TABLE OF CONTENTS In addition to the compliant structure, operation of microresonators is realized by means of actuation and/or sensing methods, which are together referred to as transduction. In actuation, a driving force or moment is applied such that the resonator is set into the desired vibrational state. Sensing is also needed, either stand-alone (as in pure sensors) or as the tool enabling evaluation of a resonator's state. Several means of transduction are available in MEMS/NEMS such as thermal, electrostatic, magnetic, electromagnetic, piezoelectric, piezomagnetic, optical, based on induced strain (bimorphs and multimorphs), with shape memory alloys or fluid. Of all these methods, the electrostatic, electromagnetic, piezoelectric/piezomagnetic, and bimorph transduction methods are briefly discussed here, as these procedures, enable us to obtain excitation and detection frequencies which are within the range of mechanical microresonators.
The electrostatic actuation or sensing is one of the most popular techniques used with microresonators. Constructively, the electrostatic transduction can be implemented in planar and out-of-the-plane resonator designs. The comb-type electrostatic transduction is one of the most employed solutions for both planar and out-of-the-plane resonant applications. Electrostatic attraction forces can be generated between a fixed plate and a mobile one in different ways, depending on the boundary conditions pertaining to the mobile plate. The y motion shown in Fig. 5.40a can be activated, in the case where the mobile plate moves parallel to the fixed one, by keeping the gap constant. This type of transduction is known as comb-finger, and it...
