Low-frequency Vibration Sources Research Articles

Experimental study of taper shape bistable beam for improved vibration energy harvesting

Unwanted vibrations cause discomfort and affect the accuracy of the machinery. Vibrations of low frequency (<30 Hz) are usually inutile. Various researchers focus on harvesting and enhancing energy output through low-frequency vibrations. This paper focuses on improving energy harvesting from low-frequency vibration sources through taper shape (TAP) bistable beam fabricated using thin Piezoelectric Polyvinylidene fluoride (PVDF) film sandwiched between thin copper and aluminium films on both sides. Voltage power output through a PVDF film depends on the film’s strain distribution; hence, in this study, five different beam designs are studied for strain distribution through the ANSYS workbench. Further, an experimental harmonic analysis study for voltage output is performed on rectangular beam (RECT) and TAP beam for both straight and bistable configuration using three different harmonic input conditions, which concluded that the voltage output for the TAP beam is much more than that of the RECT beam, with a much more significant voltage output increase in bistable conditions for all three harmonic input conditions.

A speed-amplified tri-stable piezoelectric-electromagnetic-triboelectric hybrid energy harvester for low-frequency applications

This work proposes a new speed-amplified multi-stable tri-hybrid energy harvesting technique via the multi-stable nonlinearity enhanced frequency up-conversion and rack-pinion mechanisms to efficiently harness structural and biomechanical vibration energy. In the present design, two frequency up-conversion piezoelectric generators, an array-type electromagnetic generator and a sliding-mode triboelectric nanogenerator are integrated together to form a compact and interactive system. By utilizing the rack-pinion mechanism, the relative speed between the stators and the translators of the electromagnetic and triboelectric generators are both doubled. Meanwhile, the process of frequency up-conversion in the piezoelectric generators is also doubled per each cycle. This results in better performance under wideband and low-frequency vibration sources. For verification, a prototype of this design is tested by mechanical excitations and body-induced motions. In the shaker test, the prototype can generate a peak output power of 446.16 mW under an optimal resistance load, resulting in a normalized power density of 4.20 mW cm–3 g–2 at 5 Hz under 1 g. The prototype also exhibits exceptional performance under various human motion tests, it can drive 600 commercial light-emitting diodes simultaneously. Using a commercial DC/DC voltage regulator circuit, the proposed harvester can serve as a universal power source to charge commercial electronic devices, including smartphones and GPS sensors. The present design shows great potential as a sustainable power source for wearable/portable electronics as well as wireless monitoring systems.

Frequency Up-Conversion for Vibration Energy Harvesting: A Review

A considerable amount of ambient vibration energy spreads over an ultra-low frequency spectrum. However, conventional resonant-type linear energy harvesters usually operate within high and narrow frequency bands, which cannot match the frequencies of many vibration sources. If the excitation frequency deviates a bit from the natural frequency of an energy harvester, the energy harvesting performance will deteriorate drastically. Because of the ultra-low frequency characteristic, it is challenging to reliably harvest energy from the ambient vibrations. To address this mismatching issue, the ultra-low frequency ambient vibrations are converted into high-frequency oscillations using certain mechanical mechanisms, which are termed frequency up-conversion techniques. This paper reviews the existing approaches that can realize frequency up-conversion for enhancing energy harvesting from low-frequency vibration sources. According to their working mechanisms, the existing methods are classified into three categories: impact-based, plucking-based, and snap-through-based approaches. The working principles of the three approaches are explained in detail. Representative designs from all categories are reviewed. This overview on the state-of-the-art frequency up-conversion technology would guide the better design of future kinetic energy harvesting systems.

Scavenging power from ultra-low frequency and large amplitude vibration source through a new non-resonant electromagnetic energy harvester

In this paper, a new non-resonant, free motion based electromagnetic energy harvester is proposed for harvesting energy from low-frequency vibration sources. In this design, steel frame is beneficially utilized to enhance the flux and consequently the power density of the harvester. The steel frame can also function as a magnetic shield to protect the harvester from external magnetic field interferences. Prototype of this harvester is constructed and characterized experimentally. A dedicated model and simulation method including non-linear contact characteristics is presented in this paper for predicting the dynamic response of this harvester at different vibration frequencies and amplitudes, and different operation modes are characterized. The measured results have well validated the behaviors predicted by the proposed model. In particular, the developed prototype of this harvester can generate a power density 748 μW/cm3 at a low-frequency of 4.5 Hz and 40 mm vibration amplitude. Compared to recently reported low-frequency energy harvesters summarized in Table 3, this new harvester has the superiority of high-power density. It is a non-resonant harvester so it can harvest energy for a wide frequency band.

