The proposed energy harvesting circuit system is designed for indoor solar environment especially for factories where the light energy is abundant and stable. The designed circuits are intended to power wireless sensor nodes (WSNs) or other computing unit such as microcontrollers or DSPs to provide a power solution for Internet of Things (IoTs). The proposed circuit can extract maximum power from the PV panel by utilizing the maximum power point tracking (MPPT) technique. The power stage is a synchronous dual-input dual-output non-inverting buck-boost converter operating in discontinuous conduction mode (DCM) and constant on-time pulse skipping modulation (COT-PSM) to achieve voltage regulation and maximum power delivery to the load. Battery is used as secondary input also as secondary output to achieve a longer lifecycle, a fast load response time and support higher load conditions. The proposed MPPT technique doesn't require any current sensor or computing units. Fully digitalized simple circuits are used to achieve sampling, store, and comparing tasks to save power. The whole circuits including power stage and control circuits are designed and will fabricate in TSMC BCDMOS 180 nm process. The circuits are verified through schematic level simulations and post-layout simulations. The results are validated to prove the proposed circuit and control scheme work in a manner. / Master of Science / With the growing energy demands, the efficient energy conversion systems caught great attentions. Especially, in the era of Internet of Things, powering those wireless devices can be extremely difficult. Nowadays, lots of devices such as consumer electronics, wireless sensor nodes, computing and mission system etc. are still powered by the batteries. Regular changing the batteries of those devices can be inconvenient or expensive. Energy harvesting provides a good solution to this issue because there are lots of ambient energy source is available. To design an energy efficient energy harvesting circuit system can help extend the device lifecycle per charging cycle. Even with some specific energy source which power scale is high enough, meanwhile the load doesn’t require too much power, the devices can be power-independent or standalone. In this work, the proposed circuit targets for indoor solar energy harvesting via solar panel. The target powering devices are wireless sensor nodes (WSNs). Meanwhile, WSNs can monitor the temperature, humidity, pressure, noise level etc. The proposed circuit design combines the power stage and control circuit on an integrated chip (IC), only few components are off-chip. It provides a very compact, endurable, and economical solution to the current IoT powering issue.

This work investigates the feasibility of developing a self-powered structural health monitoring (SHM) smart tire using piezoelectric materials. While this work is divided into two components: SHM and energy harvesting, the context of smart tire in this work is defined as the development of a SHM system that (i) has self-powering capabilities, and (ii) addresses the potential of embedding sensors. The use of impedance based SHM on a tire is severely limited due to the low stiffness and high damping characteristics of the tire. This work propose the use of a high voltage impedance analyzer, and the addition of electrical circuit to enhance the damage detection process. Experimental work was conducted on an aluminum beam and on a tire section with commercially available piezoelectric sensors. The use of a high voltage impedance analyzer was demonstrated to provide insight on damage type and damage location. Two sensors were connected in parallel as an effective sensory system, and was shown to reduce interrogation time, but reduce damage identification sensitivity. With added electrical circuits, a belt separation on the tire was successfully detected by the shift in electrical impedance signature. For the energy harvesting portion of this work, a bimorph piezoelectric energy harvester model was derived using extended Hamilton's principle and the linear constitutive relations of piezoelectric materials. Comparison of model with experimental data at increasing loading conditions demonstrated the monotonic increase in voltage output, with linear asymptotes at extreme loading conditions (short-circuit and open-circuit). It also demonstrated the existence of an optimal resistive load for maximum power output. To address the ability to embed sensors, an existing fabrication process to grow arrays of ZnO nanowires in carbon fiber reinforced polymer was used in this work. Comparison of power generation from a composite beam with ZnO nanowires with a composite beam without ZnO nanowires demonstrated the power generation capabilities of the nanowires. A maximum peak voltage of 8.91 mV and peak power of 33.3 pW was obtained. After the application of 10V DC, a maximum of 45 pW was obtained. However, subsequent application of 20V DC reduced the maximum peak power output to 2.5 pW. Several attempts to increase power generation including adding a tip mass and changing the geometry of the composite beam were conducted. Finally, the theoretical voltage frequency response function obtained from the theoretical piezoelectric constant and dielectric constant of a single ZnO nanowire were compared to the experimental voltage frequency response function. The discrepancies were discussed. / Master of Science

