PULLMAN, Wash. — Researchers at Washington State University have built the world’s smallest engine, an innovation with the potential to replace batteries in many portable electronics.
The researchers in the WSU School of Mechanical and Materials Engineering and the Center for Materials Research have received a more than $7 million contract from the Army Space & Missile Defense Command (SMDC) together with sponsorship by the Defense Advanced Research Projects Agency (DARPA) to build the engine and produce a portable micro-power generation system for military applications.
The engine, dubbed the P3, for Palouse Piezoelectric Power, is radically different in design, fabrication and operation from any existing engine. The engine fits inside the hole of a Lifesaver and is thinner than a piece of paper. Other researchers have tried to shrink large-scale internal combustion engines down to smaller sizes. The P3 is the result of a focused effort by the WSU team to entirely rethink the concept of an engine on the micro-scale.
Instead of a machine shop this engine is manufactured in a clean room, in which contaminants such as dust are reduced to create a more sterile environment. The engine 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 may be made in a single batch fabrication process.
With more portable electronics, batteries have become increasingly problematic because they weigh a lot for the power they produce, researchers said. The military has struggled with this problem. A light infantryman, for instance, is required to carry a nearly 80-pound pack in the field, with 10 pounds of that consisting of batteries to power electronics. Remote-controlled airplanes and robots are limited, too, by the heavy battery packs they have to carry. The logistics of recharging batteries also can be difficult.
Each engine can work on its own or be combined with other engines providing great flexibility in choosing the 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 micro engine can be reconfigured on demand to meet the needs of many applications. Effectively the P3 is the integrated circuit of engines. Just as Intel puts thousands of circuits on a chip, the WSU team aims to build multitudes of engines together to offer users power by design.
The P3 micro-heat engine also provides flexibility 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. For example, the P3 micro engine could produce electricity from the hot surface of a computer case or an exhaust pipe, researchers said.
This new type of heat engine converts thermal power to mechanical power through the use of a novel thermodynamic cycle that approaches the Carnot cycle, which gives the potential for high efficiencies. Mechanical power is converted to electrical power through the use of a thin-film piezoelectric generator.
The engine consists of a cylinder filled with a bubble and fluid sealed at the top and bottom by thin membranes. One membrane is a thin film piezoelectric membrane generator. As heat moves into and then out of the cylinder, the size of the bubble grows and shrinks, pushing on the piezoelectric generator. The piezoelectric membrane generates electrical charge as it flexes. By combining advanced materials, engineering, and design, the WSU team has developed a totally unique engine.
Because of the potential for this device, the WSU Research Foundation has filed for patent protection for the device developed by the researchers, David Bahr, Bob Richards and Cecilia Richards. The researchers are continuing with testing the first prototypes.