Thermoelectric Devices Cool, Power Electronics
- Sunday, 01 November 2009
Originating Technology/NASA Contribution
More than 10 billion miles away from Earth, a NASA spacecraft continues a journey that began in 1977. Having long since accomplished its original mission to Jupiter and Saturn, Voyager 1 is the farthest human-made object from Earth, hurtling at more than 38,000 miles per hour toward the heliopause—the very edge of the solar system.
At these extraordinary distances, the Sun’s light is too faint to power a solar panel-equipped spacecraft. In fact, the Sun does not provide a viable source of power for many NASA missions. To accommodate this need, NASA employs thermoelectric (TE) devices, which can generate electricity from temperature differentials and vice versa. In a power-generating capacity, TE devices work via the Seebeck effect, in which a circuit made from dissimilar metals creates a voltage if a temperature difference exists between its two sides. When a voltage is applied to a TE device and a current flows through it, the reverse action occurs: The electrical input creates a temperature difference, moving heat from one side of the device to the other in what is called the Peltier effect. When functioning this way, TE devices become temperature management tools, cooling or heating a surface depending on the direction of the electrical flow.
For 25 missions so far—including Apollo missions to the Moon, the Viking and Pathfinder missions to Mars, and the Voyager, Pioneer, Ulysses, Galileo, and Cassini solar system missions—radioisotope thermoelectric generators (RTGs) have powered NASA spacecraft. A solid-state technology featuring no moving parts and thus significantly reducing the possibility of failure, these TE devices provide steady, reliable supplies of power for as long as their fuel emits enough heat; powered by three RTGs each, both Voyager 1 and its sister Voyager 2 (launched the same year) are expected to continue operation until 2025, a nearly 50-year lifespan.
Engineers at NASA’s Jet Propulsion Laboratory (JPL), who built and operate the Voyager spacecraft among other deep-space missions, continue to explore the potential of thermoelectrics for providing energy and thermal management solutions for use in space. Thermoelectrics have a host of applications on Earth as well, among them semiconductor electronics, lasers, infrared sensors, air conditioners, and communication systems. In keeping with the Agency’s mission to facilitate the transfer of space technology for public benefit, JPL has partnered with a North Carolina company to share the fruits of its research.
In 2005, Dr. Jesko von Windheim and his team founded Nextreme Thermal Solutions Inc., based in Research Triangle Park, North Carolina, to commercialize thermoelectric technology acquired from RTI International, also headquartered in Research Triangle Park. Having previously licensed technology from the California Institute of Technology (Caltech) with microelectromechanical systems startup Cronos Integrated Microsystems, von Windheim was aware of JPL’s thermoelectric expertise and its expansive patent portfolio (Caltech manages JPL for NASA). He discovered a broad JPL thermoelectrics patent that complemented Nextreme’s RTI technology. In 2006, the company exclusively licensed the Caltech/JPL patent, which covers thermoelectric devices containing thermoelectric material less than 40 microns thick. The licensed technology enabled Nextreme’s development as a pioneer in solid-state thermal management for electronics and semiconductors.
“This license puts us in a strong position competitively in thin film thermoelectrics,” says Dr. Paul Magill, Nextreme’s vice president of marketing and business development.
As electronics advance, becoming faster and more powerful while at the same time smaller and more densely built, engineers are running up against a significant challenge: heat. The lack of corresponding advances in cooling techniques has become a barrier to further development in integrated circuit technologies like microprocessors, where heat buildup can affect performance and lead to device failure. The heat generated by microchips is focused in hotspots rather than uniformly distributed, making conventional thermoelectric coolers (TECs)—also referred to as bulk modules and assembled from tiny pillars of thermoelectric material—impractical options due to their relatively large size. According to Nextreme, using system cooling options like fans, heat sinks, and refrigeration to address microchip hotspots is like air conditioning an entire house just to cool an overheated element on a kitchen stove. Nextreme’s licensed NASA technology is enabling the ideal solution for this problem: thin film thermoelectrics.