Every day, everywhere we go, we are surrounded by sounds.

Most of the time, we don’t think of it as something tangible. Sure, we “feel” it at a rock concert or thunder that rattles the windows, but would you imagine it could lift something?

Newsflash: it totally can.

Acoustic levitation is a real phenomenon that uses soundwaves to float solids, liquids, and even heavy gases to float. It can take place in normal or reduced gravity, so here on earth or in gas-filled enclosures in space.

To understand how it works, you have to know something about the properties of gravity, air, and sound.

Gravity is a force that causes objects to attract one another, and the more massive an object, the more strongly it attracts others, and Earth, being huge, easily attracts objects around it.

Air is a fluid that behaves like a liquid. It’s made of microscopic particles that are farther apart and move faster than the ones in water, is all.

Sound is a vibration that travels through a medium like gas, liquid, or solid. Whatever the source object is, it moves or changes shape rapidly to produce the sound that we actually hear.  A bell, for example, vibrates as one side moves out, pushing air molecules next to it and increasing the pressure in that region of air.

The area of higher pressure is called a compression.

When the side of the bell moves back in it pulls molecules part, creating. rarefaction (a lower-pressure region), and as the series of compressions and rarefactions repeat (very quickly) each one is one soundwave wavelength.

Soundwaves travel as molecules push and pull other molecules around them, so they’re necessary for sound to exist.

Acoustic levitation uses sound traveling through a fluid (usually gas) to balance the force of gravity. A basic acoustic levitator has two parts, a transducer (a vibrating surface that makes sound) and a reflector. The transducer and reflector often have concave surfaces that help focus the sound.

A sound wave travels from the transducer and bounces off the reflector, and there are three basic properties of the wave that help the device be able to suspend objects in midair.

The wave is a longitudinal pressure wave, which means the movement of the points in the wave is parallel to the direction the wave travels – kind of like when you push and pull on one end of an extended slinky.

The wave follows the law of reflection, which states that the angle of incidence (the angle at which something strikes a surface) equals the angle of reflection (the angle it leaves the surface).

In short, a sound wave bounces off a surface at the same angle it hits the surface.

Finally, when a sound wave reflects, the interaction between its compressions and rarefactions causes interference. Compressions that meet each other amplify, and compressions that meet rarefactions create balance. Sometimes, this interference can combine to create a standing wave, which appear to vibrate in segments rather than traveling from place-to-place.

An acoustic levitator needs more than ordinary sound wave to supply the amount of pressure needed to create powerful standing waves. Extremely intense sounds are usually nonlinear, and can cause disproportionately large responses in the substances they travel through.

These include distorted wave forms, shock waves, sonic booms, acoustic streaming, and acoustic saturation.

It’s a complex field that’s difficult to understand, but nonlinear effects can combine to make painfully intense sound. They can also become strong enough to balance the pull of gravity, which is why the transducers inside many levitators produce sounds in excess of 150 decibels.

In addition to the transducer/reflector combination, scientists who want to levitate objects using sound also have to use the correct frequency to create the desired standing wave.

They also have to consider the distance between the transducer and the reflector, which must be a multiple of half the wavelength of the sound. This is because waves create a pressure zone close to the reflective surfaces.

The high pressure areas below the nodes must be large enough to support the floating object, typically one-third to one-half the wavelength of the sound. The higher the sound’s frequency, the smaller the object will have to be.

Objects have to be the right mass as well as size, so scientists have to check the density as well. If levitating a liquid, it has to have the correct ratio of surface tension and density and size considering gravity and the surrounding fluid (the Bond number).

Lastly, the intensity of the sound must not overwhelm the surface tension of any liquid being levitated.

If you’re thinking this sounds like a lot of calculation and work for what amounts to a parlor trick, you would be right. And that’s why scientists are quick to assure us that they see very practical uses for acoustic levitation, too.

They believe it could help speed up the process of manufacturing small electronic devices, since levitation could take the place of robots or complex machinery needed to hold or rotate items while they cool nd harden.

For materials that are corrosive or react with containers used during chemical analysis, levitation could be used to suspend the materials and eliminate the risk of contamination from containers.

Foam physics research has run into a big obstacle in gravity,which pulls the liquid downeard, drying and destroying the foam. If acoustic levitation was used to study it without interference from gravity, it could lead to innovations regarding the product.

Researchers are positive that more applications are out there, too, and so continue to develop new setups for systems to help make it happen.

In the meantime, it looks pretty cool.

So there’s always that.

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