With the emergence of the Internet of things (IoT) networks, the replacement of batteries for IoT devices became challenging. In particular, the battery replacement is more expensive and cumbersome for scenarios where there are many IoT devices; or where the IoT devices are in unreachable locations; or when they have to be replaced often. Some IoT devices might be lost or forgotten, and there is a risk of hazardous chemicals leakage and e-waste in large scale in nature. Radio frequency (RF) wireless power transfer (WPT) is an alternative technology for powering those devices. It has been shown that only less than one millionth of the transmitted energy is absorbed by the receivers, the rest is absorbed by the objects in the environment. We can utilize the existing infrastructure for wireless communications such as base stations (BS) to charge IoT devices. The present work is devoted to analyze the feasibility and limitations of the battery-less operation of IoT devices with RF WPT technology and energy harvesting from existing infrastructure for wireless communications. We study the indoor and outdoor scenarios for powering of IoT devices. In the first scenario, we consider an outdoor environment where an IoT device periodically harvests energy from an existing BS and transmits a data packet related to the sensor measurement under shadow fading channel conditions. We analyze the limits (e.g., coverage range) of energy harvesting from a BS for powering IoT devices. We characterize the "epsilon-coverage range, where" is the probability of the coverage. Our analysis shows a tradeoff between the coverage range and the rate of sensor measurements, where the maximal "epsilon-coverage range is achieved as the sensor measurement rate approaches zero. We demonstrate that the summation of the sleep power consumption and the harvesting sensitivity power of an IoT device limits the maximal "epsilon-coverage range. Beyond that range, the IoT device cannot harvest enough energy to operate. The desired rate of the sensor measurements also significantly impacts the "epsilon-coverage range. We also compare the operational domain in terms of the range and measurement rate for the WPT and battery-powered technologies. In the second scenario, we consider the remote powering of IoT devices inside an aircraft. Sensors currently deployed on board have wired connectivity, which increases weight and maintenance costs for aircraft. Removing cables for wireless communications of sensors on board alleviates the cost, however, the powering of sensors becomes a challenge inside aircraft. We assume that the IoT devices have fixed and known locations inside an aircraft. The design problem is to minimize the number of WPT transmitters given constraints based on the cabin geometry and duty cycle of the IoT devices. We formulate a robust optimization problem to address the WPT system design under channel uncertainties. We also derive an equivalent integer linear programming and solve that for an optimal deployment to satisfy the duty cycle requirements of the cabin sensors. / <p>QC 20220223</p><p></p>

Fluid-structure interactions occur in many engineering and industrial applications. Such interactions may result in undesirable forces acting on the structure that may cause fatigue and degradation of the structural components. The purpose of this research is to develop a solver that simulates the fluid-structure interaction, assess tools that can be used to control the resulting motions and analyze a system that can be used to convert the structure's motion to a useful form of energy. For this purpose, we develop a code which encompasses three-dimensional numerical simulations of a flow interacting with a freely-oscillating cylinder. The solver is based on the accelerated reference frame technique (ARF), in which the momentum equations are directly coupled with the cylinder motion by adding a reference frame acceleration term; the outer boundary conditions of the flow domain are updated using the response of the cylinder. We develop active linear and nonlinear velocity feedback controllers that suppress VIV by directly controlling the cylinder's motion. We assess their effectiveness and compare their performance and required power levels to suppress the motion of the cylinder. Particularly, we determine the most effective control law that requires minimum power to achieve a desired controlled amplitude. Furthermore, we investigate, in detail, the feasibility of using a nonlinear energy sink to control the vortex-induced vibrations of a freely oscillating circular cylinder. It has been postulated that such a system, which consists of a nonlinear spring, can be used to control the motion over a wide range of frequencies. However, introducing an essential nonlinearity of the cubic order to a coupled system could lead to multiple stable solutions depending on the initial conditions, system's characteristics and parameters. Our investigation aims at determining the effects of the sink parameters on the response of the coupled system. We also investigate the extent of drag reduction that can be attained through rotational oscillations of the circular cylinder. An optimization is performed by combining the CFD solver with a global deterministic optimization algorithm. The use of this optimization tool allows for a rapid determination of the rotational amplitude and frequency domains that yield minimum drag. We also perform three-dimensional numerical simulations of an inline-vibrating cylinder over a range of amplitudes and frequencies with the objective of suppressing the lift force. We compare the amplitude-frequency response curves, levels of lift suppression, and synchronization maps for two- and three-dimensional flows. Finally, we evaluate the possibility of converting vortex-induced vibrations into a usable form of electric power. Different transduction mechanisms can be employed for converting these vibrations to electric power, including electrostatic, electromagnetic, and piezoelectric transduction. We consider the piezoelectric option because it can be used to harvest energy over a wide range of frequencies and can be easily implemented. We particularly investigate the conversion of vortex-induced vibrations to electric power under different operating conditions including the Reynolds number and load resistance. / Ph. D.

