Subcategory: Materials Science
Emily English - University of Arizona
Co-Author(s): Jonathan Friduss, University of Arizona, AZ; Florian Allein, University of California San Diego, CA; Nicholas Boechler, University of California San Diego, CA; Pierre Deymier, University of Arizona, AZ; Pierre Lucas, University of Arizona, AZ
Signals transmitted in waveguides are scattered by impurities. A solution that has been shown theoretically to address this is spatiotemporally modulating the elastic properties of the waveguide, thereby opening up a unidirectional bandgap that only supports one-way wave propagation. However, there have been few experimental demonstrations of this effect for waveguides that support mechanical waves. As part of a research and mentorship program at both the University of California, San Diego, and the University of Arizona, we studied vibrations in a granular chain where it is hypothesized that the transverse stiffness can be spatiotemporally modulated by longitudinal waves to achieve non-reciprocal transverse wave propagation. To observe this, we created a low-cost photo-deflection-based vibration measuring apparatus. The granular chain is excited using a signal generator, power amplifier, and shaker. The response of the chain is measured by deflecting a continuous laser off of a particle in the chain to an amplified photodetector connected to an oscilloscope. The excitation of the system and the acquisition of its response are automated through MATLAB. Our preliminary results show that the set-up can be used to measure vibrations of the chain over a range greater than 10 kHz. To characterize the vibration transmission spectrum of the granular chain, at each driving frequency, we take a fast Fourier transform of the signal from both the shaker and the last bead in the chain and then take the ratio of the amplitudes of each Fourier component at the driving frequency. In addition to spectral peaks corresponding to the driver, we also observed other peaks above the noise floor that we hypothesize to be due to the resonances of the substrate that the granular chain is on. In addition to developing the measurement setup, we designed sphere-based particles whose mass, radius, and moment of inertia about the significant axis of rotation are balanced such that the chain is expected to exhibit nonreciprocal wave propagation. References: Allein, F., et al. ?Tunable Magneto-Granular Phononic Crystals.? Applied Physics Letters, vol. 108, no. 16, 2016, p. 161903., doi:10.1063/1.4947192. Shen, Chen, et al. ?Nonreciprocal Acoustic Transmission in Space-Time Modulated Coupled Resonators.? Physical Review B, vol. 100, no. 5, 2019, doi:10.1103/physrevb.100.054302. Wang, Yifan, et al. ?Observation of Nonreciprocal Wave Propagation in a Dynamic Phononic Lattice.? Physical Review Letters, vol. 121, no. 19, 2018, doi:10.1103/physrevlett.121.194301.
Funder Acknowledgement(s): This work is supported by the NSF grant # 1640860: EFRI NewLAW Photo-elasticity enabled non-reciprocal acoustic wave propagation in solid-state media, awarded to Pierre Deymier, Head of the Department of Materials Science and Engineering, University of Arizona.
Faculty Advisor: Nicholas Boechler, firstname.lastname@example.org
Role: I did design and construction of the experimental setup, wrote part of the MATLAB code, and researched and designed the sphere-based particles.