Energy harvesting technology has the ability to create autonomous, self-powered electronic systems that do not rely on battery power for their operation. The term energy harvesting describes the process of converting ambient energy surrounding a system into useful electrical energy through the use of a specific material or transducer. A widely studied form of energy harvesting involves the conversion of mechanical vibration energy into electrical energy using piezoelectric materials, which exhibit electromechanical coupling between the electrical and mechanical domains. Typical piezoelectric energy harvesting systems are designed as add-on systems to a host structure located in a vibration rich environment. The added mass and volume of conventional vibration energy harvesting designs can hinder to the operation of the host system. The work presented in this dissertation focuses on advancing piezoelectric energy harvesting concepts through the introduction of multifunctionality in order to alleviate some of the challenges associated with conventional piezoelectric harvesting designs. The concept of multifunctional piezoelectric self-charging structures is explored throughout this work. The operational principle behind the concept is first described in which piezoelectric layers are directly bonded to thin-film battery layers resulting in a single device capable of simultaneously harvesting and storing electrical energy when excited mechanically. Additionally, it is proposed that self-charging structures be embedded into host structures such that they support structural load during operation. An electromechanical assumed modes model used to predict the coupled electrical and mechanical response of a cantilever self-charging structure subjected to harmonic base excitation is described. Experimental evaluation of a prototype self-charging structure is then performed in order to validate the electromechanical model and to confirm the ability of the device to operate in a self-charging manner. Detailed strength testing is also performed on the prototype device in order to assess its strength properties. Static three-point bend testing as well as dynamic harmonic base excitation testing is performed such that the static bending strength and dynamic strength under vibration excitation is assessed. Three-point bend testing is also performed on a variety of common piezoelectric materials and results of the testing provide a basis for the design of self-charging structures for various applications. Multifunctional vibration energy harvesting in unmanned aerial vehicles (UAVs) is also investigated as a case study in this dissertation. A flight endurance model recently developed in the literature is applied to model the effects of adding piezoelectric energy harvesting to an electric UAV. A remote control foam glider aircraft is chosen as the test platform for this work and the formulation is used to predict the effects of integrating self-charging structures into the wing spar of the aircraft. An electromechanical model based on the assumed modes method is then developed to predict the electrical and mechanical behavior of a UAV wing spar with embedded piezoelectric and thin-film battery layers. Experimental testing is performed on a representative aluminum wing spar with embedded self-charging structures in order to validate the electromechanical model. Finally, fabrication of a realistic fiberglass wing spar with integrated piezoelectric and thin-film battery layers is described. Experimental testing is performed in the laboratory to evaluate the energy harvesting ability of the spar and to confirm its self-charging operation. Flight testing is also performed where the fiberglass spar is used in the remote control aircraft test platform and the energy harvesting performance of the device is measured during flight. / Ph. D.

