Ambient Vibration Frequency Research Articles

Design and analysis of magnetostrictive two-dimensional kinetic energy harvester

Conventional energy harvesters often require high ambient vibration frequencies and can only capture vibration energy in a single direction. To address these issues, this paper designs a magnetostrictive two-dimensional kinetic energy harvester placed under the floor and capable of capturing energy in both vertical and horizontal directions. In order to achieve higher electrical power output at low-frequency input forces, a two-stage force amplification mechanism is designed to amplify the walking kinetic energy of pedestrians and the main parameters of this structure are analyzed and optimized. On the other hand, by constructing different forms of bias magnetic field, the influence of bias magnetic field on the deflection and motion of the internal magnetic domain of Terfenol-D is systematically studied, and the best bias form that can make the material shows the strongest magnetization characteristics is determined. Next, a prototype harvester was built, and an experimental vibration system was set up to test and analyze the output characteristics of the harvester comprehensively. The experimental results show that the harvester produces 21.2 mW of peak output power under sinusoidal excitation at an operating frequency of 4 Hz. Under random excitation, a peak output voltage of 2.64 V and 170 mW peak power was obtained. Under actual pedestrian walking tests, 17.62 mW peak output power is obtained to power low-power devices. The study’s results provide preliminary evidence that the designed magnetostrictive energy harvester can stably harvest kinetic energy from pedestrian walking.

Research on pendulum-type tunable vibration energy harvesting

Sensors, as the most common electronic devices in electromechanical systems, are often scattered in huge numbers in the environment to be monitored. When the power of the sensor comes from batteries, the long-term continuous power supply and the replacement of the battery under severe working conditions are the main problems. Compared with other energy sources, vibration energy is more universal and stable, so it is often harvested and utilized by specific devices. Most of the traditional vibration energy harvesting devices have the disadvantage that the natural frequency cannot be tuned, which will lead to significant decline of energy harvesting efficiency when the environmental frequency changes. Although some energy harvesting devices are with tunable nature frequency, the linearity is relatively poor when tuning. In order to solve the problems above, a structural model of an electromagnetic energy harvesting device using motion of a pendulum rod is constructed. Natural frequency characteristics and electromagnetic field finite element simulation analysis of the model are carried out. An experimental platform of the device and a corresponding electric energy storage circuit are designed and built. Simulation and experimental results show that the natural frequency of the device can be tuned linearly in the range of 7 Hz–13.5 Hz. The maximum induced electromotive force that the device can output is 1.37 V and the maximum power is 521 mW. When the device is connected to the electric energy storage circuit, the device can output 3.4 V DC voltage. Compared with the traditional devices that can only harvest energy efficiently from a single vibration frequency, the advantage of this model is that its natural frequency can be adjusted to adapt to different ambient vibration frequencies and the linearity of tuning has been verified, which makes its energy harvesting efficiency relatively higher. The device model proposed in this paper would have potential application value in the field of vibration energy harvesting and wireless micro sensors power supply.

Development of a Nonlinear Harvesting Mechanism from Wide Band Vibrations

The main objective of this study is to present an energy harvesting approach to scavenge electrical energy from mechanically vibrated piezoelectric materials.A mechanical energy harvester device has been developed and tested. The fundamental benefit of this mechanical device is that it can function effectively in a wide range of ambient vibration frequencies, whereas traditional harvesters are limited. A suitable conditioning circuit for energy scavenging has been proposed which can achieve optimal power stream. For controlling the power flow into the battery a circuit has been designed consisting of an AC to DC rectifier, an output capacitor, a switch mode DC to DC converter, and an electromechanical battery. An adaptive control system has been described for switching any electronics devices and maximizing battery storage capacity. Experimental results reveal that the power transfer rate can be enhanced by approximately 400% by utilizing the adaptive DC to DC converter. Various investigations on the piezoelectric harvester have revealed that the energy generated by the mechanical device can exceed the 1.4-volt barrier, which is suitable for charging capacitors in electronics devices. The findings of this study will be crucial in mitigating society's energy crisis.

