As human dependence on electronic devices grows, there is an emerging need on finding sustainable power sources for low power electronics and sensors. One of the promising possibilities in this space is the human body itself. Harvesting significant power from daily human activities will have a transformative effect on wearables and implantables. One of the main challenges in harvesting mechanical energy from human actions is to ensure that there is no effect on the body itself. For this reason, any intrusive mechanism will not have practical relevance. In this dissertation, novel non-intrusive energy harvesting technologies are investigated that can capture available energy from body, motion, and surroundings. Energy harvesting from the body is explored by developing a wrist-based thermoelectric harvester that can operate at low-temperature gradients. Energy harvesting from motion is investigated by creating a backpack and shoe sole. These devices passively store kinetic energy in a spring that is later released to a generator when it is not intrusive to the user kinematics. Lastly, energy harvesting from immediate surroundings is investigated by designing a two degree of freedom vibration absorber that is excited by electromagnetic fields found in common household appliances. These novel solutions are shown to provide consistent electrical power from wasted energy. Harvester designs are extensively modeled and optimized device architectures are manufactured and tested to quantify the relevant parameters such as output voltage and power density. / Doctor of Philosophy / Energy harvesting is the action to transform energy in the form of heat, relative motion, light, etc. into useful electrical energy. An example of an energy harvester is a solar cell which converts energy in the form of light to electricity. Our body consumes a considerable amount of energy to maintain our body temperature and achieve everyday movements, i.e., walking, jumping, etc. The purpose of this research was to fabricate, model and test wearable energy harvesters in the form of a backpack, a shoe sole, a watch, and a cantilever beam to charge mobile electronics on the go. Electrical energy is harvested from human motion by using the relative displacement between the human torso and a payload. Similarly, the ankle joint is used to produce electricity by using the relative rotation between the foot and shank. The difference in temperature between the ambient air and the human body is used to generate enough electricity to power a wrist watch. Finally, energy is harvested from everyday surroundings by using a cantilever beam which absorbs magnetic fields coming from power cords and able to power sensors.

This study proposes various methods to harvest the mechanical energy present in railcar suspensions and railroad tracks to generate electricity that is suitable for onboard or trackside electronics, using electromagnetic generators. Compact electromagnetic energy harvesters that can be installed onboard railcars or wayside on railroad tracks are designed, fabricated, and tested. The designs integrate a mechanical motion rectifier (MMR) with embedded one-way clutches in the bevel gears in order to convert the bi-directional mechanical energy that commonly exists in the form of vibrations into a unidirectional rotation of the generator. The ball screw mechanism is configured such that it has reduced backlash and thus can more efficiently harvest energy from low-amplitude vibrations. Two prototype harvesters are fabricated and tested extensively in the laboratory using a suspension dynamometer and in the field onboard a railcar and on a test track. A power management system with an energy storage circuit has also been developed for this onboard harvester. The laboratory evaluation indicate that the harvesters are capable of harvesting power with sufficient current and voltage for successfully powering light electronics or charging a low demand battery pack. The harvested power varies widely from a few to tens of Watts, depending on the resistive load across the harvester and the amplitude and frequency of the mechanical motion. The laboratory test results are verified through field testing. One harvester is tested onboard a freight railcar, placing it across the wedge suspension, to use the small amount of relative displacement at the wedge suspension to harvest energy. A second harvester is placed on a test track to use the vertical motion that occurs due to passing wheels for wayside energy harvesting. Both onboard and wayside tests confirm the laboratory test results in terms of the success of the design concept in providing low-power electrical power. The harvester design is further integrated into a conventional railroad tie for ease of field installation and for improving the efficiency of harvesting the mechanical energy at the rail. The integrated design, referred to as the "smart tie," not only protects the energy harvester, the wiring harness, and supporting electronics from the maintenance-of-the-way equipment, but also positions the harvester in a mechanically advantageous position that can maximize the track-induced motion, and