Levitating objects .... with sound!

It has been known for 100 years that sound waves can exert a force (the acoustic radiation pressure effect) but not until now has this principle been used to manipulate physical objects.

I'll keep this post pretty short because the maths involved is pretty obscene but for those who are slightly masochistic and would like to take a look, the paper by Foresti et al. was published yesterday in PNAS and can be viewed here.

The basic principle used here is there is an emitting platform (that as the name suggests emits the sound wave) and then placed opposite that, there is a reflecting platform and these platforms are placed at particular places based on some complex math. The figure below is a diagram of the apparatus taken directly from the paper.

Setup of droplet manipulator (Foresti et al. (2013)

I won't get into it but take my word that the design of this system and the calculations involved is an example of some beautifully thought out elegant science and props to those involved in its development.

Now, it's all very well to make an object levitate using a sound wave, but they go one step further and actually move the object with these sound waves which again has some pretty complex equations behind it. The sound emitting mechanism is made with piezoelectric crystals, which shrink or stretch depending on the voltage applied to them and hence can alter the sound wave produced quite finely and accurately.

As a proof of principle they did several awesome things! First, I will show you the video of them moving and mixing droplets of water seen in the video below:

Then as true scientists, they wanted to make this useful for something very important to most scientists ... Making coffee ... Check it out:

Yep, they are mixing a granule of instant coffee and water in thin-air to make a drop of coffee! That video is slowed down by 100-times so you can see the fine details.

Next they took a step larger:

I don't know about you, but I find that pretty incredible!

The applications for this are not as wide-ranging as you might think unfortunately. The object being levitated and the sound waves have a very intimate relationship, the diameter of the object needs to half of the wavelength of the soundwave, so big objects are out of the question at this stage. However, it does have some exciting applications for chemistry as many chemical reactions and science experiments are influenced by the chemistry of being on the surface of something so we can now investigate questions free from surface interference.

So aside from making coffee in mid-air, the benefits of this amazing technology remain to be reaped by scientists ... For now.


Foresti D., Nabavi M., Klingauf M., Ferrari A. & Poulikakos D. (2013). Acoustophoretic contactless transport and handling of matter in air, Proceedings of the National Academy of Sciences, 110 (31) 12549-12554. DOI: 10.1073/pnas.1301860110

A boy and his atom ...

Today is going to be a very short post, but not much about a new, cutting edge piece of science! More using the incredible technology science has to offer... to create art!

This was a video created by IBM and is officially the worlds smallest stop motion film. It was created to celebrate IBM creating the smallest magnetic memory bit (comprised of only 12 atoms, the current norm is around 1,000,000 atoms, so not bad work!). So to celebrate this, they used the technology in their lab to create a stop motion film .... of individual atoms!

The project was "filmed" using what's called a scanning tunnelling microscope (which was actually invented by IBM researchers who got the Nobel Prize in Physics for it in 1986). Now, your normal everyday microscope won't cut it to see atoms, in fact you can't even use light to see atoms, so the scanning tunnelling microscope works by gently moving a super-fine needle above atoms of the material being "imaged". As the needle moves over a particular atom, a mini-chemical bond is formed between the atom and the needle tip, this can be measured through the needle. The needle tip is moved ("scanned") from left to right, right to left, left to right moving down the material. When something is higher (closer to the needle), then a stronger bond can be detected, but if the atom is far away from the needle then only a weak bond can be detected. As the needle "scans" the material to be imaged, all this data is then compiled into a viewable image!

For this film, the researchers used the bond formed between the tip and the atom to actually move some atoms around, to create a picture! Then they moved them again and took another, and so on to create this amazing stop motion film.

Each small globe is ONE INDIVIDUAL ATOM of carbon monoxide. Think about that for a second!

IBM did a (fairly) easy to follow video on how they made the atoms move, they may do a better job than I did:

And that's it! Hope you enjoyed it, fairly simple concept but done really really well in my opinion!

PS. Apologies to all physicists reading this, hate mail can be addressed to me personally :)