Mass tuning technique for a broadband piezoelectric energy harvester array

Converting the wasted ambient vibration to electric power, using a piezoelectric energy harvester, is a promising strategy for powering a sensor network for medical and industrial applications. The designed harvester must satisfy the wideband natural frequency of ambient vibration. Conventional array harvester generates peak power at the cantilever's resonance frequencies and low power between them. This challenge can be managed by controlling the inclination angle of the tip masses (α). It is observed that the range of α from 45° to 53.3° generates an output power of 2-3mW in the frequency range of 19 to 29Hz. For the second mode shape, the output power has been measured to be 9mW in the frequency range from 290 to 330 Hz. Comparing the proposed design with conventional designs, the working bandwidth broadband is increased by a factor of 26, and the output power is increased by a factor of 31. The proposed approach is modeled using finite element analysis and analytical methods. The FEM model is validated by experimental results.

A Vibration Energy Harvester With Targeted Frequency-Tuning Capability

One of the major challenges for vibration energy harvesters is to match their resonant frequency with ambient vibration frequency. The main limitation of the existing frequency-tuning techniques is the uncontrollable tuning process, i.e., the incapability of tuning the frequency to a desired value. In this article, we report a tunable electromagnetic vibration energy harvester capable of being tuned to a specific target frequency. The device adjusts the resonant frequency by changing the effective length of two polyimide springs through a set of smart tuning structures with scales. A maximum frequency tuning range of 58 Hz (46 Hz-104 Hz, 126% relative tuning range) is realized with the proposed device. At a sinusoidal acceleration of 1g, an output peak-to-peak voltage of 263.4 mV and an output power of 143.6 μW are obtained at the frequency of 56 Hz.

Multiple spring-mass oscillator for wide bandwidth piezoelectric energy harvester

This work proposed a design of unique wideband piezoelectric energy harvester. The solution toward broadband response was achieved by using multiple spring-mass oscillators integrated with piezoelectric energy harvester array. The harvester was demonstrated to harvest continuous power from vibration source under various frequencies in the range of 0-250 Hz. It is shown that the stable output power of the harvester over a wide range of source frequency was achieved. The maximum output voltage and power of each beam were 4, 3.6, 9.8, 10 V and 0.01, 0.07, 0.45, 0.52 mW for 15, 30, 45 gm of the proof masses and the superimposed case, respectively. The resonant frequencies of the harvester were in the low ambient vibration frequency range. Expanded in resonance frequency was achieved in this new design harvester.

Piezoelectric ceramic for energy harvesting from ambient vibration

Direct piezoelectric conversion is very popular in generating power from mechanical stress. There is continuous progress in power harvesting from mechanical vibration. In this article, experimental tests on a piezoelectric circular plate, to evaluate the electric power produced by the piezoelectric conversion at low acceleration over a wide range of ambient vibration frequency, are presented. The experimental analysis is presented and discussed. The results demonstrate the potentiality of using low-cost piezoelectric diaphragms to harvest energy from ambient vibration. Under low acceleration (5.36 m/s2), the vibration frequency was varied in the range of 10– 200 Hz and the generated power was measured. Under a very small dynamic force (less than 0.06 N), the output power of 1.5 mW was obtained with an 8.5 mm drum harvester across a load resistance of 17.8 kΩ at a frequency of 173 Hz.

Design and characteristic analysis of magnetostrictive bistable vibration harvester with displacement amplification mechanism

