[silk] Spray-on Antennas Make Their Mark (fwd)
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---------- Forwarded message ----------
Date: Wed, 1 Aug 2001 13:07:21 +0800
From: Ramjee Swaminathan <ramjee@...>
Subject: [silk] Spray-on Antennas Make Their Mark
Reading this interesting news item with the currently available
'printable' computing device technologies (like Rolltronics) and sub
dollar radio_freq_id tags (like Motorola) - the future has almost arrived
for sub dollar disposable tracking systems, I guess. But may be not, it
has to wait for 'printable' or 'sprayable' power systems...
Some times (not always), I find these kinds of research troubling, when I
consider the 'invasion to privacy' angle... For example, what if the
employer_provided_freebie_jackets have the tracking system invisibly
'printed' on them, in future?
©SIGNAL Magazine 2001
Spray-on Antennas Make Their Mark
Experimental technologies offer elegant, inexpensive solutions.
By Henry S. Kenyon
Researchers are studying applications and materials for creating radio
antennas that are sprayed onto a surface. Made from commercially available
materials, these devices consist of a conductive substance sprayed over a
template with a radio aerial pattern on it. The antennas can be applied
directly to walls, windows or fabric shelters, allowing military
commanders and relief workers to set up communications networks quickly.
Transporting, establishing and maintaining radio systems for military and
humanitarian operations is often a logistics balancing act because of
weight and space considerations. The ability to use any convenient surface
as a mount for an aerial provides planners with additional flexibility
when deploying in areas that are devastated or lack infrastructure.
The Defense Advanced Research Projects Agency (DARPA), Arlington,
Virginia, is considering a number of possible applications and techniques
for using spray-on antennas. According to Dr. Paul J. Kolodzy, program
manager, DARPA Advanced Technology Office, the goal is to develop easily
transportable antenna apertures that can be deployed rapidly. For example,
a command post staff could set up its communications infrastructure by
spraying antennas onto tents, walls or windows. This concept could also be
used where there is a temporary need for a large antenna. Instead of
diverting resources to transport and assemble a large structure,
communications specialists may find it more efficient to spray a pattern
onto a large piece of plastic to create a dish, he says.
Kolodzy cautions that the technology is still in its early concept phase.
DARPA is examining materials that can emit or receive radio waves and is
studying the capabilities of those substances in a particular antenna
design. Once these operational parameters have been determined,
researchers will be able to decide where to direct work on potential
applications, he explains.
The technology for the antennas is not exotic, Glynda Benham, president of
MegaWave Corporation, Boylston, Massachusetts, explains. MegaWave is
conducting a phase-two small business innovation research study for DARPA
on possible uses for sprayable antennas.
According to Benham, the antenna material is available in the form of
metal-based paints such as nickel or silver and carbon-graphite-based
paints. To create an antenna, a template is placed on the desired surface,
the paint is sprayed over it and a connector is attached.
These paints are currently used for electromagnetic interference shielding
in cases for electronic equipment such as laptop computers. Marshall
Cross, vice president for research and development at MegaWave, notes that
an antenna could be built into a laptop casing on the production line
simply by using a template to separate a section of the paint. This would
be less expensive than installing a piece of metal for an antenna, he
One potential difficulty will be creating a paint that maintains its
integrity on fabric surfaces such as tents. The antennas must be durable
enough to withstand repeated folding and washing for long-term
applications, Benham says.
DARPA research also will determine what kind of power a sprayable antenna
will be able to put out in a transmission mode. This is important because
too much power can destroy the antenna material, Kolodzy says. However,
the primary goal of the research is to develop passive receiving systems,
he adds. Additional studies seek new ways to find optimal patterns for
antenna templates and to create apertures easily.
