Search

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]

• Novel String-Driven Rectifier converts bidirectional to unidirectional rotation. • Single-clutch, gearless SCR reduces weight and complexity of mechanical rectifiers. • Extracts kinetic energy while preserving potential to maintain high pendulum speed. • Applicable to a range of energy harvesters where size and weight must be minimised. [Display omitted] This work presents a pendulum kinetic energy harvester with a unique mechanical motion rectifier design which uses a string-driven rectifier (SDR) with just a single clutch to convert bidirectional input oscillation of a pendulum to the unidirectional rotation of a DC motor to produce electricity. Unlike typical mechanical rectifiers which use two clutches, this rectification system has no gearing, minimising the complexity and weight of the rectifier for the energy harvester. Through experimentation, the energy harvester was found to have a normalised average power output of 4.39 W/g2 and a normalised average power density of 5.85 W/g2/kg when excitation was applied at the 1.5 Hz resonant frequency with a 0.75 kg pendulum mass. This corresponds to a normalised average voltage production of 55.47 V/g. Time-domain analysis of the transducer showed the successful operation of the SDR. By selectively harvesting kinetic energy during different stages of the pendulum motion, the kinetic energy of the pendulum mass was extracted while the stored potential was preserved and converted to kinetic. This allowed a high pendulum velocity to be maintained, while the rectified input motion generated a single polarity voltage from the DC motor. The construction of this system has advantages over existing designs by reducing the complexity of rectification mechanisms, providing an alternative approach to mechanical motion rectification for pendulum vibration energy harvesters. [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]

To enable wireless sensor networks to monitor rail infrastructures in real-time, a cost-effective power source is in need. This work presents the design, modelling and testing of a piezo stack energy harvester with frequency up-conversion mechanism for scavenging energy from railway track vibration. The proposed harvester is designed to meet railway track applications' size, frequency, and stress requirements. A compact design integrating the inertial mass and the piezo stack transducer systems is used to enable the mechanical collision for realising the frequency up-conversion mechanism and ensure the size of the energy harvester is suitable for the limited space on the railway track. The frequency bandwidth of the energy harvester is broadened by utilizing the longitudinal and torsional oscillation of the designed plate springs which enable the system to have two adjacent natural frequencies. The mechanical transformer of the piezo stack transducer system is designed to achieve the required stress level under both the impact force caused by the collision motion and the inertial force generated by the random vibration of the rails. A finite element model (FEM) analysing the free vibration of the piezo stack transducer caused by the frequency up-conversion mechanism is developed to analyse the dynamic characteristics of the coupled system. Lab tests are carried out to validate the proposed FEM and evaluate the impact of different factors such as load resistance, acceleration, initial interval, plate spring, and pulse excitation on power generation. Experimental results show that the energy harvester has two resonant frequencies of 17 Hz and 20 Hz. The frequency up-conversion mechanism can convert this low-frequency vibration into the piezo stack transducer's high resonant frequency vibration of 94 Hz. A maximum average power of 6.72 mW with a 1-mW-bandwidth of 15 Hz is obtained when actuated at 0.7 RMS g acceleration. [Display omitted] • A piezo stack energy harvester for railway track vibration is designed, modelled and tested. • A compact design is proposed to enable the mechanical collision for realising the frequency up-conversion mechanism. • Two adjacent natural frequencies are achieved to broaden the frequency bandwidth. • The mechanical transformer is designed to achieve the required stress level under the impact force and inertial force. • A maximum average power of 6.72 mW with a 1-mW-bandwidth of 15 Hz is obtained when actuated at 0.7 RMS g acceleration. [ABSTRACT FROM AUTHOR]

This paper presents the integration of a novel mechanical torsion spring regulator into a pendulum energy harvester system. This regulator was designed to provide the same voltage-smoothing benefits of a flywheel without the start-up issues caused by increasing system inertia. In addition, the introduction of the spring between the input and output stages of the device acts as a buffer for any sudden impacts, which not only allows the energy from such events to be fully absorbed and dissipated slowly through the output but significantly reduces the torque stress and torque fluctuation stress on critical components to improve the reliability of the system. Through experimentation and simulation, the transducer was shown to reduce the voltage fluctuation range from 13.85 to 28.16 V to 16.41 to 23.59 V for the pendulum energy harvester at resonance, and comparison of start-up response to that of a device with a flywheel shows a significant improvement in initial acceleration of the output when subjected to excitation. The energy harvester with spring has demonstrated a maximum normalised average power output of 12.09 W/g2, a maximum normalised average voltage of 109.96 V/g, and a maximum normalised power density of 7.8 W/g2/kg, at a resonant frequency of 1.2 Hz. The effectiveness of the spring mechanism for regulating output voltage and power, improving start-up performance, and reducing stress on critical components has significant implications for the real-world viability of pendulum energy harvesters, with the potential to improve their reliability in often unpredictable environments. [Display omitted] • Achieves key benefits of a flywheel, while overcoming the major drawbacks. • Spring reduces variation of output voltage, similar to the effect of a flywheel. • Improved start-up performance of energy harvester. • Significant reduction in torque on critical components e.g. clutches. [ABSTRACT FROM AUTHOR]