hence the harvested power. Although for testing purposes, the smart tie uses a modified composite tie, it can be integrated into other track tie arrangements that are used for revenue service track, including concrete and wooden ties. A prototype smart tie is fabricated for laboratory testing, and the results nearly surpass the results obtained earlier from the wayside harvester. The smart tie is currently being considered for revenue service field testing over an extended length of time, potentially at a railroad mega site or similarly suitable location. / Doctor of Philosophy / This dissertation proposes three different electromagnetic energy harvesters for harvesting railroad track and railcar suspension vibration energy. The concept is similar to what you may have seen in self-powering flashlights that are often advertised in late-night TV commercials. You shake the flashlight vigorously, which moves an energy harvester devoice and, Voila, the light bulb comes on. The device design in this study uses the mechanical energy that is present in a vehicle or at a railroad track to harvest the mechanical energy that is naturally present in the form of electrical energy, which can then be used for powering electronic devices and sensors of various kinds. Such sensors and electronics would help with improving the operational efficiency of railroads. The energy harvesters can be installed onboard a railcar or at the track. In either case, the movement of the train creates a small amount of vibration energy that is turned into electrical power. When onboard a train the power can be used for sensors, GPS, and similar devices to allow the operator to better monitor the condition and location of the train. Note that most railcars, especially the freight railcars, do not have any onboard electrical power. Similarly, the energy harvester can be installed at the track to convert the small amount of up and down motion that happens with the passing of each wheel into energy that could be used for integration of sensors that make the track "smarter." This means that the sensors can potentially alert the engineers who are responsible for monitoring the track of an existing or impending problem with the track. Both the railcar and track integration of the energy harvester that is designed, fabricated, and tested during this study are exciting concepts that can improve the rail industry in the U.S. This document includes the details of designing efficient energy harvesters, specifically for rail applications. A prototype of the energy harvester is fabricated and tested extensively in the lab and in the field, albeit to a more limited extent. The test results were quite successful, which is why I am telling you about them! Both the laboratory and field test results show that the device holds significant promise for rail applications.

A new form of organic energy storage devices (organic capacitors) is presented in the first part of this dissertation. The storage devices are made out of an organic semiconductor material and charge storage elements from synthesized nanoparticles. The semiconducting polymer is obtained by blending poly (vinyl alcohol) and poly (acrylic acid) in crystal state polymers with a known plasticizer; glycerol or sorbitol. Synthesized nanoparticles namely, zinc-oxide (ZnO), erbium (Er), cadmium sulfide (CdS), palladium (Pd) and silver-platinum (AgPt) were used as charge storage elements in fabrication of metal-insulator-semiconductor (MIS) structure. The organic semiconductor and synthesized nanoparticles are tested to evaluate and characterize their electrical performance and properties. Fabrication of the organic capacitors consisted of layer-by-layer deposition and thermal evaporation of the electrode terminals. Capacitance versus voltage (C-V) measurement tests were carried out to observe hysteresis loops with a window gate that would indicate the charging, discharging and storage characteristics. Experimental investigation of various integrated energy harvesting techniques combined with these organic based novel energy storage devices are performed in the second part of this dissertation. The source of the energy is the wind and is harvested by means of miniature wind turbines and vibrations, using piezoelectric transduction. In both cases, the generated electric charge is stored in these capacitors. The performance of the organic capacitors are evaluated through their comparison with commercial capacitors. The results show that the voltage produced from the two energy harvesters was high enough to store the harvested energy in the organic capacitors. The charge and energy levels of the organic capacitors are also reported. The third part of this dissertation focuses on harvesting energy from a self-induced flutter of a thin composite beam. The composite beam consisted of an MFC patch bonded near the clamped end and placed vertically in the center of a wind tunnel test section. The self sustaining energy harvesting from the unimorph composite beam is exploited. The effects of different operational parameters including the optimum angle of attack, wind speed and load resistance are determined. / Ph. D.

