Phononic Frequency Combs of Tuning Forks

In this paper, we investigate the formation of phononic frequency combs in tuning forks. Phononic frequency combs are the acoustic equivalents of photonic frequency combs, which have many current applications [1]. While phononic frequency combs are relatively new, they may have useful applications in RF devices [2]. Previous observations of phononic frequency combs have been made in the vibrations of beams with various mounting configurations, including cantilever beams, simply supported beams, and fixed-end beams. However, for practical use, beams are often designed as tuning forks, consisting of two or more cantilever-mounted beams on a base. This study aims to explore phononic frequency combs in quartz tuning forks. We demonstrate that phononic frequency combs in tuning forks can be generated through energy transfer from a lower-frequency mode to a higher-frequency mode. This contrasts with a standalone cantilever beam, where the combs are generated by energy transfer from a higher-frequency mode to a lower-frequency mode.