Low Frequency Environmental Vibrations Research Articles

Design a low-frequency vibration energy harvesting device based on a square spiral beam local resonant phononic crystal

Self-powered miniature wireless sensors play a crucial role in Internet of Things technology. Harvesting low-frequency environmental vibrations to achieve self-powering of sensors is a current hot topic in research. In this study, a square spiral beam local resonant phononic crystal is designed for low-frequency vibrational energy harvesting. Initially, the bandgap and vibrational modes of an ideal phononic crystal at infinite period are analyzed by the finite element method; the possibility of using the structure to harvest vibrational energy is explored. Subsequently, a PnC plate model with a unit cell is built, and its vibrational modes are analyzed, verifying that it possesses similar vibrational properties. Following this, a piezoelectric vibration energy harvesting device is assembled and its energy harvesting performance is analyzed. Numerical simulations indicate that the designed device can achieve a maximum power density of 52.14 μW/cm2. Physical experiments validate the excellent energy harvesting performance of the device. The device offering a new option for designing self-powered devices for wireless miniature sensors.

A Novel Bird-Shape Broadband Piezoelectric Energy Harvester for Low Frequency Vibrations

This work presents a novel bird-shaped broadband piezoelectric energy harvester based on a two-DOF crossed beam for low-frequency environmental vibrations. The harvester features a cantilever mounted on a double-hinged beam, whose rotating motions effectively diminish its natural frequencies. Numerical simulation based on the finite element method is conducted to analyze the modal shapes and the harmonic response of the proposed harvester. Prototypes are fabricated and experiments are carried out by a testing system, whose results indicate a good agreement with the simulation. The multi-frequency energy harvesting is achieved at the first-, second-, and fifth-order resonances. In particular, the proposed harvester demonstrates the remarkable output characteristics of 9.53 mW and 1.83 mW at frequencies as low as 19.23 HZ and 45.38 Hz, which are superior to the majority of existing energy harvesters. Besides, the influences of key parameters on the harvesting performance are experimentally investigated to optimize the environmental adaptability of the harvester. This work provides a new perspective for efficiently harvesting the low-frequency vibration energy, which can be utilized for supplying power to electronic devices.

A fish-skeleton-like metastructure isolator for low-frequency vibration isolation

Vibration isolation for vibration-isolated objects in low-frequency vibration environment has been widely concerned by researchers. In this paper, we designed a local resonant (LR) fish-skeleton-like metastructure isolator with cantilever beam oscillators for low-frequency vibration isolation. Based on the theories of wave dynamics and structural dynamics, we analytically obtained the bandgap characteristics and transmissibility of the metastructure by using the equivalent mass and stiffness method, and carried out simulations through the finite element method (FEM). This metastructure isolator was fabricated by a 3D printing equipment and the vibration isolation test was carried out. Vibration transmissibility characteristics is obtained through the analytical method, FEM and experiment show that the local resonance near the natural frequency of the oscillators can effectively suppress the vibration transmission. The specific performance shows that the vibration transmissibility is as low as 21 % at the center frequency of the bandgap, while the mass of the isolator is only increased by about 2.3 % compared with the ordinary structure which has no oscillators. With the increasing of the mass of vibration-isolated objects (650 g), the transmissibility can be as low as 4 %. In addition, the contribution of different frame bodies and different oscillators of the isolator on the isolation effect and a way of widening the isolation frequency ranges are clarified. The proposed fish-skeleton-like metastructure in the present work provides a new design approach for vibration isolation in engineering applications.

Piezoelectric vibration energy harvesting with asymmetric hybrid bracing beam

In order to reduce the natural frequency of the piezoelectric vibration energy harvester, improve the output power of the piezoelectric vibration energy harvester, and meet the demand of power supply for the low-power wireless switch in the low-frequency vibration environment, an asymmetric hybrid supported beam piezoelectric vibration energy harvester is proposed. The theoretical model of the hybrid support beam was established. The correlation factors affecting the open-circuit voltage and the total output power of the hybrid braced beam were analyzed. The dimensional parameters of the hybrid supported beam piezoelectric energy harvester were optimized by using the optimization method of orthogonal experiments. Different coincidence degrees experiments were used to further optimize the structural design of the hybrid support beam. The test results show that the maximum output power is 770 μW, when the external excitation frequency is 1.0 g and the external resistance is 50 kΩ. Finally, a wireless switch test system was established, and the piezoelectric vibration energy harvester was experimentally verified to be capable of powering the wireless switch.

