Duke Researchers Use Metamaterials to 3D Print Acoustic Holograms


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dukeTechnology futurists have been talking about holography for decades now and while we would have thought it would be front and center for image display by now, that hasn’t exactly been the case. We’ve seen holographic effect technology, gaming and conference tools, and DIY concepts, but the world is still waiting to see 3D printing technology meld with holography in a way that would offer innovation to important areas such as medicine.

Now, researchers at Duke University have been experimenting with a range of metamaterials meant to aid in the manufacturing of passive 3D acoustic holograms, created from one sound source that functions like a speaker. This device, created by the team at Duke led by Steve Cummer, an electrical and computer engineer, bears a modular design. Each one is made up of a dozen blocks, 3D printed, that can be manipulated into different designs—bearing all the benefits of 3D printing as the researchers have been able to customize a functioning form of holography that is not only simple and unique but also affordable to produce. This means that their design could open the door to a whole new world of holography, manipulated by acoustic waves.


From the research team’s paper: (a) A schematic showing the holographic rendering of a letter ‘A’ with the passive metamaterial-based hologram. (b) Comparison between holographic rendering with an active phased array and a hologram made of metamaterial-based passive phased array, which eliminates cumbersome phase-shifting electronics and a large number of transducers.

As sound travels in waves, the researchers think it should be possible to manufacture entire 3D printed fields of sound that don’t rely on a tranducer array controlled by electronics, but rather a grouping of cells that work together to control the acoustic waves. The unique metamaterials allow for the structures to morph into their 3D shapes, as well as controlling their properties. The cells operate at a frequency of 4000 Hz and the 12 cells cover 180° of relative phase delay, with a double layer allowing for 360° of relative phase delay.

In a recent interview with PhysicsWorld.com, Cummer discussed the project. While he considered the actual 3D printing of the cells to be somewhat arduous, he points out that making them was still quite straightforward. The difficult part was designing the parts to emit the correct sound.

With the cells being arranged according to the user, the device is put in front of the speaker with the hologram emerging from the other side. The research team achieved success in their project through creating two different holograms, with one projecting sound that was in a letter “A” pattern at a distance of 30 cm from the hologram. After that, they changed the shape to create circular hot spots.

While the original idea was just to test and prove this innovative scientific concept, Cummer sees that their device might be ‘deployed’ elsewhere, such as in making an “acoustic hologram that converts the sound from a single speaker into the much more complex sound field created by an orchestra.”


From the research team’s paper: (a) The desired pattern to be reconstructed at the depth of 300 mm. (b) The ideal phase pattern designed with GSW method and the actually measured phase pattern immediately behind the hologram. (c) The simulated field patterns (amplitude) at three representative depths compared to those actually measured.

More importantly, this could be used in the medical field for 3D imaging as the fields can be adjusted and customized. Currently, this could be used in simple imaging systems, making up for their lack of complexity with affordability and versatility.

The research team’s findings are outlined in ‘Acoustic Holographic Rendering with Two-dimensional Metamaterial-based Passive Phased Array,’ authored by Yangbo Xie, Chen Shen, Wenqi Wang, Junfei Li, Dingjie Suo, Bogdan-Ioan Popa, Yun Jing, and Steven Cummer.

…”this is a really nice idea,” commented Bruce Drinkwater, professor of ultrasonics at the University of Bristol in the UK. “Arrays are expensive, particularly the electronics required to drive them. This paper makes beam-forming much easier and cheaper.”

The researchers point out that their holograms should offer benefit where ‘robustness’ and ‘small volume’ are preferred.

“…our hologram, which acts as a plane to adjust the phase of the impinging sound, can be adapted to compensate for the phase aberration of human skulls for transcranial beam focusing,” state the researchers in their paper. “This could enable precise focusing for brain therapy or stimulation without over a thousand transducer elements and the same number of dedicated driving channels, both of which are very expensive and challenging to construct.”

“The challenge of scaling down for higher frequencies like ultrasound is simply manufacturing the components in a much smaller size. 3D manufacturing approaches are evolving very quickly, and we are working with colleagues with experience in this area to do exactly this.”

The researchers are also working to create another sound field design with a single source and reconfigurable hologram. Find out more about their scientific innovation by reading their research study in Scientific Reports. Discuss in the Acoustic Holograms forum at 3DPB.com.

[Source: Physics World]

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