Authors: C.B. Doody, J.S. Wadhwa, D.F. Lemmerhirt, R.D. White
Affilation: Tufts University, United States
Pages: 627 - 630
Keywords: cMUT, characterization, modeling, finite elements
The goal of this project was the experimental characterization and modeling of capacitive micromachined ultrasound transducers (cMUTs). The cMUTs being tested are fabricated using layers common to standard commercial CMOS processes. Two designs of micromachined ultrasonic array elements were considered. A lumped element acoustic model was used to create a computational model of the transducers. The model incorporated several elements such as environmental loading, diaphragm mass, diaphragm stiffness, the negative electrostatic spring, and backing cavity compliance. Some of these element parameters could be calculated analytically. Due to the complex geometry of the device, finite element analysis was required to determine some of the elements. Combining the lumped element parameters, frequency response plots were generated for the transducers in both air and water environments. In air, primary resonance occurred at approximately 7.0 MHz with a fractional percent bandwidth of 0.1%. When operating submerged, the model predicted a 3.7 MHz center frequency and a fractional percent bandwidth of 30%. Laser Doppler vibrometry was used to determine steady state scans and transient step responses. The steady state scans displayed measurements somewhat higher than predicted by the model. The transient step response showed a fundamental resonance somewhat lower than predicted by the in-air model.