PDMS/PVA composite ferroelectret for improved energy harvesting performance

This paper address the PDMS ferroelectret discharge issue for improved long- term energy harvesting performance. The PDMS/PVA ferroelectret is fabricated using a 3D-printed plastic mould technology and a functional PVA composite layer is introduced. The PDMS/PVA composite ferroelectret achieved 80% piezoelectric coefficient d33 remaining, compared with 40% without the proposed layer over 72 hours. Further, the retained percentage of output voltage is about 73% over 72 hours

Vibration energy harvesting: fabrication, miniaturisation and applications

This paper reviews work at the University of Southampton and its spin-out company Perpetuum towards the use of vibration energy harvesting in real applications. Perpetuum have successfully demonstrated vibration-powered condition monitoring systems for rail and industrial applications. They have pursued applications were volume is not a particular constraint and therefore sufficient power can be harvested. Harvester reliability and longevity is a key requirement and this can be a challenging task in high shock environments. The University of Southampton has investigated the miniaturization of the technology. MEMS electromagnetic harvesters were found to be unsuitable although miniaturized devices fabricated using bulk components did perform well. Screen printed piezoelectric harvesters were also found to perform well and were ideally suited to a low profile application where device thickness was limited. Screen printing was not only used to deposit the active piezoelectric material but also an inertial mass ink based on tungsten. This enables the device to be printed entirely by screen printing providing a low-cost route to manufacture. Finally, details of a simulation tool that can take real world vibrations and estimate vibration energy harvester output was presented. This was used to simulate linear and nonlinear harvesters and in many applications with a characteristic resonant frequency the linear approach was found to be the optimum. Bistable nonlinear harvesters were found to work better with more random vibration source

Excursion to Stamford, Collyweston, and Ketton

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Temperature dependence of a magnetically levitated electromagnetic vibration energy harvester

 This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this record Data accessibility: All data supporting this study are openly available from the University of Southampton repository at http://dx.doi.org/10.5258/SOTON/381135.Electromagnetic vibration energy harvesters including magnetically levitated devices where opposing magnets are used to form the spring have been well documented. The strength of the magnets naturally has a large influence on the dynamic characteristics and output power of such harvesters. However, it can be affected by ambient temperatures which vary from applications to applications. This paper presents investigation into the performance of a magnetically levitated electromagnetic energy harvester under various ambient temperatures. Parameters investigated include magnetic flux density, resonant frequency, damping ratio, open circuit output voltage, velocity of the relative motion and the load resistance. Both simulation and experimental results show that these properties vary with ambient temperatures. The magnetic flux density reduces as the temperature increases which results in lower resonant frequency, lower relative velocity, lower open circuit output voltage and higher damping ratio. Varying resonant frequencies with temperature can lead to harvesters being de-tuned from the target vibration frequency. Decreasing magnetic field strength and increased damping ratios will also reduce output power even if the harvester's resonant frequency still matches the environmental vibration frequency. The power transferred to the electrical load will be reduced due to the variation in the optimal load resistance with temperature. This means the harvester is no longer matched to achieve the maximum harvested power. The specified maximum operating temperature of the magnets was found to lead to partial demagnetisation. When cycling from room to the maximum specified temperature, the magnetic field was initially found to fall but remained constant thereafter. Harvesters were found to operate beyond the specified maximum operating temperature of the magnet, but suffer from a reduced magnetic strength.Engineering and Physical Sciences Research Council (EPSRC

Closed loop frequency tuning of a vibration-based micro-generator

This paper presents a tunable electromagnetic vibration-based micro-generator with closed loop frequency tuning. Frequency tuning is realized by applying an axial tensile force to the micro-generator. A closed-loop frequency tuning system has been developed to control the tuning process so that the generator always operates at the ambient vibration frequency to make the entire process automatic. Experimentally the resonant frequency has been successfully tuned from 67.6 to 98 Hz when various axial tensile forces were applied to the structure. The generator produced a power of 61.6 to 156.6 uW over the tuning range when excited at vibrations of 0.588 m/s2

Optimization a structure of MEMS based PDMS ferroelectret for human body energy harvesting and sensing

