Evaluation and validation of equivalent properties of macro fibre composites for piezoelectric transducer modelling

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordPiezoelectric 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 d31 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 με/V, which is close to the manufacturer specificationThe authors gratefully acknowledge financial support from the Engineering and Physical Sciences Research Council (EPSRC) in the UK through funding of the research into ‘En-ComE-Energy Harvesting Powered Wireless Monitoring Systems Based on Integrated Smart Composite Structures and Energy-aware Architecture’ (EP/K020331/1)

Silicon nanowire arrays for thermoelectric power harvesting

Numerous types of thermoelectric materials with best thermoelectric performances have been explored such as bismuth-telluride (Bi2Te3), which is the most commonly found in the market, has a figure-of-merit close to one. However, due to limited sources, highly toxic and expensive, the application of one-dimensional nanomaterial is proposed in thermoelectric micro-energy harvesting, which has been predicted to show improvement in thermoelectric properties. Use of Silicon Nanowire Arrays (SiNWA) as thermoelectric material was reported to reduce thermal conductivity, κ, by a hundredfold compared to bulk Silicon (Si). The properties such as heat flow, temperature difference, ΔT between hot and cold junctions and Seebeck voltage, Voc were evaluated concurrently for different lengths of p- and n-type SiNWA. This thesis reports the performance of SiNWA with two different lengths, 30 μm and 50 μm, on both p- and n-type Si for thermoelectric energy harvesting, and followed by comparing the recorded performance to its bulk Si. A simple and cost-effective technique, metal-assisted chemical etching (MACE), was used to fabricate SiNWA and the nanowires lengths were characterized. An increase in thermal resistance reduces κ for Si, which is advantageous for a thermoelectric material. In this work, heat flow was noticeably decreased in SiNWA samples, resulting in a higher ΔT and Voc than in bulk Si. A larger ΔT between junctions is also attainable in SiNWA by increasing nanowires length. The results have shown that both p- and n-type SiNWA samples (50 μm) have achieved 95 % and 96 % increases in ΔT, respectively, relative to bulk Si samples. In addition, as the length of nanowires increased, a longer time was required to reach a steady value of ΔT. The reduction on approximation values of κ by a hundred-fold which increases thermal resistance as well as Seebeck coefficient, S in the SiNWA samples. Improvement in SiNWA thermoelectric properties will expands the application of SiNWA thermoelectric micro-energy harvesters in various fields such as bio-medical, telecommunication, wireless technologies and others

Energy savvy network joining strategies for energy harvesting powered TSCH nodes

This is the author accepted manuscript. The final version is available from IEEE via the DOI in this recordThis paper presents methods that enable batteryless energy harvesting powered Time Synchronized Channel Hopping (TSCH) wireless sensor nodes to join a network with less energy wastage. Network joining of TSCH nodes is a very power hungry yet inevitable process to form a working wireless sensor network (WSN). Since the energy level from energy harvesting is scarce, energy passive methods are essential. A duty-cycled network joining process in combination with an appropriate capacitor size is proposed here as they are among the factors that can be easily controlled without extra energy. When a node joins the network in a duty-cycled manner, other nodes may join the network during the gap time, which reduces energy wastage of the nodes in waiting. With an appropriate capacitor size, the capacitor can be charged up within a reasonable time and power up the node for a sufficiently long time, which increases the probability to complete the network joining process of the node. With the combination of a join duty cycle of 50% with a 100 mF capacitor, a WSN was successfully formed by two energy harvesting powered wireless sensor nodes in one network joining attempt.Engineering and Physical Sciences Research Council (EPSRC

Self-powered and Self-configurable Active Rectifier Using Low Voltage Controller for Wide Output Range Energy Harvesters

This is the author accepted manuscript. The final version is available from IEEE via the DOI in this recordData availability: All data are provided in full in the results section of this paper.This paper presents a self-configurable and selfpowered active rectifier that operates from 0.25–20 V for energy harvesting applications. The proposed circuit self-startups from a low voltage using a charge pump and amplifies the voltage with a voltage doubler (VD) topology to provide succeeding circuits such as boost converters with a higher voltage. When the voltage of the energy harvester reaches a high threshold, the circuit switches its topology to a full-wave rectifier (FR) that does not amplify the voltage. The start-up circuit can limit its voltage intake to prevent boosting the high voltage, which may damage the whole circuit. Comparators with a maximum operating voltage of 5.5 V used in the implementation of the rectifier are protected by a diode and resistor based circuit. A piezoelectric energy harvester (PEH) that has a wide open-circuit voltage of 0.4–15 V under the acceleration of 0.04–0.3 g was used to test the circuit. The experiment results showed the rectifier can startup from 0.25 V and switch its topology according to the PEH voltage. The voltage and power conversion efficiencies are over 90% in most cases.Engineering and Physical Sciences Research Council (EPSRC)Royal Societ

Single piezoelectric transducer as strain sensor and energy harvester using time-multiplexing operation

International audienceThis 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

Energy-aware Approaches for Energy Harvesting Powered Wireless Sensor Systems

Energy harvesting (EH) powered wireless sensor systems (WSSs) are gaining increasing popularity since they enable the system to be self-powering, long-lasting, almost maintenance-free, and environmentally friendly. However, the mismatch between energy generated by harvesters and energy demanded by WSS to perform the required tasks is always a bottleneck as the ambient environmental energy is limited, and the WSS is power hunger. Therefore, the thesis has proposed, designed, implemented, and tested the energy-aware approaches for wireless sensor motes (WSMs) and wireless sensor networks (WSNs), including hardware energy-aware interface (EAI), software EAI, sensing EAI and network energy-aware approaches to address this mismatch. The main contributions of this thesis to the research community are designing the energy-aware approaches for EH Powered WSMs and WSNs which enables a >30 times reduction in sleep power consumption of WSNs for successful EH powering WSNs without a start-up issue in the condition of mismatch between the energy generated by harvesters and energy demanded by WSSs in both mote and network systems. For EH powered WSM systems, the energy-aware approaches have (1) enabled the harvested energy to be accumulated in energy storage devices to deal with the mismatch for the operation of the WSMs without the start-up issue, (2) enabled a commercial available WSMs with a reduced sleep current from 28.3 μA to 0.95 μA for the developed WSM, (3) thus enabled the WSM 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 (e.g., 388 bytes), rather than a few ten milliseconds and a few bytes. For EH powered WSN systems, on top of energy-aware approached for EH powered WSM, the network energy-aware approaches have presented additional capabilities for network joining process for energy-saving and enabled EH powered WSNs. Once the EH powered WSM with the network energy-aware approach is powered up and began the network joining process, energy, as an example of 48.23 mJ for a tested case, has been saved in the case of the attempt to join the network unsuccessfully. Once the EH-WSM has joined the network successfully, the smart programme applications that incorporate the software EAI, sensing EAI and hardware EAI allow the EH powered WSM to achieve (4) asynchronous operation or (5) synchronised operation based on the energy available after the WSM has joined the network.Through designs, implementations, and analyses, it has been shown that the developed energy-aware approaches have provided an enabled capability for EH successfully powering WSS technologies in the condition of energy mismatch, and it has the potential to be used for wide industrial applications