Ph.D. Proposal Presentation by Jeffrey J. McLean
Wednesday, March 17, 2004

( Dr. Levent Degertekin, Chair)

"Interdigital Capacitive Micromachined Ultrasonic Transducers for Microfluidic Applications "


In this proposal, directional generation and detection of Scholte waves in liquids and microfluidic channels is introduced. Capacitive micromachined ultrasonic transducers (CMUTs) are arranged in an interdigital configuration and a phased excitation scheme is used to enhance the directionality of Scholte interface waves in microfluidic environments. Finite element models are developed to study the generation and propagation of guided acoustic modes in both fluid half-spaces and microchannels. The CMUTs are fabricated using a low-temperature process that facilitates future electronics integration. Experiments on the interdigital CMUTs show that a 5 finger-pair device in a water half-space has 12dB of directionality in generating Scholte waves at the design frequency of 10MHz, which agrees with the finite element results. Using the results of the finite element model of a CMUT in a fluid half-space, it was determined that 41% of the acoustic power radiated into the fluid is contained in the Scholte wave propagating in the desired lateral direction. Transducers are demonstrated to perform bidirectional pumping in microfluidic channels with input power levels in the milliwatt range. Preliminary results demonstrating the sensitivity of the Scholte wave to changes in fluid properties are also presented. The remaining tasks for this project include further electrical characterization, an investigation of the pumping performance, and a study of the sensitivity of the Scholte wave to changes in fluid properties to assess its potential as a versatile fluidic sensor.