Batteries not included: wireless sensors harvest energy

Wireless sensor start-up GreenPeak promises you’ll never have to change a battery again. For networks that can grow to include hundreds of thousands of radio-powered sensors, that’s a big deal.

The company’s line of sensors, based on the IEEE 802.15.4 radio standard, are designed to work with various kinds of “energy harvesters.” These are well-known techniques that convert one form of energy, such as vibration or solar rays, into the tiny drip of electrical power needed to run the sensors themselves and the tiny radios that link them in an intelligent mesh. One energy harvesting technique, called piezo electricity, subjects certain materials, such as crystals, to mechanical stress in order to create an electrical current.

Wireless technology makes it possible to deploy sensor networks more easily, because it eliminates the work of running cables and power lines. But the sensors still need power, and having a battery in each device can create a massive and expensive maintenance problem, says Cees Links, founder and CEO of GreenPeak. A pilot sensor network in a British river, set up to monitor for flood conditions, would be impossible if it relied on batteries, for example.

That’s true even where batteries are designed to last five years, says Sam Lucero, an analyst with ABI Research. “Multiple sources I’ve spoken to say that there is still a desire by the end customer to reduce the need to manage the battery changing function,” he says. “At many hundreds or thousands of nodes, that could get onerous.”

Lucero says the power issue is not a critical challenge for the wireless sensor industry, but eliminating batteries is certainly a “nice to have [feature], a means for technology vendors to reduce operational complexity for the end-customer.”

To work with the energy harvesters, GreenPeak has created its own mesh protocol stack, though it also offers the standard ZigBee protocols. “The company sees no reason why energy harvesting couldn’t be used in conjunction with ZigBee and expects to have this capability eventually,” Lucero says. “They make the point that other 802.15.4 IC vendors and module providers are working in this direction and I agree with that, though I believe this is the first IEEE 802.15.4-based product with this type of capability.”

Founded in 2005 as Xandu Wireless, GreenPeak was formed to create a package of standards-based components, software and interface that would let customers quickly create and deploy large-scale wireless sensors networks. Links played a key role in early Wi-Fi products from Lucent and Agere, including the Orinoco line of 802.11 wireless LAN access points. The company is funded by a quartet of British and European venture funds.

The heart of its initial product line, called GreenPeak Lime, is an ultra low power wireless module, less than one inch square, based on the company’s own radio silicon design that minimizes power use at every point. Transmitter/receiver, antenna and power amplifier are all integrated into the package.

The mesh networking software creates a self-forming and self-healing network of devices. The software has been designed to support the still-developing ZigBee-Pro 2007 protocols, which is a ZigBee variant developed for applications that require especially high network reliability, according to Links. GreenPeak also has a ZigBee stack for customers who opt for battery-powered devices.

Among other things, the software minimizes the time the radio modules are awake, and thereby using power. A network clock synchronizes when the modules wake up to receive or send messages. If there are none, the module goes back to sleep.

Typical of GreenPeak’s approach, the company doesn’t build or design the energy harvesters. Instead, it supports interfaces to these readily available products.

There are lots of companies in the wireless sensor space, including Dust Networks, Ember and Sensicast. New entrants such as Arch Rock are introducing IPv6 protocol stacks to tie these networks into IP backbones and the Internet. But despite the acceptance of the 802.14.5 radio standard, it remains a highly fragmented market. Proprietary radios and software stacks still compete with standards-based offerings, and many vendors focus only on one or a few of the necessary elements in a final sensor network.

“We’re not a microprocessor company,” Links says. “We’re agnostic toward the underlying microprocessor. And that’s our entry point. In many applications today, Zigbee is sold with a [specific] microprocessor, and the customer has to port his app to that chip. We don’t require that.” GreenPeak is offering a starter kit, with nine wireless nodes and a gateway, along with a development tool kit. The starter kit is priced at US$1,390, the development kit at $6,900. Each Lime module is priced $21 in volumes of 100,000.

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