Structural vibration energy harvesting via bistable nonlinear attachments

A vibration-based bistable electromagnetic energy harvester coupled to a directly excited host structure is theoretically and experimentally examined. The primary goal of the study is to investigate the potential benet of the bistable element for harvesting broadband and low-amplitude vibration energy. The considered system consists of a grounded, weakly damped, linear oscillator (LO) coupled to a lightweight, damped oscillator by means of an element which provides for both cubic nonlinear and negative linear stiness components and electromechanical coupling elements. Single and repeated impulses with varying amplitude applied to the LO are the vibration energy sources considered. A thorough sensitivity analysis of the system's key parameters provides design insights for a bistable nonlinear energy harvesting (BNEH) device able to attain robust harvesting efficiency. Energy localization into the bistable attachment is achieved through the exploitation of three BNEH main dynamical regimes; namely, periodic cross-well, aperiodic (chaotic) cross-well, and in-well oscillations. For the experimental investigation on the performance of the bistable device, nonlinear and negative linear terms in the mechanical coupling are physically realized by exploiting the transverse displacement of a buckled slender steel beam; the electromechanical coupling is accomplished by an electromagnetic transducer

Nonlinear dynamics of two angles subtended by an angle

The work was based from previous analytical results that aims to facilitate rotations. It aims to initially use an elliptical track. However, from previous experimental observations, it was noted that addition of another pendulum, at an angle, instead of introducing a circular track, seemed more effective in inducing rotations. The idea of inducing rotations with a higher range of frequency is intriguing, with rotations being one of the centerpiece of energy generations or mechanical motion. Rotations are used because there is a continuous translational energy as compared to oscillations where it loses energy on it’s peak. If the experiment can induce rotations with impacts present and is still capable of rotating to generate electricity, it could lead to many more possibilities. Renewable energy using vibration is the main approach of this work, and investigating ways to achieve such energy with rotations using electromechanical device is one of the initial conditions that have been chosen to act as a motivation

Nonlinear dynamics of two angles subtended by an angle

The work was based from previous analytical results that aims to facilitate rotations. It aims to initially use an elliptical track. However, from previous experimental observations, it was noted that addition of another pendulum, at an angle, instead of introducing a circular track, seemed more effective in inducing rotations. The idea of inducing rotations with a higher range of frequency is intriguing, with rotations being one of the centerpiece of energy generations or mechanical motion. Rotations are used because there is a continuous translational energy as compared to oscillations where it loses energy on it’s peak. If the experiment can induce rotations with impacts present and is still capable of rotating to generate electricity, it could lead to many more possibilities. Renewable energy using vibration is the main approach of this work, and investigating ways to achieve such energy with rotations using electromechanical device is one of the initial conditions that have been chosen to act as a motivation

ELECTROMECHANICAL MODELING OF A HONEYCOMB CORE INTEGRATED VIBRATION ENERGY CONVERTER WITH INCREASED SPECIFIC POWER FOR ENERGY HARVESTING APPLICATIONS

Innovation in integrated circuit technology along with improved manufacturing processes has resulted in considerable reduction in power consumption of electromechanical devices. Majority of these devices are currently powered by batteries. However, the issues posed by batteries, including the need for frequent battery recharge/replacement has resulted in a compelling need for alternate energy to achieve self-sufficient device operation or to supplement battery power. Vibration based energy harvesting methods through piezoelectric transduction provides with a promising potential towards replacing or supplementing battery power source. However, current piezoelectric energy harvesters generate low specific power (power-to-weight ratio) when compared to batteries that the harvesters seek to replace or supplement. In this study, the potential of integrating lightweight cellular honeycomb structures with existing piezoelectric device configurations (bimorph) to achieve higher specific power is investigated. It is shown in this study that at low excitation frequency ranges, replacing the solid continuous substrate of a conventional piezoelectric bimorph with honeycomb structures of the same material results in a significant increase in power-to-weight ratio of the piezoelectric harvester. In order to maximize the electrical response of vibration based power harvesters, the natural frequency of these harvesters is designed to match the input driving frequency. The commonly used technique of adding a tip mass is employed to lower the natural frequency (to match driving frequency) of both, solid and honeycomb substrate bimorphs. At higher excitation frequency, the natural frequency of the traditional solid substrate bimorph can only be altered (to match driving frequency) through a change in global geometric design parameters, typically achieved by increasing the thickness of the harvester. As a result, the size of the harvester is increased and can be disadvantageous especially if the application imposes a space/size constraint. Moreover, the bimorph with increased thickness will now require a larger mechanical force to deform the structure which can fall outside the input ambient excitation amplitude range. In contrast, the honeycomb core bimorph offers an advantage in terms of preserving the global geometric dimensions. The natural frequency of the honeycomb core bimorph can be altered by manipulating honeycomb cell design parameters, such as cell angle, cell wall thickness, vertical cell height and inclined cell length. This results in a change in the mass and stiffness properties of the substrate and hence the bimorph, thereby altering the natural frequency of the harvester. Design flexibility of honeycomb core bimorphs is demonstrated by varying honeycomb cell parameters to alter mass and stiffness properties for power harvesting. The influence of honeycomb cell parameters on power generation is examined to evaluate optimum design to attain highest specific power. In addition, the more compliant nature of a honeycomb core bimorph decreases susceptibility towards fatigue and can increase the operating lifetime of the harvester. The second component of this dissertation analyses an uncoupled equivalent circuit model for piezoelectric energy harvesting. Open circuit voltage developed on the piezoelectric materials can be easily computed either through analytical or finite element models. The efficacy of a method to determine power developed across a resistive load, by representing the coupled piezoelectric electromechanical problem with an external load as an open circuit voltage driven equivalent circuit, is evaluated. The lack of backward feedback at finite resistive loads resulting from such an equivalent representation is examined by comparing the equivalent circuit model to the governing equations of a fully coupled circuit model for the electromechanical problem. It is found that the backward feedback is insignificant for weakly coupled systems typically seen in micro electromechanical systems and other energy harvesting device configurations with low coupling. For moderate to high coupling systems, a correction factor based on a calibrated resistance is presented which can be used to evaluate power generation at a specific resistive load