A Tuning Fork Frequency Up-Conversion Energy Harvester.

In this paper, a novel tuning fork structure for self-frequency up-conversion is proposed. The structure has an in-phase vibration mode and an anti-phase vibration mode. The in-phase vibration mode is used to sense the environment vibration, and the anti-phase vibration mode is used for energy conversion and power generation. The low-frequency energy collection and the high-frequency energy conversion can be achieved simultaneously. Theoretical and experimental results show that the tuning fork frequency up-conversion energy harvester has excellent performance. This structure provides the energy harvester with excellent output power in a low-frequency vibration environment. At the resonant frequency of 7.3 Hz under 0.7 g acceleration, the peak voltage is 41.8 V and the peak power is 8.74 mW. The tuning fork frequency up-conversion energy harvester causes the humidity sensor to work stably. The structure has the potential to power wireless sensor nodes or to be used as a small portable vibration storage device, especially suitable for the monitoring of the environment related to human movement.

Analysis effects on operating frequency range by geometrical nonlinearity in electromagnetic vibration energy harvesters

The paper aims to analyze and verify how geometrical nonlinearity of the microstructure affect the bandwidth of the vibration energy harvesters (EVEHs). In the paper, an electromagnetic energy harvester which has three nonlinear vibration pickup systems is analyzed and measured. Different degrees of geometric nonlinearity under certain condition can be shown by vibration pickup systems which are composed different folded beams in the EVEH. By using static simulation and numerical calculation methods, the nonlinear degree of each vibration pickup system is estimated, and the relationship between the nonlinear degree and the working bandwidth of each vibration pickup system is simulated and analyzed. The principle prototype is measured. The results show that the geometrical nonlinerity of vibration pickup systems is proportional to the excitation acceleration, and the bandwidth increases with increasing geometrical nonlinearity the bandwidth. Meanwhile, the results indicate that the vibration pickup system with greater geometrical nonlinearity has better frequency broad ability in low frequency vibration environment. The measured results and analytical results exhibit excellent agreement and the analysis method of structural nonlinearity in the paper may be helpful in designing structures of micro vibration energy harvesters.

Analytical Modeling of a Doubly Clamped Flexible Piezoelectric Energy Harvester with Axial Excitation and Its Experimental Characterization.

With the rapid development of wearable electronics, novel power solutions are required to adapt to flexible surfaces for widespread applications, thus flexible energy harvesters have been extensively studied for their flexibility and stretchability. However, poor power output and insufficient sensitivity to environmental changes limit its widespread application in engineering practice. A doubly clamped flexible piezoelectric energy harvester (FPEH) with axial excitation is therefore proposed for higher power output in a low-frequency vibration environment. Combining the Euler–Bernoulli beam theory and the D’Alembert principle, the differential dynamic equation of the doubly clamped energy harvester is derived, in which the excitation mode of axial load with pre-deformation is considered. A numerical solution of voltage amplitude and average power is obtained using the Rayleigh–Ritz method. Output power of 22.5 μW at 27.1 Hz, with the optimal load resistance being 1 MΩ, is determined by the frequency sweeping analysis. In order to power electronic devices, the converted alternating electric energy should be rectified into direct current energy. By connecting to the MDA2500 standard rectified electric bridge, a rectified DC output voltage across the 1 MΩ load resistor is characterized to be 2.39 V. For further validation of the mechanical-electrical dynamical model of the doubly clamped flexible piezoelectric energy harvester, its output performances, including both its frequency response and resistance load matching performances, are experimentally characterized. From the experimental results, the maximum output power is 1.38 μW, with a load resistance of 5.7 MΩ at 27 Hz, and the rectified DC output voltage reaches 1.84 V, which shows coincidence with simulation results and is proved to be sufficient for powering LED electronics.

Research on piezoelectric vibration energy harvester with variable section circular beam

In order to reduce the natural frequency of the piezoelectric vibration energy harvester, improve performance of the piezoelectric vibration energy harvester, and meet the requirements of energy acquisition in the low-frequency vibration environment, a variable-section circular piezoelectric vibration energy harvester is presented. The dynamic model and electromechanical coupling model of variable-section circular piezoelectric vibration energy harvester are established. The main factors affecting the output performance of piezoelectric vibration energy harvester are analyzed. The structure parameters of piezoelectric vibration energy harvester are optimized by orthogonal experiment. An experimental platform is built to test output voltage and output power of piezoelectric vibration energy harvester. The experimental results show that when the number of energy harvester is 4 and the external load is 180KΩ, the parallel output power can reach 0.213mW, which can meet the requirements of micro-power device power supply.

