Amit Lal envisions a day when tiny wireless sensor networks will be placed throughout the world in areas that can help save lives, prevent disasters, and even help sustain the environment, with a battery-free power supply that will last 100 years. Lal explained how the work of his group could help make that happen in his MOEMS/MEMS Symposium plenary talk, "Microsystem Pathways to a Greener World," Monday morning at SPIE Photonics West. Lal, an associate professor in the school of electrical and computer engineering at Cornell University, and his group have been working for over six years on self-powered sensor networks. Advances in MEMS (microelectromechanical systems) -based power sources could lead to greener power sources, with micro power harvesters that can harness power from vibration, radioisotopes, light, and sound, perhaps even eliminating the need for batteries in sensor nodes. In his talk, Lal explained that a big problem with sensor networks today is the cost of ownership and the need for someone to take responsibility for replacing the batteries in the systems on a regular basis. His group aims to eliminate the need for batteries through the use of the smallest power source available -- a radioactive atom. They harness the power that is released when an unstable radioactive isotope, nickel-63, decays into copper. Thin films of the decaying radioactive material are placed on substrates that radiate electrons onto a microcantilever. Electricity is generated by the energy produced by the microcantilever as it is charged by electrons and is pulled down, then springs back via electrostatic force. His group has achieved a 5-W pulse for 30 nanoseconds, he said. Lal said they use Ni63 because it has a half-life of 100 years in a direct charge configuration. Because radioactive decay is temperature independent, low and high temperature operation is possible, and post-CMOS integration is also possible, Lal said. Sensors using these radioisotopes could be collected and reused for more short-term applications, he said. The goal is to create power sources that can operate over a wide temperature range, for extended periods of time with high reliability. But one problem is that radioisotopes are expensive. "This won't be commercialized if you have to use a lot of it," Lal said. Lal's group also recently developed a self-powered radio frequency transponder (RFID) that allows a sensor mode at a fixed frequency, but the issue is that a long-term vacuum is required so they continue to work on improving packaging. He also discussed a solar energy harvesting project that his group started working on recently that involves using radioisotopes to combine photolithography with e-beam lithography to create large area arrays of MEMS mirrors for concentrated solar power. For more information, visit: www.spie.org See also our Photonics West coverage page Posted by Melinda Rose, Senior Editor