CRYSTAL HEAT
process doesn't just convert energy into motion, it also converts energy into heat, nearly all of which is wasted.
What if these same processes could be accomplished with less waste on the atomic scale, mimicking pistons with atoms? How could we exploit the technology?
THE ATOMIC ENGINE
Heat causes motion of the asymmetric atom (blue) in the pyroelectric crystal, which is converted to electrical power in a repeating process. (Illustration by Eric Proctor, ARL)
Back in 314 B.C., a student of Socrates described bits of sawdust that gravitated to a stone thrown into a campfire. What was an oddity then might be a solution as technology comes of age.
In 1946, more than 17,000 vacuum tubes clicked away in a crowded room and 20 seconds
later, ENIAC—the Electronic
Numerical Integrator And Computer— had calculated the trajectory of an artillery shell for the Ballistics Research Laboratory, predecessor to the U.S. Army Research Laboratory (ARL). Attendees got to keep a printout as a keepsake. Excit- ing! Te following year, John Bardeen, Walter Brattain and William Shockley would invent the semiconductor transis- tor. Te properties of the semiconductor material accomplished many of the same tasks of the vacuum tube machine, which marked the beginning of the end for vacuum tube-based systems. A material replaced a machine.
In my research, what I'd like to know is which pyroelectric material is the one that will have the best chance of success in practical use for the Army. In general terms, an engine’s job is to convert one form of energy into another. Tis pro- cess is described in thermodynamics (the study of heat, energy and work). Why is this important? Because more than 75 per- cent of the electricity production around the world starts with heat. For example, a coal-fired power plant burns coal to create steam, which in turn drives a turbine.
We’re all familiar with the internal com- bustion engines that power our cars. Energy conversion begins with the piston in your car quickly compressing the air in the cylinder. Adding gasoline and a spark creates combustion, causing a quick pres- sure rise. Pressure pushes on the piston, which spins the crankshaft, eventually transferring energy to the wheels. Te piston comes back up in the cylinder and we’re ready to start all over again. Tat
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CRYSTAL CLEAR Tese crystalline materials are made up of an ordered arrangement of atoms. Some atoms have a positive charge and some a negative charge. Te pyroelectric materials look like a box of atoms with a single atom that is almost, but not quite, in the center. Tat means that the charge is more positive on one side or another. However, when you heat the material, the atom that was slightly offset centers itself to form an evenly charged surface. Te asymmetry caused by the material’s polarization, or internal electric field, causes the electric charge on the surface to change when the polarization changes as the material is heated or cooled.
In the 1700s and 1800s, a number of today’s legendary scientists explored pyroelectric properties: Carl Linnaeus, who created the two-name system we use to classify animals, plants and minerals; Joseph Priestly, who discovered oxygen; and Pierre and Marie Curie, who were credited with advances in radiation, mag- netism and crystallography.
It was not until later that pyroelectrics were considered for everyday use. Now- adays, pyroelectrics are used primarily in home security systems, where infrared radiation is absorbed by the pyroelectric material, which enables motion detection.
CHARGE IT We explore the once mystic-crystals because we know that the material has
Army AL&T Magazine
October-December 2016
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