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Energy harvesting from ambient environment has attracted intensive attention over the years for powering low-power autonomous electronic devices. A conventional piezoelectric energy harvester (CPEH) can hardly meet the requirements of effective energy harvesting from wideband, low frequency and low amplitude vibration sources due to its simple substrate and single resonant peak response. Using sandwich structure comprised of a soft-core layer and two thin skins can drastically reduce the natural frequency and increase voltage output of the harvester. The stiffness of sandwich harvester and consequently its resonant frequency can be tuned more flexibly than the CPEH by choosing different materials and adjusting the geometric dimensions of the core and skins. In this paper, a novel multi-branch sandwich piezoelectric energy harvester (MSPEH) is proposed to harvest energy from wideband, low frequency and low amplitude vibration sources. The proposed harvester comprises of a main sandwich beam as substrate with a patch of piezoelectric layer bonded over it. Multiple inner single branches with tip masses are connected to the main substrate to generate multiple resonant peaks and tune the range of the interested frequency. Firstly, a mathematical model of the proposed harvester is presented, and the electromechanical coupling equations are obtained. Subsequently, a prototype of MSPEH with two inner single branches is fabricated and tested under harmonic base excitation to study its performance. When tested at a low harmonic excitation of 0.02 g, the harvester generates 2.48 V, 6.21 V and 1.55 V at three resonant frequencies of 18.18 Hz, 24.74 Hz and 28.12 Hz, respectively. Finally, the accuracy of derived mathematical model is verified by comparing with the predictions from finite element simulation and experimental results. The novel MSPEH offers excellent design flexibility to adjust resonant frequencies by choosing inner single branches and tip masses and thus it has potential to generate sufficient power output from wideband, low frequency and low amplitude vibration sources. This work is supported by the National Natural Science Foundation of China (Grant No 11372084) and the China Scholarship Council (Grant No 201706120082). The supports are gratefully acknowledged.

Macro fiber composite (MFC) is extensively used in vibration control and actuation applications due to its high flexibility and enhanced coupling coefficients. During these applications, MFCs are subjected to the continuous cyclic electrical loading, which may lead to the degradation in its actuation performance. In order to predict the life cycle of MFCs, an experimental setup has been devised and experiments are performed under cyclic loading condition. Efforts involved in the experiments are huge in terms of time and cost. Hence, an attempt has been made to develop a theoretical model to predict the fatigue behavior of MFCs. A nonlinear finite element method has been formulated based on Kirchhoff plate theory wherein the fatigue failure criterion based on strain energy is embedded. Simulated results based on the proposed model is compared with experimental observation and are in good agreement with each other. Variation in the life cycle of MFCs are also studied for different operating temperatures as well as structural/geometric configurations.

The number of applications of Lamb waves (LWs) based structural health monitoring (SHM) has significantly increased in recent decades. The growth of interest results from several advantages of this diagnostic technique, that is, considerable mode selectivity and directivity that allow for the assessment of the technical condition of a monitored structure. Successful applications of LWs in the field of SHM stimulate continuous improvement of the transducers' design to enable capturing more reliable diagnostic data. The paper introduces a new type of transducer that may be used in the LWs based SHM systems, namely tunable-interdigital transducer (T-IDT) based on macro-fiber composites (MFC). The authors provide a short overview on different types of transducers that may be used in SHM applications, followed by a detailed description of the structure of proposed T-IDT. Finally, the results of numerical and experimental tests carried out employing the proposed transducer are discussed and compared to those obtained with a traditional IDT.