• Pendulum with two fixed arms, utilising both a primary mass and a counterweight. • Enables ultra-low frequency vibration without increasing pendulum volume. • Average power of 0.997 W at 0.75 Hz, 0.1 g rms input acceleration. • Normalised average power of 95.8 W/g2 at 0.75 Hz, and power density of 6.11 W/g2/kg. • Linear relationship between frequency reduction ratio and ratio of pendulum arms. In this paper, a novel electromagnetic pendulum energy harvester with a counterweight is designed to harvest low frequency vibration from ocean waves for unmanned surface vehicles. This design is the first of its kind, allowing the natural resonant frequency of the pendulum to be reduced without increasing its length, thereby maintaining a high power output from the energy harvester at lower frequencies than previously possible with pendulums of the same size. Implementing a novel mechanical rotation rectifier (MRR) system for a high energy conversion efficiency, this counterweight pendulum energy harvester can provide multi-watt-level power at frequencies lower than 1 Hz, with a primary pendulum arm length of just 195mm. When actuated at 0.1 g rms, the pendulum energy harvester with a counterweight produced electrical power of 0.997 W at 0.75 Hz, compared to 0.168 W without the counterweight. The average normalised power output of the system at this frequency is 95.8 W/g2, corresponding to a power density of 6.11 W/g2/kg. Testing of a range of configurations of the pendulum mass and counterweight shows a clear linear relationship between the ratio of lengths of the pendulum arms and the reduction of the natural frequency of the system. This demonstrates empirically that this device is capable of operating under conditions in which existing energy harvesters are unable to provide adequate power, and therefore provides a significant development in energy harvesting in an ultra-low frequency marine environment. [ABSTRACT FROM AUTHOR]

• Novel mechanical rotation rectification gives efficient, high-torque transmission. • Maximum average power of 0.72 W at 1 Hz, 0.186 g rms input acceleration. • Maximum normalized average power of 20.62 W/g2, with conversion efficiency of 43.5 %. • Device deemed suitable for unmanned surface vessels (USVs). • Positive correlation between flywheel mass and power under continuous excitation. This paper proposes a novel pendulum energy harvester design for converting energy of low frequency ambient vibration, such as that found in unmanned surface vehicles (USVs) due to ocean waves, into usable electrical energy. The primary novelty of this design is the mechanical rotation rectifier (MRR) system, which is able to improve on existing designs through the use of spur gears and sprag clutches capable of handling significant torque, in an arrangement which is easily scalable to larger devices. Using a minimal number of offset gears, this system is designed to maintain high efficiency and minimal backlash. The energy harvester was proven to produce a maximum normalised average power output of 20.62 W/g2, corresponding to an average power of 0.72 W and a power density of 0.43 W/kg, at 0.186 g rms acceleration. The resonant frequency of the system is designed at 1 Hz, within the range of the expected natural frequencies of USV motion. The energy conversion efficiency at resonance was 43.5 %. Furthermore, a mathematical model was developed and verified through experimental testing, and was used to simulate the effects of various pendulum lengths, masses and flywheels on the system. This demonstrates the specific negative relationship between pendulum arm length and natural frequency of the system, as well as the positive correlation between pendulum mass and maximum power. Furthermore, higher inertia flywheels are shown to produce significantly smoothed voltages and increased output power, while extending the time it takes for the harvester to reach steady state. It is concluded that this device would be viable for assisting in powering USV communications and extending the exploration life of these vessels. [ABSTRACT FROM AUTHOR]

