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EETE MAY 2013

ENERGY HARVESTING Single-chip solar energy harvester operates wireless mesh nodes By Julien Happich At the Energy Harvesting & Storage Europe exhibition that took place around mid-April in Berlin, the organisers IDTechEx have granted Sol Chip Ltd (www.sol-chip. com) with the “Best Technical Development of Energy Harvesting” award for the single chip energy harvester it demonstrated there. The company’s so-called Everlasting Solar Battery technology was shown powering a wireless mesh network of what could be various sensors used to implement the Internet of Things, which could also find use in autonomous applications such as smart lighting control, smart water management, environmental and crop monitoring, medical, security and other uses in safety industries. The demonstration was done jointly with Virtual Extension Fig. 1: Synchronized-flooding versus multiple-hop routing networks. - www.virtual-extension.com - a company providing the networking nodes within a new networking scheme, VEmesh, operating in the ISM sub-1GHz frequency bands and based on synchronized-flooding technology – see figure 1. The technology provides true bi-directional mesh networking with space diversity and thus completely eliminates the need for routing. In such a network, all VEmesh end-nodes also act as relays, to retransmit data in order to create a mesh modular solution, hence there are no dedicated routers. This also means that the networks don’t need to have self-forming or self-healing features built-in, neither do they require any human involvement. The routers’ elimination means less communication overhead, as well as simpler and less expensive processors, while space diversity eliminates multipath effects and provides no single point of failure. Altogether, this translates into lower power requirements, which enable battery-powered applications to reliably run for many years on a single cell battery. This is where Sol Chip’s Energy Harvester comes-in. Once integrated into the nodes as suggested in the block diagram of figure 2, they eliminate the need for a replaceable battery. Sol Chip’s technology as shown in figure 3 combines a photovoltaic cell with all the components required to produce six selectable voltage levels: 0.7 volt, 1.4 volt, 2.1 volt, 2.8 volt, 4.2 volt, 8.4 volt, all in a single package measuring about 20x20mm. Each selectable voltage delivers a different current, with a maximum power output of about 8mWatt in full daylight (from 60 to 100 μWatt under typical office lighting, depending on the ambient light). The cell can also deliver several voltage and power levels simultaneously, from separate pins. Both companies expect to commercialize evaluation kits in the last quarter of this year. Before the demonstration was run on Sol Chip’s energy harvesting device, the sub-GHz mesh network had been proven based on a two-chip reference design combining Microsemi’s ZL70250 chip scale package RF transceiver (as suggested in the block diagram of figure 2) and Virtual Extension’s VE209M wireless mesh controller. Again, key to the system’s pure reliance on energy harvesting cells is the ultra-low power operation. The ZL70250 CSP operates in the unlicensed frequency bands between 795 and 965MHz and delivers a data rate of 186kbps at 2mA of current. The fully bi-directional mesh network is claimed to support an unlimited number of nodes/ hops – in the thousands, with built-in unicast and broadcast capabilities. Evaluation kits are available now from Microsemi and Virtual Extension. Fig. 2: Block diagram of the energy-harvesting VEmesh module. Fig. 3: Sol Chip’s Energy Harvester unit. 44 Electronic Engineering Times Europe May 2013 www.electronics-eetimes.com


EETE MAY 2013
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