A quarterly research and development magazine.
Since the micro-engine experiments, Sandia’s micro-scale modeling and simulation community has been occupied with questions like “What went wrong?,” “Can computational simulation ensure that a component will perform up to expectations?,” and “Can computational simulation suggest better operation and improved design?” The next step is to bring about microscale-enabled engineering solutions — ultimately a transformation in component design — through shared innovation by individuals specializing in components, engineering, and microelectronics.
Physical models must be modified, sometimes drastically, as length scales shrink because the dominant physical phenomenon is different as length scale changes. For example, gravity is more easily overcome by adhesion; friction models break down; ballistic phonon transport in solid can be as dominated as the diffusive phonon transport.
Such effects are especially important in polycrystalline silicon (including structures made with Sandia’s SUMMiT® V process), which have several levels and have geometry features up to 10 micrometers and grains in the tens to hundreds of nanometer range.
Computational simulation of a Sandia-designed microscale thermal actuator provides examples of how size affects how things work. In this device, electrical current passes through four mechanical legs, causing them to expand and displace a shuttle with a reciprocating motion. Remarkably, conventional methods predict the beam temperature at 750 kelvin, whereas Sandia’s “non-continuum” calculation, using nano-scale data, puts it at a more accurate 900 K. (See graphs at right.) With some materials, this could make the difference between melting and not melting.
The fledgling MEMS industry has a limited knowledge of materials physics at micrometer size, and currently commercialized devices are designed for specialized purposes. Partly for this reason, they do not have a broad user base, and therefore have not generated industry standards or the design and process software that would be built based upon those industry standards. However, this may change as Sandia’s materials science, engineering, and computer sciences organizations develop engineering systems which, while designed for their own use, could migrate into the private sector and revitalize the pace of invention.
While Sandia is seeing a major effort to harness nanoscience for the improvement of applications such as micro-machines, big benefits are visualized for everyday products by Jim Redmond, manager of Sandia’s Strategic Initiatives department.
“For example, carbon black can be considered a ‘nano material’ that has been used for years to enhance the performance of tires, a product that we are all familiar with,” he says. “This benefit was determined largely by trial and error. With modern computing and production tools, we ought to be able to engineer similar improvements for many products.”
“As these new perspectives evolve into reality, a new breed of engineer is coming into existence,” says Ratzel in Mechanical Engineering. “In fact, the line separating the computer scientist, the materials scientist, and the engineer is becoming blurred and indistinct. Mechanical engineering cannot help but benefit from this exciting new horizon. MEMS is here to stay, and it will transform the future.”
Technical contact: Channy Wong, (505) 844-3530, ccwong@sandia.gov
Technical contact: Jim Redmond, (505) 844-3136, jmredmo@sandia.gov
Read more: To see the full story in Mechanical Engineering, click on the
March, 2007 issue: www.memagazine.org/backissues/back.html
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