Traditional vehicle suspension system is equipped with isolated shock absorbers that can only dissipate energy by themselves. Hydraulic interconnected suspension uses hydraulic circuits to connect each shock absorber, so that the energized hydraulic fluid can be utilized to counter unwanted body motion to improve the overall dynamic performance. The hydraulic interconnected suspension is a proven concept that has shown good potential in controlling body rolling and decoupling the warp mode from other dynamic modes. Hydraulic interconnected suspension is still passive and lack of adaptivity, while some active or semi-active suspension technologies allow the shock absorbers to counter the road disturbances using external power input. Active suspensions such as electro-magnetic shock absorbers use the variable viscosity of magnetofluid to alter the damping characteristics of the suspension to adapt to quickly changing road conditions. The energy demand from an active suspension can reach the level of kilowatts in certain cases, which results in lowered fuel efficiency of the vehicle. To find a balanced solution to dynamic performance and energy efficiency, this paper introduces a new form of energy-harvesting suspension that is integrated in a hydraulically interconnected suspension (HIS) system. The combined energy-harvesting and hydraulic interconnection features provide improved energy efficiency and vehicle dynamics performance. A single cylinder model is built in AMESim for preliminary study and validated in a bench test. The bench test results proved the authenticity of the theoretical model, and the model is then used to predict the system performance and guide the hardware construction. Based on the proven single cylinder model, and a full car model are developed to validate the effectiveness of the overall system design. Different dynamic input scenarios are used for model simulation, which includes single-wheel sinusoidal input, braking test and double lane change test. In the double lane change test, the EHHIS sees averagely 70% improved in roll angle relative to a conventional suspension, and averagely 22% improvement relative to simple hydraulically interconnected suspension. The power generated is found to reach maximum at 4 Ω external resistance and the highest average power generated is more than 70 watts at 2 hz 20 mm sinusoidal input. A road test of a half vehicle EHHIS system is done. From the road test results, the EHHIS meets the expectations of reducing roll angles. The riding comfort is evaluated with the RMS value of the vertical acceleration and is found to have minimum compromise from the greater damping coefficient. / Master of Science / Better road handling dynamics and riding comfort has always been after by the automotive industry. The vehicle body may experience all kinds of movement such as roll, pitch and bounce, every type of these motion can cause safety risks and passenger fatigue. Traditional vehicle suspension system is equipped with isolated oil shock absorbers that can only dissipate energy by pushing the oil through damping valves. A concept called hydraulic interconnected suspension can use hydraulic circuits to connect each shock absorber, so that the energized hydraulic fluid can be utilized to counter unwanted body motion to improve the overall riding experience. The hydraulic interconnected suspension (HIS) is a proven concept that has shown good potential in stabilizing the vehicle body in rough road conditions. Hydraulic interconnected suspension is still passive and lack of adaptivity, while active suspensions such as electro-magnetic shock absorbers can use external power supply to force the to adapt to quickly changing road conditions. The energy demand from an active suspension can reach the level of kilowatts in certain cases, which results in lowered fuel efficiency of the vehicle. Additionally, actively supplying power to the system always have the risk of functional failure due to power loss. To find a balanced solution to dynamic performance and energy efficiency, this paper introduces a new form of energy-harvesting suspension that is integrated in a hydraulically interconnected suspension (EHHIS) system. The combined energy-harvesting and HIS system provide improved energy efficiency as well as vehicle dynamics performance. Each system is composed of four connected hydraulic cylinders on each wheel and other auxiliaries. To investigate the effectiveness of the entire system, a single cylinder model is first built in AMESim for preliminary study and validated in the experiments. The bench test results proved the authenticity of the theoretical model, and the model is then used to predict the system performance and guide the hardware construction. Based on the proven single cylinder model, and a full car model are developed to validate the effectiveness of the overall system design. Different road condition scenarios are used for model simulation, which includes single-wheel sinusoidal input, braking test and double lane change test. In the double lane change test, the EHHIS system sees averagely 70% improved in roll angle relative to a conventional suspension, and averagely 22% improvement relative to simple hydraulically interconnected suspension. In the breaking test, the EHHIS-equipped vehicle experiences smoother pitching behavior and less oscillations. The power generated is found to reach maximum at 4 Ω external resistance and the highest average power generated is more than 70 watts at 2 hz 20 mm sinusoidal input.

Advances in mechatronics have renewed interest in the harvesting and storage of ambient vibration energy. This work documents recent efforts to model a novel electromagnetic transducer design that is intended for use in energy harvesting. The thesis details methods of experimental characterization as well as model validation. Also presented are methods of state space and parametric modelling eforts. In addition, this thesis presents equivalent electrical circuit models with a focus on switched pulse-width-modulated topologies that seek to maximize harvested energy. / Master of Science

