OT tractor beam.

More press-release "science" nonsense. Complete with faked pics and absurd applications. This happens about 50 times a day.

Objects have already been levitated and manipulated with light, which is a lot more impressive.

And why does the press call any mechanism a "contraption" ?

The Nature article is OK. There is an analogy between the optical traps and acoustic traps. (Well the article says that, I don't know enough about either.) But analogies can be useful, let's you go from one field to another, without much work. The thermal to RC circuits analogy is one you know.

And moving things w/o physically touching them is just fun to think about. (Well this needs air/ atmosphere.)

George H.

A hard analogy happens when the math of one case scales directly to the math of another. I can use Spice to do quantitative analysis of thermal or mechanical systems.

But it isn't useful to call this acoustic thing a "tractor beam", except to try to propel the press release into your local newspaper. That's a fuzzy analogy.

We did that when we were kids. Vacuum cleaner outlet hose and ping-pong ball.

Oh sorry not the tractor beam, an analogy between optical and acoustic traps. There are some nice analogies with acoustics to other wave things. Acoustic cavities are like microwave cavities. If it's a sphere then the solutions are spherical harmonics, the same as for the hydrogen atom.

This was made by Rene Matzdorf, a theorist no less!

The one dimensional tube with irises is a blast. It's a Kronig-Penney model, you get bands of states, with gaps. If you screw up one of the irises and make it bigger or smaller (Or change the distance between irises) then one of the band modes moves into the gap... Impurities in semiconductors!

George H.

That's simple. Their parents didn't use effective contraception.

Seems like you added a few more experiemnets in the last few years. Any plans for Halbach arrays ;)

Cheers

Den onsdag den 28. oktober 2015 kl. 17.04.38 UTC+1 skrev John Larkin:

-Lasse

Note stupidity: "Writing in Nature Communications, they suggest the work could help develop remote surgical instruments.

In essence, an object sitting in a "quiet" region of space can be held there if it is surrounded by very high-intensity sound waves."

Stupidity lies in use of VERY high-intensity sound waves (emphasis added); good way to damage tissue, etc.

• PS: saw some pictures after the one video; no second video.

You forgot about magnetic levitation..

Remote surgical instruments using acoustics already exist--lithotripsy.

Cheers

Phil Hobbs

Works great - in the sense of pulverising the kidney stone. Also makes you feel as if you've been hit by a truck - or in my case (from my history as a field-hockey goalee) by a large forward in a hurry. No lasting damage, but you don't want to move at all for a couple of days, though you can.

Presume that would be in rather localized areas, sort-of like a spot welder.

The trouble with ultrasound in the body is that the speed of sound varies from organ to organ, so that you trying to focus on a rather localised area through a bunch of lenses and prisms.

With phased array sources you can - in principle - compensate to some extent for the different transit times along different paths, but its tricky to do it right.

It's a variation on the old Chladni plate. Get a plate of any rigid material, just so it's flat. Carve the sides so it's not just a square or rectangle, and sit it on an elastic mount (slab of urethane foam). Then sprinkle with sand, and apply a vibrator (buzzer, or vibra-tool) to a spot on the surface.

What happens, is all the sand dances out of moving areas and piles up in the nodes of the excited acoustic resonances.

This 'tractor' consists of a computed vibration,applied in three dimensions, that directs the motion of (a 3-d counterpart of) a particular pile of sand.