In an advance that might interest Q-Branch, the gadget makers for James Bond,
the National Institute of Standards
and Technology (NIST) and partners from industry and academia have designed
and tested experimental antennas that are highly efficient and yet a fraction
of the size of standard antenna systems with comparable properties.
The novel antennas may be useful in ever-shrinking and proliferating wireless
systems such as emergency communications devices, micro-sensors and portable
ground-penetrating radars to search for tunnels, caverns and other geophysical
NIST engineers are working with scientists from the University of Arizona (Tucson)
and Boeing Research & Technology (Seattle, Wash.) to design antennas incorporating
metamaterials—materials engineered with novel, often microscopic, structures
to produce unusual properties. The new antennas radiate as much as 95 percent
of an input radio signal and yet defy normal design parameters. Standard antennas
need to be at least half the size of the signal wavelength to operate efficiently;
at 300 MHz, for instance, an antenna would need to be half a meter long. The
experimental antennas are as small as one-fiftieth of a wavelength and could
In their latest prototype device,* the research team used a metal wire antenna
printed on a small square of copper measuring less than 65 millimeters on a
side. The antenna is wired to a signal source. Mounted on the back of the square
is a “Z element” that acts as a metamaterial—a Z-shaped strip
of copper with an inductor (a device that stores energy magnetically) in the
center (see photo).
“The purpose of an antenna is to launch energy into free space,”
explains NIST engineer Christopher Holloway, “But the problem with antennas
that are very small compared to the wavelength is that most of the signal just
gets reflected back to the source. The metamaterial makes the antenna behave
as if it were much larger than it really is, because the antenna structure stores
energy and re-radiates it.” Conventional antenna designs, Holloway says,
achieve a similar effect by adding bulky “matching network” components
to boost efficiency, but the metamaterial system can be made much smaller. Even
more intriguing, Holloway says, “these metamaterials are much more ‘frequency
agile.’ It’s possible we could tune them to work at any frequency
we want, on the fly,” to a degree not possible with conventional designs.
The Z antennas were designed at the University of Arizona and fabricated and
partially measured at Boeing Research & Technology. The power efficiency
measurements were carried out at NIST laboratories in Boulder, Colo. The ongoing
research is sponsored by the Defense Advanced Research Projects Agency.
* R.W. Ziolkowski, P. Jin, J.A. Nielsen, M.H. Tanielian and C.L. Holloway.
Design and experimental verification of Z antennas at UHF frequencies. IEEE
Antennas Wireless Propag. Lett., 2009 vol. 8, pp. 1329-1332.