When a bed of dry granular material or fluid is subject to vertical vibration at certain frequencies, pattern formations start to appear at the surface when the modulation exceeds a critical value. These waves have a frequency which is half that of the driving oscillations (the first sub-harmonic). This effect was first reported by Michael Faraday in 1831.
In ordinary Newtonian fluids, those that do not exhibit shear thickening or shear thinning, the wave patterns include ones with 1-fold symmetry (stripes), 2-fold symmetry (squares), and 3-fold symmetry (hexagons).
Many of the same patterns seen in the liquid version of Faraday's experiment are also seen in the granular material. These patterns are in fact the same phenomena observed on the chladni plates discussed earlier. At lower frequencies however, a new phenomena has been observed, that of localized structures called "oscillons". The granular version of this experiment is done at the University of Texas at Austin, and now also in several other places.
Oscillons can be seen in the image on the lower right of the photographs shown above. They resemble a splash of water in a puddle, but with one important difference: instead of spreading out, they slosh back and forth between a state that resembles a crater and a state that resembles a peak. When one oscillon in a crater state collides with an oscillon in the peak state, they can form a bound system, as shown in the image on the lower right.
In shear thinning non-Newtonian liquids, theory suggests that localized structures analogous to granular "oscillons" should be found. These have recently been observed in experiments using clay suspensions as shown below.
Simulating what happens when you shake a box of granular material such as sand, researchers at the University of Texas at Austin acoustically vibrate vertically an evacuated container of tiny bronze balls to make beautiful patterns such as the ones shown above. The pictures show patterns such as hexagons and states that resemble the stitches on a baseball.
Particle-like localised excitations in a bed of sand can form into molecules and even crystals structures. At a certain frequency the energy put into the system manifests itself as small isolated heaps of sand (about thirty grains in diameter) which also bob up and down. These heaps, termed "oscillons," are stable (holding together for thousands of shakings) and able to slowly drift across the sand bed. This is not like a travelling wave, were the moving peak is being shaped by different particles, but here the same grains drift around. And just as with electrical charges, when it comes to oscillons opposites attract. As long as their centers are within 1.4 diameters of each other, oscillons of opposite phase (one at its peak height and one at its shallowest depth) can enter into a dipole state to form a sort of molecule. This peak-crater pair binding may lead to more complex molecules and even long chains of oscillons which, under the right conditions, can grow into extended patterns. Current theories give us no definite answer as to how and why the oscillons form and interact, but such localized structures may exist in other dissipative systems (systems which steadily exchange energy), and not just in granular materials.
Oscillons are a soliton-like phenomenon emerging from batches of vibrated particles. Basically, researchers are studying them mostly empirically at this point. They've shown a coupling effect where smaller oscillons join into larger ones via waves of attraction. These waves of attraction or repulsion between them propagate through vacuum and seem to be driven by a force whose aim is to complete a defined pattern. Schroedinger-wavelike phenomena ensue also. In general oscillons have been observed when a large number of balls of less than 0.1 millimetres in radius are vibrated in a tray at between 10 and 100 Hz. They have so far been produced using a wide range of materials, particle sizes and frequencies of vibration. Oscillons are very stable and long lived, some having been observed to last for millions of cycles. Oscillons pulse up and down in the same way as standing waves in a fluid, such as the water waves discussed in the previous section. Because these structures attract or repel each other in vacuum as well as in air, depending on their relatives phases, they appear to act as charged particles. This is clear evidence that two neighbouring standing waves show the property of charge attraction & repulsion.
One of the neatest aspects is that the models predict 'mass' for the fundamental oscillons. I know of no modern physics theory that can claim this. All other theories assume fundamental particle masses as given constants. So, again, the 3D standing wave theory is fully compatible with the soliton mass predictions, because it defines the mass property as a property of space structure and not as a built in constant of particles. Again, despite continous research since 1996, oscillons seem to have totally escaped the attention of mainstream particle physicists as a model or direction of pursuit.