This dissertation presents innovative research at the intersection of thermoelectric solutions, additive manufacturing, and nuclear safety technology, addressing critical challenges in sensor powering for extreme environments, energy harvesting, and materials fabrication. The research is divided into three key areas, each contributing to advancements in its respective domain. First, a self-powered wireless through-wall data communication system was developed for monitoring nuclear facilities, specifically spent fuel storage dry casks. These facilities require continuous monitoring of internal conditions, including temperature, pressure, radiation, and humidity, under harsh environments characterized by high temperatures and intense radiation without any penetration through their walls. The constructed system integrated four modules: an energy harvester with power management circuits, an ultrasound wireless communication system using high-temperature piezoelectric transducers, electronic circuits for sensing and data transmission, and radiation shielding for electronics. Experimental validation demonstrated that the system harvests over 40 mW of power from thermal flow, withstands gamma radiation exceeding 100 Mrad, and survives temperatures up to 195°C. The system, designed to operate stably for fifty years, enables data transmission every ten minutes, ensuring reliable long-term monitoring for nuclear safety and security. Second, the efficiency of thermoelectric generators (TEGs), unique solid-state devices for thermal-to-electrical energy conversion, was explored through a novel manufacturing approach using selective laser melting (SLM) and direct energy deposition (DED). Conventional TEG fabrication methods have limitations in achieving optimal efficiency due to design and material constraints. SLM-based additive manufacturing offers a scalable solution for creating geometry-flexible and functionally graded thermoelectric materials. This research developed a physical model to simulate the SLM and DED process for fabricating Mg2Si thermoelectric materials with Si doping. The model incorporates conservation equations and accounts for fluid flow driven by buoyancy forces and surface tension, enabling detailed analysis of process parameters such as laser scanning speed and power input. The results provided insights into temperature distribution, powder bed shrinkage, and molten pool dynamics, advancing the understanding and optimization of thermoelectric device fabrication using additive manufacturing. One step further, SLM and DED experiments were carried out to validate the simulation results and testify to the feasibility of applying laser powder bed fusion on semiconductor materials. Third, the research investigates the application of laser additive manufacturing to improve performance and reduce the production costs of magnetic materials. Soft magnetic materials, critical for various industrial applications, are fabricated using DED. The research optimizes DED printing parameters and processes through quality control experiments inspired by the Taguchi method and analysis of variance models. The resulting silicon-iron samples exhibit minimal defects and cracks, demonstrating the feasibility of the approach. Detailed optical and scanning electron microscopy, coupled with magnetic characterization, reveal that the rapid cooling process inherent to laser-based AM enables unique microstructures that enhance magnetic properties. Collectively, this work addresses pressing technological challenges in energy harvesting, materials fabrication, and extreme environment monitoring. The developed systems and methodologies have broad implications for nuclear safety, additive manufacturing, and the efficient utilization of advanced materials. By integrating interdisciplinary approaches and leveraging cutting-edge manufacturing technologies, this dissertation contributes to the advancement of sustainable and resilient solutions for modern engineering challenges. / Doctor of Philosophy / This dissertation explores groundbreaking advancements in energy solutions, manufacturing techniques, and nuclear safety, presenting technologies that address challenges in powering sensors, creating efficient energy harvesters, and developing advanced materials. The research spans three main areas, each providing innovative contributions to these critical fields. The first part focuses on a wireless system that powers itself and communicates data from inside sealed nuclear storage containers. These containers, used to store spent nuclear fuel, must be closely monitored for temperature, pressure, radiation, and humidity to ensure safety. However, traditional monitoring methods cannot penetrate the container walls and withstand the extreme conditions inside. This project developed a system combining four key components: a thermal energy harvester, an ultrasound-based communication method, durable electronic circuits, and radiation shielding. The system successfully harvests energy from the container's heat and uses it to power sensors and transmit data wirelessly every ten minutes. It is designed to operate reliably for fifty years, even under intense radiation and high temperatures, providing long-term solutions for nuclear safety monitoring. The second area investigates thermoelectric generators (TEGs), devices that convert heat into electricity. While TEGs have significant potential, traditional manufacturing techniques limit their efficiency and adaptability. By using cutting-edge laser-based additive manufacturing methods—Selective Laser Melting (SLM) and Direct Energy Deposition (DED)—this research developed new ways to create flexible and efficient thermoelectric materials. Advanced simulations were performed to model the manufacturing process, analyzing how factors like laser speed and power affect the final material properties. These models provided valuable insights into optimizing the process, which were then validated through experimental testing. The findings open the door to scalable and efficient production of thermoelectric devices for various energy applications. The third area addresses the fabrication of magnetic materials, essential for many industrial technologies. Traditional methods of creating magnetic materials can be expensive and prone to defects. This research applied laser-based additive manufacturing to produce soft magnetic materials, such as silicon iron, with fewer flaws and improved performance. By optimizing the printing parameters through experiments and statistical analysis, the team created materials with enhanced magnetic properties. Microscopic analysis revealed that the rapid cooling during manufacturing produced unique structures that contribute to the materials' superior qualities. These advancements have the potential to reduce costs and improve the efficiency of magnetic products in various industries. In summary, this dissertation tackles some of the most pressing challenges in energy, manufacturing, and safety technology. By developing systems that can monitor nuclear storage for decades, improving methods to harvest energy from heat, and creating better magnetic materials, this work paves the way for safer and more efficient solutions to modern engineering problems. These innovations are not only critical for nuclear safety but also hold promise for broader applications in sustainable energy and advanced manufacturing, contributing to a safer and more efficient future for industries worldwide.