Performance Enhancement of a Multiresonant Piezoelectric Energy Harvester for Low Frequency Vibrations

Harvesting electricity from low frequency vibration sources such as human motions using piezoelectric energy harvesters (PEH) is attracting the attention of many researchers in recent years. The energy harvested can potentially power portable electronic devices as well as some medical devices without the need of an external power source. For this purpose, the piezoelectric patch is often mechanically attached to a cantilever beam, such that the resonance frequency is predominantly governed by the cantilever beam. To increase the power generated from vibration sources with varying frequency, a multiresonant PEH (MRPEH) is often used. In this study, an attempt is made to enhance the performance of MRPEH with the use of a cantilever beam of optimised shape, i.e., a cantilever beam with two triangular branches. The performance is further enhanced through optimising the design of the proposed MRPEH to suit the frequency range of the targeted vibration source. A series of parametric studies were first carried out using finite-element analysis to provide in-depth understanding of the effect of each design parameters on the power output at a low frequency vibration. Selected outcomes were then experimentally verified. An optimised design was finally proposed. The results demonstrate that, with the use of a properly designed MRPEH, broadband energy harvesting is achievable and the efficiency of the PEH system can be significantly increased.

Comparative study of core materials and multi-degree-of-freedom sandwich piezoelectric energy harvester with inner cantilevered beams

Conventional energy harvesters using a single metal substrate can hardly collect sufficient energies from wideband and low frequency vibration sources. A sandwich structure composed of two thin face sheets and a soft-core material can be an alternative substrate to replace a single metal layer to drop the resonant frequency of the harvester accompanied by the increment of the output voltage. The resonant frequency of the sandwich piezoelectric energy harvester (SPEH) can be adjusted more flexibly by selecting the appropriate core material and varying the geometric dimensions of the sandwich substrate. In this paper, a comparative study of different core materials for SPEH is firstly investigated. Prototypes of the SPEHs with different core materials (natural rubber, silicon rubber, polycarbonate plastic) and conventional harvesters with the same geometrical dimension are fabricated and tested. The experiment displays that the plastic sandwich energy harvester is the best of all in terms of voltage output. To extend the application of SPEH to harvester broadband vibration energies, this paper presents a novel multi-degree-of-freedom sandwich energy harvester with inner cantilevered beams to harvester energy from wideband, low frequency and low amplitude vibration sources. The proposed energy harvester comprises of a partitioned main sandwich substrate with a tip mass and two patches of piezoelectric layer bonded on it. Multiple branches with tip masses are extended from the inner substrate. The finite element model of the proposed sandwich harvester is presented to achieve close resonant frequencies in the low frequency range of interest. Then a multi-degree-of-freedom sandwich harvester with inner cantilevered beams is designed, fabricated and tested under. The novel harvester proposed in this paper has high design flexibility to work in various vibration environments.

Improving low-frequency piezoelectric energy harvesting performance with novel X-structured harvesters

Vibration energy harvesting systems via an X-structure coupled with piezoelectric patches of special arrangements are investigated in this study. Two piezoelectric harvesters are specially installed on the X-shaped structure to explore potential benefits that the X-shaped structure could provide, and each piezoelectric pad has two layers composed of a polyvinyl chloride base patch and a micro-fibre composite patch. The theoretical analysis and experiment results indicate that the energy harvesting performance of the proposed novel arrangements of the piezoelectric harvesters can be enhanced especially in low-frequency range (below 10 Hz), compared with conventional cantilevered piezoelectric harvesters. More and higher energy harvesting peaks can be created and the effective harvesting frequency band can be obviously enlarged by expanding it to low-frequency range with the proposed methods. The X-structure-based generators can enable piezoelectric materials to harvest power from low-frequency vibration sources due to its advantages in designable equivalent nonlinear stiffness, which can be easily tuned by adjusting the key structural parameters. The design and results would provide an innovative solution and insight for smart piezoelectric materials to improve the energy harvesting efficiency in the low-frequency range including small-scale ocean wave power harvesting, human motion power and animal kinetic power harvesting, etc.

