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CHIPS Articles: The Seawater Antenna

The Seawater Antenna
By Holly Quick - April-June 2011
Space and Naval Warfare Systems Center Pacific (SSC Pacific) high frequency antenna designer, Daniel Tam, developed an innovative device that uses the magnetic induction properties of salt in seawater to create a very high frequency (VHF) antenna. The patent-pending seawater antenna, recently coined the Electrolytic Fluid Antenna, was on display at the SPAWAR exhibit at AFCEA West 2011, Jan. 25-27 in San Diego.

Conference attendees were fascinated by Tam's demonstration of the seawater antenna as he, and SSC Pacific scientists P. Michael McGinnis and Lu Xu, eagerly discussed the advantages of the seawater antenna. A continuous line of spectators watched as Tam, McGinnis and Xu demonstrated how to use a jet of seawater as a communications antenna.

Tam combined water and sodium chloride to replicate seawater and pumped it into a plastic enclosed tube. The tube was then placed inside a current probe made of a ferrite magnetic core hooked to a water pump creating the jet of water. The magnetic field in the probe induced a current that spread via the salt in the seawater.

Standing approximately five feet from Tam, McGinnis spoke into a portable radio while his message was transmitted to Tam using a VHF signal. The signal transmission was possible because of the principle of magnetic induction, which uses ion conduction instead of the electron flow that is used in regular, metallic antennas.

The width and length of the water stream projected from the Electrolytic Fluid Antenna determine bandwidth and frequency capabilities. An 80-foot high stream could transmit and receive from two to 400 megahertz (MHz) with a relatively small onboard footprint.

The Electrolytic Fluid Antenna can transmit and receive HF, VHF and ultra-high frequency (UHF) signals and has been tested at a receiving range of more than 30 miles. A typical Navy vessel has 80 metallic antennas that could theoretically be replaced with only 10 Electrolytic Fluid Antennas of varying heights and streams to cover the same frequencies.

"The advantage of the seawater antenna is that we no longer have topside real estate restrictions. We can place the antenna anywhere along the deck of the ship," Tam said.

As the use of wireless communication continues to grow, an increasing number of antennas are required to support data transmission, and many conditions limit available space for antenna placement. The Electrolytic Fluid Antenna could decrease the footprint for antennas in situations where shipboard space is scarce by decreasing the need for metallic antenna structures.

The Electrolytic Fluid Antenna can be turned off when not in use, with no unsightly obscuring views, and even allow ships to avoid radar detection by adversaries. The system could be used portably as an emergency antenna for watercraft, potentially powered by battery, solar panel or manually with a foot pump.

The technology could possibly be used on land with salt-supplemented water, replacing large unsightly antenna towers with fountains. Another use for a seawater antenna could be as an emergency antenna system for watercraft.

In the future, Tam said the technology will be able to use the salt solution in human bodies to turn body parts into communications antennas.

"My vision for the future for Navy warfighters is to design a small antenna using your own finger as an antenna element. For women, I can design earrings, a necklace and a bracelet. For men, a necktie and a belt," Tam said.

Using human body parts as communications antennas will give warfighters a winning edge by dramatically reducing the weight they have to carry.

Holly Quick is a contributor to CHIPS and sup¬ports the public affairs office of SPAWARSYSCEN Atlantic. Claire Dobransky from the SSC Pacific Technology Transfer Office contributed to this article. For more information, contact the SSC Pacific public affairs office at (619) 553-2725.

Electrolytic Fluid Antenna Facts
• Sends and receives HF, VHF and UHF signals.
• Frequency range is based on the height of the water stream:
-- HF – 70 to 80 feet;
-- VHF – 6 feet; and
-- UHF – 2 feet.
• Transmits and receives from 2 to 400 MHz.
• Capability to turn jet stream on and off.
• Consists of only a stream of saltwater, a current probe made of magnetic coil, an antenna signal cable, and a plastic tube (if indoors or in an area with extreme wind).
SPAWARSYSCEN Pacific scientists, Daniel Tam, P. Michael McGinnis and Lu Xu, demonstrate the Electrolytic Fluid Antenna at West 2011 in San Diego, Calif. The antenna can transmit HF, VHF and UHF signals. Photo by Rick Naystatt/SPAWAR A/V specialist.
SPAWARSYSCEN Pacific scientists, Daniel Tam, P. Michael McGinnis and Lu Xu, demonstrate the Electrolytic Fluid Antenna at West 2011 in San Diego, Calif. The antenna can transmit HF, VHF and UHF signals. Photo by Rick Naystatt/SPAWAR A/V specialist.
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