Dynamic Spectrum Access (DSA) is now a commonly used spectrum sharing paradigm to mitigate the spectrum shortage problem. DSA technology allows unlicensed secondary users to access the unused frequency bands without interfering with the incumbent users. The key technical challenges in DSA systems lie in spectrum allocation problems and spectrum user's security issues. This thesis mainly focuses on spectrum monitoring technology in spectrum allocation and incumbent users' (IU) privacy issue. Spectrum monitoring is a powerful tool in DSA to help commercial users to access the unused bands. We proposed a crowdsourcing-based unknown IU pattern monitoring scheme that leverages the power of masses of portable mobile devices to reduce the cost of the spectrum monitoring and demonstrate the ability of our system to capture not only the existing spectrum access patterns but also the unknown patterns where no historical spectrum information exist. Due to the energy limit of the battery-based system, we then leverage solar energy harvesting and develop an energy management scheme to support our spectrum monitoring system. We also provide best privacy-protection strategies for both static and mobile IUs in terms of hiding their true location under the detection of Environmental Sensing Capabilities system. In this thesis, the heuristic approach for our mathematical formulations and simulation results are described in detail. The simulation results show our spectrum monitoring system can obtain a high spectrum monitoring coverage and low energy consumption. Our IU privacy scheme provides great protection for IU's location privacy. / Master of Science / Spectrum relates to the radio frequencies allocated to the federal users and commercial users for communication over the airwaves. It is a sovereign asset that is overseen by the government in each country to manage the radio spectrum and issue spectrum licenses. In addition, spectrum bands are utilized for various purposes because different bands have different characteristics. However, the overly crowded US frequency allocation chart shows the scarcity of usable radio frequencies. The actual spectrum usage measurements reflect that multiple prized spectrum bands lay idle at most time and location, which indicates that the spectrum shortage is caused by the spectrum management policies rather than the physical scarcity of available frequencies. Dynamic spectrum access (DSA) was proposed as a new paradigm of spectrum sharing that allows commercial users to access the abundant white spaces in the licensed spectrum bands to mitigate the spectrum shortage problem and increase spectrum utilization. In DSA, two of the key technical challenges lie in how to dynamically allocate the spectrum and how to protect spectrum users’ security. This thesis focuses on the development of two types of mechanisms for addressing the above two challenges: (1) developing efficient spectrum monitoring schemes to help secondary users (SU) to accurately and dynamically access the white space in spectrum allocation and (2) developing privacy preservation schemes for incumbent users (IU) to protect their location privacy. Specifically, we proposed an unknown IU pattern monitoring scheme that leverages the power of masses of portable mobile devices to reduce the cost of common spectrum monitoring systems. We demonstrate that our system can track not only the existing IU spectrum access patterns but also the unknown patterns where no historical spectrum information exists. We then leverage the solar energy harvesting and design energy management scheme to support our spectrum monitoring system. Finally, we provide a strategy for both static and mobile IUs to hide their true location under the monitoring of Environmental Sensing Capabilities systems.

The objective of this thesis is to develop a dual-functional approach to effectively mitigate the earthquake induced vibrations of low- or mid-rise buildings, and at the same time to efficiently harvest utility-scale energy by using an optimally configured multi-resonant electromagnetic shunt in base isolation. In this research, two multi-resonant shunt configurations, parallel and series, were proposed and optimized based on the H2 criteria when the base isolation system is subjected to ground acceleration excitations. The performance of the proposed multi-resonant electromagnetic shunt was compared with traditional multiple tuned mass dampers (TMDs) applied to the base isolation system. It shows that, for multiple TMDs and multi-resonant electromagnetic shunt dampers with 5% total stiffness ratio, the parallel shunt electromagnetic shunt can achieve the best vibration mitigation performance among other types of multi-resonant dampers, including parallel TMDs, series TMDs and the series electromagnetic shunt damper. Case study of a base-isolated structure was analyzed to investigate the effectiveness of the proposed multi-resonant electromagnetic shunt. It shows that both multi-mode shunt circuits outperform single mode shunt circuit by suppressing the primary and the second vibration modes simultaneously. Comparatively, the parallel shunt circuit is more effective in vibration mitigation and energy harvesting, and is also more robust in parameter mistuning than the series shunt circuit. The time history response analysis shows that, under the recorded Northridge earthquake, the instant peak power and total average power capable to be harvested by the multi-resonant shunt can reach up to 1.18 MW and 203.37KW, respectively. This thesis further experimentally validated the effectiveness of the multi-resonant electromagnetic shunt on a scaled-down base-isolated building. The impact hammer test shows that the multi-resonant electromagnetic shunt can achieve enhanced vibration suppression by reducing the first resonant peak by 27.50dB and the second resonant peak by 22.57dB regarding the primary structure acceleration. The shake table test shows that under scaled Kobe and Northridge earthquake signals, the electromagnetic shunt can effectively reduce the vibration resonant peak value by 38.92% and 66.61%, respectively. The voltage simultaneously generated in the multi-mode shunt circuit was also obtained, which demonstrated the dual functions of the multi-resonant electromagnetic shunt in base isolation. / Master of Science