As traditional wireless systems that only operate on fixed frequency bands are reaching their capacity limits, advanced frequency-agile radio systems are developed for more efficient spectrum utilization. For example, white space radios dynamically leverage locally unused TV channels to provide high-speed long-distance connectivity. They have already been deployed to connect the unconnected in rural areas and developing countries. However, such application scenarios are still limited due to low commercial demand. Hence, exploring better applications for white space radios needs more effort. With the benefits come the threats. As frequency-agile radio systems (e.g., software-defined radios) are flexible and become extremely low-cost and small-sized, it is very convenient for attackers to build attacking tools and launch wireless attacks using these radios. For example, civilian GPS signals can be easily spoofed by low-cost portable spoofers built with frequency-agile radio systems. In this dissertation, we study both the threat and application of frequency-agile radio systems. Specifically, our work focuses on the spoofing threat of frequency-agile radio towards GPS-based systems and the application of TV white space radio for ocean communications. Firstly, we explore the feasibility of using frequency-agile radio to stealthily manipulate GPS-based road navigation systems without alerting human drivers. A novel attacking algorithm is proposed, where the frequency-agile radio transmits fake GPS signals to lead the victim to drive on a wrong path that looks very similar with the navigation route on the screen. The attack's feasibility is demonstrated with real-world taxi traces in Manhattan and Boston. We implement a low-cost portable GPS spoofer using an off-the-shelf frequency-agile radio platform to perform physical measurements and real-world driving tests, which shows the low level of difficulty of launching the attack in real road environment. In order to study human-in-the-loop factor, a deceptive user study is conducted and the results show that 95% of the users do not recognize the stealthy attack. Possible countermeasures are summarized and sensor fusion defense is explored with preliminary tests. Secondly, we study similar GPS spoofing attack in database-driven cognitive radio networks. In such a network, a secondary user queries the database for available spectrum based on its GPS location. By manipulating GPS locations of surrounding secondary users with a frequency-agile radio, an attacker can potentially cause serious primary user interference and denial-of-service to secondary users. The serious impact of such attacks is examined in simulations based on the WhiteSpaceFinder spectrum database. Inspired by the characteristics of the centralized system and the receiving capability of cognitive radios, a combination of three defense mechanisms are proposed to mitigate the location spoofing threat. Thirdly, we explore the feasibility of building TV white space radio based on frequency-agile radio platform to provide connectivity on the ocean. We design and implement a low-cost low-power white space router ($523, 12 watts) customized for maritime applications. Its communication capability is confirmed by field link measurements and ocean-surface wave propagation simulations. We propose to combine this radio with an energy harvesting buoy so that the radio can operate independently on the ocean and form a wireless mesh network with other similar radios. / PHD / As traditional wireless systems, such as mobile phones and WiFi access points, only operate on some fixed frequency bands, it becomes increasingly crowded for those popular bands. Hence, for more efficient frequency resource utilization, frequency-agile radio systems that can dynamically operate on different frequency bands are developed. With these new technologies come new threats and applications, which are the focus of our work. On the one hand, as frequency-agile radio systems become low-cost and portable, attackers can easily launch wireless attacks with them. For example, we explored the feasibility, impact, and countermeasures for GPS spoofing attacks using frequency-agile radio systems in different scenarios. In a GPS spoofing attack, an attacker transmits false GPS signals to manipulate users’ GPS receivers. This kind of attack can be very dangerous and even life-threatening if it is launched against critical GPS-based applications. For example, once GPS-based navigation systems in self-driving cars are stealthily manipulated by remote attackers, attackers can divert self-driving cars to pre-defined destinations or dangerous situations like wrong-way driving on highway. On the other hand, since there is rich under-utilized spectrum resource in remote areas with no broadband connection yet, frequency-agile radio systems can be used to provide broadband internet connectivity there. For example, based on frequency-agile radio platform, we developed a low-cost low-power wireless router that can dynamically operate on TV broadcasting band. It is able to provide high-speed wireless connection to a large area on the ocean. This technology has the potential to bring low-cost high-speed connection to people and industry on the ocean, which will facilitate various maritime applications.

Instead of dissipating vibration energy into heat waste via viscous damping elements, this dissertation proposes an innovative vibration control method which can simultaneously mitigate vibration and harvest the associated vibration energy using electromagnetic energy harvesters. This dissertation shows that the electromagnetic energy harvester can work as a controllable damper as well as an energy harvester. The semi-active control of a linear electromagnetic energy harvester, for improvement of suspension performance, has been experimentally implemented in a scaled-down quarter-car suspension system. While improving performance, power produced by the harvester can be harvested through energy harvesting circuits. This dissertation also proposes a mechanical-motion-rectifier(MMR)-based electromagnetic energy harvester using a ball-screw mechanism and two one-way clutches for the application of replacing the viscous damper in vehicle suspensions. Compared to commercial linear harvesters, the proposed design is able to provide large damping forces and increase power-dissipation density, making it suitable to vehicle suspensions. In addition, the proposed MMR-based harvester can convert reciprocating vibration into unidirectional rotation of the generator. This feature significantly increases energy-harvesting efficiency by enabling the generator to rotate at a relatively steady speed during irregular vibrations and improves the system reliability by reducing impact forces among transmission gears. Extensive theoretical and experimental analysis have been conducted to characterize the proposed MMR-based energy harvester. The coupled dynamics of the suspension system with the MMR-based energy harvester are also explored and optimized. Furthermore, a new control algorithm is proposed to control the MMR-based energy harvester considering its unique dynamics induced by the one-way clutches. The results show that the controlled proposed electromagnetic energy harvester can possibly improve ride comfort of vehicles over conventional oil dampers and simultaneously harvest the associated vibration energy. / Ph. D.