Influence of vibration caused by sound on migration of sea cucumberApostichopus japonicus

Vibrations exist widely in the ocean, and the one caused by sound and biological movement plays an important role in the sensory system of marine organisms. The vibration caused by sound has many characteristics that make it a good candidate for modifying the movements of marine organisms. However, few studies have tested whether hydraulic vibration caused by sound has effects on the migration of sea cucumbers, and this has never been systematically studied previously in Apostichopus japonicus (Selenka). In order to understand whether hydraulic vibration caused by sound at different frequencies could affect the migration of sea cucumbers, in the present study, hydraulic vibration caused by sound at various frequencies was tested in the laboratory to determine their effects on the migration of A. japonicus at different sizes. The mean probability distribution was used as a statistical index to demonstrate the moving tendencies of the species. The experimental results showed that medium and small A. japonicus (<10 g ind.−1) tend to move towards the low-frequency vibration source caused by sound (100 Hz), whereas all sizes of A. japonicus tend to move backwards the high-frequency vibration source caused by sound (10 000 and 28 000 Hz). This study provides basic data on the behavioural ecology of this species, as well as theoretical reference for the design of artificial reefs and harvesting equipment for A. japonicus.

Low-frequency wideband vibration energy harvesting by using frequency up-conversion and quin-stable nonlinearity

This work presents models and experiments of an impact-driven and frequency up-converted wideband piezoelectric-based vibration energy harvester with a quintuple-well potential induced by the combination effect of magnetic nonlinearity and mechanical piecewise-linearity. Analysis shows that the interwell motions during coupled vibration period enable to increase electrical power output in comparison to conventional frequency up-conversion technology. Besides, the quintuple-well potential with shallower potential wells could extend the harvester's operating bandwidth to lower frequencies. Experiments demonstrate our proposed approach can dramatically boost the measured power of the energy harvester as much as 35 times while its lower cut-off frequency is two times lower than that of a conventional counterpart. These results reveal our proposed approach shows promise for powering portable wireless smart devices from low-intensity, low-frequency vibration sources.

Digital Fluxgate Magnetometer for Detection of Microvibration

In engineering practice, instruments, such as accelerometer and laser interferometer, are widely used in vibration measurement of structural parts. A method for using a triaxial fluxgate magnetometer as a microvibration sensor to measure low-frequency pendulum microvibration (not translational vibration) is proposed in this paper, so as to detect vibration from low-frequency vibration sources, such as large rotating machine, large engineering structure, earthquake, and microtremor. This method provides vibration detection based on the environmental magnetic field signal to avoid increased measurement difficulty and error due to different relative positions of permanent magnet and magnetometer on the device under test (DUT) when using the original magnetic measurement method. After fixedly connecting the fluxgate probe with the DUT during the test, the angular displacement due to vibration can be deduced by measuring the geomagnetic field’s magnetic induction intensity change on the orthogonal three components during the vibration. The test shows that the microvibration sensor has angular resolution of over 0.05° and maximum measuring frequency of 64 Hz. As an exploring test aimed to detect the microvibration of earth-orbiting satellite in the in-orbit process, the simulation experiment successfully provides the real-time microvibration information for attitude and orbit control subsystem.

Energy conversion by ‘T-shaped’ cantilever type electromagnetic vibration based micro power generator from low frequency vibration sources