The working frequency of a traditional cantilever magnetostrictive vibration harvester is often higher than ambient vibration frequency. In order to make it better applied to the actual ambient vibration and improving its harvesting capacity, a bistable Fe-Ga alloy vibration harvester with displacement amplification mechanism is systematically studied in this paper. On the one hand, a bistable structure is designed based on its two unique restoring force potential wells. On the other hand, a displacement amplification mechanism is added. Utilizing magnetic dipole model theory, harmonic balance theory, etc., a nonlinear lumped-parameter coupled model of the entire system is established. Moreover, the output characteristics of the system are simulated and experimentally tested. Simulation results show that when the distance of repulsive permanent magnets is 8 mm, bistable phenomenon is the most obvious. When the stiffness ratio is 1.852, the entire system has better output characteristics. Experimental results show that when excitation level is 6.272 m/s2, the first-order resonance frequency is reduced from 60 Hz to 22 Hz, and the peak voltage is increased from 51 mV to 510 mV. In addition, two lower second-order and third-order resonance frequencies appear, which are respectively 28 Hz and 34 Hz. Currently, the voltages are also larger, reaching 590 mV and 550 mV. It is concluded that the bistable vibration harvesting system with displacement amplification mechanism can work well in the low and wide frequency region and greatly increase the voltage. Compared with a traditional cantilever magnetostrictive vibration harvester, it has better dynamic response.

Piezoelectric vibration energy harvesting device based on water sloshing-inspired extensions

Inspired by shallow-water sloshing in a moving tank, a novel type of vibration-based piezoelectric energy harvesting device composed of a piezoelectric bimorph beam and an extension tank is proposed in this paper. The structure and working principle of the proposed device are provided. Then, the effects of different heights of water filling in the tank on the performances of the harvester are studied and analyzed. Experiments are set up to investigate the actual device performance by changing the base excitation frequency and load resistance for different water heights. The results show that by modulating the water height, the resonant frequency and bandwidth can be adjusted, which can enhance the energy harvesting performance of the device at different ambient vibration frequencies. This study provides some clues to improve the performance of the vibration-based energy harvesting devices.

Dynamic Response and Stability Analysis of High-Speed Railway Subgrade in Karst Areas

The increase in railway coverage significantly increased the railway mileage in karst areas. However, the fragile ecosystem in karst areas and weak mechanical performance in cavities cause hidden railway safety hazards. Even with the crucial stability and safety of railways in karst areas, there is only limited research conducted on the dynamic response of railway subgrade and the influence of hidden soil holes on the stability under different conditions. In this study, the Guizhou section of the Shanghai–Kunming high-speed railway was chosen as the research area. On-site monitoring and simulations using ABAQUS were performed to study the dynamic response of the subgrade under the dynamic load of a train. The influence of the soil hole, axle load, and vehicle speed on the dynamic response law and stability of the subgrade were considered based on the model rationality verification. Previous studies have demonstrated the considerable impact of soil holes on the dynamic response characteristics and stability of roadbeds. The ambient vibration frequency of the train was concentrated at 10–60 Hz. Under train load, the amplitude of the dynamic response parameters of each subgrade structural layer increased with the axle load; however, the increase in speed exhibited a greater impact on the vertical dynamic displacement and dynamic stress than on the dynamic acceleration, which affected the stability of the soil hole and roadbed. This study summarized the dynamic response characteristics of subgrade in karst areas under different conditions, thereby providing a design reference for high-speed railways in karst areas.

Impact of mechanical properties of historical masonry bridges on fundamental vibration frequency

The fundamental frequency of a historical monument like a masonry bridge or any other structure provides a better and detailed seismic assessment of its demand to provide protection against unexpected seismic ground motion. On this basis, this paper aims to develop an empirical formulation to fit the ambient vibration frequency of historical masonry bridges using a nonlinear regression model. For this purpose, data series were collected from the literature especially focused on both ambient vibration measurement and finite element models of historical masonry bridges modeled on a full scale to get the first global natural frequency. The first approach is to forecast the natural vibration frequency by using only physical characteristics of the historical masonry bridges obtained from the literature-based experimental ambient vibration frequency data. The second approach consists of forecasting the first natural vibration frequency considering the unit weight and elasticity modulus of the dominant construction material based on the homogenization approach. In addition to mechanical characteristics, physical properties of historical masonry bridges were used, such as the length, height, width, and Main Arch Span (MAS) length of the masonry bridge, to predict the first natural vibration frequency. Among the proposed equations, a maximum accuracy of 58% was reached with the literature-based experimental approach. Moreover, an empirical formulation with 81% accuracy was proposed by using both physical characteristics and mechanical properties of the bridges on the basis of finite element model results. Also, this study highlights that this accuracy decreases to 35% if the modulus of elasticity and unit weight are ignored. In addition, the developed formulations are compared with other empirical formulations using the Mean Square Error (MSE), as a measure of the average of the squares of the errors. Consequently, the smallest MSE value of 1.95 was obtained with the proposed equation, whose accuracy was 81% in this study.

