Rotational energy harvesting using bi-stability and frequency up-conversion for low-power sensing applications: Theoretical modelling and experimental validation

A low-frequency, wideband quad-stable energy harvester using combined nonlinearity and frequency up-conversion by cantilever-surface contact

Piezoelectric energy harvesters (PEHs) promote the construction of a smarter world through powering electric devices with energy scavenged from environmental vibrations by means of piezoelectric effect. To enable the piezoelectric effect, piezoelectric materials are usually attached to mechanical structures (e.g. flexible beams) that can deform due to mechanical vibration and produce strain in piezoelectric material. The mechanical structure for energy harvesting in nature is a Compliant Mechanism (CM). A large variety of structural solutions have been proposed aiming to expend the working frequency range and maximizing the energy output of PEHs. To advance PEHs, a comprehensive review on existing structural solutions and materials is necessary. According to structural characteristics of current PEHs from the aspect of CMs, designs in state of the art are analyzed and categorized into five configurations, mono-stable, multi-stable, multi-degrees-of-freedom, frequency up-conversion and stress optimization. For each configuration, working principles and compatibilities with miniaturization to MEMS scale are analyzed and assessed. Additionally, several CMs are first proposed for PEHs in different configurations as inspirations and references to prompt the development of PEHs. Piezoelectric materials are also important factors in enhancing the energy harvesting performance. Characters of several widely adopted piezo-materials are summarized and compared. The metric of Normalized Power Density (NPD) is introduced to compare and assess the energy generation capability of PEHs with several widely-used piezoelectric materials and in different scales. A NPD-Volume graph is first presented based on the data collected in literature. It shows that PEHs with PZT have the highest NPD and stable energy generation performance in a wide volume range. Both the structural categorization and NPD-Volume graph provide guidance and reference for design and optimization of PEHs.

A review on vibration-based piezoelectric energy harvesting from the aspect of compliant mechanisms

Piezoelectric energy harvester (PEH) is emerging as a novel device which can convert mechanical energy into electrical energy. It is mainly used to collect ambient vibration energy to power sensors, chips and some other small applications. This paper first introduces the working principle of PEH. Then, the paper elaborates the research progress of PEH from three aspects: piezoelectric materials, piezoelectric modes and energy harvester structures. Piezoelectric material is the core of the PEH. The piezoelectric and mechanical properties of piezoelectric material determine its application in energy harvesting. There are three piezoelectric modes, d31, d33 and d15, the choice of which influences the maximum output voltage and power. Matching the external excitation frequency maximizes the conversion efficiency of the energy harvester. There are three approaches proposed in this paper to optimize the PEH’s structure and match the external excitation frequency, i.e., adjusting the resonant frequency, frequency up-converting and broadening the frequency bandwidth. In addition, harvesting maximum output power from the PEH requires impedance matching. Finally, this paper analyzes the above content and predicts PEH’s future development direction.

A Review of MEMS Scale Piezoelectric Energy Harvester

In the field of piezoelectric energy harvesting from ambient low-frequency vibrations, frequency up-converting effect is a classical approach to improve the efficiencies of energy conversion and extraction. However, most of the frequency up-converting harvesters are implemented by either mechanical impacts or non-contact impulse-like accelerations, which needs high-level excitations and usually leads to reduced longevity or considerable noise. To address these limitations, this paper introduces and demonstrates a novel frequency up-converting energy harvester based on 1:3 internal resonance. The nonlinear harvester mainly consists of two asymmetric cantilever beams in which the ratio of their resonant frequencies is 1:3. The harvester features two vibrational degrees-of-freedom (DOFs) corresponding to the two cantilevers: The primary DOF picks up the ambient low-frequency vibrations and excites the secondary one to vibrate drastically at its resonant frequency. Because the secondary resonance is three times higher than the excited frequency, the harvester realizes the frequency up-conversion. The underlying mechanisms of this design are thoroughly analyzed in the numerical simulation and experiment.

