DARPA’s AMEBA developing transmitters that could communicate through walls, undersea and underground environment

Modern day radio transmitters and receivers, the devices that uses electromagnetic wave signals to communicate through cellphones, radios and television, seem to be present everywhere.  The propagation of these electromagnetic waves has some limitation too,   Key among these is that radio frequency signals hit veritable and literal walls when they encounter materials like water, soil, and stone, which can block or otherwise ruin those radio signals. This is why scuba buddies rely on sign language and there are radio-dead zones inside tunnels and caves.

 

US Militaries are reportedly constructing of numerous Top Secret underground and undersea bases, as well as secret tunnels, all over the world. “Many governments have contracted with major civil and marine engineering firms to construct massive installations underground and undersea. These bases are found in many countries, including the USSA, Russia, China, Switzerland, Norway, Israel, Saudi Arabia, Australia, Canada, Great Britain and more,” Martin. Communications is a vital component of such facilities.

 

Ultra-low frequency (ULF) signals have very large wavelengths that can penetrate areas usually prohibitive to radio signals such as within caves or underwater. Commonly used radio wave frequencies and radar bands do not penetrate water or the ground due to their electrical conductivity and in the case of the earth, iron ores that strongly attenuate radio signals.

 

While ULF wavelengths do not carry large amounts of data – typically short encoded messages – they could enable communication that is impossible with typical radio equipment, such as with divers, troops in caves or difficult terrain, or personnel housed underground. “That’s why people trapped in mines must communicate with the surface by tapping on pipes, because typical radio communication cannot be used,” said Geoff McKnight, co-lead researcher on the project from HRL’s Sensors and Materials Laboratory.

 

A nearby band of very-low-frequency (VLF) signals (3 KHz to 30 KHz) opens additional communications possibilities because for these wavelengths the atmospheric corridor between the Earth’s surface and the ionosphere—the highest and electric-charge-rich portion of the upper atmosphere—behaves like a radio waveguide in which the signals can propagate halfway around the planet.

 

Currently U.S.  ground forces employ PRC 117 SATCOM and PRC-150 high frequency radios for over-the-horizon communications but with substantial drawbacks, according to Olsson. While High frequency radios require the transmitter to know the precise location of the receiver, and the operator must change antenna construction for night and day operations to match the lowered ionosphere. SATCOM radios are vulnerable to Jamming attacks by sophisticated state agents such as China and Russia.

 

ULF and VLF can also be utilized as a search and rescue tool for buried miners or victims trapped in earthquake rubble because of its ability to penetrate rocks and building materials. “For those people in mine disasters, or in buildings collapsed after earthquakes, a portable low-frequency beacon could also make a dramatic difference in search and rescue,” said Walter Wall, project co-lead from HRL’s Advanced Electromagnetics Laboratory. And because of that atmospheric waveguide effect, VLF systems might ultimately enable direct soldier-to-soldier text and voice communication across continents and oceans.

 

However, the free-space wavelengths of electromagnetic fields at ULF and VLF frequencies measure tens to thousands of kilometers in length, resulting in either very large or severely inefficient transmitter structures when constructed using conventional antenna approaches.

 

And since longer wavelengths have required taller antennas, communications in these frequency bands have entailed the construction of enormous and costly transmitter structures. A VLF antenna that the Navy built on a remote peninsula in Cutler, Maine, in the heat of the Cold War just to send a trickle of data to submarines makes the point: the gargantuan transmitter complex occupies 2,000 acres, features 26 towers up to 1,000 feet high, and operates with megawatt levels of power. Such transmitters are impractical in many operational scenarios, especially those requiring mobility.

 

DARPA’s Microsystems Technology Office, with his newly announced A Mechanically Based Antenna (AMEBA) effort, is betting on a little-exploited aspect of electromagnetic physics that could expand wireless communication and data transfer into undersea, underground, and other settings where such capabilities essentially have been absent. The basis for these potential new abilities are ultra-low-frequency (ULF) electromagnetic waves, ones between hundreds of hertz and 3 kilohertz (KHz), which can penetrate some distance into media like water, soil, rock, metal, and building materials.

 

With the AMEBA program, Olsson aims to develop entirely new types of VLF and ULF transmitters that are sufficiently small, light, and power efficient to be carried by individual warfighters, whether they are on land, in the water, or underground. The transmitters developed in AMEBA will consume less than 20 W of power and weigh less than 10 kg, making them suitable for man-portable wireless communications.

 

“If we are successful, scuba divers would be able to use a ULF channel for low bit-rate communications, like text messages, to communicate with each other or with nearby submarines, ships, relay buoys, UAVs, and ground-based assets, Through-ground communication with people in deep bunkers, mines, or caves could also become possible,” Olsson said. Low frequencies can allow underwater communications at distances to hundreds of meters and through-earth communications at distances of hundreds of meters though soil and rock of heterogeneous composition and moisture content.