Wireless communication enabled 40 m underground

Researchers from South Korea’s Electronics and Telecommunications Research Institute (ETRI) have found a way to enable wireless communication below the Earth’s surface, in a significant departure from their traditional focus on terrestrial communication systems.

The team managed to send and receive voice signal-level capacity up to 40 metres below the Earth’s surface, opening new avenues for confirming the survival of individuals trapped due to accidents such as mine collapses. Their work was presented at the 20th Annual IEEE International Conference on Sensing, Communication, and Networking (SECON 2023), held in September.

Conventional wisdom held that wireless communication in the complex underground environments of mines was virtually impossible due to signal attenuation. However, ETRI overcame these obstacles by developing a new communication system, dubbed Subterranean Magnetic Field Communication Core Technology, which leverages the unique boundary conditions of magnetic fields within the medium.

The research team miniaturised the size of their transmitting antenna to one metre, contrasting with the tens-of-metres scale antennas used in previous international research. The system also features small receiving sensors based on magnetic induction, with dimensions in the order of centimetres.

According to the researchers, the newly developed transmitting and receiving antennas function akin to an access point (AP), essentially serving as a base station linking the surface and the underground. Therefore, it is expected that once transmitting devices on the surface and receiving devices underground are installed, individuals awaiting rescue could communicate through personal devices like mobile phones, connected to these antennas.

The successful communication test was conducted over a distance of 40 metres inside a mine composed of limestone bedrock, where stable communication was previously unfeasible. The team used a very narrow low-frequency band of 20 kHz, rather than the MHz or GHz range commonly used in general wireless communication; this frequency band was chosen to minimise material loss in the subterranean environment, and to suit the size of the antennas. The data transmission rate for voice signals was maintained at around 4 Kbps, sufficient for basic two-way communication.

According to the researchers, this successful application of magnetic field communication promises to bring substantial changes to the underground mining industry; notably, the technology is expected to offer a reliable mode of communication during emergencies such as mine collapses, underground fires and other disaster scenarios that typically disrupt conventional communication systems. This is because magnetic field communication systems should maintain connections between miners and rescue teams during accidents, thereby facilitating better-coordinated rescue efforts. The technology is also seen as a means to reduce response time in emergencies and to enhance safety measures.

“We have conducted successful communication trials between the first and second layers of underground mines using magnetic field communication systems,” said ETRI’s In-kui Cho, Director of the EM Wave Basic Technology Research Section. “This greatly reduces the likelihood of communication network disruptions caused by mine collapses.”

Beyond mining, magnetic field communication is expected to offer effective communication solutions in other underground structures like gas and oil pipelines, contributing to increased safety measures during various emergencies. As noted by Seung-keun Park, Assistant Vice President of Radio Research Division at ETRI, “This technology is anticipated to be a groundbreaking mode of reliable communication in complex and unpredictable environments like underground construction, tunnelling and ocean excavation.”

ETRI is currently concentrating its research on overcoming the limitations of propagating material in extreme conditions like underwater and subterranean environments, having previously executed underwater communications up to a depth of 40 metres in freshwater regions such as rivers and streams. Collaborating with industry partners, the researchers aim to further develop their technology for long-distance and miniaturised systems exceeding 100 metres.

Image caption: Subterranean Magnetic Field Communication Technology. Image credit: Electronics and Telecommunications Research Institute (ETRI).