Exploiting Stiffness Nonlinearities to Improve the Performance of Galloping Flow Energy Harvesters

Fluid-structure coupling mechanisms such as galloping and wake galloping have recently emerged as effective methods to develop scalable flow energy harvesters (FEHs) that can be used to power remote sensors and sensor networks. The oper-ation concept of these devices is based on coupling the pressure forces culminating from the motion of the fluid past a mechanical oscillator to its natural modes of vibration. As a result, the mechanical oscillator undergoes large-amplitude motions that can be transformed into electricity by utilizing an electromechanical transduc-tion mechanism, which is generally piezoelectric or electromagnetic in nature. Due to their scalability and design simplicity, FEHs are believed to be more effective for micro-power generation than their traditional rotary-type counterparts whose efficiency is known to drop significantly as their size decreases. Furthermore, FEHs can be used to harvest energy from unsteady flow patterns which permits targeting a niche market that traditional rotary-type generators do not address. In the open literature, galloping FEHs have always been designed to possess a linear restoring force. This dissertation considers the design and performance analysis of galloping FEHs with a nonlinear restoring force. Specifically, the objective of this dissertation is three fold. First, it assesses the influence of stiffness nonlinearities on the performance of galloping FEHs under steady and laminar flow conditions. Second, it studies the influence of the nonlinearity on the response of a wake gal-loping FEH to single- and multi-frequency Von Karman vortex streets. Third, for known flow characteristics, the dissertation provides directions for how to choose the restoring force of the harvester to maximize the output power. To achieve the objectives of this dissertation, a nonlinear FEH which consists of a thin piezoelectric cantilever beam augmented with a square-sectioned bluff body at the free end is con-sidered. Two magnets located near the tip of the bluff body are used to introduce the nonlinearity which strength and nature can be altered by changing the distance between the magnets. For a steady laminar flow, three types of nonlinear restoring forces are compared: bi-stable, mono-stable hardening, and mono-stable softening. To study the influ-ence of the restoring force on the performance, a physics-based nonlinear lumped-parameter aero-electromechanical model adopting the quasi-steady assumption for aerodynamic loading is developed. A closed-form solution of the nonlinear response is obtained by employing a multiple-scales perturbation analysis using the Jacobi el-liptic functions. The attained solution is validated experimentally using wind tunnel tests performed at different wind speeds for the three types of restoring forces con-sidered. The validated solution is then used to study the influence of the nonlinearity on the harvesters response. In general, it is shown that, under optimal operating conditions, a harvester designed with a bi-stable restoring force outperforms the other designs. For single- and multi-frequency vortex streets, only linear and bi-stable restoring forces were considered and compared. A nonlinear lumped-parameter model adopt-ing the common uncoupled single-frequency force model for aerodynamics loading is developed and solved using the method of multiple scales. The model is validated against experimental data obtained in a wind tunnel. It is demonstrated that when subjected to a single-frequency periodic wake, the broadband characteristics of wake-galloping FEHs can be dramatically improved by incorporating a bi-stable restoring force. This has the influence of reducing the harvester’s sensitivity to variations in the wind speed around the nominal design value. It is also demonstrated that the shape of the potential function has a considerable influence on the performance of the bi-stable wake galloping FEH. Specifically, it is shown that, for shallower poten-tial wells and smaller separation distances between the wells, the harvester starts performing large inter-well motions at lower wind speeds, but the resulting inter-well motions are generally smaller. On the other hand, for deeper potential wells and larger separation distances between the wells, the harvester starts performing large inter-well motions at higher wind speeds, but the magnitude of the resulting inter-well motions are generally larger. The dissertation also compared the performance of linear and bi-stable wake-galloping FEHs under a multi-frequency vortex street. Results demonstrated that the bi-stable system outperforms the linear harvester as long as the vortices have sufficient time to interact and build a multi-frequency vortical structure. Maximum voltage levels were generated at locations where the interacting vortices result in powerful modes close to the harvesters natural frequency

