Monostable Energy Harvester Research Articles

Numerical analysis and experimental validation of nonlinear broadband monostable and bistable energy harvesters

Vibration based piezoelectric energy harvesting has been receiving more and more attention for supplying usable electrical energy to low-power electronic devices. This type of energy can produce the desired voltage to power any low electronic device or wireless sensor. But most of them provide lower voltage and insufficient power. In this paper, the nonlinear magnetic field is introduced to broaden the effective resonant bandwidth for overcoming this issue. The dynamic linear and nonlinear model of magnetic coupling piezoelectric vibration energy harvester is established based on the Hamilton principle, Euler-Bernoulli beam theory, piezoelectric theory, and Kirchhoff's law and law of mechanics. Numerical solutions of nonlinear energy harvesting systems are studied by using the Runge-Kutta method. The bifurcation diagram, Poincare map, power spectrum, and phase trajectory of voltage output are investigated with different excitation amplitudes and frequencies. Simulation of linear and nonlinear model were illustrated at given excitation levels. Simulation results show the harvesting performance can be improved by proper external magnetic coupling and potential energy function. The theoretical harmonic balance analysis results verify the numerical solution and influence the mechanism of excitation levels and interface resistances. Experimental verification is carried out to measure the nonlinear restoring force and examine the performance of nonlinear bistable and monostable energy harvesters. The experiment results show the nonlinear bistable and monostable energy harvesters can provide larger voltage and more power.

Response Analysis of Asymmetric Monostable Harvesters Driven by Color Noise and Band-Limited Noise

In this paper, we investigate the response of asymmetric potential monostable energy harvesters (MEHs) excited by color noise and band-limited noise. The motivation for this study is that environmental vibrations always have the characteristic of randomness, and it is difficult to modulate a perfectly symmetric MEH. For the excitation of exponentially correlated color noise, the moment differential equation was applied to evaluate the output performance of the asymmetric potential MEHs. Numerical and theoretical analyses were carried out to investigate the influence of noise intensity and internal system parameters on the output power of the system. Our results demonstrate that the output performance of the asymmetric MEH decreases with the increase in the correlation time, which determines the character of the color noise. On the contrary, the increase in the asymmetric degree enhances the output power of the asymmetric MEH subjected to color noise. For the band-limited noise excitation, numerical simulation is undertaken to consider the response of the asymmetric MEHs, and outcomes indicate that the frequency bandwidth and center frequency have a significant influence on the output performance. Regarding the asymmetric potential, its appearance leads the MEHs to generate higher output power at lower frequencies and this phenomenon is more obvious with the increase in the degree of asymmetry. Finally, we observed that the characteristics of the response bandwidth of asymmetric MEHs subjected to band-limited noise excitation are similar to the response under harmonic excitation.

Power enhancement of a monostable energy harvester by orbit jumps

Energy harvesting has been regarded as a potential solution for power problems in wireless sensor network applications over batteries. Nonlinear configurations, as one of the most promising methods for broadening bandwidth, still make the system suffer from the coexistence of high-energy orbit and low-energy orbit, which significantly reduces output power. This paper proposes the electromagnetic kick method to enhance the output power of a monostable energy harvester through orbit jumps. The so-called electromagnetic kick is introduced by a solenoid consisting of a coil from the electromagnetic energy harvester and a three-volt button battery. The modeling and analysis demonstrate the excitation capability of the electromagnetic kick for orbit jumps. Inspired by a swing, two strategies are derived as the single kick and cycled kick. Based on an experimental setup, parameters for two strategies are first determined. The single kick and the cycled kick are then respectively employed to realize orbit jumps for the energy harvester under varying excitation and loading conditions. For each scenario, twenty trials are repeated to investigate the probability and capability. The system power output can be boosted from null to over 360 µW after orbit jumps, and the consumed energy can be resumed within 20 s. In addition, to evaluate different orbit jumping approaches in the literature, a figure of merit is developed, and the comprehensive advantages of the electromagnetic kick approach are demonstrated. The proposed effortless and efficient orbit jumping strategy expands the possibilities of realistic applications of nonlinear energy harvesters. The defined figure of merit not only makes it possible to compare different orbit jumping methods but also opens the door to new strategy development.

Robust design optimization of a nonlinear monostable energy harvester with uncertainties

Based on the improved interval extension, a robust optimization method for nonlinear monostable energy harvesters with uncertainties is developed. In this method, the 2nd order terms in the interval extension formula of the objective function (output voltage) are kept so this approach is suitable for a nonlinear energy harvesting system. To illustrate this method, uncertain mass, uncertain capacitance and uncertain electromechanical coupling coefficient are optimized to maximize the central point of output voltage whose deviation of which is simultaneously minimized. Then, an optimal design with different robustness is obtained. The results also show that the robustness of the optimal design of nonlinear monostable energy harvesters is increased, but the cost of performance has to be paid for. Overall, the framework provides the optimal design for nonlinear energy harvesters (monostable, bistable, tristable, multistable harvesters).

