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Abstract Piezoelectric transducers based on macro fibre composites (MFCs) are widely used for energy harvesting, actuation and sensing because of the high conformability, reliability and strong piezoelectric effect of MFCs. Analytical or numerical modelling of the heterogeneous MFC as a homogenous material with equivalent properties is usually required to predict the performance of the transducers. However, the equivalent properties reported in the literature are not suitable for this purpose. This work proposes an equal power-output method to numerically evaluate the equivalent properties of d 31 type MFCs for piezoelectric transducer modelling. Taking energy harvesting application as a study case, it departs from the traditional method by applying electric assumptions that ensure the equal voltage, electric charge, and thus equal power output between the heterogeneous and homogeneous MFCs. The equivalent properties were characterised through the finite element (FE) analysis of the MFC's representative volume element (RVE), which is the minimum periodic unit in the MFC and takes account all the constitutes. The validity of these equivalent properties for energy harvesting transducer modelling was verified by FE modelling as well as experimental testing. The application of the equivalent properties for actuation and sensing transducer modelling was analysed and validated. FE modelling results showed that a homogeneous RVE with the equivalent properties accurately simulated the energy harvesting and actuation behaviours of the heterogeneous RVE. The simulated power output of MFC-based strain energy harvesters matched the mean experimental results with a mean error of 2.5%. When used for actuation, the MFC produced a free strain of 0.93 μ ε / V , which is close to the manufacturer specification. [ABSTRACT FROM AUTHOR]

This paper develops a coupled piezoelectric-circuit finite element (FE) model for a mechanically plucked piezoelectric energy harvester (Mech-PEH), which uses plastic plectra to pluck piezoelectric bimorph cantilevers. The Mech-PEH was modelled as a piezoelectric cantilever with either a displacement or a force applied at the tip, and a load resistor connected across its electrodes. The FE model was validated with a difference around 2.7% between the simulated and measured energy outputs and able to predict the vibration- and energy-related characteristics of the Mech-KEH. It was used to investigate the effects of the bimorph’s geometric parameters and the plucking frequency on the energy outputs. It is concluded that (1) when the same plucking force is used, the energy output of the Mech-PEH can be increased by reducing the stiffness of the bimorph through reducing its width or thickness, or increasing its length, and (2) a high plucking frequency with a free vibration period is beneficial in improving the energy output. It is pointed out that the bending fatigue strength of the piezoelectric material limits the designed highest energy output, and that when designing bimorph parameters for the Mech-PEH, both the energy output and the expected life time should be considered. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a micropump fabricated from low cost materials with specific goal of cost reduction. The micropump does not require any valve flap and comprises one plastic pump polyether–ether–ketone (PEEK) body, one metal diaphragm, and three piezoelectric ceramics to form piezoelectrically actuated diaphragm valves. The valve actuation simplifies micropump structural designs and assembly processes to make the pump attractive for low cost bio-medical drug delivery applications. A detailed optimization design of geometric parameters of the piezoelectrically actuated diaphragm is undertaken by use of 3D finite element method (FEM) to maximize piezoelectric actuation capability and ensure actuation reliability. An optimized geometric dimensional design: the ratio of thicknesses between the piezoelectric ceramics and the metal diaphragm, and the lateral dimension of the piezoelectric ceramic, is obtained through simulations. Based on the optimized design, a good agreement has been reached between simulated and measured strokes of the micropumps. The tested results show that the micropump has a high pump flow rate for air, up to 39ml/min, and for water, up to 1.8ml/min, and is capable of ensuring diaphragm’s maximum stress and strain is within material strength for reliable work. [Copyright &y& Elsevier]

Abstract: A new mechanical filter structure is presented which comprises two silicon cantilevers mechanically coupled by a silicon linkage with thin film piezoelectric transducers providing electrical input and output signals. The resonance behaviour of such a structure results in a band-pass filter response, having a band-width determined by the frequency separation between the closely spaced in-phase and out-of-phase vibrational modes of the two coupled cantilevers. A detailed configuration design analysis, filter simulation and optimisation of performance is undertaken using a new modelling approach combining microwave circuit theory and finite element analysis to evaluate the generalised (A, B, C and D) and scattering (S) circuit parameters of the filter. Two significant features of the filters have emerged from the derived analyses and simulations: (1) with correct design filter Q-values can reach several thousand which is much higher than the Q-values (∼80) of uncoupled cantilevers, (2) the Q-value is determined by the configuration of the silicon linkage and so is under the designer''s control. The position and length of the linkage that give optimum Q and minimum insertion loss are determined. [Copyright &y& Elsevier]

