  Controlling infrasound signals is crucial to many processes ranging from
predicting atmospheric events and seismic activities to sensing nuclear
detonations. These waves can be manipulated through phononic crystals and
acoustic metamaterials. However, at such ultra-low frequencies, the size
(usually on the order of meters) and the mass (usually on the order of many
kilograms) of these materials can hinder its potential applications in the
infrasonic domain. Here, we utilize tunable lattices of repelling magnets to
guide and sort infrasound waves into different channels based on their
frequencies. We construct our lattices by confining meta-atoms (free-floating
macroscopic disks with embedded magnets) within a magnetic boundary. By
changing the confining boundary, we control the meta-atoms' spacing and
therefore the intensity of their coupling potentials and wave propagation
characteristics. As a demonstration of principle, we present the first
experimental realization of an infrasound phonon demultiplexer (i.e., guiding
ultra-low frequency waves into different channels based on their frequencies).
The realized platform can be utilized to manipulate ultra-low frequency waves,
within a relatively small volume, while utilizing negligible mass. In addition,
the self-assembly nature of the meta-atoms can be key in creating
re-programmable materials with exceptional nonlinear properties.
