Finite element analysis of capacitive micromachined ultrasonic transducers beyond conventional operation

Capacitive micromachined ultrasonic transducers offer several advantages such as ease of fabrication and larger bandwidth compared to piezoelectric transducers. The advances in CMUTs required exploring new modes of operation to achieve high transmit pressure and better receive sensitivity.; This dissertation focuses on static and dynamic finite element analysis of CMUTs in nonlinear operation modes introduced for the first time: collapsed and collapse-snapback. Commercial packages ANSYS and LS-DYNA are used in this research. Collapsed operation enables generating 6 times larger acoustic pressure at a frequency twice of the center frequency in the conventional operation. Additional benefits of this mode include adjustable center frequency, better linearity and reduced crosstalk between array elements. This mode, applicable for both transmit and receive of the ultrasound, was combined with the conventional mode to generate unprecedented acoustic output pressures in a transmit only mode: collapse-snapback. This higher acoustic pressure comes with a trade-off in linearity. Pulse-echo and interferometer measurements of CMUTs in these modes are also presented.; Acoustic crosstalk is the coupling of energy between the elements of an ultrasonic transducer array. This coupling degrades the performance of transducers in applications such as medical imaging and therapeutics. Interferometer measurements and finite element analysis are used to determine the crosstalk waves for a 1-D CWT array operating in the conventional and collapsed modes. The main crosstalk mechanism is the dispersive guided modes propagating in the fluid-solid interface. Conventional operation has a crosstalk level of -23 dB and the guided modes are not present above the cut-off frequency.; Using our verified FEA, we implemented a powerful method for the first time to reduce the acoustic crosstalk by impeding the propagation of the guided interface waves. This method is based on the acoustic bandgap resulting from the periodic CMUT membranes on the fluid-solid interface. The acoustic crosstalk was effectively reduced by 10 dB down to -33 dB in the conventional operation without loss of acoustic pressure of the transmitter element.