A Multi-Mechanisms Composite Frequency Up-Conversion Energy Harvester

In this paper, a novel broadband hybrid piezoelectric-electromagnetic-electrostatic energy harvester with frequency up-conversion is proposed to improve the harvesting bandwidth and energy conversion efficiency. The designed device generates vibration energy with much higher frequency than ambient vibration frequency, which uses the magnet to impact periodically on the piezoelectric cantilever with the top electrode of electrostatic element. The dynamic model of the hybrid energy harvester is established, and performances are experimental tested under the sinusoidal excitation and practical application environment. The results show that multi-mechanisms composite structure can realize the complementary advantages of electrostatic-piezoelectric-electromagnetic mechanisms and improve the energy conversion efficiency effectively compared with a single harvesting mechanism. The fabricated harvester can output electric energy in the frequency range of 1–38 Hz, which significantly reduces frequency dependence, and the maximum power is measured to be 11.7 mW and 12 mW during cycling and walking respectively, which is the sum of the power generated by three different elements. Furthermore, the fabricated prototype can also light up six light-emitting diodes (LEDs) simultaneously when handy shaking.

A Novel Design and Performance Results of An Electrically Tunable Piezoelectric Vibration Energy Harvester (TPVEH)

The need for energy harvesters for various applications, including structural health monitoring (SHM) in remote and inaccessible areas, is well established. Energy harvesters can utilize the ambient vibration of the body on which they are mounted to generate energy, thus eliminating the need for an external source of power. One such type of harvester is designed using piezoelectric materials and using a cantilever type set-up. However, the challenge associated with cantilever-based Piezoelectric Vibration Energy Harvesters (PVEH) is that its output power reduces when the ambient vibration frequency deviates from the resonant frequency of the harvester. This calls for a mechanism to tune its resonant frequency to match with the ambient frequency. This article presents an innovative design of an electrically tunable PVEH. The PVEH is integrated with an Ionic Polymer Metal Composite (IPMC) as an actuator that loads the cantilever beam, changing the stiffness of the beam. IPMC utilizes low power, and the authors demonstrate in this paper that a net gain of power can be achieved by this novel design. For the configuration used, it is experimentally proven that a frequency shift from 5.9 Hz to 8 Hz is achieved with three actuation values. Typical power output from the harvester is 52.03 µW when the power spent on actuation is only 0.765 µW. On-going modeling of this system using simulation software is expected to lead to further optimization and prototyping of design.

A broadband piezoelectric energy harvester with movable mass for frequency active self-tuning

A broadband active self-tuning frequency piezoelectric energy harvester (AST-PEH) is proposed in this paper. It consists of a piezoelectric cantilever beam, an energy harvesting and control circuit (EHCC), a miniature stepper motor, a screw rod and a T-section mass. It can actively adjust the position of the T-section mass according to the ambient vibration frequency. It matches the AST-PEH’s resonant frequency with the ambient vibration excitation frequency, and it widens the operating frequency range of the AST-PEH. The expression of the AST-PEH’s resonant frequency function is constructed based on the dynamic and static theoretical analysis. The theoretical model of the AST-PEH under different position of the T-section mass is analyzed by ANSYS15.0 APDL, which is verified by two different materials and sizes. The tested two type substrate materials are steel and polylactic acid (PLA). The experimental results show that the frequency range of the two type harvesters are 4.8 Hz–6.3 Hz and 8.17 Hz–14.3 Hz respectively, and the widening rates of the working frequency are 31.25% and 75% respectively. The tested maximum output power of steel type AST-PEH is 0.32 mW at 6.3 Hz under 0.32 g acceleration and with a 100 KΩ load resistance.

