SUBJECT: Ph.D. Dissertation Defense
BY: Sai Aditya Raman Kuchibhatla
TIME: Thursday, April 4, 2024, 11:00 a.m.
PLACE: Love Building, 295
TITLE: Non-reciprocal and Topological Wave Propagation in Electroacoustic Systems
COMMITTEE: Dr. Michael Leamy, Chair (ME)
Dr. Karim Sabra (ME)
Dr. Alper Erturk (ME)
Dr. Julien Meaud (ME)
Dr. Claudio Di Leo (AE)


Non-reciprocal and topological wave propagation has become an active area of acoustics research owing to the anomalous and exceptional wave behavior with potential applications in robust and high-speed communication devices, analog computing, advanced sensors, and vibration isolation. This dissertation explores such phenomena and their applications through numerical modeling of and experiments with one- and two-dimensional electroacoustic systems. The research commences with an investigation of non-reciprocity achieved by means of an electromechanical cell incorporating a field effect transistor. The study demonstrates giant non-reciprocity in wave propagation between two coupled 1-D mechanical lattices. The dissertation then moves on to the design, analysis and implementation of topological interfaces and defects in reconfigurable electroacoustic systems. The first of these systems is a beam with periodically bonded piezoelectric plates. A topological interface with energy localization is established in the system by shunting the piezoelectric plates via negative capacitance circuits. Typically, adiabatic pumping is used to shift the position of a topological interface in such a system. In this dissertation, the transition of energy localization upon non-adiabatic shifting of the interface is studied. This reveals that some topological protection to the energy localization may be present even with abrupt changes which may be advantageous for topologically-protected devices such as switches and multiplexers. Next, with a focus on low-cost robust acoustic logic, the thesis proposes topologically-protected electroacoustic transistor featuring shunted piezoelectric disks in a hexagonal plate-like lattice. In such a device, the presence of an incoming wave at a ‘gate’ terminal allows wave propagation between ‘source’ and ‘drain’ terminals located elsewhere in the domain. Numerical modeling of the dependent topological interfaces required for the device provides design guidelines and functional limitations, thereby aiding the construction of an experimental setup. The experiments demonstrate the functioning of the electroacoustic transistor. Additionally, numerical simulations are used to explore designs that implement Boolean logic. Finally, tuning the spectral flow of topological modes through a bandgap is numerically explored in a 2-D hexagonal lattice made of beams. A topologically-protected resonator is experimentally demonstrated in such a lattice using shunted piezoelectric plates. This dissertation provides valuable insights into the design of electroacoustic systems with non-reciprocal and topological wave propagation. The findings from this work may guide future exploration of novel acoustic effects and inspire metamaterial designs to be implemented in the next-generation wave-based devices for communication, computing, in-situ monitoring in harsh environments and energy harvesting.