With the rise of wireless sensor networks and the internet of things, many sensors are being developed to help us monitor our environment. Sensor applications from marine animal tracking to implantable healthcare monitoring require small and non-invasive methods of powering, for which purpose traditional batteries are considered too bulky and unreasonable. If appropriately designed, energy harvesting devices can be a viable solution. Solar and wind energy are good candidates of power but require constant exposure to their sources, which may not be feasible for in-vivo and underwater applications. Mechanical energy, however, is available underwater (the motion of the waves) and inside our bodies (the beating of the heart). These vibrations are normally low in frequency and amplitude, thus resulting in a low voltage once converted into electrical signals using conventional mechanical harvesters. These mechanical harvesters also suffer from narrow bandwidth, which limits their efficient operation to a small range of frequencies. Thus, there is a need for a mechanical energy harvester to convert mechanical energy into electrical energy with enhanced output voltage and for a wide range of frequencies. In this thesis, a new mechanical harvester is introduced, and two different methods of rectifying it are investigated. The designed harvester enhances the output voltage and extends the bandwidth of operation using a mechanical frequency up-convertor. This is implemented using magnetic forces to convert low-frequency vibrations to high-frequency pulses with the help of a piezoelectric material to generate high output voltage. The results show a 48.9% increase in the output voltage at 12.2Hz at an acceleration of 1.0g, and a bandwidth increase from 0.23Hz to 11.4Hz. For the rectification, mechanical rectifiers are discussed, which would obviate the need for electrical rectification, thus preventing the losses normally caused by the threshold voltage of electronics. Two designs of mechanical rectifiers are investigated and implemented on the frequency up-converter: a static rectifier and a rotating rectifier. The results show a voltage rectification, which required a sacrifice in the bandwidth and boosted voltage.