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.

Given the ever-growing need for device autonomy and renewable sources of energy, energy harvesting has become an increasingly popular field of research. This research focuses on energy harvesting using the piezoelectric effect, from vibrating membrane structures by converting mechanical energy into electric energy. Specific applications of this research include powering components of bio-inspired micro air vehicles (MAVs), which require long range with as little regular maintenance as possible, and powering sensors for structural health monitoring on otherwise inaccessible locations (the roof of the Denver Int'l Airport is a good example). Coming up with an efficient, high-fidelity model of these systems allows for design optimization without the extensive use of experimental testing, as well as a deeper understanding of the physics involved. These are the twin goals of this research. This work describes a modeling algorithm using COMSOL, a multi-physics software, to predict the structural mechanics of and subsequent power harvested from a piezoelectric patch placed on a prestressed membrane structure. The model is verified by an FE comparison of the modeled system's dynamic response. For a 0.5 x 0.5 x 0.001 m nylon membrane with a 0.1 x 0.1 x 0.001 m piezoelectric patch placed on its corner, a maximum power output of ~10 microwatts was achieved, using a resistance of 100 Ohms and exciting the system around resonance. When the patch was placed on the side of the membrane, the power output was ~100 milliwatts. The ultimate goal is to estimate the energy harvested by a network of these piezoelectric patches and optimize the harvesting system based on the size, shape and location of the patches. / Master of Science

As Internet of Things (IoT) technology continues to become more commonplace, demand for self-sustainable and low-power networking schemes has increased. Future IoT devices will require a ubiquitous energy source and will need to be capable of low power communication. RF energy can be harvested through ambient or dedicated RF sources to satisfy this energy demand. In addition, these RF signals can be modified to convey information. This thesis surveys a variety of RF energy harvesting methods. A new low complexity energy harvesting system (circuit and antenna) is proposed. Low power communication schemes are examined, and low complexity and efficient transmitter designs are developed that utilize RF backscattering, harmonics, and intermodulation products. These communication schemes operate with minimal power consumption and can be powered solely from harvested RF energy. The RF energy harvester and RF-powered transmitters designs are validated through simulation, prototyping, and measurements. The results are compared to the performance of state-of-the-art devices described in the literature. / Master of Science / Future devices are expected to feature high levels of interconnectivity and have long lifetimes. RF energy from dedicated power beacons or ambient sources, such as Wi-Fi, cellular, DTV, or radio stations can be used to power these devices allowing them to be battery-less. These devices that harvest the RF energy can use that energy to transmit information. This thesis develops various methods to harvest RF energy and use this energy to transmit information as efficiently as possible. The designs are verified through simulation and experimental results.

