33 State-Space Modeling of Nonlinear Electrostatic Transducers and Experimental Characterization Using LDV 263 Fig. 33.5 Scanning electron micrograph of a MEMS microphone die from a Knowles microphone model SPM0687LR5H-1 Fig. 33.6 (a) Profile of the Knowles diaphragm at pull-in and (b) Measured center-point diaphragm displacement it past its equilibrium or rest position. Figure 33.6a shows a line scan of the diaphragm displacement at an instant in time corresponding to peak positive displacement, where the diaphragm is in contact with the backplate at its center. To provide context and to emphasize the technological significance of the displacement amplitude achieved by both actuators studied in this work, the so-called surface pressure of the actuator can be computed as .p =Zo ×v where .Zo is the acoustic impedance of air and v is the diaphragm velocity. The surface pressure is the acoustic pressure that would be realized at the surface of a transducer if the transducer were vibrating with uniform velocity v and generating planar waves. A1.μm displacement amplitude at 100 kHz, as achieved by the first device demonstrated, corresponds to a surface pressure equal to 261 Pa, or a sound pressure level (SPL) equal to approximately 140 dB. These levels are significantly loud, and transducers capable of generating such levels may be considered for interesting ultrasonic applications in air such as acoustic micro-tapping and parametric arrays [17, 18].
RkJQdWJsaXNoZXIy MTMzNzEzMQ==