Uncertainty Analysis of Excitation Conditions on Performance of Nonlinear Monostable Energy Harvesters

Nonlinear energy harvesters were found to be sensitive to excitation conditions. In order to reveal the influence mechanism of the excitation condition on the energy harvesting performance, this paper presents an uncertainty analysis for nonlinear monostable energy harvesters (NMEHs). An improved interval extension based on the second-order Taylor’s series is presented as a new uncertainty analysis method. A mathematic example is used to demonstrate that the bounds of responses based on this method are more accurate than the classic interval extension when the dependence of the response on the uncertain variable is nonlinear. Meanwhile, the results from the Monte Carlo simulation are used to verify the accuracy of the proposed method. It is confirmed that the proposed method is suitable for quantifying the propagation of the uncertain level and frequency of the excitation for the NMEH. The results show that the output voltage of the NMEH is more sensitive to the frequency than the level of excitation, for which the influence mechanism is revealed.

Comparison of harmonic balance and multi-scale method in characterizing the response of monostable energy harvesters

Abstract Harmonic balance and multi-scale methods have been widely applied to investigate the nonlinear dynamics and performance enhancement methods of nonlinear vibration energy harvesters. However, there are rare works considering the relative accuracy of the two methods in characterizing the response of nonlinear harvesters. Therefore, new insights into the analytical accuracy of harmonic balance and multi-scale methods are provided based on a monostable energy harvester in this paper. Frequency response functions of displacement and voltage for a monostable harvester are derived according to harmonic balance expansion and multi-scale method respectively. Monostable system parameters identified from experimental measurements are obtained for numerical investigation of the theoretical solution from harmonic balance and multi-scale methods. Results demonstrate that harmonic balance method is more accurate to characterize the frequency response under different acceleration levels, as well as the amplitude response for various excitation frequencies. While for multi-scale method, it is of great importance to choose proper keeping parameter to describe the nearness of excitation frequency to the resonance frequency.

Theoretical analysis and experimental verification for improving energy harvesting performance of nonlinear monostable energy harvesters

Theoretical analysis and experimental verification of nonlinear monostable energy harvesters are presented to enhance energy harvesting performance from low-level ambient vibrations. Harmonic balance analysis of these harvesters demonstrates that there are two stable orbits (high-branch orbit and low-branch orbit) in a specific multi-solution range when the excitation level is larger than a threshold. Under the same excitation, these nonlinear harvesters may finally vibrate at different orbits depending on different initial conditions or disturbances. The energy harvesting efficiency will be greatly improved if high-branch oscillations could be induced in the multi-solution range. Numerical investigations into the influence of a disturbance method and initial conditions on high-branch oscillations are performed for energy harvesting enhancement of nonlinear monostable energy harvesters. Experimental results verify the effectiveness of adding disturbances by using an impact method for improving energy harvesting performance and the capability of nonlinear monostable energy harvesters in maintaining high-branch oscillations at low-level vibrations.

Nonlinear Energy Harvesting Using Electromagnetic Transduction for Wide Bandwidth

We report the relative performances of monostable and bistable miniaturized electromagnetic energy harvesters (EMEHs) using micromachined fiberglass-epoxy spring structures. Monostable nonlinearity is realized in our device using the specially designed spring arms, whereas bistable nonlinearity is introduced through the interactions between repulsively oriented magnets. For devices of similar size, the monostable electromagnetic harvester generates larger output power compared to the bistable system under the same mechanical input. This is due to the additional damping provided by the strong bistable force, which also restricts the bandwidth widening of the bistable device compared to that of the monostable energy harvester. However, as the bistable force changes the linear stiffness of the system as well, the overall frequency response shifts toward the low-frequency region. Hence, low-frequency, wideband harvesting can be obtained in bistable devices compared to monostable devices of the same mechanical dimensions.

The benefits of Duffing-type nonlinearities and electrical optimisation of a mono-stable energy harvester under white Gaussian excitations

This work is concerned with the performance of a single degree of freedom electromagnetic energy harvester when subjected to a broadband white noise base acceleration. First, using the Fokker–Planck–Kolmogorov equation, it is shown that Duffing-type nonlinearities can be used to reduce the size of energy harvesting devices without affecting their power output. This is then verified using the technique of Equivalent Linearisation. Second, it is shown analytically that the optimum load resistance of the device is different to that which is dictated by the principle of impedance matching. This result is then verified experimentally.