In a wide range of industries, machine condition monitoring is one of the most cost effective ways to minimise maintenance efforts and machine downtime. To implement such a system, wireless solutions have increasingly become an attractive proposition due to the ease of installation and minimal infrastructure alternation. However, currently most wireless sensors in the world are powered by a finite battery source. The dependence of batteries not only requires frequent maintenance, but also has adverse environmental consequences associated with battery disposal. These reasons render massive deployment of wireless sensors in the industry problematic. With the advances in semiconductors, power consumption of wireless sensors has been continuously decreasing. It is an inevitable trend for self-powered wireless sensors to emerge and become the norm for machine and environmental monitoring. In this research, vibration is chosen to be the energy source to enable self-powered wireless sensors due to its ubiquitousness in machinery and industrial environments. As a result of relying on resonance, the biggest challenge for vibration-based energy harvesters is their narrow bandwidth. Even a small deviation of the vibration frequency can dramatically reduce the power output. The primary goal of this research is to address this problem. In particular, Piezoelectric generators are identified to be the most suitable technology. In this work, extensive theoretical and experimental studies are conducted in single mass and multi-modal harvesters, and in resonance tuning harvesters by modulus and impedance matching as well as by mechanical actuation. Mathematical modelling plays a significant role in energy harvester designs. A dynamic model that generalises the single degree of freedom models and the continuum models is derived and validated by experiments. The model serves as the building block for the whole research, and it is further refined for the investigation of modulus and impedance matching. In the study of multi-modal harvesters, a continuum model for double-mass piezoelectric cantilever beams is derived and experimentally validated. To study the feasibility of resonance tuning by mechanical means, prototypes were built and performance evaluated. This document details the theoretical basis, concepts and experimental results that extend the current knowledge in the field of energy harvesting. This research work, being highly industrially focused, is believed to be a very significant step forward to a commercial energy harvester that works for a wide range of vibration frequencies.

Simulations are a good method for the verification of the correct operation of solar-powered sensor nodes over the desired lifetime. They do, however, require accurate models to capture the influences of the loads and solar energy harvesting system. Artificial neural networks promise a simplification and acceleration of the modeling process in comparison to state-of-the-art modeling methods. This work focuses on the influence of the modeling process's different configurations on the accuracy of the model. It was found that certain parameters, such as the network's number of neurons and layers, heavily influence the outcome, and that these factors need to be determined individually for each modeled harvesting system. But having found a good configuration for the neural network, the model can predict the supercapacitor's charge depending on the solar current fairly accurately. This is also true in comparison to the reference models in this work. Nonetheless, the results also show a crucial need for improvements regarding the acquisition and composition of the neural network's training set.

The work described in this thesis is aimed at developing a novel piezoelectric cantilever energy harvesting circuit, so that more energy can be obtained from a particular piezoelectric harvester than is possible using conventional circuits. The main focus of the work was to design, build and test a proof of principle system, and not a commercial version, so as to determine any limitations to the circuit. The circuit functions by cancelling the capacitive output reactance of the piezoelectric harvester with a simulated inductance, and is based on an idea proposed by Qi in 2011. Although Qi's approach demonstrated that the circuit could function, the system proved too lossy, and so a less lossy version is attempted here. Experimental and software simulations are provided to verify the theoretical predictions. A prototype amplified inductor circuit was simulated and tested. From the simulation results, although harmonic current losses were found in the circuit, it was found that the circuit should produce an amplified effective inductance and a maximum output power of 165mW. The effective inductance is derived from the voltage across the 2H inductor, and this voltage is amplified and applied to the circuit via an inverter, to provide an extra simulated inductance, so that the overall inductance can be resonated with the piezoelectric harvester output capacitance. Hence the capacitive impedance of the harvester is nearly cancelled. The study and analysis of the amplified inductor circuit was carried out for a single cantilever harvester. Both open loop and closed loop testing of the system were carried out. The open loop test showed that the concept should function as predicted. The purpose of the closed loop test was to make the system automatically adjust for different resonance frequencies. The circuit was tested at 52Vpp inverter output voltage, and demonstrated a harvested power of 145.5mW. Experimental results show that the harvester output power is boosted from 8.8mW as per the manufacturer data sheet to 145.5mW (16.5 times). This is approximately double the power available using circuits described in the literature.