Decorated granular crystal as filter of low-frequency ultrasonic signals

We numerically study uncompressed granular crystals excited by sinusoidal signals at 1-100 kHz. A simple system such as two beads in a line reveals that for a fixed driven frequency, incident signals can be transmitted or filtered depending on the driving amplitude. We show that using square tapered crystals with decoration it becomes possible to enhance the low frequency filtration properties of granular systems. In addition to filtration, we find that 80% or more of the input force is attenuated using a crystal thickness of 4 grains.