A 2-degree-of-freedom cubic nonlinear piezoelectric harvester intended for practical low-frequency vibration

An impact-based frequency-up-conversion (FUC) energy harvesting system has been studied for realizing high power density from ambient vibration. It can harvest the lower frequency environment vibration and convert into a higher frequency self-oscillation. The energy output is greatly improved. In this paper, theoretical modeling of the FUC energy harvesting system is established, including a lower frequency piezoelectric bimorph (LFPB) and a higher frequency piezoelectric bimorph (HFPB). The dynamic analysis is carried out and the output performance is simulated. Experiments indicate that the developed FUC system can generate a high peak power of 2.62 mW and an average power of 0.58 mW from an external excitation acceleration of 1 g at 29 Hz. The peak power output of the HFPB operating at 153.8 Hz is about 4.5 times higher than that of the LFPB at 29 Hz. This work provides a theoretical basis and methodology for developing impact-based FUC energy harvesting system, which opens up a way for achieving high power output at low ambient frequency.

Modeling and verification of a piezoelectric frequency-up-conversion energy harvesting system

This paper proposes a piezoelectric frequency-up-conversion (FUC) energy harvesting system induced non-contact magnetic force. The FUC system is composed of a lower frequency piezoelectric cantilever (LFPC) of 40Hz and a higher frequency piezoelectric cantilever (HFPC) of 85Hz. Both the LFPC and HFPC contain a magnetic proof mass at the end of the piezoelectric cantilevers. The experiment shows that the output power of the HFPC is 0.3 mW at 40 Hz and 1g, which is about three times higher than that of the LFPC. The FUC system is able to provide high energy conversion even at lower frequency vibration of less than 50Hz, which is more efficient compared to a conventional one.

A magnetic force induced frequency-up-conversion energy harvesting system

The maneuvering and electrical characterization of nanotubes inside a scanning electron microscope (SEM) has historically been time-consuming and laborious for operators. Before the development of automated nanomanipulation-enabled techniques for the performance of pick-and-place and characterization of nanoobjects, these functions were still incomplete and largely operated manually. In this paper, a dual-probe nanomanipulation system vision-based feedback was demonstrated to automatically perform 3D nanomanipulation tasks, to investigate the electrical characterization of nanotubes. The XY-position of Atomic Force Microscope (AFM) cantilevers and individual carbon nanotubes (CNTs) were precisely recognized via a series of image processing operations. A coarse-to-fine positioning strategy in the Z-direction was applied through the combination of the sharpness-based depth estimation method and the contact-detection method. The use of nanorobotic magnification-regulated speed aided in improving working efficiency and reliability. Additionally, we proposed automated alignment of manipulator axes by visual tracking the movement trajectory of the end effector. The experimental results indicate the system’s capability for automated measurement electrical characterization of CNTs. Furthermore, the automated nanomanipulation system has the potential to be extended to other nanomanipulation tasks.

Visual Servoing-Based Nanorobotic System for Automated Electrical Characterization of Nanotubes inside SEM.

Determining the metallicity and semiconductivity of a multi-walled carbon nanotube (MWCNT) bundle plays a particularly vital role in its interconnection with the metal electrode of an integrated circuit. In this paper, an effective method is proposed to determine the electrical transport properties of an MWCNT bundle using a current-voltage characteristic curve during its electrical breakdown. We established the reliable electrical nanoscale contact between the MWCNT bundle and metal electrode using a robotic manipulation system under scanning electron microscope (SEM) vacuum conditions. The experimental results show that the current-voltage curve appears as saw-tooth-like current changes including up and down steps, which signify the conductance and breakdown of carbon shells in the MWCNT bundle, respectively. Additionally, the power law nonlinear behavior of the current-voltage curve indicates that the MWCNT bundle is semiconducting. The molecular dynamics simulation explains that the electron transport between the inner carbon shells, between the outermost carbon shells and gold metal electrode and between the outermost carbons shells of two adjacent individual three-walled carbon nanotubes (TWCNTs) is through their radial deformation. Density functional theory (DFT) calculations elucidate the electron transport mechanism between the gold surface and double-wall carbon nanotube (DWCNT) and between the inner and outermost carbon shells of DWCNT using the charge density difference, electrostatic potential and partial density of states.

https://www.mdpi.com/2079-4991/11/5/1290/pdf

Li Ma

Papers

Modeling and verification of a piezoelectric frequency-up-conversion energy harvesting system

A magnetic force induced frequency-up-conversion energy harvesting system

Visual Servoing-Based Nanorobotic System for Automated Electrical Characterization of Nanotubes inside SEM.

Electrical Conductivity of Multiwall Carbon Nanotube Bundles Contacting with Metal Electrodes by Nano Manipulators inside SEM.

Length-controllable picking method and conductivity analysis of carbon nanotubes