Microstructures, piezoelectric properties and energy harvesting performance of undoped (K0.5Na0.5)NbO3 lead-free ceramics fabricated via two-step sintering

Piezoelectric energy harvesters have become increasingly popular in the field of green energy because of the ability to convert low-frequency environmental vibrations into usable electricity. To fabricate high-performance energy harvesters, the key requirements are piezoelectric ceramics with a small grain size, of near-full density, the intended stoichiometric ratio and a high transduction coefficient. In this work, the effects of two-step sintering on the sinterability, microstructure, piezoelectric properties and energy harvesting performance of (K0.5Na0.5)NbO3 were systematically investigated. Compared with conventional single-step sintering, two-step sintering samples were of higher density, increasing from 91 % to 95 % of theoretical, reduced mean grain size, down from 17 μm to 7.5 μm, and decreased evaporation of the alkali metals. This translated into an improved piezoelectric performance (d33 ∼122 pC/N, kp ∼36 % and Qm ∼76), a higher transduction coefficient and energy conversion efficiency as well as a higher open-circuit voltage and power density. This demonstrates the potential of two-step sintering as a high through-put sintering technique for moderate-performance, pure KNN ceramics.

Design and experimental study of broadband hybrid energy harvester with frequency-up conversion and nonlinear magnetic force

In this paper, a novel broadband hybrid piezoelectric and electromagnetic energy harvester using in the low frequency vibration environment is proposed, which combines nonlinear magnet force and frequency-up conversion mechanism simultaneously. Performances are studied by theoretical analysis and experimental test. Electromechanical governed equations of harvester are established, and analytical solutions of vibration response, output voltage and power are derived. Then, effects of nonlinear force, spacing between low frequency vibration beam and piezoelectric beam, load resistance and input excitation on harvester performances are investigated by experimental test. It can be concluded that the harvester can be used to work at the low-frequency environment efficiently, and the resonant frequency and harvesting bandwidth can be tuned by the nonlinear force between the magnets and the spacing between beams. Moreover, the larger the nonlinear magnetic force and the smaller the distance between two beams, the lower working frequency and the larger bandwidth. Compared with the corresponding linear apartment, output power and bandwidth of proposed harvester are improved 90% and 125% respectively.

Dynamic characteristics and response research of low-frequency vibration harvester based on diamagnetic levitation

A low-frequency vibration energy harvester used to collect environmental vibration is proposed in this paper. The energy harvester mainly includes a diamagnetic stabilized levitation structure and elastic films as the stoppers. The floating magnet maintains a stable levitation in the vertical direction under the action of gravity, magnetic force and diamagnetic force. The elastic film is introduced to build a piecewise linear system which can increase the resonant frequency and extend the operating bandwidth for the energy harvester. The energy harvester prototype is designed, manufactured and tested. During the experiment, the working frequency range is extended from 2.1 Hz to 5.1 Hz under the excitation amplitude of 5 mm. The output voltage increases steadily from 59 mV to 159 mV within this frequency range. The experimental results under different harmonic excitation show that the harvester has the potential to work at a broadband and low-frequency range. The proposed harvester could power micro and intelligent equipment in a low-frequency vibration environment.

Design and analysis of a hollow triangular piezoelectric cantilever beam harvester for vibration energy collection

The vibration of transportation infrastructure is random and of low frequency. The vibration energy can be collected and converted into electric energy by installing the piezoelectric cantilever beam (PCB) harvesters on the transportation infrastructure. The resonance frequency and the resonance number of the PCB harvesters within the low frequency range play critical roles. This paper presents an analysis of four types of PCB harvesters designed according to the characteristics mentioned above to evaluate the influence of three different shapes (rectangle, trapezoid and triangle) on the power generation capacity of the piezoelectric cantilever beams. The results show that the triangular PCB harvesters are more suitable for the low-frequency vibration environment of transportation infrastructure, and they usually have higher voltage outputs. In order to widen the resonant frequency of the triangular cantilever to better adapt to the random vibration environment of the transportation infrastructure, the performance of a hollow triangular piezoelectric cantilever beam (HTPCB) was also assessed. Through modeling and analysis, the resonant frequency of the HTPCB has a broader low frequency range. In practical applications, deployment of the HTPCB harvesters on transportation infrastructures such as pavements and bridges can collect more energy in the random and low-frequency vibration environment of the transportation infrastructures.

