Levitation has long been the domain of stage magicians, charlatans, and fiction, but there are technological means of achieving the same result. Aside from aircraft that could be considered to be levitating on air and boats that do the same on water, the most common examples of levitation in real world are maglev (magnetic levitation) trains. But you’ll probably never be able to build your own maglev train in your backyard. You can, however, experiment with acoustic levitation. We’ve seen a handful of notable acoustic levitators here on Hackster, but nothing is cooler than Redditor We-Make-Projects’ acoustic levitation wand that makes them a modern wizard.
Acoustic levitation is exactly what it sounds like: soundwaves being used to hold material aloft. Ultrasonic soundwaves are generally used for this purpose, because their frequency is appropriate for small objects and so humans don’t have to hear the loud noise. Ultrasonic acoustic levitators are sometimes used in scientific instruments, but they’re more common as novelties and physics demonstrations. Acoustic levitation works by suspending an object in a low air pressure zone created by two or more sound waves as they cross each other. If you think of a soundwave like the waves in an ocean, this is like a boat being caught in the trough between waves. The second soundwave is used to counteract the first, so that the object isn’t carried away. The sizes of the “troughs” are dependent on the frequency of the soundwaves, which is why ultrasound around 40KHz is used for acoustic levitation.
Normally, we see acoustic levitators built with one transducer on the bottom facing upward and a second transducer on the top facing downward in order to create the crossing waves. But We-Make-Projects took a different approach and used a concave array of transducers. Those create a low pressure zone at the focal point of the waves, where a small piece of foam can be suspended. The cool thing is that this is still affected by the frequency of the waves, so buttons can be pressed to adjust the position of the low pressure zone. That causes the piece of foam to move further or closer to the transducer array on demand.
We-Make-Projects built this levitation wand using an Arduino Nano. That controls the array of transducers. There are a total of 24 transducers which were mounted onto the 3D-printed wand and then hand-wired. Power comes from a pair of 18650 lithium-ion battery cells through a boost converter. This is already a very neat project, but We-Make-Projects has plans to improve it even further in the future. By controlling each transducer individually, they can gain better control over the position of the low pressure zone and should even be able to move it perpendicularly to the wand’s axis. With some preprogrammed adjustment sequences, they will be able to create “animations” for the suspended foam particle to follow.