The design, development, and analyses of low-frequency vibration based T-shaped cantilever type electromagnetic micro power generators (EVMPGs) are presented in this paper. Four different configurations (Configurations A to D) of EVMPGs were designed and fabricated and subsequently characterized using detailed experimental and limited analytical techniques. Configuration A and B consisted of a single and a double cylindrical moving magnets (NdFeB), respectively, while Configuration C consisted of four rectangular moving magnets with respect to a fixed copper coil. In contrast, Configuration D used a moving coil between four rectangular magnets with a back-iron bar. The open circuit RMS voltage output was observed to be a maximum from Configuration D (98.2mV at 6.29Hz) with a base vibration acceleration of 0.8ms−2. Therefore, Configuration D was selected for further experimental investigations, which included changing the back-iron bar thickness, changing the base acceleration level, and changing the air gap separation between the magnets in order to optimize this configuration. The maximum load RMS voltage and power outputs of Configuration D were 105.4mV and 1.35mW at 6.29Hz for load resistance 8.2Ω and a base acceleration of 0.8ms−2 with a 4.2mm back-iron bar when the air gap between the magnets was 20mm. Finally, a small portable EVMPG prototype was developed based on the Configuration D and was tested at different human movement conditions (i.e., walking, quick walking, and running). The developed EVMPG prototype was capable of harvesting 35.2mV and 0.22mW at 7Hz with load resistance 5.6Ω for a base acceleration of 0.8ms−2.

Beam design for voice coil motors used for energy harvesting purpose with low frequency vibrations: A finite element analysis

In this study, a numerical approach is established to design a beam coupled to a Voice Coil Motor (VCM) with the aim to maximize the displacement in the inductive transducer. A finite element model is developed to simulate a VCM with different beams applying a harmonic analysis. The VCM is extracted from a recycled hard disk drive (HDD) and a parametric modal analysis is performed to identify the material parameters of the HDD and the beam. These parameters are obtained comparing the real vibration modes and natural frequencies (VCM-beam) with those determined from the finite element model. A numerical-experimental case study is carried out to demonstrate that if a beam is designed for a specific low frequency vibration between 0 and [Formula: see text], the displacements are maximized in the VCM. For this purpose, real acceleration measurements taken from three individuals are used to provide the vibration signals in the numerical model. A beam is designed for one of the individuals using the natural frequency values determined from the measured signals. Results show that the displacements are maximized in the model which coincides with the natural frequency of the chosen individual. The main purpose of this research is to establish a design tool for energy harvesting purposes with VCM based on low frequency vibration sources as for example gait motions.

Energy harvesting efficiency optimization via varying the radius of curvature of a piezoelectric THUNDER

In this work the energy harvesting performance of a piezoelectric curved energy generator (THin layer UNimorph DrivER (THUNDER)) is studied via experimental and analytical methods. The analytical model of the THUNDER is created based on the linear mechanical electrical constitutive law of the piezoelectric material, the linear elastic constitutive law of the substrate, and the Euler–Bernoulli beam theory. With these linear modal functions, the Rayleigh-Ritz approach was used to obtain the reduced mechanical–electrical coupled modulation equations. The analytical model is verified by the experimental results. Both the experimental and analytical results of the THUNDER’s AC power output, DC power output with Rectifier Bridge and a capacitor, as well as the power output with a microcontroller energy harvesting circuit are reported. Based on the theoretical model, the analytical solution of the DC power is derived in terms of the vibration amplitude, frequency, and the electrical load. To harvest energy from low-frequency vibration source by a piezoelectric generator requires the piezoelectric device possessing low resonance frequency and good flexibility. The THUNDER developed by Langley Research Center exhibits high power when it is used as an energy generator and large displacement when it is used as an actuator. Compared to the less flexible PZT, although THUNDER is more difficult to model, THUNDER has better vibration absorption capacity and higher energy recovery efficiency. The effect of the THUNDER’s radius of curvature on energy harvesting efficiency is mainly investigated. We set the THUNDER’s radius of curvature as a dynamic tuning parameter which can tune the piezoelectric generators’ frequency with the source excitation frequency.

Modeling of geometric, material and damping nonlinearities in piezoelectric energy harvesters