La polyvalence de la technique de track-etching a permis d’étudier plus avant l’effet piezoélectrique direct et indirect d’un film polarisé en poly(fluorure de vinylidène) PVDF en créant des membranes nanostructurées hybrides de nanofils de nickel (Ni NWs)/PVDF. Les propriétés magnétiques du nanofil de nickel, telle que la magnétorésistance anisotrope (AMR), ont été exploitées afin d’étudier la réponse de l’aimantation à la déformation mécanique de la matrice PVDF. En particulier, les déformations ont été induites soit par contrainte thermo-mécanique, soit par contrainte électromécanique (effet piezoélectrique indirect). La sensibilité d’un nanofil unique a permis de déterminer l’amplitude et la direction de la contrainte mécanique exercée à l’échelle nanométrique par la matrice PVDF. La résistance exceptionnelle de la réponse piezoélectrique directe du film PVDF polarisé à l’irradiation, telle que l’irradiation aux ions-lourds accélérés et aux électrons (domaine de doses < 100kGy) a été observée. Mis à part la conservation de la réponse piezoélectrique, les défauts engendrés par l’irradiation dans ce domaine de dose (scissions de chaines, augmentation de phase crystalline, réticulations) ont eu un impact significatif sur la structure du matériau polymère. L’ensemble de ces défauts, les uns prépondérants en-dessous de la dose-gel ( 10kGy), les autres au-dessus, forme une compensation d’effets antagonistes qui mènent à une réponse piezoélectrique globalement inchangée. Stimulé par la grande résistance du PVDF à l’irradiation en termes de réponse piezoélectrique, l’idée a été d’exploiter, en vue d’une application dans la récupération d’énergie, le réseau de nanofils de nickel inclus dans la membrane en PVDF polarisé pour étudier l’influence des nanofils de nickel sur la l’efficacité piezoélectrique. La présence du réseau de nanofils de nickel mène à un accroissement non négligeable de l’efficacité piezoélectrique. Reliée à la présence des nanofils, une augmentation de la permittivité diélectrique dans le PVDF nanostructuré a également été enregistrée. Une polarisation interfaciale entre les nanofils de nickel et la matrice PVDF pourrait expliquer cette valeur accrue par rapport au PVDF nanoporeux sans nanofils. / The versatility of the track-etching technique has allowed to investigate deeper the direct and inverse piezoelectric effect of a polarized Poly(vinylidene fluoride) (PVDF) film in building nanostructured hybrid Nickel nanowires (Ni NWs)/PVDF membrane. The magnetic properties of the Ni NW, such as anisotropic magneto resistance (AMR), are exploited to investigate the response of the magnetization to a mechanical deformation of the PVDF matrix. In particular, the deformations were induced either by thermo-mechanical or an electro-mechanical (inverse piezoelectric effect) stress. The sensitivity of the single NW has allowed to determine the amplitude and direction of a mechanical stress exerted at the nano-scale by the PVDF matrix. The outstanding resistance of the direct piezoelectric response of polarized PVDF film to radiation, such as SHI and e-beam, (doses range < 100kGy) was reported. Beyond the conservation of the piezoelectric response, in this dose range, irradiation defects (chain scissions, increase of the crystalline -phase, crosslinking) had a significative impact on the polymer material. All these defects, ones predominant above the gel dose (herein 10 kGy), and the other ones below, compensate their antagonistic effects towards the globally unchanged piezoelectric responses. Motivated by the high radiation resistance of the PVDF in terms of piezoelectric response, the idea was to exploit Ni NWs array embedded in the polarized PVDF membrane to study the influence of the Ni NWs on the piezoelectric response in view of harvesting energy application. The presence of the Ni NWs array leads a non-negligible increase of the piezoelectric efficiency. Related to the presence of the NWs, an increase of the dielectric permittivity in the nanostructured PVDF was also reported. An interfacial polarization between the Ni NWs and the PVDF matrix could explain the higher efficiency value respect to nanoporous PVDF, without NWs.

Piezoelectric materials have had widespread application since their discovery both in bulk crystal and thin film applications, but thin film piezoelectrics have unlocked key applications like acoustic filtering and energy harvesting. [1] This work investigates a small subset including energy harvesting, multifunctional nanocomposites, acoustic wave resonators, and gravimetric and infrared sensing. Electroactive polymers such as PVDF-TrFE have a unique combination of characteristics including a high dielectric constant, piezoelectricity, pyroelectricity, biocompatibility, and mechanical flexibility. [2, 3, 4, 5, 6] This unique combination gives them a wide potential application space including energy harvesting, biomedical devices, drug delivery, flexible electronics, and tactile sensing. [7] In recent years, there has been significant work investigating potential composite materials based on electroactive polymers and nanoparticles. [8] This interest has been primarily driven by the increased commercial availability, tunability, and available functionalities of nanoparticles. In this work, nanocomposites of PVDF-TrFE, barium titanate (BTO), and europium barium titanate (EBTO) are investigated. EBTO is an optically active material which can add optical functionality to these active polymer composites. [9] Acoustic wave resonators including bulk acoustic wave resonators and surface acoutstic wave resonators are widely used for front end filtering technologies, but their high quality factor, small size, and low power makes them good candidates for sensing technologies. [10, 11, 12] In this work, FBARs are applied to VOC sensing and infrared sensing sucessfully.