The Internet of Things will include many resource-constrained lightweight wireless sensing devices, hungry for energy, bandwidth and compute cycles. The sheer amount of devices involved will require new solutions to handle issues such as identification and power provisioning. First, to simplify identity management, device identification is moving from symmetric-key solutions to public-key solutions. Second, to avoid the endless swapping of batteries, passively-powered energy harvesting solutions are preferred. In this contribution, we analyze some of the feasible solutions from this challenging design space. We have built an autonomous, energy-harvesting sensor node which includes a micro-controller, RF-unit, and energy harvester. We use it to analyze the computation and communication energy requirements for Elliptic Curve Digital Signature Algorithm (ECDSA) with different security levels. The implementation of Elliptic Curve Cryptography (ECC) on small microcontrollers is challenging. Most of the earlier literature has considered optimizing the performance of ECC (with respect to cycle count and software footprint) on a given architecture. This thesis addresses a different aspect of the resource-constrained ECC implementation wherein the most suitable architecture parameters are identified for any given application profile. At the high level, an application profile for an ECC-based lightweight device, such as wireless sensor node or RFID tag, is defined by the required security level, signature generation latency and the available energy/power budget. The target architecture parameters of interest include core-voltage, core-frequency, and/or the need for hardware acceleration. We present a methodology to derive and optimize the architecture parameters starting from the application requirements. We demonstrate our methodology on a MSP430F5438A microcontroller, and present the energy/architecture design space for 80-bit and 128-bit security-levels, for prime field curves secp160r1 and nistp256. Our results show that energy cost per authentication is minimized if a microcontroller is operated at the maximum possible frequency. This is because the energy consumed by leakage (i.e., static power dissipation) becomes proportionally less important as the runtime of the application decreases. Hence, in a given energy harvesting method, it is always better to wait as long as possible before initiating ECC computations which are completed at the highest frequency when sufficient energy is available. / Master of Science

From 2012 - 2015 a foundation for future research in Goodwin Hall was designed, tested,developed, and implemented through an instrumentation project supported by the College of Engineering at Virginia Polytechnic Institute and State University. This required the design and implementation of a distributed, networked, and synchronized data acquisition system along with supporting hardware and software capable of measuring 227 accelerometers placed in 129 locations throughout the building. This system will provide a platform for research into a variety of topics, including structural health monitoring, building dynamics, human motion, and energy harvesting. Additionally, the system will be incorporated into the education curriculum by providing real-world data and hardware for students to interact with. This thesis covers the contributions of the author to the project. / Master of Science

As worldwide energy consumption continues to increase, so does the demand for renewable energy sources. The total available wave energy resource for the United States alone is 2,640 TWh/yr; nearly two thirds of the 4,000 TWh of electricity used in the United States each year. It is estimated that nearly half of that available energy is recoverable through wave energy conversion techniques. In this thesis, a two-body 'point absorber' type wave energy converter with a mechanical power-takeoff is investigated. The two-body wave energy converter extracts energy through the relative motion of a floating buoy and a neutrally buoyant submerged body. Using a linear frequency-domain model, analytical solutions of the optimal power and the corresponding power-takeoff components are derived for the two-body wave energy converter. Using these solutions, a case study is conducted to investigate the influence of the submerged body size on the absorbed power of the device in regular and irregular waves. Here it is found that an optimal mass ratio between the submerged body and floating buoy exists where the device will achieve resonance. Furthermore, a case study to investigate the influence of the submerged body shape on the absorbed power is conducted using a time-domain numerical model. Here it is found that the submerged body should be designed to reduce the effects of drag, but to maintain relatively large hydrodynamic added mass and excitation force. To validate the analytical and numerical models, a 1/30th scale model of a two-body wave energy converter is tested in a wave tank. The results of the wave tank tests show that the two-body wave energy converter can absorb nearly twice the energy of a single-body 'point absorber' type wave energy converter. / Master of Science

