CMU MEMS Laboratory Publication Abstract

 

in SPIE Symposium on Smart Structures & Materials/NDE 2004 (Smart Structures 2004), March 14-18, 2004, San Diego, CA.
Comparison of Piezoresistive and Capacitive Ultrasonic Transducers
J. Neumann, D. Greve and I. J. Oppenheim
ABSTRACT:
MEMS ultrasonic transducers for flaw detection have heretofore been built as capacitive diaphragm-type devices. A diaphragm forms a moveable electrode, placed at a short gap from a stationary electrode, and diaphragm movement has been detected by capacitance change. Although several research teams have successfully demonstrated that technology, the detection of capacitance change is adversely affected by stray and parasitic capacitances, limiting the sensitivity of such transducers and typically requiring relatively large diaphragm areas. We describe the design and fabrication of what to our knowledge is the first CMOS-MEMS ultrasonic phased array transducer using piezoresistive strain sensing. Piezoresistors have been patterned within the diaphragms, and diaphragm movement creates bending strain which is detected by a bridge circuit, for which conductor losses will be less significant. The prospective advantage of such piezoresistive transducers is that sufficient sensitivity may be achieved with very small diaphragms. We compare transducer response under fluid-coupled ultrasonic excitation and report the experimental gauge factor for the piezoresistors. We also discuss the phased array performance of the transducer in sensing the direction of an incoming wave.
© 2004 SPIE - The International Society for Optical Engineering. Any request of reprint should be addressed to spie@spie.org or phone +1 260 676 3290.
Full paper not available from outside CMU


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