Nonlinear Oscillations: Exact Solutions and their Approximations

https://northumbria-test.eprints-hosting.org/id/document/270135

Origami-inspired electret-based triboelectric generator for biomechanical and ocean wave energy harvesting

With the rapid development of the Internet of Things (IoT), the number of sensors utilized for the IoT is expected to exceed 200 billion by 2025. Thus, sustainable energy supplies without the recharging and replacement of the charge storage device have become increasingly important. Among various energy harvesters, the triboelectric nanogenerator (TENG) has attracted considerable attention due to its high instantaneous output power, broad selection of available materials, eco-friendly and inexpensive fabrication process, and various working modes customized for target applications. The TENG harvests electrical energy from wasted mechanical energy in the ambient environment. Three types of operational modes based on contact-separation, sliding, and freestanding are reviewed for two different configurations with a double-electrode and a single-electrode structure in the TENGs. Various charge transfer mechanisms to explain the operational principles of TENGs during triboelectrification are also reviewed for electron, ion, and material transfers. Thereafter, diverse methodologies to enhance the output power considering the energy harvesting efficiency and energy transferring efficiency are surveyed. Moreover, approaches involving not only energy harvesting by a TENG but also energy storage by a charge storage device are also reviewed. Finally, a variety of applications with TENGs are introduced. This review can help to advance TENGs for use in self-powered sensors, energy harvesters, and other systems. It can also contribute to assisting with more comprehensive and rational designs of TENGs for various applications.

Triboelectric Nanogenerator: Structure, Mechanism, and Applications.

Wearable triboelectric nanogenerators for biomechanical energy harvesting

The triboelectric nanogenerator (TENG) is a new type of energy generator first demonstrated in 2012. TENGs have shown potential as power sources for electronic devices and as sensors for detecting mechanical and chemical stimuli. To date, studies on TENGs have focused primarily on optimizing the systems and circuit designs or exploring possible applications. Even though triboelectricity is highly related to the material properties, studies on materials and material designs have been relatively less investigated. This review article introduces recent progress in TENGs, by focusing on materials and material designs to improve the electrical output and sensing performance. This article discusses the current technological issues and the future challenges in materials for TENG. The development of materials for a technology that uses the movement of the human body to provide power has been reviewed by scientists in South Korea. A triboelectric nanogenerator converts mechanical energy into electricity by harnessing the fact that two surfaces rubbing against one another can become electrically charged. This is known as the triboelectric effect. One exciting use for these nanogenerators is in wearable electronics, where the motion of the body provides the power. Unyong Jeong and colleagues from Pohang University of Science and Technology have reviewed recent progress in material advances in the four main elements of a triboelectric nanogenerator: the charge-generating layer, the charge-trapping layer, the charge-collecting layer, and the charge-storage layer. These improvements all aim to increase the electrical output of such devices. Over the last decade, triboelectric nanogenerator (TENG) has been verified to be an effective way of converting daily mechanical energy into electric power or detecting various stimuli in the external environment. To promote the material researches in TENG, we introduce recent progresses in materials and material designs to improve the power generation and sensing performance. Also, we discuss on the future challenges and suggest possible approaches to solve the challenges.

/pdf/material-aspects-of-triboelectric-energy-generation-and-2j8tumglpy.pdf

Material aspects of triboelectric energy generation and sensors

This paper reports a precision mode-localized accelerometer operating in a higher-order flexural mode. The accelerometer consists of two symmetric resonators coupled by a central rigid coupler to generate an ultra-weak coupling factor. A reduced noise floor is observed when the resonators operate in the higher-order flexural mode compared to the basic lower-order mode. The mode-localized accelerometer working in the fifth-order mode demonstrates an input-referred bias instability of 130 ng and noise floor of 85 ng/ $\surd $ Hz, which are the best results obtained for accelerometers employing the mode localization paradigm to date. These results indicate that the performance of the mode-localized sensors can be improved by operating at a higher working frequency if the coupling factor and quality factor do not drop significantly. [2020-0365]

