This paper presents, for the first time, a coupled piezoelectric-circuit finite element model (CPC-FEM) to analyze the power output of a vibration-based piezoelectric energy-harvesting device (EHD) ...when it is connected to a load resistor. Special focus is given to the effect of the load resistor value on the vibrational amplitude of the piezoelectric EHD, and thus on the current, voltage, and power generated by the device, which are normally assumed to be independent of the load resistor value to reduce the complexity of modeling and simulation. The presented CPC-FEM uses a cantilever with a sandwich structure and a seismic mass attached to the tip to study the following characteristics of the EHD as a result of changing the load resistor value: 1) the electric outputs: the current through and voltage across the load resistor; 2) the power dissipated by the load resistor; 3) the displacement amplitude of the tip of the cantilever; and 4) the shift in the resonant frequency of the device. It is found that these characteristics of the EHD have a significant dependence on the load resistor value, rather than being independent of it as is assumed in most literature. The CPC-FEM is capable of predicting the generated output power of the EHD with different load resistor values while simultaneously calculating the effect of the load resistor value on the displacement amplitude of the tip of the cantilever. This makes the CPC-FEM invaluable for validating the performance of a designed EHD before it is fabricated and tested, thereby reducing the recurring costs associated with repeat fabrication and trials. In addition, the proposed CPC-FEM can also be used for producing an optimized design for maximum power output.
Intensive research on energy harvesting powered wireless sensor nodes (WSNs) has been driven by the needs of reducing the power consumption by the WSNs and increasing the power generated by energy ...harvesters. The mismatch between the energy generated by the harvesters and the energy demanded by the WSNs is always a bottleneck as the ambient environmental energy is limited and time varying. This paper introduces a combined energy-aware interface with an energy-aware program to deal with the mismatch through managing the energy flow from the energy storage capacitor to the WSNs. These two energy-aware approaches were implemented in a custom developed vibration energy harvesting powered WSN. The experimental results show that, with the 3.2-mW power generated by a piezoelectric energy harvester under an emulated aircraft wing strain loading of 600 με at 10 Hz, the combined energy-aware approaches enable the WSN to have a significantly reduced sleep current from 28.3 μA of a commercial WSN to 0.95 μA and enable the WSN operations for a long active time of about 1.15 s in every 7.79 s to sample and transmit a large number of data (388 B), rather than a few ten milliseconds and a few bytes, as demanded by vibration measurement. When the approach was not used, the same amount of energy harvested was not able to power the WSN to start, not mentioning to enabling the WSN operation, which highlighted the importance and the value of the energy-aware approaches in enabling energy harvesting powered WSN operation successfully.
Wearable medical and electronic devices demand a similarly wearable electrical power supply. Human-based piezoelectric energy harvesters may be the solution, but the mismatch between the typical ...frequencies of human activities and the optimal operating frequencies of piezoelectric generators calls for the implementation of a frequency up-conversion technique. A rotary piezoelectric energy harvester designed to be attached to the knee-joint is here implemented and characterized. The wearable harvester is based on the plucking method of frequency up-conversion, where a piezoelectric bimorph is deflected by a plectrum and permitted to vibrate unhindered upon release. Experiments were conducted to characterize the energy produced by the rotary piezoelectric energy harvester with different electric loads and different excitation speeds, covering the range between 0.1 and 1 rev s−1 to simulate human gait speeds. The electrical loads were connected to the generator either directly or through a rectifying bridge, as would be found in most power management circuits. The focus of the paper is to study the capability of energy generation of the harvester for knee-joint wearable applications, and study the effects of the different loads and different excitation speeds. It is found that the energy harvested is around 160-490 µJ and strongly depends on the angular speed, the connected electric loads and also the manufacturing quality of the harvester. Statistical analysis is used to predict the potential energy production of a harvester manufactured to tighter tolerances than the one presented here.
This letter presents a piezoelectric bimorph with auxetic (negative Poisson’s ratio) behaviors for increased power output in vibration energy harvesting. The piezoelectric bimorph comprises a 2D ...auxetic substrate sandwiched between two piezoelectric layers. The auxetic substrate is capable of introducing auxetic behaviors and thus increasing the transverse stress in the piezoelectric layers when the bimorph is subjected to a longitudinal stretching load. As a result, both 31- and 32-modes are simultaneously exploited to generate electric power, leading to an increased power output. The increasing power output principle was theoretically analyzed and verified by finite element (FE) modelling. The FE modelling results showed that the auxetic substrate can increase the transverse stress of a bimorph by 16.7 times. The average power generated by the auxetic bimorph is 2.76 times of that generated by a conventional bimorph.
In this study, we investigate a delayed reaction-diffusion predator-prey system with the effect of toxins. We first investigate whether the internal equilibrium exists. We then provide certain ...requirements for the presence of Turing and Hopf bifurcations by examining the corresponding characteristic equation. We also study Turing-Hopf and Hopf bifurcations brought on by delays. Finally, numerical simulations that exemplify our theoretical findings are provided. The quantitatively obtained properties are in good agreement with the findings that the theory had predicted. The effects of toxins on the system are substantial, according to theoretical and numerical calculations.