This is the author accepted manuscript.The final version is available from IOP Publishing via the DOI in this record.A ferroelectret is typically a charge-storing cellular foam that demonstrates excellent piezoelectric properties making them potentially suitable for both sensing and energy harvesting applications. In this work we developed a numerical finite element analysis (FEA) model to describe ferroelectret materials and to further improve their piezoelectric properties. Using this FEA model, ferroelectret materials with rectangular and parallelogram void structure were designed and then fabricated by casting polydimethysiloxane (PDMS) in microfabricated silicon moulds. The piezoelectric properties and energy harvesting output of the fabricated PDMS ferroelectrets were both simulated and evaluated experimentally. For a single layer PDMS parallelogram void structure, the predicted piezoelectric coefficient d 33 from the ANSYS simulations is around 320 pC N−1. The fabricated PDMS ferroelectret has a low Young's modulus of 670 kPa and a piezoelectric coefficient of 240 pC N−1. A maximum d 33 of 520 pC N−1 was observed in a multilayer ferroelectret structure. When applying compressive forces simulating a footstep, the material demonstrated an output power of 2.73 μW when connected to a 65 MΩ resistive load

Bimetallic Pt(II)-bipyridyl-diacetylide/Ln(III) tris-diketonate adducts based on a combination of coordinate bonding and hydrogen bonding between the metal fragments: syntheses, structures and photophysical properties

The luminescent Pt(II) complex [Pt(4,4'-Bu-t(2)-bipy){CC-(5-pyrimidinyl)}(2)] (1) was prepared by coupling of [Pt(4,4'-Bu-t(2)-bipy)Cl-2] with 5-ethynyl-pyrimidine, and contains two pyrimidinyl units pendant from a Pt(H) bipyridyl diacetylide core; it shows luminescence at 520 nm which is typical of Pt(II) luminophores of this type. Reaction with [Ln(hfac)(3)(H2O)(2)] (hfac = anion of hexafluoroacetylacetone) affords as crystalline solids the compounds [1 center dot {Ln(hfac)(3)(H2O)}{Ln(hfac)(3)(H2O)(2)}] (Ln = Nd, Gd, Er, Yb), in which the {Ln(hfac)(3)(H2O)} unit is coordinated to one pyrimidine ring via an N atom, whereas the {Ln(hfac)(3)(H2O)(2)} unit is associated with two N atoms, one from each pyrimidine ring of 1, via N center dot center dot center dot HOH hydrogen-bonding interactions involving the coordinated water ligands on the lanthanide centre. Solution spectroscopic studies show that the luminescence of 1 is partly quenched on addition of [Ln(hfac)(3)(H2O)(2)] (Ln = Er, Nd) by formation of Pt(II)/Ln(III) adducts in which Pt(II)-> Ln(III) photoinduced energy-transfer occurs to the low-lying f-f levels of the Ln(Ill) centre. Significant quenching occurs with both Er(Ill) and Nd(III) because both have several f-f states which match well the (MLCT)-M-3 emission energy of 1. Time-resolved luminescence studies show that Pt(II)-Er(III) energy-transfer (7.0 x 10(7) M-1) is around three times faster than Pt(II)-> Nd(III) energy-transfer (approximate to 2 x 10(7) M-1) over the same distance because the luminescence spectrum of l overlaps better with the absorption spectrum of Er(111) than with Nd(III). In contrast Yb(111) causes no significant quenching of 1 because it has only a single f-f excited level which is a poor energy match for the Pt(II)-based excited state

A design study of a wireless power transfer system for use to transfer energy from a vibration energy harvester

A wirelessly powered remote sensor node is presented along with its design process. The purpose of the node is the further expansion of the sensing capabilities of the commercial Perpetuum system used for condition monitoring on trains and rolling stock which operates using vibration energy harvesting. Surplus harvested vibration energy is transferred wirelessly to a remote satellite sensor to allow measurements over a wider area to be made. This additional data is to be used for long term condition monitoring. Performance measurements made on the prototype remote sensor node are reported and advantages and disadvantages of using the same RF frequency for power and data transfer are identified