Collaborative Research: Implementing Topologically Protected Gigahertz Acoustic Circuits

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Microwave acoustic devices are widely used in wireless communication technology and quantum information science. This NSF project aims to realize acoustic devices with lower propagation loss than traditionally engineered circuits. The project will bring transformative change to the design and characterization of low-loss acoustic systems operating in the gigahertz regime. This will be achieved by implementing the acoustic analogues of topological electronic states and characterizing them with network analysis and microwave microscopy. The intellectual merits of the project include (1) design of acoustic devices with nontrivial topology, (2) simulation of acoustic transport in complex structures, (3) fabrication of advanced microwave circuits, and (4) nanoscale visualization of wave propagation on piezoelectric membranes. The broader impacts of the project include (1) implementation of practical devices for wireless communication applications, (2) integrated research and education programs in both institutions for optimal training and learning experience, (3) outreach to local high-school students and teachers with a strong focus on underrepresented/minority groups, and (4) promoting the effectiveness of local summer camps for K-12 students.In the Ultra High Frequency and Super High Frequency regime, conventional acoustic devices suffer from narrow bandwidth and high propagation loss. Drawing inspiration from condensed matter physics, it is possible to design topologically nontrivial phononic systems, where acoustic waves can propagate without being backscattered. Due to the challenge in fabrication and the lack of appropriate characterization tools, however, acoustic topological metamaterials are mostly demonstrated with kilohertz to megahertz operating frequencies. This NSF project aims to implement gigahertz acoustic integrated circuits with topologically protected phononic transport by combining theoretical analysis, numerical simulation, device fabrication, and nanoscale visualization. In particular, the direct information on nanoscale acoustic fields is expected be crucial for the inspection and refinement of novel microwave circuitry. Such a design-validation loop will expedite the prototyping of acoustic elements such as waveguides, delay lines, dividers/combiners, resonators, frequency division multiplexer, and filters based on quantum valley Hall, quantum spin Hall, or quantum-Hall-like effects. Integrated research and education programs at both institutions will be established so that students are trained to master modern nanofabrication techniques, state-of-the-art microwave acoustic systems, and scanning probe microscopy. The research teams will outreach to local high school students and teachers through lab experience, Saturday workshop, and summer camps. The active involvement in frontier research will influence their career path towards STEM fields.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.