Researchers at the University of illinois have experimented with omnidirectional printing techniques using metallic nanoparticle inks and a 3D controlled dispensing nozzle to manufacture very compact and high performance antennas.
So far, antennas produced by screen-printing, inkjet printing, and liquid metal-filled microfluidics were designed in simple motifs, such as dipoles and loops, but with limited spatial resolution and dimensionality. This yielded planar antennas that occupy a large area relative to the achieved performance.
"Omnidirectional printing of metallic nanoparticle inks offers an attractive alternative for meeting the demanding form factors of 3D electrically small antennas (ESAs)," stated Jennifer A. Lewis, the Hans Thurnauer Professor of Materials Science and Engineering and director of the Frederick Seitz Materials Research Laboratory at Illinois.
These antennas are electrically small relative to a wavelength (typically a twelfth of a wavelength or less) and exhibit performance metrics that are an order of magnitude better than those realized by monopole antenna designs, claim the researchers.
"There has been a long-standing problem of minimizing the ratio of energy stored to energy radiated, the Q of an ESA," ECE Professor Jennifer Truman Bernhard explained. "By printing directly on the hemispherical substrate, we have a highly versatile single-mode antenna with a Q that very closely approaches the fundamental limit dictated by physics (known as the Chu limit). Conformal printing allows the antenna's meander lines to be printed on the outside or inside of hemispherical substrates, adding to its flexibility.
A 3D antenna during the printing process on a dome-shaped structure.
"Unlike planar substrates, the surface normal is constantly changing on curvilinear surfaces, which presents added fabrication challenges," Lewis noted. To conformally print features on hemispherical substrates, the silver ink must strongly wet the surface to facilitate patterning even when the deposition nozzle (100 µm diameter) is perpendicular to the printing surface.
To fabricate an antenna that can withstand mechanical handling, for example, the silver nanoparticle ink is printed on the interior surface of glass hemispheres. Other non-spherical ESAs can be designed and printed using a similar approach to enable integration of low Q antennas on, for example, the inside of a cell phone case or the wing of an unmanned aerial vehicle. The antenna's operating frequency is determined primarily by the printed conductor cross-section and the spacing (or pitch) between meander lines within each arm.
According to the researchers, their design can be rapidly adapted to new specifications, including other operating frequencies, device sizes, or encapsulated designs that offer enhanced mechanical robustness. This conformal printing technique could lend itself to other potential applications, including flexible, implantable, and wearable antennas, electronics, and sensors.
For further information: http://www.illinois.edu.
This article originally appeared on EE Times Europe.