Compact, autonomous computing systems with integrated transducers are imperative to deliver advances in healthcare, navigation, livestock monitoring, point of care diagnostics, remote sensing, internet-of-things applications, smart cities etc. Reflecting this need, there has been sustained growth in the market for transducers. Polymer based transducers, which meld highly desirable properties such as low cost, light weight, high manufacturability, biocompatibility and flexibility, are quite attractive. Doping polymers with magnetic materials results in the formation of magnetic composite polymers, enhancing the attractive traits of polymer transducers with magnetic properties. This dissertation is dedicated to the development of magnetic polymer transducers, which are suitable for energy harvesting and saline fluid transduction. The first-ever magnetic composite energy harvester capable of converting vibrations from the practically relevant low-frequency range into electrical energy was fabricated and tested. The harvester was realized by fabricating an array of PDMS-iron nanowire nanocomposite cilia on a planar coil array and exhibits a linear frequency response. This energy harvester design was further improved by increasing the doping concentration of the composite, adding a composite proof mass and improving the microfabricated coil. These changes manifest in an energy harvester that not only increases the power density by 4 orders of magnitude over the previous design but also possesses large operational bandwidth. The composite structure, comprising of the cilia and the proof mass has a frequency response comprised of two closely spaced resonant peaks facilitating the desirable broadband behavior at low frequency.A polymer-based magneto hydrodynamic pump prototype capable of actuating saline fluids was developed. The benefit of this pumping concept to operate without any moving parts is combined with simple and cheap fabrication methods and a magnetic composite material, enabling a high level of integration together with the advantages of mechanical flexibility. The pump electrodes are created by laser printing of graphene on polyimide, while the permanent magnet is molded from an NdFeB powder - polydimethylsiloxane (PDMS) composite. These materials were leveraged to fabricate an integrated, low profile magneto hydrodynamic pump, suitable for deployment in lab on chip systems.

Indiana University-Purdue University Indianapolis (IUPUI) / With the growing popularity and use of devices under the great umbrella that is the Internet of Things (IoT), the need for devices that are smaller, faster, cheaper and require less power is at an all time high with no intentions of slowing down. This is why many current research efforts are very focused on energy harvesting. Energy harvesting is the process of storing energy from external and ambient sources and delivering a small amount of power to low power IoT devices such as wireless sensors or wearable electronics. A charge pumps is a circuit used to convert a power supply to a higher or lower voltage depending on the specific application. Charge pumps are generally seen in memory design as a verity of power supplies are required for the newer memory technologies. Charge pumps can be also be designed for low voltage operation and can convert a smaller energy harvesting voltage level output to one that may be needed for the IoT device to operate. In this work, an integrated FinFET (Field Effect Transistor) charge pump for low power energy harvesting applications is proposed. The design and analysis of this system was conducted using Cadence Virtuoso Schematic L-Editing, Analog Design Environment and Spectre Circuit Simulator tools using the 7nm FinFETs from the ASAP7 7nm PDK. The research conducted here takes advantage of some inherent characteristics that are present in FinFET technologies, including low body effects, and faster switching speeds, lower threshold voltage and lower power consumption. The lower threshold voltage of the FinFET is key to get great performance at lower supply voltages. The charge pump in this work is designed to pump a 150mV power supply, generated from an energy harvester, to a regulated 650mV, while supplying 1uA of load current, with a 20mV voltage ripple in steady state (SS) operation. At these conditions, the systems power consumption is 4.85uW and is 31.76% efficient. Under no loading conditions, the charge pump reaches SS operation in 50us, giving it the fastest rise time of the compared state of the art efforts mentioned in this work. The minimum power supply voltage for the system to function is 93mV where it gives a regulated output voltage of $25mV. FinFET technology continues to be a very popular design choice and even though it has been in production since Intel's Ivy-Bridge processor in 2012, it seems that very few efforts have been made to use the advantages of FinFETs for charge pump design. This work shows though simulation that FinFET charge pumps can match the performance of charge pumps implemented in other technologies and should be considered for low power designs such as energy harvesting.

Yes / Concrete with smart and functional properties (e.g., self-sensing, self-healing, and energy-harvesting) represents a transformative direction in the field of construction materials. Energy-harvesting concrete has the capability to store or convert the ambient energy (e.g., light, thermal, and mechanical energy) for feasible uses, alleviating global energy and pollution problems as well as reducing carbon footprint. The employment of energy-harvesting concrete can endow infrastructures (e.g., buildings, railways, and highways) with energy self-sufficiency, effectively promoting sustainable infrastructure development. This paper provides a systematic overview on the principles, fabrication, properties, and applications of energy-harvesting concrete (including light-emitting, thermal-storing, thermoelectric, pyroelectric, and piezoelectric concretes). The paper concludes with an outline of some future challenges and opportunities in the application of energy-harvesting concrete in sustainable infrastructures.

Fabrication process of capacitors and Schottky diodes with nanogap electrodes is explained in this Thesis. The Schottky diode is made with IGZO in the nanogap, whereas the capacitor is made with ZrO2 in the nanogap which acts as the dielectric. Moreover, the electric characterization of both the diode and capacitor was obtained for different frequencies and different diameters. The end result showed that as the frequency increases the diode performance increases, but the capacitance of the capacitors decreases. Also, the barrier height and concentration were obtained using the Mott-Schottky plot for different frequencies. The 10MHz had the highest carrier concentration (5.9E+18cm-3) and barrier height (1V).

In this research work, we propose a novel energy harvester which converts solar electromagnetic radiation into DC energy at infrared regime. The proposed device consists of a dual polarized nanoantenna loaded with an anisotropic material at its gap. The dual polarized nanoantenna focuses the randomly polarized radiation into its gap resulting in high electric field. This high local electric field at the gap interacts with the anisotropic material. In our proposed design, the anisotropic material possesses nonlinear electrical conductivity and converts the dual polarizations at the gap into a DC voltage difference across the terminals of the nanoantenna. The novelty of our proposed design is in the rectification of the electromagnetic radiation without utilizing a diode. The theory of the energy harvester depends on the utilization of the dual polarized nanoantennas at high frequency regime. Therefore, we carry out a parametric study to investigate the resonance characteristic of the dual polarized nanoantenna. In addition, we investigate the effect of the geometrical parameters on the local field enhancement at the gap of the dual polarized nanoantenna. Also, another parametric study is carried out to determine the effect of the governing parameters of the anisotropic material on the generated DC voltage across the harvester. Our approach is illustrated through electromagnetic simulations. / Thesis / Master of Applied Science (MASc)

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.

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.