A Polymer-based Piezoelectric Vibration Energy Harvester with a 3D Meshed-Core Structure.

The use of a sacrificial water-soluble BaO layer was investigated for the purpose of fabricating free-standing single-crystalline BaTiO3 membranes for vibrational energy harvesting applications. An epitaxial BaTiO3/SrTiO3/BaO heterostructure was deposited on a SrTiO3(001) substrate by pulsed laser deposition. The sacrificial BaO layer was dissolved by immersing the heterostructure in water. A single-crystalline BaTiO3 membrane was thereby released from the SrTiO3(001) substrate and transferred onto a glass or polyethylene terephthalate (PET) substrate coated with a polydimethylsiloxane (PDMS) adhesion layer. A 200 nm-thick BaTiO3 membrane was sandwiched between two flexible PDMS/ITO/PET electrode layers, forming a vibrational energy harvester test device that could operate at an average electrical power output of over 1 μW. This membrane fabrication process is applicable to various flexible structures and materials in vibrational energy harvesting or dynamic strain-sensing applications.

A vibration energy harvester is typically composed of a spring–mass system, with the advantage of high energy density, simple structure and easily being miniaturized. Recently, effects of cantilever beam’s structural parameters and cross-section shape on energy-harvesting micro-device is concerned and investigated in this paper, so as to study its performance of energy harvesting to meet the needs of low resonant frequency and maximum output power. The effect of a cantilever beam’s structure dimensions as well as quality of the mass on the device’s resonance frequency and maximum output power can be detected through formula computing. Further study on effect of a cantilever beam’s cross-section shape has also been worked out. According to the simulation experimental results gained from ANSYS with appropriate parameters defined by theoretical derivation, we manage to receive concordant conclusions. To receive a better performance of the energy harvester, we should choose a shorter, wider and thicker cantilever beam with rectangular cross-section and heavier mass at its end. However, to meet the requirement of low resonant frequency for piezoelectric vibration energy harvesting, we still need to define either an upper or a lower limit while choosing parameters of the device.

Vibration Energy Harvester (VEH) has attracted a great attention recently both in academia and industry. One of the most challenging issues in VEH is the possibility to harvest vibration energy in multiple directions. In fact, Conventional VEH (CVEH) using cantilever beam’s structure may possibly become inefficient for the application under multi-directional vibration sources. To overcome this shortcoming of CVEH, this paper proposes a novel design of piezoelectric cylindrical energy harvester (PCEH) which is using patches of piezoelectric material attached to the surface of a cylindrical structure. The Finite Element Method (FEM) analysis using COMSOL Multiphysics software package showed that PCEH has a great potential for the applicability of VEH in the multi-directional vibrating applications such as wearable devices and biomedical devices.

The tri-stable vibrational energy harvester (VEH) is commonly designed to achieve the large-orbit motion, but it is always trapped in one potential well and performs an intra-well motion under weak vibration excitations. To solve this problem, a tri-stable piezoelectric VEH with stops is proposed in this paper. The analytic expressions of the first-order and second-order moments for system response are derived based on the multiple scale method. It is found that the harvesting frequency bandwidth of the tri-stable VEH becomes wider under an optimal impact distance. Compared with the tri-stable VEH without stops, the consideration of stops can help the system achieve the multiple high-energy solutions. The choice of high-stiffness stops at high frequencies can enhance the harvesting efficiency of the tri-stable VEH with stops. Moreover, the experimental results and analysis also are presented to verify the obtained theoretical results. It is found that the energy harvesting efficiency can be increased to 140% of the unrestricted state at the optimal impact distance. Compared with the tri-stable VEH with rubber and stiff springs, the one with silica gel stops has a higher output voltage.

This work studies the resonant frequency reduction of vibration energy harvesters so as to adapt low-frequency ambient vibrations. In a typical electromagnetic vibration energy harvester, it is common sense that the resonant frequency decreases with the spring stiffness. However, the mass gravity will result in a large initial deformation of the spring with small stiffness when the energy harvester is vertically installed. To solve the problem, this work proposes a method of resonant frequency reduction by adding a negative-stiffness magnetic spring which is arranged symmetrically at the two sides of the equilibrium point. The theoretical expression of resonant frequency is derived based on magnetic field calculation. Comparisons between the energy harvesters with and without negative-stiffness magnetic spring are implemented through simulations and experiments. The results show that the resonant frequency of the vertical energy harvester can be reduced as expected without an increase of initial spring deformation by using the negative-stiffness magnetic spring. This work can provide an effective approach to designing energy harvesters for applications with low-frequency vibrations.

Design and modeling a frequency self-tuning vibration energy harvester for rotational applications

Compact reliable structure and strong electromechanical coupling are hot pursuits in piezoelectric vibration energy harvester (PVEH) design. PVEH with a static arc stopper makes piezoelectric stress uniformly distributed and widens the frequency band by collision but wastes space. This Article proposes a hinged PVEH with two arc mass stoppers (AS-H-PVEH). Two arc stoppers as movable masses increase the vibration energy and the effective electromechanical coupling coefficient to achieve strong electromechanical coupling. AS-H-PVEH generates a 4.1 mW power output at 11.6-12.0 Hz and 0.2 g. AS-H-PVEH sustains 4 g acceleration vibration for 10 min without attenuation. To offset the resonance frequency increase caused by arc contact, we discuss the magnetic coupling, and axial force effects are discussed. The design of the arc stopper radius, nonlinear electromechanical coupling model, and system parameter identification method are presented. The displacement varied mechanical quality factor and effective electromechanical coupling coefficient are considered in the modified model for the first time. The model obtained good agreement under experiments. The power generation and driven wireless sensor performance of AS-H-PVEH was verified. This research has important theoretical and application value for the performance optimization of PVEH with an arc stopper.

