Michael Joseph Leamy

We fabricate a discrete phononic crystal with hysteretic force–deflection behavior analogous to elastic–plastic material response, and then measure its response to harmonic excitation. Slider (or Jenkins) elements are introduced to mimic plastic deformation and a ten-cell phononic crystal is constructed from modular unit cells. Modular construction enables calibration and validation of individual components prior to full integration, which is particularly important for the sliding elements. Subsequent frequency-sweep experiments at both elastic and plastic excitation amplitudes demonstrate pronounced wave attenuation aligned with bandgap frequencies arising from Bragg scattering. The presence of this strong attenuation, even at plastic amplitudes, reveals experimentally that bandgaps can continue to block frequencies into the strongly nonlinear, plastic regime. The fabricated system is expected to facilitate future experimental studies of large-amplitude, elastic–plastic wave propagation.

We experimentally demonstrate the tunability of a topological defect mode and its spectral flow within the bandgap of a periodic structure made of beams and cylindrical masses and hosting a topological bandgap in its frequency spectrum. A defect is introduced by incorporating a pair of piezoelectric plates into a single unit cell of the lattice, giving rise to a localized mode inside the bandgap. We experimentally observe this mode and its spectral flow in the bandgap by altering the elastic modulus of the piezoelectric plates using negative capacitance shunt circuits. Further, through finite element simulations and experiments, we show that the spectral flow can be tuned by modulating the mass of the defect cell alone. This work introduces additional degrees of freedom in the design of elastic wave-based devices for applications in acoustic logic, waveguiding, and energy harvesting.

We experimentally demonstrate a topologically protected electroacoustic transistor. We construct a reconfigurable phononic analog of the quantum valley-Hall insulator composed of electrically shunted piezoelectric disks bonded to a patterned plate forming a monolithic structure. The device can be dynamically reconfigured to host one or more topological interface states via breaking inversion symmetry through selective powering of shunt circuits. Above a threshold, the amplitude of wave energy at a chosen location in one topological interface creates a second interface by dynamically switching power between two groups of shunts using relays. This enables the flow of wave energy between two locations in the reconfigured interface analogous to the voltage-controlled electron flow in a field effect transistor. The amplitude of wave energy in the second interface is used for bit abstraction to implement acoustic logic. We illustrate the various states of the transistor and experimentally demonstrate wave-based switching. The proposed electroacoustic transistor is envisioned to find applications in wave-based devices and edge computing in extreme environments and inspire novel technologies leveraging acoustic logic.