CMUT Crosstalk Reduction Using Crosslinked Silica Aerogel

Inter-element acoustic crosstalk is one of the major concerns which restricts the potential deployment of Capacitive Micromachined Ultrasonic Transducers (CMUTs) in Nondestructive Evaluation (NDE) despite its superior transduction capabilities. This thesis investigates the causes of acoustic crosstalk in CMUTs and develops a novel method of CMUT crosstalk reduction by passivating the CMUT top surface by a thin layer of Di-isocyanate enhanced crosslinked silica aerogel. This powerful technique derives its inspiration from the Scholte waves attenuation techniques as used in boreholes at the permeable formations. Analytical and 3D finite element analysis in MATLAB and COMSOL Multiphysics, respectively, show that the developed technique can minimize the crosstalk due to Scholte waves at the fluid-solid interfaces by at least 5 dB more at the nearest neighbor as compared to other published techniques. An added advantage of the developed technique is that the level of Scholte wave attenuation can be controlled by altering the porosity of the aerogel layer. A simple and cost-effective fabrication process employing sol-gel and ambient pressure drying processes for the aerogel layer deposition has been developed that doesn’t interfere with the basic CMUT operation or fabrication techniques

A 77 GHz BCB BASED HIGH PERFORMANCE ANTENNA ARRAY FOR AUTONOMOUS VEHICLE RADARS

A bisbenzocyclobutene (BCB) based 77 GHz aperture coupled microstrip antenna array for frequency modulated continuous wave (FMCW) automotive radars has been developed for use in automotive collision avoidance and cruise control applications. Each of the microstrip patches of the developed antenna array has been desiged to have a microfbaricated airfilled cavity to realize a synthesized effective dielectric constant of 1.46 in contrast to original BCB dielectric constant of 2.6 to improve the diecrectivity, gain, and bandwidth in a compact footprint suitable for small automotive radars. The developed antenna array has a foot print area of 20 x 21 mm2 to accommodate 56 micorstrip patches in a 7 x 8 matrix configuration. Each of the gold patches has a length of 1.46 mm and a width of 1.7 mm. The anteena array exhibits an ADS™ (Advanced Dsign Systems) 3D simulated -10 dB bandwidth of 4.2 GHz, 22.5 dBi directivity, and a gain of 19.78 dBi with sidelobe levels lower than 13.78 dB to meet the auto industry roadmap reccommendations. A fabrication process table has been developed and simualated successfully using IntelliSuite™, an industry standard software. The developed process table can be used to fabricate the device. The developed antenna array will pave the way to manufacture low cost high performance automotive radars to mitigate fatal crashes to save lives and minimize property and infrastructural damage while also forming an integral part of the adaptive cruise control system for autonomous vehicles