We have proposed that BiFeO3 films are suitable for piezoelectric vibrational energy harvester (VEH) applications, because BiFeO3 has high spontaneous polarization and low dielectric permittivity. We demonstrated that energy can be harvested by a micromachined VEH using a BiFeO3 film deposited using a sol–gel process. A VEH with a resonant frequency of ∼98 Hz produced an output voltage of 1.5 V·G-1 and electrical power of 2.8 µW·mm-3·G-2 (G=9.8 m/s2) at a load resistance of 1 MΩ. Using the analytical model for VEH, the generalized electromechanical coupling factor was estimated to be 0.41%. These results were comparable to those of the best-performing VEHs using other piezoelectric films.

A quarter-circular arc piezoelectric Vibration energy harvester (VEH) based on nonlinear geometry is proposed with both bending moment and torque deformation mode, so it can effectively absorb multi-directional vibration at the same resonance frequency. The theoretical model of quarter-circular arc piezoelectric VEH is established to study the resonance frequency and the output voltage. In order to demonstrate multi-directional performance of the quarter-circular arc VEH, the stress distribution is compared with that of the traditional piezoelectric VEH in multi-direction vibration, and the output voltage of the circular arc piezoelectric VEH are relatively increased 267.26% in X-direction, 463.18% in Y-direction, and 17.24% in Z-direction. The external load is equipped in circuit to measure output power, whose matching resistance is around 21k$\bm{\Omega}$, and the maximum output powers are 7.57mW in X-direction, 2.39mW in Y-direction, and 9.93mW in Z-direction.

The concept of Internet of Things has prompted the need for a sustainable energy source to power wireless sensor networks. Vibration energy harvesting emerges as an applicable option. This paper presents a finite element analysis of a new electromagnetic vibration energy harvester design aimed to increase the power output of an electromagnetic vibration energy harvester by making the coil and a pair of magnets vibrate in the opposite direction, hence increasing the speed of the coil cutting through the magnetic flux of the magnets. The design consist of a regular cantilever beam And one uniquely shaped cantilever beam designed to move in the opposite direction to the regular beam under the same base excitation. Results show that due to the opposite motion, the speed of the coil moving through the magnetic flux for the new design is equal to the sum of velocities from the two individual beams. This lead to a 99.3% increase in power output generated from the new design when compared with the sum of the individual power outputs produced by the two beams. Further analysis demonstrates that the maximum power decreases if a time lag was introduced between the two beams, hence stating the importance of matching their natural frequencies.

Systematic study of dual resonant rectilinear-to-rotary motion converter for low frequency vibrational energy harvesting

Although wireless sensors show extensive promise across a wide range of applications, one requirement necessary for widespread deployment is a suitable long-life power source. Self sustainable powering techniques allow for efficient use of these sensors, whose potential life is usually longer than that of the power sources. Vibration energy harvesting techniques offer to have the potential to be employed in powering these devices. The most important requirement of vibration energy harvesting devices is that they be in resonance to harvest energy efficiently. Most of the vibration energy harvesting devices built, irrespective of the mechanism involved, are based on a single resonance frequency, with the efficiency of these devices is very much limited to that specific frequency. In this paper, a frequency tunable mechanism is presented which allows the energy harvesting device to generate power over a wide range of frequencies. External magnetic forces have been used to induce additional stiffness which is variable depending on the distance between the magnets. This technique allowed us to tune the resonance frequencies to have +/− 20% of the original (untuned) resonant frequency. Further, the device can be tuned to higher and lower frequency with respect to the untuned resonance frequency by using attractive and repulsive magnetic forces, respectively. As a proof-of-concept, a piezoelectric cantilever-based energy harvesting device with a natural frequency of 26 Hz was fabricated whose resonance frequency was successfully tuned over a frequency range of 22 Hz to 32 Hz, enabling a continuous power output of 240 μW to 280 μW over the entire frequency range. The tuning mechanism can be employed to any vibrating structure.

Piezoelectric vibration energy harvesters (VEHs) with unimorph structure have been developed using Si micro-electrical mechanical systems (MEMS) technology. Since we revealed that (100) epitaxial BiFeO3 (BFO) piezoelectric films have high figure-of-merit on energy conversion, (100)-oriented BFO films have been prepared on (100)-oriented LaNiO3 bottom electrodes by the sol-gel method. We fabricated the piezoelectric VEHs using BFO films with resonance frequencies of ~100 Hz. The maximum output power density of these VEHs was determined to be 10.5 μWmm−3G−2 (G=9.8 ms−2) at a load resistance of 1 MΩ, which exceeds or is comparable to those of the best-performing VEHs using other piezoelectric films.

Nonlinear vibration energy harvester: Design and oscillating stability analyses

A low-frequency piezoelectric-electromagnetic-triboelectric hybrid broadband vibration energy harvester