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DESIGN & PRODUCTS EnErgy harvEsting ators. the company has the know-how to bond PMn-Pt single crystals onto silicon wafers and then micro-machine them into resonating structures of appropriate thicknesses (down to 15 microns), in effect, designing what it calls piezoelectric micro- machined ultrasonic transducers (P-Mut). The efficiency of PMN-PT vibrational energy harvesters is about seven times that of PZt-based devices, highlighted lee. iBule Photonics has built up prototypes of monolayer acoustic generators ar- rays measuring 30x30mm, featuring arrangements of 10x10 microgenerator cells each 2.5mm in diameter and only 0.01mm thin – see figure 4. With 15mWh delivered Fig. 5: AIST’s thermoelectric conversion film devices fabricat- by each cell at a sound ed by stencil printing yields a fully flexible prototype. pressure of 1Pa at 12.5kHz, Fig. 4: One of iBULe Photonics’ the whole array could yield microgenerator cells, 2.5mm in up to 1500mWh of usable diameter and only 0.01mm thin. power. the company is also looking at superposing several such arrays to increase power output. Future developments include the use of PMN-PT/epoxy piezocomposite materials to build up 3-dimensional energy har- vesting structures and the use of thin-film batteries for energy storage on the same device. a researcher at the national institute of advanced industrial science and technology (aist) from Japan, Kouji suemori pre- sented new materials printable into thermoelectric conversion devices. unlike many competing thermoelectric materials, the Fig. 6: A flexible thermoelectric conversion film generating carbon nanotube-polymer composite developed by the aist power through the temperature difference created by a hand does not contain rare metals such as Bi and te. on the film installed on a 10 °C plate generated 108.9mV. the composite is mixed mechanically at a nanometer-level with a resin matrix in an inking solvent and can then be printed Taking a look at everything thin, Wibicom should be cited onto flexible substrates such as plastic films and papers. Add- for its innovative approach to antenna design, directly powered ing drying and sintering steps, this process enables the manu- by dye sensitised cells fabricated on top of an antenna foil. facture of thermoelectric conversion devices onto 20µm-thick the small technical consulting company from the netherlands substrates that conform to any shape for optimum conversion presented its WibiSol concept antenna capable of harvesting efficiency. energy from ambient light or the sun and simultaneously trans- the thermoelectric energy harvester is obtained through mitting and receiving RF signals – see figure 7. stencil printing, patterning tiny material sections between top in previous papers, the company founder & ceO Mina and bottom electrodes to form many thermoelectric cells that danesh detailed the implementation of dipole and loop anten- are connected in series – see figure 5. nas designed for 3.1 to 10.6GHz ultrawideband communica- As shown in figure 5, the researchers prototyped a flexible tions, covered with amorphous-silicon Pv cells based on thermoelectric conversion film featuring 1000 such devices in hydrogenated amorphous silicon (asi:H). the dipole antenna series, each cell measuring 0.5×0.8×0.3mm. uses two separate Pv cells measuring 20×20mm2, each having this thermoelectric conversion its own dc connections, film remained operational even connected in parallel. when bent at 5mm of curvature. the loop antenna has it has shown to be conformable five-series DC-connected to both curved and spherical sur- cells. in this case the Pv faces while being able to gener- module is 25mm wide ate power with small temperature and 110mm long with a differences. loop diameter of 36mm. this could even be used in Here again for the contin- garments for wearable power uous operation of sensor generation. as a lab experiment, nodes, the photovoltaic the temperature difference cre- energy would have to be ated by one’s hand placed on stored in supercapacitors top of the film fixed to a 10°C Fig. 7: Wibicom’s photovoltaic antennas for UWB or in thin-film recharge- plate generated 108.9mv - see able batteries. transceivers. (a) Dipole antenna. (b) Loop antenna. figure 6. 20 Electronic Engineering Times Europe September 2012 www.electronics-eetimes.com


EETE SEPTEMBER 2012
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