Date of Award

Spring 2020

Document Type

Open Access Dissertation

Department

Mechanical Engineering

First Advisor

Sourav Banerjee

Abstract

Due to the limited availability and high depletion rates of nonrenewable sources of energy as well as environmental concerns, the scientific community has started to explore many alternative clean sources of energies. It is identified that civil, mechanical and Aerospace structures are always subjected to acoustic noises and vibration which could potentially be used as renewable source of energy. Roads and Industrial noise barriers are used inside industrial facilities alongside the walls, around construction pillars, nearby machinery and other equipment to separate quite work zones, protect walls, deliver extra safety and precautions while diminish sound and vibrational pressure. We hypothesized if these noise barriers/structures could serve dual purposes, while harvest energies from the filtered noises and vibrations, significant energies could be renewed. Such renewable energies could be then used for different purposes, like charging cell phones, wearable devices, powering small electronics and remote sensors etc. Additionally, due to gravity, it is natural that our heavy mechanical equipment runs, operates, walks on the ground which are covered by cosmetic materials. Such materials encounter continuously changing pressure on the surface which is otherwise waisted if not harvested. Keeping these applications in mind for walls/ barriers/ tiles, oin this dissertation, utilizing one unique physics, two different type of renewable energy harvesting technologies are proposed. While proposing the application of harvesting and noise filtering, similar physics/mechanics prevalent in cochlea of human inner ear, further motivated this dissertation to device bio-inspired acoustic bandpass sensor. The harvesting and sensing devices that are conceptualized, analytically modeled, numerically simulated via COMSOL Multiphysics software, optimized, fabricated and tested to present the proof of concept are presented below. All models are numerically

1) A novel three-dimensional piezoelectric energy harvester based on a metamaterial structure is proposed, which is capable of scavenging energy at very low frequencies (<~1kHz) from multi-axial ambient vibrations. The proposed structure and its unit cell exploit the negative mass at local resonance frequencies and entraps the vibration energy as dynamic strain. The captured kinetic energy is then transformed to electric potential using three Lead Zirconate Titanate wafers, optimally embedded in the cell's soft constituent.

2) In the second design, a multi-frequency vibration-based energy harvester unit cell which is inspired from the design of human inner-ear, i.e. a snail-shaped model to enhance differential shear deformation of a membrane is proposed. Next an array of the proposed cell in the form of metamaterial bricks in a wall or a metamaterial tiles on the ground (Meta-tile) are modeled and fabricated to experimentally validated the concept. A spiral snail shaped PVDF membrane is embedded inside a Polydimethylsiloxane (PDMS) matrix that entraps the kinetic energy of the vibration within its structure. Numerical and experimental studies show that the unit cell and the Meta-tiles can harvest electrical power of up to ~1.8 mW and 11 mW against a 10KΩ resistive load, respectively.

3) Concurrent to the development of electronic processing of frequencies, mechanical sensors capable of selecting, processing, filtering specific single or a distinct band of frequencies are contributing an essential role in many sciences, technologies and industrial applications. After developing the energy harvester devices, the next objective of this PhD dissertation is to present a scalable numerical model along with a fabricated proof of concept of a bio-inspired acoustic bandpass sensor with a user-defined range of frequencies. In the proposed sensor, the geometric structure of a human’s basilar membrane is adopted as the main model to capture the sonic waves with a target frequency ranges. Human’s basilar membrane in the inner ear could be investigated in two ways, a) plate type and b) beam type. Both models are numerically and experimentally validated. In the first step, a predictive mathematical model of the proposed bandpass sensor is developed based on a plate type model. Next, the dynamic behavior of beam-type basilar membrane with 100 Zinc-Oxide electrodes is modeled and numerically verified. A sensor array is fabricated with using photolithography techniques with Polyvinylidene Difluoride (PVDF) piezoelectric material as a proof-of-concept. The fabricated plate-type sensor is experimentally tested, and its effective performance is validated in the frequency range of ~3 kHz-8 kHz. Similarly, in beam model the longest electrode is near the Apex region (8 mm x 300 μm x 20 μm thick) and the shortest electrode is near the Base side of the sensor with (3 mm x 300 μm x 110 μm thick) are proposed. Eventually, the effective performances of the proposed acoustic sensors are verified using COMSOL Multiphysics Software and the functionality of the proposed sensor appeared in the frequency range of ~ 0.5 kHz near Apex and to ~ 20 kHz near base side.

To run all the required experiments on the fabricated energy harvesters and acoustic sensors in this dissertation, a novel three-dimensional exciter is developed as a miscellaneous work. A high percentage of failures in sensors and devices employed in harsh industrial environments and airborne electronics is due to mechanical vibrations and shocks. Therefore, it is important to test the equipment reliability and ensure its survival in long missions in the presence of physical fluctuations. Traditional vibration testbeds employ unidirectional acoustic or mechanical excitations. However, in reality, equipment may encounter uncoupled (unidirectional) and/or coupled (multidirectional) loading conditions during operation. Hence, to systematically characterize and fully understand the proposed energy harvesters’ and acoustic sensors’ behaviors, a testbed capable of simulating a wide variety of vibration conditions is required which is designed, and fabricated. The developed testbed is an acousto electrodynamic three-dimensional (3-D) vibration exciter (AEVE 3-D), which simulates coupled and decoupled (with unpowered arms) 3-D acoustic and/or 3-D mechanical vibration environments. AEVE 3-D consists of three electromagnetic shakers (for mechanical excitation) and three loudspeakers (for acoustic excitation) as well as a main control unit that accurately calculates and sets the actuators' input signals in order to generate optimal coupled and decoupled vibrations at desired frequencies. In this paper, the system's architecture, its mechanical structure, and electrical components are described. In addition, to verify AEVE 3-D's performance, various experiments are carried out using a 3-D piezoelectric energy harvester and a custom-made piezoelectric beam.

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