018-019-020_EETE

EETE SEPTEMBER 2012

DESIGN & PRODUCTS EnErgy harvEsting Energy harvesters: a thin film approach By Julien Happich during idtecHex’last energy Harvesting and stor- age europe conference held in Berlin, thin piezoelectric and low foot-print thermoelectric materials were cited in many new energy harvesting research programs and design implementa- tions. the ultimate goal, as for many electronic applications, is to replace bulky energy harvesting units by lower cost and conformable film-like solutions that are easier to integrate or to wear. Michele guizzetti, erling ringgaard and tomasz Zawada from Meggitt sensing systems presented their use of lead Zirconate Titanate (PZT) piezoelectric thick films for energy harvesting through the conversion of kinetic energy into electrical energy. the conversion is done through the vibration of a cantilever beam covered with piezoelectric material. Fig. 1: Meggitt’s clamped cantilever device showing a silicon the stress induced by the vibrations (kinetic energy) creates proof mass at the free end of the cantilever. the electrical charges which are harvested as a micro-current. after studying the optimal design of a piezoelectric bending structure where the neutral bending axis should be located at dr. venkatesh sivasubra- the interface between the PZt materials and the passive (si) maniam from swiss-based materials, the team established that for the typical device layer company algra showcased a thickness of the silicon on insulator (soi) wafer being used (20 wireless piezoelectric switch μm), a layer of 30 to 40 μm of active PZT material should be for handheld or wall-mounted used. applications. commercialized Meggitt sensing system implements this through its pro- as Dynapic Wireless, the low prietary thick film InSensor technology, screen-printing and actuation force (5n) switch integrating piezoelectric layers from 10 to 100 µm in thickness relies on a simple piezoelectric Fig. 2: A wafer showing with a surface resolution of 100x100µm. dispersed in an organic membrane sandwiched be- several piezoelectric bending vehicle, the piezoelectric material can be screen-printed on a tween an overlaid electrode, structures. number of substrates that are compatible with MeMs manu- a spacer defining the actua- facture for the design of the bending structures. using silicon tion displacement and a thin PcB on which the electronics is micromachining and screen-printing techniques, the research- assembled. ers developed single clamped cantilever devices measuring the circuitry includes a custom power management asic, 10x10mm2, featuring a silicon proof mass at the free end of the a low power Mcu and an rF transceiver capable of running cantilever – see figure 1 and 2. standard low-power wireless protocols. the switches have been they tried various cantilever shapes and mass-beam length tested to over 10 million cycles, a longevity that is due to the ratios (MBR) in both unimorph and bimorph configurations. low homogeneous stress level applied to the circular piezoelec- designed in cooperation with the department of micro and tric membrane, claims the company. as well as its noise-free nanotechnology of the techni- switch, Algra discussed flexible cal university of denmark (dtu piezoelectric polymer composite nanotech), the devices yielded a sensor foils – see figure 3. Instead charge sensitivity up to 37nC/g of a sintered piezoelectric disc, at 0.5 g peak, delivering up to algra’s dynasim foils feature a 4V at 0.5 g peak for the bimorph screen printable piezoelectric device, generating 15 to 20μW of lacquer built up on electrode ma- power at moderate accelerations terial using a roll-to-roll thick film of about 0.5 g. deposition technique. to be used the team demonstrated that in flexural mode, the foil could the bandwidth of these micro- deliver enough energy to wake generators can be increased by up a microprocessor from a deep introduction of non-linear effects sleep mode. such as magnetic coupling or mechanical non-linearity. these a supplier of PMn-Pt (lead PZT thick-film micro-generators magnesium niobium-lead tita- can be used to power sensor nate) single piezoelectric crystals, nodes for energy-autonomous, iBule Photonics’ ceO sang-goo Fig. 3: Algra’s Dynasim foils with a screen printable wireless measurement of accelera- lee presented his company’s piezoelectric lacquer can be used in flexural mode. tion and temperature. approach to acoustic micro-gener- 18 Electronic Engineering Times Europe September 2012 www.electronics-eetimes.com


EETE SEPTEMBER 2012
To see the actual publication please follow the link above