Piezoelectric energy harvesting techniques are increasingly seen as promising power sources for wireless sensor networks that monitor railway infrastructure. However, the piezoelectric generators currently available for railway applications suffer from low power output, as well as inadequate durability and robustness. To tackle these issues, this study introduces a novel, high-power, sturdy piezo stack energy harvester's design, optimization, and testing for powering wireless sensor networks in rail systems. The aim is to improve both the power output and the durability and robustness of the device. The proposed harvester's high-power generation is facilitated by a frequency up-conversion mechanism, mechanical transformer design and optimization, and the application of the piezo stack's compression mode (d 33 mode). The frequency up-conversion mechanism allows the harvester to function at low-frequency track vibrations with high power. The mechanical transformer significantly magnifies the force exerted on the piezo stack. The compression mode boots the energy conversion efficiency due to its higher coupling factor. To enhance durability and robustness, innovative approaches are employed. The mechanical transformer is optimized for maximum energy transmission efficiency without exceeding the material's fatigue limit. Moreover, the piezo stack is designed to operate under pre-compression, preventing tensile stress and taking advantage of the piezoelectric ceramics' remarkable compressive strength. Plate springs are also integrated into the mechanical transformer to maintain motion along the vibration direction. Experimental results from prototype testing provide strong evidence for the high-power output of the proposed harvester and its ability to power a wireless sensor. A maximum power of 511 mW and an average power of 24.5 mW are achieved at a harmonic excitation with 21 Hz and 0.7 RMS (Root Mean Square) g, while a maximum power of 568 mW and an average power of 7.3 mW are generated under a measured railway track vibration signal. [Display omitted] • A high-power, robust piezo stack vibration energy harvester is proposed for railway track applications. • Frequency up-conversion mechanism and optimization of mechanical transformer are used to achieve high-power generation. • Novel strategies are implemented to improve durability and robustness. • An average power of 24.5 mW is obtained at 21 Hz and 0.7 RMS g. • The capability of powering the wireless sensor is demonstrated. [ABSTRACT FROM AUTHOR]

Highlights • An auxetic substrate increases power output of a piezoelectric element. • This substrate increases the stress in the element both axially and laterally. • A power gain of up to 14.4 times a plain harvester was observed experimentally. Abstract This paper develops an auxetic (negative Poisson's ratio) piezoelectric energy harvester (APEH) to increase the power output when harnessing strain energy. The APEH consists of a piezoelectric element bonded to an auxetic substrate. The auxetic substrate concentrates the applied stress and strain into the region of the piezoelectric element and introduces auxetic behaviour in the piezoelectric element, both of which increase the electric power output. A finite element model was developed to optimise the design and verify the mechanism of the power increase. Three APEHs were manufactured and characterised. Their performance was compared with two equivalent strain energy harvesters with plain substrates. Experimental results show that the APEHs, excited by sinusoidal strains of 250 με peak-to-peak at 10 Hz, are able to produce electric power of up to 191.1 μW, which is 14.4 times that of the peak power produced by the plain harvesters (13.4 μW). The power gain factor is constant between samples as the amplitude and frequency of their applied strains are varied. The model and experimental results are in good agreement, once accounting for the imperfect bonding of the epoxy using the spring constant of the Thin Elastic Layers on the modelled epoxy surfaces. [ABSTRACT FROM AUTHOR]

The continuous progress made in wearable energy harvesting technology is delivering sophisticated devices with increasing power outputs, which are possible to provide sustainable energy supply for body sensors to achieve energy-autonomous wireless sensing systems. This paper reports the development and characterisation of a wearable energy harvesting powered wireless sensing system with system-level strategies to address the challenges in energy harvesting, power conditioning, wireless sensing and their integration into a system. The system comprises four parts: (1) a magnetically plucked wearable knee-joint energy harvester (Mag-WKEH) to scavenge energy from knee-joint motions during human walking, (2) a power management module (PMM) with a maximum power point tracking (MPPT) function, (3) an energy-aware interface (EAI) for dealing with the mismatch between the energy generated and demanded, and (4) an energy-aware wireless sensor node (WSN) for data sensing and transmitting. Experiments were performed with a human subject wearing the system and walking on a treadmill at different speeds. The experimental results showed that as the walking speed increased from 3 to 7 km/h, the power output of the Mag-WKEH increased from 1.9 ± 0.12 to 4.5 ± 0.35 mW, and the generated power was able to power the WSN to work at duty cycles from 6.6 ± 0.36% to 13 ± 0.5% with an active time of 2.0 ± 0.1s. In each active time, the WSN was able to sample 482 readings with an interval of 10 ms from the sensors and transmit all data to a base station at a distance of 4 m. [ABSTRACT FROM AUTHOR]