Fabrication process for very-low frequency operation of guided two-beam piezoelectric energy harvester

MEMS-based piezoelectric vibration energy harvesters found suitable to power wireless sensor nodes, typically in a remote area of operation. In MEMS technology, piezoelectric type vibration energy harvesters are realized using fixed-fixed or fixed-free cantilever structures. These structures are spring mass damper systems that have a fixed resonance frequency which is to be matched with ambient vibration frequency. The low resonance frequency of the cantilever gives better output with the low-frequency mechanical vibrations. Parameters such as width, length and thickness must be critically controlled to achieve low-frequency response during device fabrication. This paper presents the optimized fabrication process for guided two-beam type piezoelectric vibration energy harvester device. The device thickness is critically controlled using tetramethylammonium hydroxide zig during wet bulk micromachining followed by beam thinning process using deep reactive ion etching on the back side of the silicon wafer. A highly c-axis oriented zinc oxide layer of 2.5 µm thickness is sandwiched between aluminum electrodes on the front side of the silicon wafer for harvesting electric potential. The laser Doppler vibrometer test gives the resonance frequency of the fabricated device around 466 Hz which is lowest reported so far for the guided two-beam device. The resonance frequency of the device reported has been reduced by 32.85% than the earlier reported guided two-beam device. The device when vibration shaker tested was found to be operational in the very low-frequency range up to 10 Hz giving a sensitivity of 1.648 mV/m/s2 near resonance frequency.

Experimental study on the natural frequency of tunable piezoelectric cantilever plate

PEH (piezoelectric energy harvester) outputs a higher voltage when the natural frequency matches ambient vibration frequency. How to widen working frequency band is a hot issue in study of PEH. In this paper, an auto-tuning PEH is presented by attaching a box to each corner of its free sides and a ball is placed in each box. Change of the balls position makes natural frequency of PEH variable, which expands working bandwidth of the device to accommodate complex ambient vibration. Fixing the equipment on experimental platform by designing fixture, hammering experiments are carried out to measure natural frequency of the structure when balls are in different positions. It is found that the maximum and minimum natural frequencies exist in the auto-tuning PEH, which form a resonance bandwidth. Moreover, there are multiple position combinations of two balls at the same natural frequency in the range of resonance bandwidth. Fixed the apparatus on exciter by the fixture, and a constant excitation frequency is selected in the bandwidth to perform auto-tuning experiments on the instrument. It is observed that location of balls is automatically changed to make natural frequency of the system coincide with the excitation, and the law of variation in balls position is obtained. The converter is subjected to sweeping experiments through an exciter and an oscilloscope. Using voltage-frequency diagrams, it is shown that the auto-tuning PEH outputs a higher voltage and its frequency band is wider when the ball rolls freely compared to two cases where balls are fixed.

Theoretical study of micro/nano-scale bistable plate for flexoelectric energy harvesting

Flexoelectricity offers a number of advantages in micro/nano-scale devices when compared with piezoelectricity as confirmed through numerous experiments and theoretical analyses. Snap-through behavior in bistable plate would convey a higher conversion efficiency for energy harvesting. However, there is no theoretical research on micro/nano-scale energy harvester with flexoelectricity based on bistable plate. This paper describes an electro-thermo-mechanical coupling system of micro/nano-scale bistable plates for piezoelectric energy-harvesting applications. The nonlinear geometric theory of Von Karman, strain gradient theory, the flexoelectric effect, and Hamilton’s principle were used to derive nonlinear dynamic formulas. The ambient vibration frequency and snap-through behavior both have an effect on the output voltages calculated by Matlab® software. An expression for the energy conversion efficiency of the bistable plate was derived and the influence of resistance on this efficiency was investigated. The result showed that the snap-through behavior delivered a large-amplitude vibration and a higher output voltage at the range of one-third super-harmonic resonance (2.8–3.5 MHz) for the micro/nano-scale bistable plate. This work will be helpful in the design of micro/nano-scale bistable plates with higher output voltages and improved conversion efficiencies for energy harvesting.