Design and performance of hybrid piezoelectric-electromagnetic energy harvester with trapezoidal beam and magnet sleeve

At present, piezoelectric energy harvesters are disadvantaged by their low efficiency and high operating frequencies. To address these shortcomings, we propose herein a hybrid piezoelectric-electromagnetic energy harvester (HPEH) for the low-frequency vibration environment, which is composed of a piezoelectric part featured with a double-clamped trapezoidal beam and an electromagnetic part featured with a magnet sleeve and plane coils. The modeling and experiment of the HPEH were carried out to optimize the structure and performance. We find experimentally that the proposed device not only increases the piezoelectric output but also highly improves the electromagnetic output. At the excitation acceleration 2 m/s2, the average output power of the piezoelectric part and the electromagnetic part is increased by 30.5% and 20 times, respectively. The total output power of the HPEH is increased by 52.4%, reaching 0.637 mW. The results show that the proposed HPEH can efficiently use vibration energy to improve its output performance, which has the potential to power wireless intelligent sensor network and wearable electronic devices.

Modeling and simulation for low-frequency vibration energy harvesting based on piezoelectric unimorph cantilever beam

In order to solve the problem of sustainable energy supply for low-power electronic products used in low-frequency vibration environment, the mathematic model was established based on the theory of piezoelectricity and Euler-Bernoulli beam. Also, the effects of different parameters of PZT unimorph beams such as the length, width, and tip mass on generating capacity were studied by FEM. The results show that the energy harvester with PZT unimorph beam and tip mass is suitable for low-frequency vibration environment. Increasing the length or reducing the width of the beam can significantly lower the first-order modal frequency of energy harvester when other conditions remain the same. Within certain range, the first-order modal frequency of the beam also gradually reduced as the tip mass increasing. When the size of the PZT unimorph beam is 60x60x0.33mm, the tip mass is 8.92g and an exciting force of 0.01N is applied to it along z axis, an output of 8.1V can be obtained. Meanwhile, the PZT unimorph beam is under the first vibration mode and the resonant frequency is 16.296Hz.

An Impact-Based Frequency Up-Converting Hybrid Vibration Energy Harvester for Low Frequency Application

In this paper, a novel impact-based frequency up-converting hybrid energy harvester (FUCHEH) was proposed. It consisted of a piezoelectric cantilever beam and a driving beam with a magnetic tip mass. A solenoid coil was attached at the end of the piezoelectric beam. This innovative configuration amplified the relative motion velocity between magnet and coil, resulting in an enhancement of the induced electromotive force in the coil. An electromechanical coupling model was developed and a numerical simulation was performed to study the principle of impact-based frequency up-converting. A prototype was fabricated and experimentally tested. The time-domain and frequency-domain analyses were performed. Fast Fourier transform (FFT) analysis verified that fundamental frequencies and coupled vibration frequency contributes most of the output voltage. The measured maximum output power was 769.13 µW at a frequency of 13 Hz and an acceleration amplitude of 1 m/s2, which was 3249.4%- and 100.6%-times larger than that of the frequency up-converting piezoelectric energy harvesters (FUCPEH) and frequency up-converting electromagnetic energy harvester (FUCEMEH), respectively. The root mean square (RMS) voltage of the piezoelectric energy harvester subsystem (0.919 V) was more than 16 times of that of the stand-alone PEH (0.055 V). This paper provided a new scheme to improve generating performance of the vibration energy harvester with high resonant frequency working in the low-frequency vibration environment.

A Multiple Vibration Modes Separation Technique Based on 3*5 Element Energy Harvester Array: Frequency, Bandwidth Adjustment, and Electrical Characterization

A neat 3*5 element energy harvester array exploiting multiple vibration modes separation technique, has been designed, fabricated, and characterized. A considerable wideband of 15.6 Hz at simulation and 13 Hz at experiment has been gained in a very low frequency range (below 50 Hz), with the acceleration of 1g. Experimental results show that the adjusted harvester could generate the output power of about 2.1 mW at an 8 Hz resonant frequency with the optimum load resistance 350 $\text{k}\Omega $ . Meanwhile, the half-power (1.05 mW) bandwidth could reach up to 15.3 Hz. These results enable the designed device to improve viability for power supply of low power micro electron devices in some special low frequency vibration environment, such as large engineering applications, bridge monitoring, and wildlife monitoring.