•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.
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.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPUK, ZRSKP
Predictive industrial maintenance promotes proactive scheduling of maintenance to minimize unexpected device anomalies/faults. Almost all current predictive industrial maintenance techniques ...construct a model based on prior knowledge or data at build-time. However, anomalies/faults will propagate among sensors and devices along correlations hidden among sensors. These correlations can facilitate maintenance. This paper makes an attempt on predicting the anomaly/fault propagation to perform predictive industrial maintenance by considering the correlations among faults. The main challenge is that an anomaly/fault may propagate in multiple ways owing to various correlations. This is called as the uncertainty of anomaly/fault propagation. This present paper proposes a correlation-based event routing approach for predictive industrial maintenance by improving our previous works. Our previous works mapped physical sensors into a soft-ware-defined abstraction, called proactive data service. In the service model, anomalies/faults are encapsulated into events. We also proposed a service hyperlink model to encapsulate the correlations among anomalies/faults. This paper maps the anomalies/faults propagation into event routing and proposes a heuristic algorithm based on service hyperlinks to route events among services. The experiment results show that, our approach can reach 100% precision and 88.89% recall at most.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The capability of monitoring the differentiation process in living stem cells is crucial to the understanding of stem cell biology and the practical application of stem-cell-based therapies, yet ...conventional methods for the analysis of biomarkers related to differentiation require a large number of cells as well as cell lysis. Such requirements lead to the unavoidable loss of cell sources and preclude real-time monitoring of cellular events. In this work, we report the detection of microRNAs (miRNAs) in living human mesenchymal stem cells (hMSCs) by using polydopamine-coated gold nanoparticles (Au@PDA NPs). The PDA shell facilitates the immobilization of fluorescently labeled hairpin DNA strands (hpDNAs) that can recognize specific miRNA targets. The gold core and PDA shell quench the fluorescence of the immobilized hpDNAs, and subsequent binding of the hpDNAs to the target miRNAs leads to their dissociation from Au@PDA NPs and the recovery of fluorescence signals. Remarkably, these Au@PDA–hpDNA nanoprobes can naturally enter stem cells, which are known for their poor transfection efficiency, without the aid of transfection agents. Upon cellular uptake of these nanoprobes, we observe intense and time-dependent fluorescence responses from two important osteogenic marker miRNAs, namely, miR-29b and miR-31, only in hMSCs undergoing osteogenic differentiation and living primary osteoblasts but not in undifferentiated hMSCs and 3T3 fibroblasts. Strikingly, our nanoprobes can afford long-term tracking of miRNAs (5 days) in the differentiating hMSCs without the need of continuously replenishing cell culture medium with fresh nanoprobes. Our results demonstrate the capability of our Au@PDA–hpDNA nanoprobes for monitoring the differentiation status of hMSCs (i.e., differentiating versus undifferentiated) via the detection of specific miRNAs in living stem cells. Our nanoprobes show great promise in the investigation of the long-term dynamics of stem cell differentiation, identification and isolation of specific cell types, and high-throughput drug screening.
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IJS, KILJ, NUK, PNG, UL, UM
The modification of methyltransferase-like (METTL) enzymes plays important roles in various cellular responses by regulating microRNA expression. However, how m6A modification is involved in stress ...granule (SG) formation in the early stage of acute ischemic stroke by affecting the biogenesis processing of microRNAs remains unclear. Here, we established a middle cerebral artery occlusion (MCAO) model in rats and an oxygen-glucose deprivation/reperfusion (OGD/R) model in primary cortical neurons and PC12 cells to explore the potential mechanism between m6A modification and SG formation. The in vivo results showed that the level of infarction and apoptosis increased while SG formation decreased significantly within the ischemic cortex with improved reperfusion time after 2 h of ischemia. Consistent with the in vivo data, an inverse association between the apoptosis level and SG formation was observed in PC12 cells during the reperfusion period after 6 h of OGD stimulation. Both in vivo and in vitro results showed that the expression of METTL3 protein, m6A and miR-335 was significantly decreased with the reperfusion period. Overexpression of the METTL3 and METTL3 gene-knockdown in PC12 cells were achieved via plasmid transfection and CRISPR-Cas9 technology, respectively. Overexpression or knockdown of METTL3 in oxygen-glucose deprivation of PC12 cells resulted in functional maturation of miR-335, SG formation and apoptosis levels. In addition, we found that miR-335 enhanced SG formation through degradation of the mRNA of the eukaryotic translation termination factor (Erf1). In conclusion, we found that METTL3-mediated m6A methylation increases the maturation of miR-335, which promotes SG formation and reduces the apoptosis level of injury neurons and cells, and provides a potential therapeutic strategy for AIS.
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