This Machine Does Science by Levitating and Mixing Liquid Droplets

Levitation may still conjure images of the occult and hokey stage magicians, but we’ve achieved real levitation through several different means. Magnetic levitation, for example, lets high-speed trains zip along without pesky wheel friction to hold them back. If you happen to have access to a volume of air — and the Earth conveniently provides that — then you can also levitate objects with sound waves. Ultrasonic levitation isn’t used for much outside of scientific demonstrations, but maybe it could serve a practical purpose. To facilitate that, this Magic Drops machine levitates and mixes liquid droplets.

Unlike waves on the electromagnetic spectrum, soundwaves require a physical medium to travel through (they can’t travel through a vacuum). As soundwaves travel through material, including air, they vibrate. In air, that vibration can produce enough movement to keep a small amount of material aloft, which is levitation. Ultrasonic soundwaves work well for this because people nearby don’t want to hear constant blaring sound and because the wavelength is ideal for the size of objects that are light enough to levitate. A 440Hz soundwave (the musical note A) has a wavelength of more than two and a half feet, which would be far less useful.

To do ultrasonic levitation, you just need some ultrasonic transducers aimed in the right direction. This machine contains two huge arrays of ultrasonic transducers aimed towards each other. This setup makes it possible to move levitating matter in any direction within the 3D volume. Adjust the frequencies to move the matter along the X axis (lines going from one transducer array to the other), or decrease amplitude to create a low pressure zone for the matter to move into on the YZ plane.

None of that is new, but Magic Drops takes advantage of it to independently move liquid droplets and mix them. The purpose is “spherification” for molecular gastronomy (scientific food). Basically, this means encasing a flavored droplet inside of a gel coating that solidifies into a shell. But traditional fabrication methods don’t work well, as gravity pushes the tasty droplet down before the gel hardens. Magic Drops can theoretically solve that by pushing the flavor drop inside the gel drop and suspending the two in air until the gel solidifies

In practice, Magic Drops seems to struggle to actually accomplish that—the vibrations cause the droplets to shake too much. But it does have utility in science. Mixing two liquids in air would help to avoid contamination from surfaces and instruments. As long as the air is clean, then the two liquids could mix without making physical contact with anything aside from the syringes they came from.

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