A narrowband ultrasound source has been used to generate solitary wave impulses in finite-length chains of spheres. Once the input signal is of sufficient amplitude, both harmonics and sub-harmonics of the input frequency can be generated as non-linear normal modes of the system, allowing a train of impulses to be established from a sinusoidal input. The characteristics of the response have been studied as a function of the physical properties of the chain, the input waveform and the level of static pre-compression. The results agree with the predictions of a theoretical model, based on a set of discrete dynamic equations for the spheres for finite-length chains. Impulses are only created for very small pre-compression forces of the order of 0.01 N, where strongly non-linear behaviour is expected.
Hutchins, D. A., Yang, J., Akanji, O., Thomas, P. J., Davis, L. A. J., Freear, S., … Gelat, P. (2016). Ultrasonic propagation in finite-length granular chains. Ultrasonics, 69, 215–223. https://doi.org/10.1016/j.ultras.2015.10.018