Nonlinear dynamics of inverse tapered granular chains for mechanical amplification in voice frequency range.

Here, the dynamics of inverse tapered granular chains, which are alignments of beads with progressively increasing radii, are investigated. These chains are subjected to harmonic excitation by a moving wall and probed at the tapered end. Intermediate taperings using Ni-Ti (metal) and Teflon (plastic) granules are considered. The proposed chain is based on the frequency responses. The incident signal is set between 1 Hz and 3 kHz. The system transmits or filters incident signals at low or high driving frequencies, respectively. For intermediate frequencies, similar to the human voice and most musical instruments, the driving frequency is amplified, presenting a median gain of 24 dB (an increase in energy by a factor of 250) over long durations. A transition map, showing regions of transmission, amplification, and filtration as a function of driving amplitude and frequency, is provided. This system could serve as a starting point for studies on natural voice amplifiers, which are important for addressing hearing loss and vocal disorders, as well as other applications requiring mechanical signal amplification. The findings suggest that a proper granular arrangement could enable the amplification of low or extremely low driving frequencies.

Granular chains with fixed side decoration as impact protector and signals filter.

We propose a granular architecture as a potential impact protector and signal filter. The system consists of monodispersed granular chains decorated with side beads fixed (welded) on sidewalls. Numerical results from usual monodispersed chains and simple tapered chains are employed as reference. An appropriate material combination and an optimal radii ratio between the side and axial granules show that more than 90% of the momentum amplitude of solitary pulses can be attenuated using a small and scalable system composed of five axial granules. Considering sinusoidal signals, the findings suggest that regular chains (monodispersed and tapered) are low-pass filters with cutoff frequencies as functions of the driven amplitude, restitutional losses, and tapering. The granular chain with fixed decoration filters all the input signals.