Fundamental vibration frequency prediction of historical masonry bridges

It is very common to find an empirical formulation in an earthquake design code to calculate fundamental vibration period of a structural system. Fundamental vibration period or frequency is a key parameter to provide adequate information pertinent to dynamic characteristics and performance assessment of a structure. This parameter enables to assess seismic demand of a structure. It is possible to find an empirical formulation related to reinforced concrete structures, masonry towers and slender masonry structures. Calculated natural vibration frequencies suggested by empirical formulation in the literatures has not suits in a high accuracy to the case of rest of the historical masonry bridges due to different construction techniques and wide variety of material properties. For the listed reasons, estimation of fundamental frequency gets harder. This paper aims to present an empirical formulation through Mean Square Error study to find ambient vibration frequency of historical masonry bridges by using a non-linear regression model. For this purpose, a series of data collected from literature especially focused on the finite element models of historical masonry bridges modelled in a full scale to get first global natural frequency, unit weight and elasticity modulus of used dominant material based on homogenization approach, length, height and width of the masonry bridge and main span length were considered to predict natural vibration frequency. An empirical formulation is proposed with 81% accuracy. Also, this study draw attention that this accuracy decreases to 35%, if the modulus of elasticity and unit weight are ignored.

A Wideband Piezoelectric Energy Harvester Design by Using Multiple Non-Uniform Bimorphs

This paper presents an analytical approach for the development of a new wideband piezoelectric energy harvesting system. The proposed model is based on Adomian decomposition method to derive the dynamic response of the general non-uniform smart structures under external environmental excitations over a wide frequency domain efficiently harvesting the subsequent vibrational energy. The steady-state response of a nonlinearly tapered piezoelectric harvester subjected to harmonic base motion is obtained, and the higher potential electromechanical outputs compared with traditional uniform harvester are analytically derived. Afterward, a group of nonlinearly tapered cantilevers with the same volume and length but different taper ratios and surface bonded piezoelectric layers are assembled together in order to build a broadband piezoelectric energy harvester. Through numerical studies, it is proven that with the proposed non-uniform configuration, the new energy harvester design can function effectively and efficiently with high voltage output over a wide frequency range. The designed wideband harvester can automatically activate one of the non-uniform bimorphs to resonate at particular ambient vibration frequencies and eventually reach the maximum electromechanical output. Based on the proposed theoretical model, an optimum structural design for the wideband piezoelectric energy harvester in the required operational frequency range can be efficiently achieved.

Analytical modelling of spiral cantilever structure for vibration energy harvesting applications

Research on harvesting energy from natural resources is more focused as it can make microelectronic devices self-powered. MEMS based vibration energy harvesters are gaining its popularity in recent days to extract energy from vibrating objects and to use that energy to power the sensors. A solution for the major constrain for vibration energy harvesting in micro scale has been addressed in this paper. Cantilever beams coated with piezoelectric materials which are optimized to resonate at the source vibration frequency are used in most of the traditional vibration energy harvesting applications. In micro scale such structures have very high natural frequency compared to the ambient vibration frequencies due to which frequency matching is a constrain. Tip mass at the end of the cantilever reduces the resonant frequency to a great extent but adds to complexity and fabrication difficulties. Here, we propose a spiral geometry for micro harvester structures with low fundamental frequencies compared to traditional cantilevers. The spiral geometry is proposed, simulated and analyzed, to show that such a structure would be able to vibrate near resonance at micro scale. The analysis consists of Modal analysis, Mises stress analysis and displacement analysis in COMSOL Multiphysics. The result shows that the frequency has been reduced by a factor of 300 when compared to normal cantilever in the same volume. The work provides guideline for vibration energy harvesting structure design for an improved performance.