Think small. R-e-a-l s-m-a-l-l !
That’s the kind of thinking that has netted the researchers in the School of Mechanical and Materials Engineering and the Center for Materials Research a whopping $7 million in funding. The Army Space and Missile Defense Command together with sponsorship by the Defense Advanced Research Projects Agency are backing WSU researchers to build the tiniest engine possible and to produce a portable micropower generation system for military applications.
In response, researchers have built what may indeed be the world’s smallest engine. It would fit inside the hole of a lifesaver and is thinner than paper. One day, it may replace batteries in many portable electronics.
Batteries can be a problem because they weigh a lot for the power they produce. The military knows this well — infantrymen who carry an 80-pound pack in the field are toting 10 pounds of that load in batteries for electronics. Remote-controlled airplanes and robots are limited by the heavy battery packs they must carry. And the logistics of recharging batteries can be difficult.
The engine, dubbed P3, for Palouse Piezoelectric Power, is radically different in design, fabrication and operation from any existing engine. The P3 is the result of a focused effort by the WSU team to entirely rethink the concept of an engine on the microscale.
For example, this engine is manufactured in a “clean room” rather than a machine shop. It is fabricated from silicon, using the same techniques developed by the microelectronics industry. And like the integrated circuit, thousands of identical copies of the same engine can be made in a single batch-fabrication process.
Each engine can stand alone or combine with others for greater flexibility in power output. From the low-power, long-duration missions of unattended sensors to the high-power short-duration missions of micro air vehicles and robots, the P3 can be reconfigured, on demand, to meet the needs of many applications.
The P3 is flexible in the choice of fuel or energy source. The engine could run off a variety of sources, from diesel fuel to solar energy or even waste heat. It could produce electricity from the hot surface of a computer case or an exhaust pipe.
This engine converts thermal power to mechanical power through the use of a novel thermodynamic cycle that approaches the Carnot cycle, for potentially very high efficiencies. A thin-film piezoelectric generator converts mechanical power to electrical power.
The engine consists of a cylinder partially filled with a fluid — the type of which depends on the application — sealed at the top and bottom by membranes. One membrane is a thin-film piezoelectric generator. As heat moves into the cylinder, the fluid forms a bubble, which pushes on the piezoelectric membrane. As the heat drops off, the bubble diminishes, relieving the pressure. The flexing of the membrane as heat alternately increases and decreases generates electrical charge.
Because of the potential for this device, the Washington State University Research Foundation has filed for patent protection for the device developed by the researchers, David Bahr, Bob Richards, and Cecilia Richards. The researchers are testing the first prototypes.
