Vibration energy harvesters work effectively only when the operating conditions match with the available vibration source. Typical resonating MEMS structures cannot be used with low-frequency, low-amplitude and unpredictable nature of ambient vibrations. Bi-stable nonlinear oscillator based energy harvesters are developed for lowering the operating frequency while widening the bandwidth, and are realized at MEMS scale for the first time. This design concept does not rely on the resonance of the MEMS structure but operates with the large snapping motion of the beam at very low frequencies when proper conditions are provided to overcome the energy barrier between the two energy wells of the structure. A fully functional piezoelectric MEMS energy harvester is designed, monolithically fabricated and tested. An electromechanical lumped parameter model is developed to analyze the nonlinear dynamics and to guide the design of the multi-layer buckled beam structure. Residual stress induced buckling is achieved through the progressive control of the deposition along the fabrication steps. Static surface profile of the released device shows bi-stable buckling of 200 [mu]m which matches very well with the design. Dynamic testing demonstrates the energy harvester operates with 35% bandwidth under 70Hz at 0.5g, operating conditions that have not been met before by MEMS vibration energy harvesters.

We have designed and built macro-scale wideband electrostatic and electromagnetic power harvesters for low frequency vibration. Initially, MEMS capacitive plates for power harvesting have been designed, modeled and fabricated, and characterized. It was designed with a 2×2 mm2 movable metallic plate with a thickness of 10 [micro]m suspended by four straight beams above a fixed electrode with a gap of 10 [micro]m to form a variable capacitor. The suspension beams are made with a width, thickness and total length of 20 [micro]m, 10 [micro]m and 1500 [micro]m, respectively. It was found that the single cavity device can harvest almost 180 nW peak power across a 100 k[omega] load resistor at 5g. The harvested power was dependent on excitation amplitude and supplied DC voltage. The MEMS capacitive energy harvester was integrated with two impact oscillators at 18 Hz and 25 Hz for transferring energy from low frequency structural vibration with varying mechanical spectra to high frequency vibration of a high resonance frequency cantilever at 605 Hz. The results demonstrate that the device was able to harvest power on a wide range from 14 to 39 Hz at 1g excitation. The harvested power was 96 nW on a 100 k[omega] load resistor. We also studied a macro-scale electromagnetic power harvester with multi-impact oscillations to achieve a broad bandwidth at low frequency vibrations. The device consists of three low frequency cantilever designed to resonate at 12 Hz, 19 Hz and 40 Hz, a high frequency cantilever with resonance frequency of 210 Hz and a pick-up coil fixed at the tip of the high frequency cantilever. This results in a wide bandwidth response from 11-62 Hz at 1 g. A maximum output power of 23.5 [micro]W can be harvested at 1 g acceleration on an optimum load resistor of 22 [omega].

The transformation of vibrations into electric energy through the use of piezoelectric devices is an exciting and rapidly developing area of research with a widening range of applications constantly materialising. With Piezoelectric Energy Harvesting, world-leading researchers provide a timely and comprehensive coverage of the electromechanical modelling and applications of piezoelectric energy harvesters. They present principal modelling approaches, synthesizing fundamental material related to mechanical, aerospace, civil, electrical and materials engineering disciplines for vibration-based energy harvesting using piezoelectric transduction. Piezoelectric Energy Harvesting provides the first comprehensive treatment of distributed-parameter electromechanical modelling for piezoelectric energy harvesting with extensive case studies including experimental validations, and is the first book to address modelling of various forms of excitation in piezoelectric energy harvesting, ranging from airflow excitation to moving loads, thus ensuring its relevance to engineers in fields as disparate as aerospace engineering and civil engineering. Coverage includes: Analytical and approximate analytical distributed-parameter electromechanical models with illustrative theoretical case studies as well as extensive experimental validations Several problems of piezoelectric energy harvesting ranging from simple harmonic excitation to random vibrations Details of introducing and modelling piezoelectric coupling for various problems Modelling and exploiting nonlinear dynamics for performance enhancement, supported with experimental verifications Applications ranging from moving load excitation of slender bridges to airflow excitation of aeroelastic sections A review of standard nonlinear energy harvesting circuits with modelling aspects.

Ambient motion and vibration frequencies of 1 to 16 Hz is the focus of this research for the design of a MEMS power generator to scavenge mechanical energy of a typical human body motion. A lead zirconate titanate coated cantilever, on which a proof mass is attached, is used as the energy harvesting structure. Lumpled element model is created adn overall performance of the device is predicted. Single crystal silicon is attached to the cantilever for large proof mass which results in high power density in the targeted spectrum. Deep reactive ion etching based micro fabrication processes are proposed for the fabrication of the structure without implementing the fabrication. COMSOL, a multiphysics simulation tool is used in structure design. Flip-bias charge-voltage converting interface is introduced, and a total power density of 370 [Greek letter mu] W/cm3 at targeted motion frequency can be harvested based on the COMSOL and circuit simulations.