Nonlinear dynamics of new magneto-mechanical oscillator

Funding Information: ZH and DW acknowledge the financial supports of CSC (China Scholarship Council) and the Shandong Province Natural Science Foundation, China (No. ZR2017BA031 , ZR2017QA005 ), the National Natural Science Foundation of China (No. 11702111 , 11732014 ). The authors also thank Drs Dimitri Costa and Vahid Vaziri for their experimental support. Publisher Copyright: © 2021 Elsevier B.V.Peer reviewedPostprin

Modeling of Magnetoelectric Microresonator Using Numerical Method and Simulated Annealing Algorithm

A comprehensive understanding of the linear/nonlinear dynamic behavior of wireless microresonators is essential for micro-electromechanical systems (MEMS) design optimization. This study investigates the dynamic behaviour of a magnetoelectric (ME) microresonator, using a finite element method (FEM) and machine learning algorithm. First, the linear/nonlinear behaviour of a fabricated thin-film ME microactuator is assessed in both the time domain and frequency spectrum. Next, a data driven system identification (DDSI) procedure and simulated annealing (SA) method are implemented to reconstruct differential equations from measured datasets. The Duffing equation is employed to replicate the dynamic behavior of the ME microactuator. The Duffing coefficients such as mass, stiffness, damping, force amplitude, and excitation frequency are considered as input parameters. Meanwhile, the microactuator displacement is taken as the output parameter, which is measured experimentally via a laser Doppler vibrometer (LDV) device. To determine the optimal range and step size for input parameters, the sensitivity analysis is conducted using Latin hypercube sampling (LHS). The peak index matching (PIM) and correlation coefficient (CC) are considered assessment criteria for the objective function. The vibration measurements reveal that as excitation levels increase, hysteresis variations become more noticeable, which may result in a higher prediction error in the Duffing array model. The verification test indicates that the first bending mode reconstructs reasonably with a prediction accuracy of about 92 percent. This proof-of-concept study demonstrates that the simulated annealing approach is a promising tool for modeling the dynamic behavior of MEMS systems, making it a strong candidate for real-world applications

Nonlinear dynamics of a vibro-impact system subjected to electromagnetic interactions

Impact moling is an effective method of pile driving and percussive drilling to bore underground tunnel for various civil applications such as pipe, cable and ducts installation. An effective electro-vibroimpact system has been built on the basis of interactions between two sources of electromagnetic force. A vertical downward progression of mechanism into hard or brittle material required an increased magnitude of impact force within a compact geometry. Horizontal progression into clay is tested by combining periodic impact and static forces that produces an effective progression rate. As a consequence of this experimental work, a prototype electro-vibroimpact system is tested. Electrical circuitry consists of a timer and batteries which is a compact arrangement, functioning as waveform generator, and power supply. A cylindrical hollow aluminium tube houses the main components such as electromagnetic solenoids and oscillating bar within. This protects the main components from clay while progressing into soil and also reduces soil resistance with a minimal surface area. A mathematical model has also been numerically solved for both single and two degreeof-freedom system. Correlation has been achieved to a certain extent, and it is possible either deploy or further optimise this system

Vibration Energy Harvesting for Wireless Sensors

Kinetic energy harvesters are a viable means of supplying low-power autonomous electronic systems for the remote sensing of operations. In this Special Issue, through twelve diverse contributions, some of the contemporary challenges, solutions and insights around the outlined issues are captured describing a variety of energy harvesting sources, as well as the need to create numerical and experimental evidence based around them. The breadth and interdisciplinarity of the sector are clearly observed, providing the basis for the development of new sensors, methods of measurement, and importantly, for their potential applications in a wide range of technical sectors