Through-the-Earth (TTE) signalling is a type of

radio Radio is the technology of signaling and communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmi ...

signalling used in mines and

cave A cave or cavern is a natural void in the ground, specifically a space large enough for a human to enter. Caves often form by the weathering of rock and often extend deep underground. The word ''cave'' can refer to smaller openings such as sea ...

s that uses low-frequency waves to penetrate dirt and rock, which are opaque to higher-frequency conventional radio signals. In mining, these lower-frequency signals can be relayed underground through various

antennas In radio engineering, an antenna or aerial is the interface between radio waves propagating through space and electric currents moving in metal conductors, used with a transmitter or receiver. In transmission, a radio transmitter supplies an ...

repeater In telecommunications, a repeater is an electronic device that receives a signal and retransmits it. Repeaters are used to extend transmissions so that the signal can cover longer distances or be received on the other side of an obstruction. Som ...

or mesh configurations, but communication is restricted to line of sight to these antenna and repeaters systems.

Overview

Radio communication within caves is problematic because rock is a conductor and therefore absorbs radio waves. Ordinary radios typically have a very short range within caves. Low frequency (LF) or

very low frequency Very low frequency or VLF is the ITU designation for radio frequencies (RF) in the range of 3–30 kHz, corresponding to wavelengths from 100 to 10 km, respectively. The band is also known as the myriameter band or myriameter wave a ...

(VLF) radio with single-sideband modulation is more commonly used today. Through-the-Earth transmission can overcome these restrictions by using ultra-low frequency (300–3000 Hz) signals, which can travel through several hundred feet of rock strata. The antenna cable can be located on the surface only at a mine site, and provide signal coverage to the mine. The antenna may be placed in a "loop" formation around the perimeter of the mine site (or wherever coverage is needed) for systems using magnetic fields to carry signals. Systems that use electric fields as the signal carrier are not subject to this limitation. Transmissions propagate through rock strata which is used as the medium to carry the ultra-low-frequency signals. This is important in mining applications, particularly after any significant incident, such as fire or explosion, which would destroy much of the fixed communication infrastructure underground. If the terrain makes a loop surface antenna impractical to install, then the antenna can be installed underground or a non-magnetic field type carrier may be used. But because the signal travels through rock, the antenna does not need to run into all parts of the mine to achieve mine wide signal coverage, thus minimizing the risk of damage during an incident.

Cave radios

Portable magnetic-loop cave radios have been used by

cavers Caving – also known as spelunking in the United States and Canada and potholing in the United Kingdom and Ireland – is the recreational pastime of exploring wild cave systems (as distinguished from show caves). In contrast, speleology is ...

for two-way communication and cave surveying since the 1960s. In
typical setup
the transmitting loop, consisting of many turns of copper wire, is oriented horizontally within the cave using a spirit level, and driven at a few kHz. Though such a small antenna is a very poor radiator of propagating radio waves at this low frequency, its local AC magnetic field is strong enough to be detected by a similar receiving antenna up to a few hundred meters (yards) away. The received signal's strength and its dependence on orientation of the receiving coil yields approximate distance and directional information. Early models were called " speleophones"—examples include Bob Mackin's "Molefone". The Molefone is called "one of the first practical cave radios," though it is no longer manufactured. Other popular LF/VLF radios include the HeyPhone and the Nicola System. All three operate single (upper) sideband on 87 kHz in the LF band. Systems like ''Molefone'' and ''HeyPhone'' operate as single-sideband (USB) 87 kHz radio with earthed electrodes of 25–100 metres (80' to 330') length. Design for ''HeyPhone'' system is openly available.

Personal emergency device

There are several systems that have been recently developed. One system is known as the PED System, where PED is an acronym for personal emergency device. Initially developed after a mining disaster in Australia at Moura No. 4 Coal Mine in 1986, and further developed after the Moura No. 2 Coal Mine explosion in 1994 where the need for a communication system to survive major incidents underground was identified in the inquiries into the disasters. PED is a one-way text paging device, with wide use in Australia, as well as installations in the

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, China,

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, and Sweden. Australian compan
MST Global (formerly Mine Site Technologies)
began the development of PED in 1987, and it became commercially available and Mine Safety & Health Administration (MSHA) approved in 1991. The best documented use of PED during a mine emergency is from the Willow Creek Mine Fire in 1998 in

Utah Utah ( , ) is a state in the Mountain West subregion of the Western United States. Utah is a landlocked U.S. state bordered to its east by Colorado, to its northeast by Wyoming, to its north by Idaho, to its south by Arizona, and to it ...

, where it was able to quickly alert miners underground of the need to evacuate before toxic fumes from the fire filled the mine. Reports of this use can be seen on the MSHA website.

Development

Emerging technologies have recently been developed such as th
Rescue Dog Emergency Through the Earth Communication System
developed by E-Spectrum Technologies. The Rescue Dog is a two-way extended-range portable through-the-Earth solution that was developed in the US in cooperation with The National Institute for Occupational Safety and Health (or NIOSH) which does not rely on large loop surface antennas for signal transmission. New non-portable systems have also been developed by companies such a
Lockheed Martin
for use in emergency chambers to provide post-accident, two-way, emergency voice and text communications independent of surface or in-mine infrastructure.

New technologies

A new wireless "Miner Lifeline" telecommunication technology is being tested in 2012 at the

West Virginia West Virginia is a state in the Appalachian, Mid-Atlantic and Southeastern regions of the United States.The Census Bureau and the Association of American Geographers classify West Virginia as part of the Southern United States while the B ...

Robinson Run mine (recent production per year of coal using 600 miners). The system supports

voice The human voice consists of sound made by a human being using the vocal tract, including talking, singing, laughing, crying, screaming, shouting, humming or yelling. The human voice frequency is specifically a part of human sound producti ...

text Text may refer to: Written word * Text (literary theory), any object that can be read, including: **Religious text, a writing that a religious tradition considers to be sacred **Text, a verse or passage from scripture used in expository preachin ...

, or SOS sent on a "bubble" of magnetic waves, and "can move more than up or down and laterally, arriving in less than a minute." The Israeli company Maxtech has developed a software system that automates the optimal organization of a set of limited-range communications devices, using any mixture of types of communication (through-the-earth radio, line-of-sight radio or optical, etc.). This system was used in the

Tham Luang cave rescue In June and July 2018, a junior association football team and their assistant coach were rescued from the Tham Luang Nang Non cave in Chiang Rai Province in northern Thailand. Twelve members of the team, aged 11 to 16, and their 25-year-old ass ...

References

External links

Rescue Dog Emergency Communication System

Nicola System
A two-way communication system developed for

speleologists Speleology is the scientific study of caves and other karst features, as well as their make-up, structure, physical properties, history, life forms, and the processes by which they form (speleogenesis) and change over time (speleomorphology). ...

.
CREG
Journal of the Cave Radio and Electronics Group of the British Cave Research Association
MST Global (formerly Mine Site Technologies)
for more information on the PED through-the-earth communications system.
Radius 2
Russian wireless TTE underground system of alarm reporting, personal calling, observation and people search in case of mine accidents
Cave-Link
Data communication and measurement system for cave research and mining. {{DEFAULTSORT:Through The Earth Mine Communications Radio communications Telecommunications techniques Underground mining