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BACKGROUND: Recent epidemiological data indicate that one-third of the U.S. adult population is obese. As a result, healthcare professionals and policy makers are looking to identify creative methods to address this critical health concern. One way that may show promise to promote positive health changes is to convert mechanical energy produced through exercise into stored electricity via energy harvesting (EH) exercise. Previous research has linked pro-environmental attitudes with increased participation in sustainable behaviors. Other research has examined associations between consumption of fruits and vegetables and exercise participation. However, little research examines the association between exercise behavior and environmental concern. And more specifically, EH exercise. OBJECTIVE: To identify if EH exercise can act as a motivating factor to increase exercise participation. METHODS: Phase 1: Qualitative data were collected through a series of one-hour focus groups with ENERGIA Studio members who participate in EH exercise. Four focus groups were completed with 1-5 participants per group (n=12). Topics examined included: 1) perceived effect of EH exercise on the environment and its ability to act as a motivating factor to increase exercise participation; 2) participation in sustainable behaviors and attitudes toward energy conservation and environmental concerns; and 3) perceived benefits of and barriers to fruit and vegetable consumption and exercise participation. Data were used to inform a survey to examine the relationship between how environmental concern influences exercise and dietary practices. Phase 2: Fifteen participants from UMass Permaculture who had irregular exercise participation and pro-environmental beliefs completed an online survey. RESULTS: Significant results were found for associations between: environmental concern and sustainable and organic fruit and vegetable purchasing (p=0.008; p=0.048) among non-exercisers; health concern and organic purchasing (p=0.015) among exercisers; and sustainable practices and fruit and vegetable intake (X2 (1, 12) = 5.285, p=0.022) among non-exercisers. No significant results were found between environmental concern and EH exercise self-efficacy or exercise and fruit and vegetable intake. CONCLUSIONS: This study provides additional research examining how environmental concern may affect dietary and exercise habits. Using the threat of the environment may serve as a potential motivator to increase EH exercise participation and fruit and vegetable intake.

Failure of a machine can lead to production downtime and significant financial losses. Condition monitoring is implemented to avoid such downtime and devices can be used to collect data used for monitoring machine health. Vibration data is the most common type of data used for predicting machine failure. To reduce the need for hazardous cables, such devices are often battery-operated, but this can decrease monitoring device lifespans to less than 3 years, if non-rechargeable batteries are used. This thesis first proposes a design framework for implementing radio frequency energy harvesting (RFEH) at a network level. All of the necessary inputs and parameters to ensure the successful implementation of RFEH for a wireless sensor network are explored. A second design framework is then proposed for using RFEH as a source of energy to power devices for condition monitoring. This includes a power analysis of all device components, as well as the design details for an implementation of wireless power transfer using a wireless transmitter and receiver. A comparison of different types of energy sources for the device is given, followed by a case study, using commercially-available components. A simulation is used to analyze the trade-offs for different values of RFEH parameters, trading off the total cost of implementation with the system's lifetime, based on total energy consumed.

Piezoelectric-based energy harvesting devices provide an attractive approach to powering remote devices as ambient mechanical energy from vibrations is converted to electrical energy. These devices have numerous potential applications, including actuation, sensing, structural health monitoring, and vibration control -- the latter of which is of particular interest here. This work seeks to develop an understanding of energy harvesting behavior within the framework of a semi-active technique for reducing turbomachinery blade vibrations, namely resonance frequency detuning. In contrast with the bulk of energy harvesting research, this effort is not focused on maximizing the power output of the system, but rather providing the low power levels required by resonance frequency detuning. The demands of this technique dictate that harvesting conditions will be far from optimal, requiring that many common assumptions in conventional energy harvesting research be relaxed. Resonance frequency detuning has been proposed as a result of recent advances in turbomachinery blade design that have, while improving their overall efficiency, led to significantly reduced damping and thus large vibratory stresses. This technique uses piezoelectric materials to control the stiffness, and thus resonance frequency, of a blade as the excitation frequency sweeps through resonance. By detuning a structure*s resonance frequency from that of the excitation, the overall peak response can be reduced, delaying high cycle fatigue and extending the lifetime of a blade. Additional benefits include reduced weight, drag, and noise levels as reduced vibratory stresses allow for increasingly light blade construction. As resonance frequency detuning is most effective when the stiffness states are well separated, it is necessary to harvested at nominally open- and short-circuit states, corresponding to the largest separation in stiffness states. This presents a problem from a harvesting standpoint however, as open- and short-circuit correspond to zero charge displacement and zero voltage, respectively, and thus there is no energy flow. It is, then, desirable to operate as near these conditions as possible while still harvesting sufficient energy to provide the power for state-switching. In this research a metric is developed to study the relationship between harvested power and structural stiffness, and a key result is that appreciable energy can be harvested far from the usual optimal conditions in a typical energy harvesting approach. Indeed, sufficient energy is available to power the on-blade control while essentially maintaining the desired stiffness states for detuning. Furthermore, it is shown that the optimal switch in the control law for resonance frequency detuning may be triggered by a threshold harvested power, requiring minimal on-blade processing. This is an attractive idea for implementing a vibration control system on-blade, as size limitations encourage removing the need for additional sensing and signal processing hardware.