What makes these small electronic bugs from the likes of Dust, Crossbow Technology and Ember so compelling is that they’re projected to be very inexpensive. Second, they only turn on when activated by stimuli like movement or temperature or when another mote sends a signal. Knowing how to sleep is part of the reason these miniature machines can live much longer than other battery-powered devices.
But longer does not mean forever and motes face battery-life challenges of their own. Swapping out batteries is still not desirable (or practical) for customers, especially, say, on an oil platform in the middle of the ocean.
That’s where PowerMEMS Technologies fits into the picture. The company has developed what it calls a 3-Dimensional Ambient Energy Harvester for extending the battery life of motes. The Harvester, which looks like a layer cake, has three stacks–solar, kinetic and temperature–to generate a trickle of electricity to extend the battery life. PowerMEMS is making its micropower-generation devices using MEMS fabrication techniques.
The average power dissipation for motes is roughly three to five milliwatts a day, which means a lithium ion battery lasts 20 days and a lithium metal battery goes for 80 days. But the goal is five-year battery life, so there’s plenty of room for improvement. Here’s how the PowerMEMS approach works.
The trick the company has seemingly solved is matching the vibration frequency of a buzzing environment with that of a Piezo generator. The team, led by Dr. Don Murphy, a former Bell Labs researcher who was director of applied materials research, decided against a cantilever system in favor of its proprietary design, which yields a 32-times power increase over the cantilever scheme.
To use heat to recharge the battery, PowerMEMs has a thermo-activation engine that employs ferromagnetic material membrane. By suspending the heat and cold source in a kind of trampoline construction between a set of magnets, the spring action of up and down driven by temperature generates current.
The company is currently at work on the third generation of its prototype. It’s been granted $5 million from the Office of Naval Research for its work, in conjunction with UCLA and Livermore National Labs. The company is in the process of raising its first venture round of $10 million series A financing. –Lee Bruno