A Low-Noise High-Order Mode-Localized MEMS Accelerometer

Miniaturized physical transducers based on weakly coupled resonators have previously demonstrated the twin benefits of high parametric sensitivity and the first-order common-mode rejection of environmental effects. Current approaches to sensing based on coupled resonator transducers employ strong coupling where the modal overlap of the responses is avoided. This strong coupling limits the sensitivity for such mode-localized sensors that utilize an amplitude ratio (AR) output metric as opposed to tracking resonant frequency shifts. In this article, this limitation is broken through by theoretically and experimentally demonstrating the operation of the weakly coupled resonators in the weak-coupling (modal overlap) regime. Especially, a prototype microelectromechanical systems (MEMS) sensor based on this principle is employed to detect shifts in stiffness, with a stiffness bias instability of $10.3~\mu \text{N}$ /m (9.5 ppb) and a corresponding noise floor of $7.1~\mu \text{N}$ /m/ $\surd $ Hz (6.8 ppb/ $\surd $ Hz). The linear dynamic range of such AR readout sensors is first explored and found to be defined by the dynamic range of the secondary resonator. The proposed method provides a promising approach for high-performance resonant force and inertial sensors.

On Weakly Coupled Resonant MEMS Transducers Operating in the Modal Overlap Regime

This paper reports a new design for an electrostatic actuated microgripper with a ratchet self-locking mechanism. The self-locking mechanism enables long-time gripping without continuously applying the external driving signal, such as an electrical, thermal or magnetic field, which significantly reduces the effect and damage on the gripped micro-scale objects that are induced by the external driving signals. The microgripper is fabricated using a silicon-on-insulator (SOI) wafer with a 30µm device layer. The jaw gap is 100 µm, and the ratchet locking interval is 10 µm. A metal wire is successfully gripped to demonstrate the feasibility of the ratchet self-locking mechanism.

A microgripper with a ratchet self-locking mechanism

With the introduction of the working principle of coupled resonators, the coupled bulk acoustic wave (BAW) Micro-Electro-Mechanical System (MEMS) resonators have been attracting much attention. In this paper, coupled BAW MEMS resonators are discussed, including the coupling theory, the actuation and sensing theory, the transduction mechanism, and the applications. BAW MEMS resonators normally exhibit two types of vibration modes: lateral (in-plane) modes and flexural (out-of-plane) modes. Compared to flexural modes, lateral modes exhibit a higher stiffness with a higher operating frequency, resulting in a lower internal loss. Also, the lateral mode has a higher Q factor, as the fluid damping imposes less influence on the in-plane motion. The coupled BAW MEMS resonators in these two vibration modes are investigated in this work and their applications for sensing, timing, and frequency reference are also presented.

/pdf/a-review-on-coupled-bulk-acoustic-wave-mems-resonators-2f559a3f.pdf

A Review on Coupled Bulk Acoustic Wave MEMS Resonators

Electrostatic kinetic energy harvester and more particularly triboelectric nanogenerators (TENG) can generate very high output AC voltages of several hundred volts. In addition, the losses due to the energy transfer between the typically small inner capacitance of the generators and a necessary large reservoir capacitance for collecting the harvested energy, severely limits the energy storage efficiency. In this paper, we propose a 2-stage conditioning system that efficiently manages the high-voltages of a TENG without any external active control. It includes, as the 1st stage, an unstable charge pump (a Bennet doubler) for the signal rectification and, as the 2nd stage, a novel self-actuated electrostatic switch having a narrow hysteresis followed by a DC-DC Buck converter. With this system, the converted energy is improved by 24 times compared to a classical full-wave diode bridge, while the output voltage remains below 20 V and then is compatible with commercial regulators.

Hemin Zhang

Papers

A Low-Noise High-Order Mode-Localized MEMS Accelerometer

On Weakly Coupled Resonant MEMS Transducers Operating in the Modal Overlap Regime

A microgripper with a ratchet self-locking mechanism

A Review on Coupled Bulk Acoustic Wave MEMS Resonators

A Conditioning System for High-Voltage Electrostatic/Triboelectric Energy Harvesters Using Bennet Doubler and Self-Actuated Hysteresis Switch