Clever Halloween Hack Uses Sound Waves to Simulate a Spooky Doodling Ghost

There’s really no wrong way to decorate for Halloween. It’s the effort that counts, even if all you do is toss some pumpkins on the porch, or set up an inflatable witch on the lawn. But there are those that go above and beyond the call of duty, like Dan Beaven, who leverages some cutting-edge levitation tech to make it look like ghosts are actually real.

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It hasn’t made its way into consumer gadgets just yet, but scientists have figured out how to make objects levitate without the need for high-powered magnets. The technology isn’t going to make hoverboards a real thing any time soon, but in laboratory tests, arrays of ultrasonic transducers—essentially speakers that produce sounds outside the range of human hearing—can generate sound waves strong enough to cause lightweight polystyrene balls to float, and even control the movements of a small foam bead floating in mid-air. It’s wild stuff, but the research, at least in its current form, hasn’t had any practical applications—until now.

Following a free tutorial that’s available over on Instructables Circuits, Beaven built a 256-transducer array that’s suspended over a dark surface lightly sprinkled with baking powder. The array is not only able to generate sound waves powerful enough to physically blast the powder away, but with enough focus and control it makes it appear as if an invisible finger is actually drawing in the dust.

It’s a wonderfully spooky effect, and one that’s hard to figure out how it works. There’s no visible writing tool making the baking powder move, and no other obvious indicators given the sound waves are invisible and inaudible. Beaven eventually—before Oct. 31 rolls around, we hope—plans to expand the setup to use two side-by-side transducer arrays to create a larger writing surface for a spirit to communicate through, which should allow for longer, creepier messages to magically appear.