Antennas aren’t just for listening to the radio anymore. They’re used in everything from cell phones to GPS devices. Research from North Carolina State University is revolutionizing the field of antenna design – creating shape-shifting antennas that open the door to a host of new uses in fields ranging from public safety to military deployment.
Modern antennas are made from copper or other metals, but there are limitations to how far they can be bent – and how often – before they break completely. NC State scientists have created antennas using an alloy that “can be bent, stretched, cut and twisted – and will return to its original shape,” says Dr. Michael Dickey, assistant professor of chemical and biomolecular engineering at NC State and co-author of the research.
The researchers make the new antennas by injecting an alloy made up of the metals gallium and indium, which remains in liquid form at room temperature, into very small channels the width of a human hair. The channels are hollow, like a straw, with openings at either end – but can be any shape. Once the alloy has filled the channel, the surface of the alloy oxidizes, creating a “skin” that holds the alloy in place while allowing it to retain its liquid properties.
“Because the alloy remains a liquid,” Dickey says, “it takes on the mechanical properties of the material encasing it.” For example, the researchers injected the alloy into elastic silicone channels, creating wirelike antennas that are incredibly resilient and that can be manipulated into a variety of shapes. “This flexibility is particularly attractive for antennas because the frequency of an antenna is determined by its shape,” says Dickey. “So you can tune these antennas by stretching them.”
While the alloy makes an effective antenna that could be used in a variety of existing electronic devices, its durability and flexibility also open the door to a host of new applications. For example, an antenna in a flexible silicone shell could be used to monitor civil construction, such as bridges. As the bridge expands and contracts, it would stretch the antenna – changing the frequency of the antenna, and providing civil engineers information wirelessly about the condition of the bridge.
Flexibility and durability are also ideal characteristics for military equipment, since the antenna could be folded or rolled up into a small package for deployment and then unfolded again without any impact on its function. Dickey thinks these new applications are the most likely uses for the new antennas, since the alloy is more expensive than the copper typically used in most consumer electronics that contain antennas.
Dickey’s lab is performing further research under a National Science Foundation grant to better understand the alloy’s properties and means of utilizing it to create useful devices.
The research is co-authored by Dickey, NC State doctoral students Ju-Hee So, Amit Qusba and Gerard Hayes, NC State undergraduate student Jacob Thelen, and University of Utah professor Dr. Gianluca Lazzi, who participated in the research while a professor at NC State. The research, “Reversibly Deformable and Mechanically Tunable Fluidic Antennas,” is published in Advanced Functional Materials.
Note to editors: The study abstract follows.
“Reversibly Deformable and Mechanically Tunable Fluidic Antennas”
Authors: Ju-Hee So, Jacob Thelen, Amit Qusba, Gerard J. Hayes and Michael D. Dickey, North Carolina State University; Gianluca Lazzi, University of Utah
Published: November 2009, Advanced Functional Materials
Abstract: This paper describes the fabrication and characterization of fluidic dipole antennas that are reconfigurable, reversibly deformable, and mechanically tunable. The antennas consist of a fluid metal alloy injected into microfluidic channels comprising a silicone elastomer. By employing soft lithographic, rapid prototyping methods, the fluidic antennas are easier to fabricate than conventional copper antennas. The fluidic dipole radiates with ~90% efficiency over a broad frequency range (1910–1990 MHz), which is equivalent to the expected efficiency for a similar dipole with solid metallic elements such as copper. The metal, eutectic gallium indium (EGaIn), is a low-viscosity liquid at room temperature and possesses a thin oxide skin that provides mechanical stability to the fluid within the elastomeric channels. Because the conductive element of the antenna is a fluid, the mechanical properties and shape of the antenna are defined by the elastomeric channels, which are composed of polydimethylsiloxane (PDMS). The antennas can withstand mechanical deformation (stretching, bending, rolling, and twisting) and return to their original state after removal of an applied stress. The ability of the fluid metal to flow during deformation of the PDMS ensures electrical continuity. The shape and thus, the function of the antenna, is reconfigurable. The resonant frequency can be tuned mechanically by elongating the antenna via stretching without any hysteresis during strain relaxation, and the measured resonant frequency as a function of strain shows excellent agreement (+/- 0.1–0.3% error) with that predicted by theoretical finite element modeling. The antennas are therefore sensors of strain. The fluid metal also facilitates self-healing in response to sharp cuts through the antenna.