Transduction, defined as conversion from one form of energy to another, is the essential purpose of many microelectromechanical/MEMS optical (MEMS/MOEMS devices). In this context, a transducer is a device that is actuated by energy of one form and supplies energy of another form. An example of a common MEMS transducer is the piezoresistive pressure sensor, in which variations in environmental pressure (fluidic energy) are transformed into the deflection of a micromachined membrane (mechanical energy). Using embedded resistors in the membrane, and an externally supplied current or voltage, a bridge circuit allows electronic sensing of a signal proportional to strain (electrical energy). Transducers encompass both actuators and sensors. More often than not, MEMS sensors convert a mechanical or optical signal into an electrical one. MEMS actuators do the converse, using electrical input to affect mechanical or optical devices, altering the environment. Although the number of phenomena and applications in the MEMS arena are vast, the initial sections of this chapter will review these most commonly used in MEMS/MOEMS. After this review of operational basics, the design of micromachines using these effects will be covered.
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