3D-Printed 'Lego' Bricks Could Bend Sound into Acoustic Holograms

3D-printed bricks that look like Lego pieces could provide a simple, low-cost way of creating acoustic holograms — 3D shapes and structures made of sound — for applications as varied as entertainment, medicine or wireless charging, according to a recent study.

Anyone who's watched "Star Wars" will be familiar with the concept of an optical hologram — a 3D image that floats in midair — though real-life technology is significantly less advanced than what was portrayed on-screen.

Holograms are effectively a recording of a 3D light field that can project a reproduction of the original object when lit properly. (The term hologram can refer to both the recording medium and the resulting projection.) The hologram concept can be applied to sound waves to create acoustic holograms, though this field of research is still very new, according to the scientists who developed this new method.

Building the "bricks"

The bricks are so-called metamaterials, a family of materials featuring specially engineered microstructures that result in unusual properties not found in nature. The team designed 12 different types of bricks that effectively slow down sound waves at different rates.

These bricks are fabricated using a conventional 3D printer and act as the pixels of the hologram. A modified version of an algorithm for designing optical holograms was used to determine the configuration of bricks needed to reproduce the desired 3D sound field.

In a paper published Oct. 14 in the journal Scientific Reports, the researchers described using the approach to create a 256-pixel hologram that converted a uniform sound wave into a sound field in the shape of the letter A. The scientists created another hologram that acted as a holographic lens by focusing sound energy onto multiple circular spots of different sizes.

Cummer stressed that the research is exploratory at this stage. But Yangbo "Abel" Xie, a doctoral student in Cummer's laboratory and first author of the paper, said the approach has significant advantages over previous methods that relied on speaker arrays.

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3D-Printed 'Lego' Bricks Could Bend Sound into Acoustic Holograms