An investigation of PDMS structures for optimized ferroelectret performance

This paper reports the ANSYS simulation and fabrication processes for optimising PDMS ferroelectret performance. The proposed model extends the previously published analytical models and compares this with simulation of individual void geometry. The ferroelectret material is fabricated from PDMS using 3D-printed plastic moulds. The analytical model and Ansys simulation results predict the variation in performance of the PDMS ferroelectret with the different void geometry and surface charge density. The theoretical maximum piezoelectric coefficient d33 achieved was about 220 pC/N. The experimental maximum d33 obtained was 172 pC/N

Kinetic energy harvesting

This paper reviews kinetic energy harvesting as a potential localised power supply for wireless applications. Harvesting devices are typically implemented as resonant devices of which the power output depends upon the size of the inertial mass, the frequency and amplitude of the driving vibrations, the maximum available mass displacement and the damping. Three transduction mechanisms are currently primarily employed to convert mechanical into electrical energy: electromagnetic, piezoelectric and electrostatic. Piezoelectric and electrostatic mechanisms are best suited to small size MEMS implementations, but the power output from such devices is at present limited to a few microwatts. An electromagnetic generator implemented with discrete components has produced a power 120 ?W with the highest recorded efficiency to date of 51% for a device of this size reported to date. The packaged device is 0.8 cm3 and weighs 1.6 grams. The suitability of the technology in space applications will be determined by the nature of the available kinetic energy and the required level of output power. A radioactively coupled device may present an opportunity where suitable vibrations do not exist

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

A new 2-D model of a thin annular disk using a modified assumption

The work describes an improved 2-D model for a thin annulus by using a modified assumption with regard to coupled vibration. With this approach, the impedance spectrum and displacements due to radial modes, both in radial and thickness direction of a thin ring, are obtained. Bending displacement is investigated by finite element analysis (FEA) and matches our model. The bending in the thickness direction is coupled to radial modes and shows several node circles in the high radial overtone frequency range. The model is validated by FEA with excellent agreement between the new theory and FEA result

Screen printed flexible Bi2Te3-Sb2Te3 based thermoelectric generator

This paper reports the fabrication and testing of Bismuth Tellurium (Bi2Te3) – Antimony Tellurium (Sb2Te3) based thermocouples using screen printing technology. In this study, screen printable thermoelectric pastes were developed and the transport properties of cured material were measured. The dimension of each planer thermoleg is 39.3 mm × 3 mm with a thickness of 67 µm for Bi2Te3 leg and 62 µm for Sb2Te3 leg. A single thermocouple with this dimension can generate a voltage of 6 mV and a peak output power of 48 nW at a temperature difference of 20°C. The calculated Seebeck coefficient of a single thermocouple is in the range of 262 to 282 µV/K. The Seebeck coefficient at room temperature were measured to be -134 to -119 µV/K and 128 to 134 µV/K for Bi2Te3 and Sb2Te3 respectively. This work demonstrates that the low-cost screen printing technology and low-temperature materials are promising for the fabrication of flexible thermoelectric generators (TEGs)

Improving the dielectric and piezoelectric properties of screen-printed low temperature PZT/polymer composite using cold isostatic pressing

This paper reports an improvement in dielectric and piezoelectric properties of screen-printed PZT/polymer films for flexible electronics applications using Cold Isostatic Pressing (CIP). The investigation involved half and fully cured PZT/polymer composite pastes with weight ratio of 12:1 to investigate the effect of the CIP process on the piezoelectric and dielectric properties. It was observed that the highest dielectric and piezoelectric properties are achieved at pressures of 5 and 10 MPa for half and fully cured films respectively. The relative dielectric constants were 300 and 245 measured at 1 kHz for the half and fully cured samples. Using unoptimised poling conditions, the initial d33 values were 30 and 35 pC/N for the half and fully cured films, respectively. The fully cured sample was then poled using optimized conditions and demonstrated a d33 of approximately 44 pC/N which is an increase of 7% compared with non-CIP processed material

Fully spray-coated organic solar cells on woven polyester cotton fabric for wearable energy harvesting applications

This paper presents the novel use of spray coating to fabricate organic solar cells on fabrics for wearable energy harvesting applications. The surface roughness of standard woven 65/35 polyester cotton fabric used in this work is of the order of 150 µm and this is reduced to few microns by a screen printed interface layer. This pre-treated fabric substrate with reduced surface roughness was used as the target substrate for the spray coated fabric organic solar cells that contains multiple layers of electrodes and active materials. A fully spray coated photovoltaic (PV) devices fabricated on fabric substrates has been successfully demonstrated with comparable power conversion efficiency to the glass based counterparts. All PV devices are characterised under simulated AM 1.5 conditions. Device morphologies were examined by scanning electron microscopy (SEM). This approach is potentially suitable for the low cost integration of PV devices into clothing and other decorative textilesThis work was supported by Sensor Platform for HEalthcare in a Residential Environment (SPHERE) project (EP/K031910/1). Professor S. P. Beeby acknowledges EPSRC support through his Fellowship ‘Energy Harvesting Materials for Smart Fabrics and Interactive Textiles’ (EP/I005323/1). Professor P. J. Skabara thanks the Royal Society for a Wolfson Research Merit Award

Feasibility of vibration energy harvesting powered wireless tracking of falcons in flight

The use of wireless tagging of birds has been widely used for monitoring or tracking purposes. This include over 10 thousand wireless tracking devices currently used by the UK falconers alone. However, due to the concern of not burdening the birds with a heavy battery, the existing lightweight telemetry tracking systems can only last for days, if not hours. Falcons can have top flight speeds in excess of a hundred miles an hour, which makes it a near impossible task to track a missing falcon after the battery has been depleted. This paper investigates the feasibility of incorporating a piezoelectric vibration energy harvesting system to act as a secondary power source for the wireless tracking of falcons. The ultimate aim is to both extend the primary battery life and enable periodic burst transmissions of telemetry after the depletion of the primary battery. The presented tracking and harvesting system is lightweight and has been field trialled on a gyrfalcon at the Chester Cathedral Falconry

Magnetically Levitated Autoparametric Broadband Vibration Energy Harvesting

Some of the lingering challenges within the current paradigm of vibration energy harvesting (VEH) involve narrow operational frequency range and the inevitable non-resonant response from broadband noise excitations. Such VEHs are only suitable for limited applications with fixed sinusoidal vibration, and fail to capture a large spectrum of the real world vibration. Various arraying designs, frequency tuning schemes and nonlinear vibratory approaches have only yielded modest enhancements. To fundamentally address this, the paper proposes and explores the potentials in using highly nonlinear magnetic spring force to activate an autoparametric oscillator, in order to realize an inherently broadband resonant system. Analytical and numerical modelling illustrate that high spring nonlinearity derived from magnetic levitation helps to promote the 2:1 internal frequency matching required to activate parametric resonance. At the right internal parameters, the resulting system can intrinsically exhibit semi-resonant response regardless of the bandwidth of the input vibration, including broadband white noise excitation