The research presented in this thesis is based on improving current structural health monitoring (SHM) technology. Structural health monitoring is a damage detection technique that involves placing intelligent sensors on a structure, periodically recording data from the sensors, and using statistical methods to analyze the data in order to assess the condition of the structure. This work focuses on improving two areas of SHM; baseline management and energy supplies. Several successful SHM methods have been developed in which prerecorded baseline measurements are compared to current measurements in order to identify damage. The need to compare new data to a prerecorded baseline can present several complications including data management issues and difficulty in controlling the effects of varying environmental conditions on the data. Another potential area for improvement in SHM systems deals with their energy supplies. Many SHM systems currently require wired power supplies or batteries to operate. Practical SHM applications often require inexpensive, stand alone sensors, data acquisition, and processing hardware that does not require maintenance. To address the issue of baseline management, a novel SHM technique is developed. This new method accomplishes instantaneous baseline measurements by deploying an array of piezoelectric sensors/actuators used for Lamb wave propagation-based SHM such that data recorded from equidistant sensor-actuator paths can be used to instantaneously identify several common features of undamaged paths. Once identified, features from these undamaged paths can be used to form a baseline for real-time damage detection. This method utilizes the concept of sensor diagnostics, a recently developed technique that minimizes false damage identification and measurement distortion caused by faulty sensors. Several aspects of the instantaneous baseline damage detection method are explored in this work including the implementation of sensor diagnostics, determination of the features best used to identify damage, development of signal processing algorithms used to analyze data, and the comparison of two sensor/actuator deployment schemes. The ultimate goal in the development of practical SHM systems is to create autonomous damage detection systems. A limiting factor in current SHM technology is the energy supply required to operate the system. Many existing SHM systems utilize wired power supplies or batteries to power sensors, data transmission, data acquisition, and data processing hardware. Although batteries eliminate the need to run wires to SHM hardware, their periodic replacement requires components to be placed in easily accessible locations which is not always practical, especially in embedded applications. Additionally, there is a high cost associated with battery monitoring and replacement. In an effort to eliminate replaceable energy supplies in SHM systems, the concept of energy harvesting is investigated. Energy harvesting devices are designed to capture surrounding ambient energy and convert it into usable electrical energy. Several types of energy harvesting exist, including vibration, thermal, and solar harvesting. A solar energy harvesting system is developed for use in powering SHM hardware. Integrating energy harvesting technology into SHM systems can provide autonomous health monitoring of structures. / Master of Science

Wearable and mobile devices are an important part of our daily life. Most of those devices are powered by batteries. The limited life span of batteries constitutes a limitation, especially in a multiple-day expedition, where electrical power can not access conveniently. At the same time, there is a huge amount of energy stored in the human body. While walking, there is a large amount of power dissipated in the human body as negative muscle work and the energy loss by impact. By sourcing locally and using locally, human body energy harvesting is a promising solution. This dissertation focuses on harvesting energy from the human body to power wearable and mobile devices while poses a minimum burden on the human body. Three topics related to the human body energy harvesting are explored, i.e, energy harvesting backpack, negative muscle work harvester, and energy harvesting tile/paver. The energy harvesting backpack was invented in 2006. Extensive work was done to improve the performance of backpack energy harvester. The backpack is modeled as a spring-mass-damper system. Mechanical Motion Rectifier was added to the spring-mass-damper system to increase the frequency bandwidth. A spring is added to the spring-mass-damper system, between the harvester and the backpack mass, and a inerter-based 2DOF (degree-of-freedom) backpack is created. The inerter-based 2DOF backpack improves the power output, frequency bandwidth, and power stroke ratio performance. MMR was added to the inerter-based 2DOF backpack to reduce the peak stroke. Compared with the conventional spring-mass-damper backpack, the MMR and inerter-based 2DOF backpack can harvest more power with large bandwidth at a small sacrifice of stroke. The electric damping was also tuned to increase the power output and bandwidth for the energy harvesting backpack. The negative work harvester mounts on the human ankle and harvests energy in the terminal stance phase in human walking, when the calf muscle is doing negative muscle work. This harvester is an analogy to regenerative brake in vehicles. The energy harvesting paver/tile harvests energy when the heel contacts with ground and energy are dissipated by impact. / Doctor of Philosophy / Wearable and mobile devices are an important part of our daily life. Most of those devices are powered by batteries. The limited life span of batteries constitutes a limitation, especially in a multiple-day expedition, where electrical power can not access conveniently. At the same time, there is a huge amount of energy stored in the human body. While walking, there is a large amount of power dissipated in the human body as negative muscle work and the energy loss by impact. By sourcing locally and using locally, human body energy harvesting is a promising solution. This dissertation focuses on harvesting energy from the human body to power wearable and mobile devices while poses a minimum burden on the human body. Three topics related to the human body energy harvesting are explored, i.e, energy harvesting backpack, negative muscle work harvester, and energy harvesting tile/paver. The energy harvesting backpack was invented in 2006. Extensive work was done to improve the performance of backpack energy harvester. The backpack is modeled as a spring-mass-damper system. Extensive work have been done to make the energy harvesting backpack broad frequency bandwidth. The negative work harvester mounts on the human ankle and harvests energy in the terminal stance phase in human walking. This harvester is an analogy to regenerative brake in vehicles. The energy harvesting paver/tile harvests energy when the heel contacts with ground and energy are dissipated by impact.

