Page 11

EETE DECEMBER 2012

of wireless link, planning to launch ultra low power, low cost integrated radio transceivers and controllers in the middle of next year, says Ceo geir Førre, both for 2.4ghz and sub 1gHz bands. it has been demonstrating low power developments systems running from energy harvesting sources from heat, solar and mechanical sources. Atmel also launched a low power Zigbee transceiver with a static consumption of just 20nA, a five-fold reduction over pre- vious devices. the transceiver uses a 1.8v supply and a 16mHz 8bit Avr controller, it features a listening receive mode of just 6mA and has 14.5mA of transmit power at +3dBm. there is also a lot of activity behind the scenes. “energy harvesting ties into wireless by not having to replace batteries,” said Mike Britchfield vice president of the industrial and instru- mentation group at Analog Devices. “we think there is going to be a drive for energy harvesting mostly with the energy storage devices and we are working on various products, mainly on the power management piece. the real issue is for someone to come up with the killer product that gives higher power output for a relatively small temperature difference.” european companies such as greenpeak and energy micro are leading the way with low power radio devices, while enocean is integrating the technologies into modules that use energy harvesting sources. As the power consumption is driven Cees Link, CEO and founder of GreenPeak Technologies down, so the lifetime from a low cost battery exceeds the life- time of the sensor, making energy harvesting unnecessary. yet “My bet is that in the next ten years there will be at least 50 for applications from the radiator to the light switch there is still Zigbee devices in the home if not 100” a key role for energy harvesting. All-carbon solar cell could shave off expensive materials from today’s photovoltaics By Julien Happich sCieNtists From stANForD UNiversity have built the first so far, one drawback of the all-carbon prototype is that it solar cell made entirely of graphene sheets and carbon nano- primarily absorbs near-infrared wavelengths of light, contribut- tubes, a promising alternative to the expensive materials used ing to a laboratory efficiency of less than 1 percent. “We clearly in photovoltaic devices today. have a long way to go on efficiency,” Bao said. “But with better materials and better processing techniques, we expect that the “Carbon has the potential to deliver high efficiency will go up quite dramatically.” performance at a low cost,” said study “roughness can short-circuit the device senior author Zhenan Bao, a professor of and make it hard to collect the current,” Bao chemical engineering at stanford. “to the said. “We have to figure out how to make best of our knowledge, this is the first dem- each layer very smooth by stacking the onstration of a working solar cell that has all nanomaterials really well.” the researchers of the components made of carbon.” are also experimenting with carbon nano- Unlike silicon-based solar cells that materials that can absorb more light in a require a lot of processing steps, the entire broader range of wavelengths, including the device can be built using simple coating visible spectrum. methods, using a photoactive layer which Due to the high stability of carbon, the absorbs sunlight sandwiched between two electrodes. ability of carbon solar cells to out-perform conventional devices For the study, Bao and her colleagues replaced the silver under extreme conditions could overcome the need for greater and ito used in conventional electrodes with graphene - sheets efficiency, though. of carbon that are one atom thick -and single-walled carbon the research was funded by the global Climate and en- nanotubes. ergy Project at Stanford and the Air Force Office for Scientific For the active layer, the scientists used material made of car- research. bon nanotubes and “buckyballs” - soccer ball-shaped carbon molecules just one nanometer in diameter. the research team source and top image of all carbon solar cell: stanford recently filed a patent for the entire device University - www.stanford.edu www.electronics-eetimes.com Electronic Engineering Times Europe December 2012 11


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