The batteries used to power wireless sensor nodes have become a major roadblock for the wide deployment. Harvesting energy from mechanical vibrations using piezoelectric cantilevers provides possible means to recharge the batteries or eliminate them. Raw power harvested from ambient sources should be conditioned and regulated to a desired voltage level before its application to electronic devices. The efficiency and self-powered operation of a power conditioning and management circuit is a key design issue. In this research, we investigate the characteristics of piezoelectric cantilevers and requirements of power conditioning and management circuits. A two-stage conditioning circuit with a rectifier and a DC-DC converter is proposed to match the source impedance dynamically. Several low-power design methods are proposed to reduce power consumption of the circuit including: (i) use of a discontinuous conduction mode (DCM) flyback converter, (ii) constant on-time modulation, and (iii) control of the clock frequency of a microcontroller unit (MCU). The DCM flyback converter behaves as a lossless resistor to match the source impedance for maximum power point tracking (MPPT). The constant on-time modulation lowers the clock frequency of the MCU by more than an order of magnitude, which reduces dynamic power dissipation of the MCU. MPPT is executed by the MCU at intermittent time interval to save power. Experimental results indicate that the proposed system harvests up to 8.4 mW of power under 0.5-g base acceleration using four parallel piezoelectric cantilevers and achieves 72 percent power efficiency. Sources of power losses in the system are analyzed. The diode and the controller (specifically the MCU) are the two major sources for the power loss. In order to further improve the power efficiency, the power conditioning circuit is implemented in a monolithic IC using 0.18-μ­m CMOS process. Synchronous rectifiers instead of diodes are used to reduce the conduction loss. A mixed-signal control circuit is adopted to replace the MCU to realize the MPPT function. Simulation and experimental results verify the DCM operation of the power stage and function of the MPPT circuit. The power consumption of the mixed-signal control circuit is reduced to 16 percent of that of the MCU. / Ph. D.

Unsteady aerodynamic modeling is indispensable in the design process of rotary air vehicles, flapping flight and agile unmanned aerial vehicles. Undesirable vibrations can cause high-frequency variations in motion variables whose effects cannot be well predicted using quasi-steady aerodynamics. Furthermore, one may exploit the lift enhancement that can be generated through an unsteady motion for optimum design of flapping vehicles. Additionally, undesirable phenomena like the flutter of fixed wings and ensuing limit cycle oscillations can be exploited for harvesting energy. In this dissertation, we focus on modeling the unsteady nonlinear aerodynamic response and present various applications where unsteady aerodynamics are very relevant. The dissertation starts with experiments for measuring unsteady loads on an NACA-0012 airfoil undergoing a plunging motion under various operating conditions. We supplement these measurements with flow visualization to obtain better insight into phenomena causing enhanced lift. For the model, we present the frequency response function for the airfoil at various angles of attack. Experiments were performed at reduced frequencies between 0.1 and 0.95 and angles of attack up to 65 degrees. Then, we formulate an optimization problem to unify the transfer function coefficients for each regime independently to obtain one model that represents the global dynamics. An optimization-based finite-dimensional (fourth-order) approximation for the frequency responses is developed. Converting these models to state-space form and writing the entries of the matrices as polynomials in the mean angle of attack, a unified unsteady model was developed. In the second set of experiments, we measured the unsteady plunging forces on the same airfoil at zero forward velocity. The aim is to investigate variations of the added forces associated with the oscillation frequency of the wing section for various angles of attack. Data of the measured forces are presented and compared with predicted forces from potential flow approximations. The results show a significant departure from those estimates, especially at high frequencies indicating that viscous effects play a major role in determining these forces. In the second part of this dissertation, we consider different applications where unsteady loads and nonlinear effects play an important role. We perform a multi-objective aerodynamic optimization problem of the wing kinematics and planform shape of a Pterosaur replica ornithopter. The objective functions included minimization of the required cycle-averaged aerodynamic power and maximization of the propulsive efficiency. The results show that there is an optimum kinematic parameter as well as planform shape to fulfill the two objectives. Furthermore, the effects of preset angle of attack, wind speed and load