Vibration control is a large branch in control research, because all moving systems may induce desired or undesired vibration. Due to the limitation of passive system's adaptability and changing excitation input, vibration control brings the solution to change system dynamic with desired behavior to fulfill control targets. According to preference, vibration control can be separated into two categories: vibration reduction and vibration amplification. Lots of research papers only examine one aspect in vibration control. The thesis investigates the control development for both control targets with two different control applications: vehicle suspension and ocean wave energy converter. It develops control methods for both systems with simplified modeling setup, then followed by the application of a novel mechanical motion rectifier (MMR) gearbox that uses mechanical one-way clutches in both systems. The flow is from the control for common system to the control design for a specifically designed system. In the thesis, active (model predictive control: MPC), semi-active (Skyhook, skyhook-power driven damper: SH-PDD, hybrid model predictive control: HMPC), and passive control (Latching Control) methods are developed for different applications or control performance comparison on single system. The thesis also studies about new type of system with switching mechanism, in which other papers do not talk too much and possible control research direction to deal with such complicated system in vibration control. The state-space modeling for both systems are provided in the thesis with detailed model of the MMR gearbox. From the simulation, it can be shown that in the vehicle suspension application, the controlled MMR gearbox can be effective in improving vehicle ride comfort by 29.2% compared to that of the traditional hydraulic suspension. In the ocean wave energy converter, the controlled MMR WEC with simple latching control can improve the power generation by 57% compared to the passive MMR WEC. Besides, the passive MMR WEC also shows its advantage on the passive direct drive WEC in power generation improvement. From the control development flow for the MMR system, the limitation of the MMR gearbox is also identified, which introduces the future work in developing active-MMR gearbox by using an electromagnetic clutch. Some possible control development directions on the active-MMR is also mentioned at the end of the thesis to provide reference for future works. / Master of Science / Vibration happens in our daily life in almost all cases. It is a regular or irregular back and forth motion of particles. For example, when we start a vehicle, the engine will do circular motion to drive the wheel, which causes vibration and we feel wave pulses on our body when we sit in the car. However, this kind of vibration is undesirable, since it makes us uncomfortable. The car manufacture designs cushion seats to absorb vibration. This is a way to use hardware to control vibration. However, this is not enough. When vehicle goes through bumps, we do have suspension to absorb vibration transferred from road to our body. The car still experiences a big shock that makes us feel dizzy. On the opposite direction, in some cases when vibration becomes the motion source for energy harvesting, we would like to enhance it. Hardware can be helpful, since by tuning some parameters of an energy harvesting device, it can match with the vibration source to maximize vibration. However, it is still not enough due to low adaptability of a fixed parameter system. To overcome the limitation of hardware, researches begin to think about the way to control vibration, which is the method to change system behavior by using real-time adjustable hardware. By introducing vibration control, the theory behind that started to be investigated. This thesis investigates the vibration control theory application in both cases: vibration reduction and vibration enhancement, which are mentioned above due to opposite application preferences. There are two major applications of vibration control: vehicle suspension control and ocean wave energy converter (WEC) control. The thesis starts from the control development for both fields with general modeling criteria, then followed by control development with specific hardware design-mechanical motion rectifier (MMR) gearbox-applied on both systems. The MMR gearbox is the researcher designed hardware that targets on vibration adjustment with hardware capability, which is similar as the cushion seats mentioned at the beginning of the abstract. However, the MMR cannot have capability to furtherly optimize system vibration, which introduces the necessity of control development based on the existing hardware. In the suspension control application, the control strategy introduced successfully improve the vehicle ride comfort by 29.2%, which means the vehicle body acceleration has been reduced furtherly to let passenger feel less vibration. In the WEC application, the power absorbed from wave has been improved by 57% by applying suitable control strategy. The performance of improvement on vibration control has proved the effect on further vibration optimization beyond hardware limitation.