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Miuri-Ori pattern Rob Felt
Silver dipoles are arranged across the folds of a Miuri-Ori pattern to enable frequency blocking.

Origami Builds Tunable RF Filter

A filter built using simply folded paper can change the frequencies it filters out by adjusting its shape.

Researchers at the Georgia Institute of Technology have come up with a way to use an origami-based structure as a radio frequency filters with adjustable dimensions. Changing the filter’s shape lets the device change which signals it blocks.

The tunable filters could have a variety of uses, from antennas that adapt in real-time to ambient conditions to the next generation of electromagnetic cloaking that could be reconfigured on-the-fly to reflect or absorb different frequencies.

The team focused on one particular origami pattern, Miura-Ori, which can expand and contract like an accordion. “The Miura-Ori pattern has an infinite number of possible positions along its range of extension, from fully compressed to fully expanded,” says engineering professor Glaucio Paulino. “A spatial filter made like this has built-in versatility, changing which frequency it blocks as the filter is compresses or expands.”

The research team used a special printer that scored paper, enabling the sheet be folded in the origami pattern. An inkjet-type printer then applies lines of silver ink across those perforations, forming the dipole elements that gave the object its radio frequency filtering ability.

“The dipoles were placed along the fold lines so that when the origami was compressed, the dipoles bend and become closer together, which causes their resonant frequency to shift higher into the spectrum,” explains Manos Tentzeris, an engineering professor.

To prevent the dipoles from breaking along the fold line, the perforations were stopped when they reached a silver element and continued on the other side. Additionally, along each of the dipoles, a separate cut forms a “bridge” that lets the silver bend more gradually. For testing various positions of the filter, the team used 3D-printed frames to hold it in place.

The researchers found that a single-layer Miura-Ori-shaped filter blocked a narrow band of frequencies, while several layers of stacked filters stacked blocked a wider band of frequencies.

The Miura-Ori formation is flat when fully extended and quite compact when fully compressed, so it could be used for antennas that need to stay in compact spaces until deployed, such as those used on spacecraft. Additionally, the shape expands along a single plane and this could let it use less space compared to antennas that take several steps to deploy.

“A device based on Miura-Ori could both deploy and be re-tuned to a broad range of frequencies compared to traditional frequency-selective surfaces, which typically use electronic components to adjust the frequency rather than a physical change,” says Georgia Tech grad student Abdullah Nauroze. “Such devices could be good candidates to be used as reflect arrays for the next generation of cubesats or other space communications devices.”

There were also physical advantages to using origami.

“The Miura-Ori pattern exhibits remarkable mechanical properties, despite being assembled from sheets barely thicker than a tenth of a millimeter,” notes grad student Larissa Novelino. “Those properties could make lightweight-yet-strong structures that could be easily transported.”

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