resistance on the levels of harvested power from a composite beam bonded with the piezoelectric patch are determined experimentally. The results point to a complex relation between the aerodynamic loading and its impact on the static deflection and amplitudes of the limit cycle oscillations as well as the level of power harvested. This is followed by testing of a centimeter scale micro wind turbine that has been proposed to power small devices and to work as a micro energy harvester. The experimental measurements are compared to predicted values from a numerical model. The methods developed in this dissertation provide a systematic approach to identifying unsteady aerodynamic models from numerical or experimental data that may work within different regimes. The resulting reduced-order models are expressed in a state-space form, and they are, therefore, both simple and efficient. These models are low-dimensional linear systems of ordinary differential equations so that they are compatible with modern flight dynamic models. The specific form of the obtained added force model, which defines the added forces as a function of plunging velocity and drag forces, guarantees that the resulting model is accurate over a range of high frequencies. Moreover, presented applications give a sense of the broad range of application of unsteady aerodynamics. / Ph. D.

Biological systems offer novel and efficient solutions to many engineering applications, including marine propulsion. It is of interest to determine how fish interact with the water around them, and how best to utilize the potential their methods offer. A stingray-like fin was chosen for analysis due to the maneuverability and versatility of stingrays. The stingray fin was modeled in 2D as a sinusoidal wave with an amplitude increasing from zero at the leading edge to a maximum at the trailing edge. Using this model, a parametric study was performed to examine the effects of the fin on surrounding water in computational fluid dynamics (CFD) simulations. The results were analyzed both qualitatively, in terms of the pressure contours on the fin and vorticity in the trailing wake, and quantitatively, in terms of the resultant forces and the mechanical power requirements to actuate the desired fin motion. The average thrust was shown to depend primarily on the relationship between the swimming speed and the frequency and wavelength (which both are directly proportional to the wavespeed of the fin), although amplitude can be used to augment thrust production as well. However, acceleration was shown to significantly correlate with a large variation in lift and moment, as well as with greater power losses. Using results from the parametric study, the potential for power regeneration was also examined. Relationships between frequency, velocity, drag, and power input were determined using nonlinear regression that explained more than 99.8% of the data. The actuator for a fin was modeled as a single DC motor-shaft system, allowing the combination of the energetic effects of the motor with the fin-fluid system. When combined, even a non-ideal fin model was able to regenerate more power at a given flow speed than was required to swim at the same speed. Even in a more realistic setting, this high proportion of regenerative power suggests that regeneration and energy harvesting could be both feasible and useful in a mission setting. / Master of Science / Animals interact with the world much differently than engineered systems, and can offer new and efficient ways to solve engineering problems, including underwater vehicles. To learn how to move an underwater vehicle in an environmentally conscious way, it is useful to study how a fish’s movements affect the manner in which it moves through the water. Through careful study, the principles involved can be implemented for an efficient, low-disturbance underwater vehicle. The particular fish chosen for in-depth study was the stingray, due to its maneuverability and ability to travel close to the seafloor without disturbing the sediment and creatures around it. In this work, computational analysis was performed on a model of a single stingray fin to determine how the motion of the fin affects the water around it, and how the water affects the fin in turn. The results were analyzed both in terms of the wake behind the fin and in terms of how much power was required to make the fin move in a particular way. The speed of the fin motion was found to have the strongest effect in controlling swimming speed, although the lateral motion of the fin also helped with accelerating faster. Additionally, the potential for a robotic stingray fin to harness power from the water around it was examined. Based on results from simulations of the fin, a mathematical model was formulated to relate energy harvesting with the flow speed past the fin. This model was used to determine how worthwhile it was to use energy harvesting. Analysis of the model showed that harvesting energy from the water was quite efficient, and would likely be a worthwhile investment for an exploration mission.

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