Piezo stack energy harvesting from railway vibrations shows substantial potential for powering wireless sensor networks responsible for monitoring railway infrastructure. Nevertheless, assuring the safety and durability of these energy harvesters in the condition of the dynamically fluctuating railway vibrations remains a considerable challenge. In this paper, we present two innovative protection methods designed for piezo stack energy harvesters with a frequency up-conversion mechanism. These methods involve the incorporation of ring-type and circular stoppers within the resonant system and the utilisation of proposed impact protection components within the impact system. Two distinct harvesters incorporating the proposed protection components, Harvester Types I and II, are designed to align with their respective operating acceleration targets, which are determined based on the amplitudes of railway vibration acceleration. Finite element modelling is used to guide the design process, involving the evaluation and selection of various design parameters aligned with the acceleration target and stress limits. The protection mechanisms' effectiveness and impact on energy harvesting performance have been validated through experimental testing under measured rail vibration signals, and their performance has been further assessed through stress analyses. Harvester Type I operates seamlessly within a 5 g threshold, effectively mitigating the increase in maximum output acceleration and stress beyond this limit. In contrast, Harvester Type II efficiently dissipates excess energy, enabling the harvester to operate at a 15 g acceleration while reducing the rate of acceleration and stress growth. The results demonstrate that both proposed harvesters provide effective protection from unexpected railway vibration overloads. This research makes a significant impact on the practical, real-world implementation of piezo stack energy harvesters operating within the dynamic environment of railway vibrations. [Display omitted] • Two strategies are proposed to protect energy harvesters with frequency up-conversion from mechanical overload. • Harvester Types I and II are developed to incorporate the proposed strategies considering the railway requirements. • FEM modelling is developed to evaluate and determine the design parameters. • Experiments are carried out to assess the protection mechanism and energy harvesting performance of the harvesters. • The proposed harvesters can provide effective protection from unexpected railway vibration overloads. [ABSTRACT FROM AUTHOR]

[Display omitted] • Two innovative strategies have been proposed to protect energy harvesters with frequency up-conversion mechanism from mechanical overload. • Finite element method has been used to model and analyse the proposed protection strategies. • Experiments have been conducted to verify the strategies and modelling. • The capability of protecting the harvesting device from unexpected overload is demonstrated. • The protection mechanisms and damping effects of the proposed strategies are discussed. Vibration energy harvesters utilising the frequency up-conversion mechanism have been effective in harvesting low-frequency ambient vibrations. However, the mechanical impact required for this process could also damage the devices when excessive load is applied. To address this issue, this paper presents novel protection strategies for energy harvesters with a frequency up-conversion mechanism, including a ring-type stopper within the resonant system and specially designed impact protection components (IPC) within the impact system. By applying these methods, the influence of excessive input excitation has been mitigated, and thus, the reliability and durability of the device have been improved. Finite element modelling has been employed to model the proposed protection methods, and then experiments have been conducted to verify and refine the modelling. Stress analysis is finally conducted based on the refined model to validate the effectiveness of the protection strategies. The results demonstrate that the proposed strategies are capable of protecting the harvesting system from excessive input excitations, which means the device functions effectively in the operating state and decelerates the growth rate of maximum stress and acceleration in the limiting state. This research contributes valuable insights into the development of effective protection strategies for energy harvesters with frequency up-conversion mechanisms, thereby improving their durability and performances in real-world applications. [ABSTRACT FROM AUTHOR]

• Magnetic rolling pendulum with low mechanical loss and strong nonlinear behaviours. • Normalised mechanical loss <30% of those reported in the literature. • Consecutive primary and subharmonic resonance when excitation ≥5 m/s2. • 1-mW-bandwidth up to 9.7 Hz with linear resonance frequency of 4.6 Hz. • Subharmonic resonance contributes up to 2/3 of the bandwidth. Nonlinear systems may exhibit secondary resonances, which can provide an additional and thus broadened bandwidth for energy harvesting. However, the secondary resonances of nonlinear energy harvesters reported in the literature suffer from low-power output and limited bandwidth. This work proposes a novel magnetic rolling pendulum (MRP) with a large bandwidth and high power output in both primary and secondary resonances for energy harvesting. The MRP employs the rolling motion of a magnetically levitated permanent magnet with minimal mechanical damping. A prototype was fabricated and characterised. An analytical model combined with finite element analysis was developed and validated by experiment. Both experiment and simulation show that the MRP has a linear resonance frequency of 4.6 Hz and peak power of 3.7 mW. It exhibits strong nonlinear behaviours and broadband characteristics with excitation amplitude as low as 2 m/s2 in the primary resonance. As the excitation amplitude is larger than 5 m/s2, the secondary resonance (1/2 order subharmonics) is excited. The responses of the MRP at the subharmonic resonance take the same form as the primary resonance in terms of displacement and power outputs. This helps the subharmonic resonance to produce the same power level as the primary resonance but with a larger bandwidth. When excited at 14 m/s2, the MRP shows 1-mW-bandwidth of 9.7 Hz, 2/3 of which is attributed to the subharmonic resonance. [ABSTRACT FROM AUTHOR]