast was attributed to a difference in yield early in the morning. Further, PVsyst simulated the annual energy with a deviation of less than 1% than what was measured, whereas SAM measured a deviation in energy measurement of 2.5% higher than the actual measured energy. These values were obtained using the detailed design options for both softwares. A point to keep in mind is that prior experience of working with both these softwares is recommended prior to carrying out the simulations on these softwares. An underlying point to note in this study is its limitations. This study is valid in the northern latitudes, such as the Nordic climates, since other regions would not have such low (sub-zero) temperatures to account for while sizing the inverter. In regions of high irradiance, a system re-powered in a way such as the system in this case would have higher clipping losses. Relevant previous studies and related topics have been visited, summarized and cited.

<p>Implantable biomedical devices have been widely used to treat a variety of diseases for many decades. If allowed by the size and form factor, batteries have been the power source of choice in implantable devices (e.g., cardiac pacemakers). Batteries are, however, still big and come in shapes that are not ideal for minimally invasive deployment. Inductive powering is another commonly used energy source in which two well-aligned coils allow a transmitter to power the implanted receiver (e.g., cochlear implants). Once the receiver coil becomes small (mm-scale), the inductive powering link becomes very inefficient and sensitive to slight misalignment between the coils. Hence, it becomes increasingly difficult to power small devices implanted deep (>5 cm) within the tissue using inductive powering. Ultrasonic powering is an attractive alternative for powering miniature devices since it can penetrate deep into the tissue, it has greater efficiency at mm-scale receiver size, it can be omni-directional, and it is more amenable to miniaturization.</p> <p>In this dissertation, I describe the use of ultrasonic waves to power and control mm-scale implantable devices. After a detailed look at ultrasonic transmission link, I will discuss factors affecting the power transfer efficiency. These include the effect of receiver aspect ratio and size on the resonant frequency and factors related to acoustic and electrical matching. A 3D printed acoustic matching layer in then described. I will discuss two applications using ultrasound to power and control implantable devices. The first is a low-power on-off acoustic control scheme to reduce the standby power consumption in implantable devices. The second is an ultrasonically powered electrolytic ablator with an on-board micro-light-source for the treatment of cancer.</p>

Wireless power transfer (WPT) is the key enabler for a myriad of applications, from low-power RFIDs, and wireless sensors, to wirelessly charged electric vehicles, and even massive power transmission from space solar cells. One of the major challenges in designing implantable biomedical devices is the size and lifetime of the battery. Thus, replacing the battery with a miniaturized wireless power receiver (WPRx) facilitates designing sustainable biomedical implants in smaller volumes for sentient medical applications. In the first part of this dissertation, we propose a miniaturized, fully integrated, wirelessly powered implantable sensor with on-chip antenna, designed and implemented in a standard 0.18μm CMOS process. As a batteryless device, it can be implanted once inside the body with no need for further invasive surgeries to replace batteries. The proposed single-chip solution is designed for intraocular pressure monitoring (IOPM), and can serve as a sustainable platform for implantable devices or IoT nodes. A custom setup is developed to test the chip in a saline solution with electrical properties similar to those of the aqueous humor of the eye. The proposed chip, in this eye-like setup, is wirelessly charged to 1V from a 5W transmitter 3cm away from the chip. In the second part, we propose a self-biased, differential rectifier with enhanced efficiency over an extended range of input power. A prototype is designed for the medical implant communication service (MICS) band at 433MHz. It demonstrates an efficiency improvement of more than 40% in the rectifier power conversion efficiency (PCE) and a dynamic range extension of more than 50% relative to the conventional cross-coupled rectifier. A sensitivity of -15.2dBm input power for 1V output voltage and a peak PCE of 65% are achieved for a 50k load. In the third part, we propose a wide-range, differential RF-to-DC power converter using an adaptive, self-biasing technique. The proposed architecture doubles the dynamic range of conventional rectifiers. Unlike the continuously self-biased rectifier proposed in the second part, this adaptive rectifier extends the dynamic range while maintaining both the high PCE peak and the sensitivity advantage of the conventional cross-coupled scheme, and can operates in the GHz range.

No description available.

No description available.