What is Micromechanics?

Jennifer Voight

Micromechanics, also referred to as MicroElectricalMechanical Systems (MEMS), is the study of engineered structures and systems at a smaller level, usually measured in millimeters to microns, a unit measuring 1 1-millionth of a meter. Principles of mechanics and engineering change as objects grow smaller, requiring that scale be taken into account when analyzing and developing micro-devices. Micromechanics of materials is the analysis of composite materials at the level of their individual constituents to predict how these materials will react under various conditions.

Silicon surface micromachining uses a silicon wafer as a pattern surface.
Silicon surface micromachining uses a silicon wafer as a pattern surface.

The medical field, watch industry, and automotive industries commonly use applications of micromechanics. Virtually all fields that use engineered products and systems benefit from micromechanics. For instance, the study of micromechanics can help engineers determine which materials are safest for use in automobiles and are most resistant to damage from forces during a crash.

The basis of micromechanics is that as objects grow smaller, forces related to volume grow less significant. Weight and inertia become less of a concern in the microscopic world, opening up new engineering opportunities for small objects and systems that are difficult or not possible in the macroscopic world. In the same manner, forces related to surface area, like friction and surface tension, become highly significant as objects become smaller.

Micromechanical parts use less power, are usually less expensive, and weigh less than their normally sized counterparts. These types of machines can be fabricated using a high degree of precision using special techniques. For example, engineers may use electro discharge machining (EDM) to make parts like turbines from electrically conductive materials.

Another growing area of interest in micromechanics is the use of silicon to create extremely small machines using a photographic-type process. These machines are created already assembled and fully functioning. Silicon surface micromachining uses a silicon wafer as a pattern surface. Once the pattern is etched layer by layer onto the wafer, the excess silicon is removed, leaving a functional microcomponent. Bulk micromachining accomplishes a similar task by removing parts of the silicon wafer, leaving a functioning micromachine that is already assembled.

LIGA is an acronym from the German word for lithography. The LIGA technique uses X-ray lithography to apply an image to polymethylmethacrylate (PMMA). The PMMA is then dipped in an etching medium to remove unwanted material, leaving a micromachine.

Micromechanics of inhomogeneous materials states that composites, or materials made up of two or more differentiated materials, must be treated differently than homogeneous materials. Homogenization is used to make predictions about how two materials will react to various conditions in composite form based on their individual qualities. This helps microengineers predict how small changes in composite materials can change the durability and other properties of materials.

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