Unsymmetrical, interdigital vibration energy harvester: Bandwidth adjustment based on mode separation technique

Vibration-based piezoelectric energy harvesting technique is a promising way for power supply of smart and mobile wireless sensor networks. The novel structures of harvester with low frequency, wide bandwidth and large output power have drawn great attention. In this paper, vibration energy harvester with unsymmetrical, interdigital pick-up structure and voltage synchronous management circuit have been designed, fabricated, and characterized. The working bandwidths of 11.2Hz at simulation and 12.3Hz at experiment have been gained for the designed structure based on mode separation technique in a low vibrational frequency range (below 25Hz) with the acceleration of 1g. Experimental results show that the proposed harvester can generate the output power of about 151.3μW (5.91 times of our previous work), which can maintain the normal work of given electronic devices (containing 18 light emitting diodes) by using a matched voltage synchronous management circuit. These results make it a promising candidate for power supply of low power micro electron devices in some special low frequency vibration environment, such as large engineering, bridge monitoring, wildlife monitoring, etc.

Prototype observation and influencing factors of environmental vibration induced by flood discharge

Due to a wide range of field vibration problems caused by flood discharge at the Xiangjiaba Hydropower Station, vibration characteristics and influencing factors were investigated based on prototype observation. The results indicate that field vibrations caused by flood discharge have distinctive characteristics of constancy, low frequency, small amplitude, and randomness with impact, which significantly differ from the common high-frequency vibration characteristics. Field vibrations have a main frequency of about 0.5–3.0 Hz and the characteristics of long propagation distance and large-scale impact. The vibration of a stilling basin slab runs mainly in the vertical direction. The vibration response of the guide wall perpendicular to the flow is significantly stronger than it is in other directions and decreases linearly downstream along the guide wall. The vibration response of the underground turbine floor is mainly caused by the load of unit operation. Urban environmental vibration has particular distribution characteristics and change patterns, and is greatly affected by discharge, scheduling modes, and geological conditions. Along with the increase of the height of residential buildings, vibration responses show a significant amplification effect. The horizontal and vertical vibrations of the 7th floor are, respectively, about 6 times and 1.5 times stronger than the corresponding vibrations of the 1st floor. The vibration of a large-scale chemical plant presents the combined action of flood discharge and working machines. Meanwhile, it is very difficult to reduce the low-frequency environmental vibrations. Optimization of the discharge scheduling mode is one of the effective measures of reducing the flow impact loads at present. Choosing reasonable dam sites is crucial.

A low frequency piezoelectric energy harvester with trapezoidal cantilever beam: theory and experiment

With the development of low power MEMS device and outdoor wireless sensor network, new energy supply has been a key to replace the traditional energy which has some disadvantages. We have found that obtaining energy from the daily low frequency vibration environment is a very efficient solution to ease the pressure of energy sources. In this paper, a utility low frequency piezoelectric energy harvester with trapezoidal cantilever beam is presented. Then, a relevant theoretical model, optimization method and comparison experiment are made. The results show that the theoretical analysis results are in agreement with the experimental results; under the condition of constant beam length, open-circuit voltage and output power of the trapezoidal beam piezoelectric energy harvester are 81.6 and 167% more than those of the rectangular beam piezoelectric energy harvester. In addition, In order to further broaden the frequency band and improve output characteristics, we use the nonlinear method to redesign the experiment based on the above experiments. The results show that distance and magnet polarity change have an important effect on output characteristics.

Piezoelectric energy harvester operated by noncontact mechanical frequency up-conversion using shell cantilever structure

In this study, we propose and demonstrate a piezoelectric energy harvester with a shell cantilever for mechanical frequency up-conversion to generate electric power in a low-frequency vibration environment. The proposed device is composed of a clamped semicylindrical shell cantilever as a driving beam and a piezoelectric cantilever attached to the proof mass of the shell cantilever as a generating beam. The shell cantilever bends downward when the external acceleration is over the threshold value for buckling transition. When the acceleration direction is reversed, the shell cantilever makes abrupt stop at its initial position, inducing impact-like force on the generating beam and resulting in free vibration at high resonance frequencies. Experimental results show that a maximum power of 101 µW at 20 Hz can be obtained.