MegaWave also has experimented with wideband antenna designs with
bandwidth ranges from 200 megahertz to 3 gigahertz. While efficiency
remains a concern, the goal of the current research is to see where the
engineering and design boundaries lie. Kolodzy notes that if the broadband
studies are successful, the results can be applied directly to narrowband
The paints currently used for the antenna material are opaque. DARPA is
interested in possible applications for transparent paints. Transparent
antennas would be unobtrusive and could be installed on vehicle
windshields, Kolodzy says. He notes that the military would like very
large apertures for their antennas, and a windshield is often the largest
uninterrupted surface on a vehicle that is available for mounting such a
However, MegaWave researchers determined that no commercially available
aerosol spray products currently meet transmission requirements because
high temperatures are required to make the paint transparent. While
several companies make metal-oxide-based materials for use at room
temperature, they do not possess the minimum conductivity capacity of 100
to 500 ohms per square inch necessary for an antenna.
The study did reveal how much conductivity is needed to make this class of
antennas, Cross observes. "It's almost like negative research. We figured
out that with today's state of the art, you couldn't do it," he says.
DARPA and MegaWave are also cooperating on developing "invisible" antennas
built into transparent surfaces such as glass or plastic. Unlike sprayable
antennas, these devices consist of films embedded into or placed over a
windshield or a window to create a receiver. This technology also utilizes
Cross notes that automobile windows are coated with a metal-oxide film.
This material currently serves three functions: as a safety laminate to
hold the glass together during an accident, as protection for the
vehicle's interior and occupants from ultraviolet and infrared rays, and
as a demister or defogger when a current passes through it. A fourth and
new function would be as a wideband antenna, he adds.
In much the same way spray-on antennas can be created by separating a
small template from a larger painted area, a transparent antenna can be
made by cutting out and isolating an area of window film, Cross explains.
This type of device could receive a variety of signals such as amplitude
modulation, frequency modulation, global positioning system, cellular
telephone and personal communications systems transmissions. Megawave
currently is working with Southwall Technologies Incorporated, Palo Alto,
California, to develop this technology for automotive use, Benham says.
MegaWave also developed a prototype aircraft window for the Federal
Aviation Administration. While the program did not proceed beyond the
concept stage, it did demonstrate possible aerospace applications for the
technology, Cross observes.
The concept was to place a metal-oxide film on commercial aircraft windows
to provide protection from sunlight and to shield communications and
navigation systems from electromagnetic radiation emitted by personal
electronic devices. The windows also could be used to detect and locate
individual personal devices affecting aircraft avionics. "It's more bang
for the buck. One piece of film does three things," Cross contends.
Kolodzy hopes that these antenna technologies will be employed in areas
such as the automotive industry and disaster relief. He believes that
continued research will reveal more uses and capabilities for these
devices. "It's going to be fun. If this works out, you're only limited by
your imagination," he says.
Besides developing unobtrusive and sprayable antenna technologies, DARPA
is focusing on combining multiple aerials into a single unit. As part of
its phase-two SBIR program with the agency, MegaWave developed a broadband
antenna that would allow multiple radios to transmit and receive signals.
According to Cross, the goal of the research is to develop multifunction
antennas for law enforcement vehicles. "The idea is that you wouldn't
drive around in a vehicle with five or six antennas on it because that
tips off who you are. We got a used Ford Taurus and developed the whip and
invisible windshield antennas and demonstrated that you could put many
very high frequency and ultrahigh frequency radios on a single antenna and
communicate just as well as with many antennas," he says.
The modified device functions as a broadband whip antenna operating over
multiple octaves. It is a resistantly loaded antenna--the resistances are
distributed along the aerial's length in a manner that allows for wideband
use without compromising much of its gain, Cross notes.
The company has recently redesigned the whip with genetic algorithm
techniques to optimize it for certain frequency bands, Benham explains.
Genetic algorithms generate and produce efficient functions, much like
real genetic traits are passed along by the dominant genes. This creates
an automated method for optimizing antenna configurations. "When you do
this process with genetic algorithms, instead of getting a continuous
loading process, you get a piecewise, continuous profile that is totally
random. It's not something you would ever get if you sat for 100 years and
optimized it by hand," she says. --HSK
Additional information on MegaWave Corporation's military antenna programs
is available on the World Wide Web at http://www.megawave.com
R a m j e e S w a m i n a t h a n
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