Acoustic Levitation with a Twist

Don’t blame us for the click-baity titles in the source articles about this handheld “acoustic tractor beam”. You can see why the popular press tarted this one up a bit, even at the risk of drawing the ire of Star Trek fans everywhere. Even the journal article describing this build slipped the “tractor beam” moniker into their title. No space vessel in distress will be towed by [Asier Marzo]’s tractor beam, unless the aliens are fruit flies piloting nearly weightless expanded polystyrene beads around the galaxy.

That doesn’t detract from the coolness of the build, revealed in the video below. There’s no tutorial per se, but an Instructables post is promised. Still, a reasonably skilled hacker will be able to replicate the results with ease straight from the video. Using mostly off the shelf hardware, [Marzo] creates a bowl-shaped phased array of ultrasonic transducers driven by an Arduino through a DC-DC converter and dual H-bridge driver board to boost the 40 kHz square waves from 5 Vpp to 70 Vpp. By controlling the phasing of the signals, the tractor beam can not only levitate small targets but also move them axially. It looks like a lot of fun.

Acoustic levitation is nothing new here – we’ve covered 3D acoustic airbending, as well as an acoustic flip-dot display. Being able to control the power of sound waves in a handheld unit is a step beyond, though.

Thanks to [Brian Andersen] and [Sak] for the nearly simultaneous tips.

 

26 thoughts on “Acoustic Levitation with a Twist

      1. I think instructables is an old site and the ‘one step per page’ is leftovers to help slow internet connections. Not sure why it’s still the default other than to get more accidental ad clicks.

          1. No, they ask you if you want to registre or subscribe, but you aren’t forced to do anything!
            But I agree that it is annoying.. Even if my connection is slow, I would préfet to load the whole thing rather than to go through All the pages.. (In which you have to load All the surrounding stuff..)

          2. Yes, that’s exactly how it used to work, I guess they eventually wizened up to the fact that a lot of people were refusing to put content on their site due to that policy alone. Makes me wonder how many others like myself have never gotten past the reputation they built for themselves in those days and still won’t have anything to do with them.

  1. OK, now make two of those, attach them to two separate robotic arms (to be able to hold it in air over longer distances = from oposite sides), and made it autonomously transport light dots without touching.. voilá telekinesis!

    1. I would assume so.
      There’s been work to use transducers in VR/AR either to provide ‘obstacles’ or to give the user tactile feedback when they’re using a robot arm. These transducers probably make it feel like someone threw a styrofoam pellet at you though, so you may miss it if you’re not paying attention.

    2. Next step, people designing this not for fingers but for application of other body parts. The adult industry is always pushing boundaries, right? Gives new meaning to the term hummer.

    3. Those mist pumps that make a thin column of water rise up about an inch then blast it into cold vapor at the top of the column will give you a little but nasty bruise if you’re dumb enough to ignore the warnings and stick a body part into the focus of the ultrasonic transducer.

      How do I know that? A friend of mine was dumb enough to ignore the warnings and poked a finger into the water column, very briefly.

      Those pumps have a sensor that shuts them down when the water level gets too low, and also keeps it from operating in open air. Likely both for safety and to keep the transducer from overheating.

      Supplied with proper cooling I bet an array of those transducers could levitate heavier objects, and pulverize things like expanded styrene beads. Wouldn’t want to use it on anything organic, especially nothing living.

      1. Normally I would agree but as usual there are some cases where slight modifications can make a huge difference.

        http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.105.125501

        The authors describe how acoustic phonons can directly tunnel through vacuum and, therefore, transmit energy and conduct heat between bodies that are separated by a vacuum gap. This effect is enabled by introducing a coupling mechanism, such as piezoelectricity, that strongly couples electric field and lattice deformation. The electric field leaks into the vacuum as an evanescent field, which leads to finite solid-vacuum-solid transmission probability. Because of strong resonances in the system, some phonons can go through the vacuum gap with (or close to) unity transmission, which leads to significant thermal conductance and heat flux.

        Also see:

        Not exactly a high quality vacuum though.

        1. Also relevant would be this link.

          http://proftimobrien.com/2014/03/sounds-of-space/

          “Sound waves can travel in space. There are even sonic booms (shock waves) from stellar explosions. But the densities and pressures are so low they would not be directly audible. So many sounds from space are modified in some way e.g. their frequencies are brought into the range of human hearing, or they are “sonifications” of data i.e. scientific data turned into a sound in some way.”

          1. True but you can create the media, in theory.

            “This effect is enabled by introducing a coupling mechanism, such as piezoelectricity, that strongly couples electric field and lattice deformation. The electric field leaks into the vacuum as an evanescent field, which leads to finite solid-vacuum-solid transmission probability. Because of strong resonances in the system, some phonons can go through the vacuum gap with (or close to) unity transmission, which leads to significant thermal conductance and heat flux.”

    1. Actually that would be an interesting experiment, perhaps if we attach them in opposing senses and send it to outer space, then by not deviating from free fall motion, it could prove the 2 forces are as strong as each other! This would suggest we can set up an equation F_1=-F_2 ….

  2. So the transducers he uses, are they just like the type of transducers on ultrasonic sensors? I’ve seen other acoustic levitation projects but never understood what part they used. Some looked just like an ordinary piezo.

  3. Do someone have the math behind it? Just the basic 1 speaker+ plate would interest me.
    I made a project on this, it worked, but I wasn’t able to find any document which would explain it..

    I understood that it’s a standing wave, but how van you calculate the pressure generated on the little ball?

  4. I wonder if manipulating acoustic waves in this fashion be used to control fire or dampen ignition. Imagine being able to move water vapor like giant cloud over a forest fire. Just a thought.

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