Shape-Shifting Origami Could Help Antenna Systems Adapt On-the-Fly
Conventional reconfigurable electrical and radio frequency (RF) structures commonly used in applications involving real-time reconfigurability in response to fast varying operational scenarios require specialized substrates or complex electrical circuits. Origami-based RF reconfigurable components and modules offer a solution with unique properties. First, they enable re-configurability over continuous-state ranges (as opposed to discrete states). Second, they do not require specialized mechanical support for multilayer frequency-selective surface structures. Moreover, deployable origami-based RF structures can achieve large surface re-configurability ratios from folded to unfolded states. Finally, these structures allow for independent control of multiple figures of merit: bandwidth, frequency of operation, and angle of incidence.
The tremendous increase in the number of components in typical electrical and communication modules requires low-cost, flexible, and multifunctional sensing, energy harvesting, and communication modules that can readily reconfigure, depending on changes in their environment. Current subtractive manufacturing-based reconfigurable systems offer limited flexibility (limited finite number of discrete reconfiguration states) and have high fabrication cost and time requirements.
Researchers at the Georgia Institute of Technology have devised a method for using an origami-based structure to create RF filters that have adjustable dimensions, enabling the devices to change which signals they block throughout a large range of frequencies.
The new approach could have a variety of uses, from antenna systems capable of adapting in real time to ambient conditions, to the next generation of electromagnetic cloaking systems that could be reconfigured on-the-fly to reflect or absorb different frequencies.
This approach solves the adjustability problem by combining additive manufacturing and origami principles to realize tunable electrical components that can be reconfigured over continuous-state ranges from folded (compact) to unfolded (large surface) configurations. Special “bridge-like” structures are introduced along the traces that increase their flexibility, thereby avoiding breakage during folding. These techniques allow creating truly flexible conductive traces that can maintain high conductivity even for large bending angles, further enhancing the states of reconfigurability.
The researchers used a special printer that scored paper to allow a sheet to be folded in the origami pattern. An inkjet-type printer was then used to apply lines of silver ink across those perforations, forming the dipole elements that gave the object its RF 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 along the spectrum,” said Manos Tentzeris, the Ken Byers Professor in Flexible Electronics in the Georgia Tech School of Electrical and Computer Engineering.
To prevent the dipoles from breaking along the fold line, the perforations were suspended at the location of each silver element and then continued on the other side. Additionally, along each of the dipoles, a separate cut was made to form a bridge that allowed the silver to bend more gradually. For testing various positions of the filter, the team used 3D-printed frames to hold it in place.
To demonstrate the idea, the team focused on one particular pattern of origami called Miura-Ori that has the ability to expand and contract like an accordion. The Miura-Ori pattern was used to fabricate spatial filters — frequency-selective surfaces (FSSs) with di-pole resonant elements placed along the fold lines. The electrical length of the dipole elements in these structures changes when the Miura-Ori is folded, which facilitates tunable frequency response for the proposed shape-reconfigurable FSS structure.
Higher-order spatial filters were realized by creating multilayer Miura-FSS configurations, which further increase the overall bandwidth of the structure. Such multilayer Miura-FSS structures feature the unprecedented capability of on-the-fly reconfigurability to different specifications (multiple bands, broadband/narrowband bandwidth, wide angle of incidence rejection), requiring neither specialized substrates nor highly complex electronics, holding frames, or fabrication processes.
FSSs have found many applications, ranging from design of radomes, reflectors, and spatial filters to reduction of antenna radar cross-section and realization of artificial electromagnetic band-gap materials. FSS structures typically consist of periodic arrangement of resonant elements on a thin sheet of substrate that reflect, absorb, or allow certain electromagnetic waves to pass through them based on their frequency, thus exhibiting either bandpass or band-reject characteristics.
A typical single-layer Miura-FSS consists of a single sheet of the Miura-Ori pattern with two dipole elements per unit cell. The dipole elements were inkjet-printed over the mountain fold such that they are centered to demonstrate highly flexible conductive traces — a key requirement for origami-inspired tunable electrical/radio frequency structures over a continuous range of states. Dipoles are fundamental electromagnetic structures, which would help to fully understand the frequency behavior of a Miura-FSS with folding.
The researchers found that a single-layer Miura-Ori-shaped filter blocked a narrow band of frequencies while multiple layers of the filters stacked could achieve a wider band of blocked frequencies. By stacking two Miura-FSS sheets, two multilayer configurations were created: a mirror multilayer stacking and an inline multilayer stacking. The former consists of two identical Miura-FSS layers connected along the valleys in a mirror fashion, and the latter consists of distinct and kinematic compatible layers connected along the valley folds. Both stacking types preserve the flat-foldability and in-plane kinematics of the Miura-Ori.
Because the Miura-Ori formation is flat when fully extended and quite compact when fully compressed, the structures could be used by antenna systems that need to stay in compact spaces until deployed such as those used in space applications. Additionally, the single plane along which the objects expand could provide advantages, such as using less energy, over antenna systems that require multiple physical steps to deploy.
“The Miura-Ori pattern has an infinite number of possible positions along its range of extension from fully compressed to fully expanded,” said Glaucio Paulino, the Raymond Allen Jones Chair of Engineering and a professor in the Georgia Tech School of Civil and Environmental Engineering. “A spatial filter made in this fashion can achieve similar versatility, changing which frequency it blocks as the filter is compressed or expanded.”
“A device based on Miura-Ori could both deploy and be re-tuned to a broad range of frequencies as compared to traditional frequency selective surfaces, which typically use electronic components to adjust the frequency rather than a physical change,” said Abdullah Nauroze, a Georgia Tech graduate student who worked on the project. “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,” said Larissa Novelino, a Georgia Tech graduate student who worked on the project. “Those properties could make lightweight yet strong structures that could be easily transported.”