This book presents device design, layout design, FEM analysis, device fabrication, and packaging and testing of MEMS-based piezoelectric vibration energy harvesters. It serves as a complete guide from design, FEM, and fabrication to characterization. Each chapter of this volume illustrates key insight technologies through images. The book showcases different technologies for energy harvesting and the importance of energy harvesting in wireless sensor networks. The design, simulation, and comparison of three types of structures – single beam cantilever structure, cantilever array structure, and guided beam structure have also been reported in one of the chapters. In this volume, an elaborate characterization of two-beam and four-beam fabricated devices has been carried out. This characterization includes structural, material, morphological, topological, dynamic, and electrical characterization of the device. The volume is very concise, easy to understand, and contains colored images to understand the details of each process.

MEMS based energy harvesters have recently been investigated for scavenging, otherwise useless, ambient vibration energy. Piezoelectric materials are fabricated on micro-devices to convert the mechanical vibration energy into electrical energy. The main focus for these harvesters is low frequency (under 500 Hz) ambient vibration which is the source of a fundamental challenge with MEMS oscillators. The smaller the oscillator is, the higher its natural frequencies will become. Various techniques have been proposed to decrease the natural frequency of micro-energy harvesters such as increasing the length of the devices or assembling extra proof mass to the fabricated devices which could potentially affect the mass production of the MEMS devices. Another challenge is that most of the reported piezoelectric energy harvesters in the literature have cantilever designs. These structures have a high mechanical quality factor providing a sharp peak at their resonant frequency. Since microfabricating resonators with a resonant frequency exactly matching their designed value is very challenging, linear cantilever designs seem to be less practical for real applications where excitation frequency could change. Therefore, some techniques in vibration have been adapted to widen the frequency bandwidth of the harvesters. One of the most effective methods to broaden the frequency bandwidth is taking advantage of large deflection effect of oscillators. However, some of the proposed designs such as a fixed-fixed beam design have high resonant frequencies (≥1 kHz), whereas the focus for energy harvesters is low frequency range. In this work, a silicon based structure has been designed and fabricated to carry an electronic chip and potentially provide in-situ supplementary power for it. This design provides capability of harvesting at three different frequencies because the resonant frequencies of this structure at its first three mode shapes are within the low ambient vibration frequency range. The widening frequency bandwidth has been investigated for this design. Natural frequencies as low as 71.8, 84.5, and 188.4 Hz have been measured using a laser vibrometer. A frequency bandwidth of ~10 Hz has been obtained for the 2nd mode shape of the structure under the base excitation of 0.2g. A maximum open circuit voltage of ~1V and maximum power output of 136nW have been obtained using this harvester. In addition, as opposed to the conventional silicon-based harvesters, polymeric materials have been investigated as the main structural material for energy harvesters. Due to the much lower stiffness of polymers compared to silicon, the resonant frequency of the harvesters could be reduced. To prove the concept, a SU-8 (ESU-8=5GPa vs. ESi=160GPa) membrane has been designed and fabricated with Aluminum Nitride harvesting elements. The membrane configuration provides the capability to widen the harvester's frequency bandwidth. Testing results reveal a linear resonant frequency of 381 Hz, frequency bandwidth of 146Hz, maximum output power of 1.37μW, and power density of 3.81 μW/cm2 at the base excitation of 4g with this design. The much lower resonant frequency of polymeric structures compared to the similar silicon-based structures (more than 5 times lower) makes them a strong candidate for the future harvesters. The objective of this thesis is to develop a platform using silicon-based and polymer-based energy harvesters to improve the performance of the energy harvesters by reducing the resonant frequencies and widening the frequency bandwidth. Throughout this research, all stages including design, fabrication, packaging, testing, and characterization of both silicon- and polymer-based harvesters have been developed or adapted for the purpose of this work. Finite element simulations have been conducted to examine the mechanical response of the structures as well as their electrical output at the design stage. A scalable microfabrication process flow has been developed in this work to fabricate piezoelectric layers on SU-8 micro-structures. An improved approach for cleaving fabricated devices from the silicon substrate has been developed to overcome challenges of the dicing process. Various 3-D micro-assembly techniques have been adapted to package the fabricated harvesters. In addition, 3-D printed parts were used to enhance the yield of the packaging and testing stages. This technique could potentially be used for bio-compatible packaging, as well. In conclusion, the polymer-based and wideband energy harvesters seem promising for real applications at low ambient vibration frequencies. This research introduces opportunities to further improve the performance of the harvesters by decreasing their resonant frequencies.

This book discusses the expertise, skills, and techniques needed for the development of new materials and technologies. It focuses on finite element and finite volume methods that are used for engineering simulations, and present many state-of-the-art applications and advances to highlight these methods’ importance. For example, modern joining technologies can be used to fabricate new compound or composite materials, even those formed from dissimilar component materials. These composite materials are often exposed to harsh environments, must deliver specific characteristics, and are primarily used in automotive and marine technologies, i.e., ships, amphibious vehicles, docks, offshore structures, and even robots. To achieve the desired material performance, computer-based engineering tools are widely used for simulation, data evaluation, and design processes.