The performance of piezoelectric energy harvesters (PEHs) operating in the anticipated vibration environments depends upon various nonlinearities existing in electromechanical dynamic system. In this paper, the influence of geometric, material and damping nonlinearities on the dynamic response of PEH is investigated. So far, the nonlinear geometric finite element analysis has not been used for analyzing PEHs. Moreover, the criterion for inclusion/exclusion of geometric nonlinearity in analyzing PEHs is not studied in detail. In this paper, firstly, the finite element modeling is used for analyzing the effect of geometric nonlinearity for low-frequency vibration sources. Simulations are carried out using ANSYS for different PEH configurations to assess the influence of geometric nonlinearity on harvester’s performance, and a parameter is proposed to determine the inclusion/exclusion of geometric nonlinearity in the analyzing PEHs. Subsequently, a nonlinear electromechanical model considering material and damping nonlinearities is derived for a cantilever-type PEH which uses macro-fiber composite (MFC) for power generation. In the earlier works on PZT-5A and PZT-5H, the nonlinear elastic and damping coefficients were identified by matching the analytical responses (e.g., voltage or displacement) with a set of experimental responses, which is an indirect method and might result in erroneous estimation of unknown coefficients as pointed out in the present work. In this study, the material behavior of MFC is directly obtained from tensile tests. The observed nonlinear stress–strain behavior of MFC is included in the nonlinear model to study the dynamics of the harvester. Energy harvesting experiments are conducted, and the harvester’s response is compared with the predictions from the proposed nonlinear model. The comparison shows very good agreement between the experimental and predicted responses. Moreover, the damping parameters are identified using the energy balance method, and it is shown that nonlinear damping is essential in accurate modeling of PEHs.

Broadband electromagnetic power harvester from vibrations via frequency conversion by impact oscillations

In this paper, we propose an electromagnetic power harvester that uses a transformative multi-impact approach to achieve a wide bandwidth response from low frequency vibration sources through frequency-up conversion. The device consists of a pick-up coil, fixed at the free edge of a cantilever beam with high resonant frequency, and two cantilever beams with low excitation frequencies, each with an impact mass attached at its free edge. One of the two cantilevers is designed to resonate at 25 Hz, while the other resonates at 50 Hz within the range of ambient vibration frequency. When the device is subjected to a low frequency vibration, the two low-frequency cantilevers responded by vibrating at low frequencies, and thus their thick metallic masses made impacts with the high resonance frequency cantilever repeatedly at two locations. This has caused it along with the pick-up coil to oscillate, relative to the permanent magnet, with decaying amplitude at its resonance frequency, and results in a wide bandwidth response from 10 to 63 Hz at 2 g. A wide bandwidth response between 10–51 Hz and 10–58 Hz at acceleration values of 0.5 g and 2 g, respectively, were achieved by adjusting the impact cantilever frequencies closer to each other (25 Hz and 45 Hz). A maximum output power of 85 μW was achieved at 5 g at 30 Hz across a load resistor, 2.68 Ω.

여러 종류의 표면 진동원에 대한 연조직에서의 진동 변위 비교

인체 연조직에서 기계적인 진동의 전달 특성은 조직의 탄성 특성에 의존한다. 연조직의 진동 특성으로부터 암이나 종양을 진단할 수 있기 때문에 진동의 전달 특성에 대한 연구는 중요한 의미를 가진다. 이 논문은 연조직의 표면에 위치하는 여러 형태의 응력 진동원에 의해 연조직 내에 발생되는 변위 패턴을 분석하고 비교하였다. 진동원으로는 수직하중, 접선하중, 그리고 면외전단하중이 고려되었다. 점탄성 단일층에서의 변위에 대한 이론적 표현식을 구하였고, 수치계산은 반공간 및 무한평판조직에서 수행되었다. 그리고 유한크기조직에서의 변위패턴을 유한요소법으로 시뮬레이션하였다. 응력 형태, 진동원 크기 및 주파수, 그리고 경계면이 변위에 미치는 영향이 분석되었다. The propagation characteristics of a mechanical wave in human soft tissue depend on its elastic properties. Investigation of these propagation characteristics is of paramount importance because it may enable us to diagnose cancer or tumor from the vibration response of the tissue. This paper investigates and compares displacement patterns generated in soft tissue due to several forms of low-frequency vibration sources placed on a surface. Among vibration sources considered are a normal load, tangential load, and antiplane shear load. We derive analytical expressions for displacements in viscoelastic single layers, and calculate displacement patterns in half space and infinite plate type tissue. Also, we simulate the vibration response of a finite-sized tissue using finite element method. The effects of the type of stress, the size and frequency of vibration sources, and medium boundaries on displacement patterns are discussed.

A study on detection of low-frequency vibration sources using high speed camera

A study on detection of low-frequency vibration sources using high speed camera

Method and apparatus for using Doppler modulation parameters for estimation of vibration amplitude

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