Search

This paper presents an adaptive power management circuit, which maximizes the energy transfer from the energy harvester to wireless sensor nodes in real-world applications. Low power consumption techniques were adopted in the power management circuit to maximize the delivery of the harvested energy to the load instead of being consumed by the circuit. The presented circuit incorporates an analogue control circuit (ACC) for maximum power transfer from the energy harvester to the storage capacitor and an energy-aware interface (EAI) for controlling the energy flow from the storage capacitor to the load. To evaluate the performance of the presented circuit, piezoelectric energy harvesting was used as a studied case. The piezoelectric energy harvester (PEH) was mechanically excited at different strain loadings and frequencies. The experimental results show the circuit can self-start and powered directly by the PEH since the EAI and ACC have low power consumption in the range of microwatts. The circuit is adaptive to energy harvesters of varying output and various electrical loads, with a peak efficiency of 76.18% in transferring the harvested energy from the PEH to the storage capacitor. More than 96% of the energy released from the storage capacitor is effectively transferred to the electrical load. [ABSTRACT FROM AUTHOR]

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]

Conventional engineering design optimization requires a large amount of expensive experimental tests from prototypes or computer simulations, which may result in an inefficient and unaffordable design process. In order to overcome these disadvantages, a surrogate model may be used to replace the prototype tests. To construct a surrogate model of sufficient accuracy from limited number of tests/simulations, a multi-level surrogate modeling strategy is introduced in this article. First, a chosen number of points determined by optimal Latin Hypercube Design of Experiments are used to generate global-level surrogate models with genetic programming and the fitness landscape can be explored by genetic algorithms for near-optimal solutions. Local-level surrogate models are constructed then from the extended-optimal Latin Hypercube samples in the vicinity of global optimum on the basis of a much smaller number of chosen points. As a result, an improved optimal design is achieved. The efficiency of this strategy is demonstrated by the parametric optimization design of a piezoelectric flex transducer energy harvester. The optimal design is verified by finite element simulations and the results show that the proposed multi-level surrogate modeling strategy has the advantages of faster convergence and more efficiency in comparison with the conventional single-single level surrogate modeling technique. [ABSTRACT FROM AUTHOR]

This paper presents the implementation of a single piece of macro fiber composite (MFC) piezoelectric transducer as a multifunctional device for both strain sensing and energy harvesting for the first time in the context of an energy harvesting powered wireless sensing system. The multifunction device is achieved via time-multiplexing operation for alternating dynamic strain sensing and energy harvesting functions at different time slots associated with different energy levels, that is, when there is insufficient energy harvested in the energy storage for powering the system, the MFC is used as an energy harvester for charging up the storage capacitor; otherwise, the harvested energy is used for powering the system and the MFC is used as a strain sensor for measuring dynamic structural strain. A circuit is designed and implemented to manage the single piece of MFC as the multifunctional device in a time-multiplexing manner, and the operation is validated by the experimental results. The dynamic strains measured by the MFC in the implemented system match a commercial strain sensor of extensometer by 95.5 to 99.99%, and thus the studied method can be used for autonomous structural health monitoring of dynamic strain. [ABSTRACT FROM AUTHOR]

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]

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]