Underground Acoustic Signals Expose Hidden Tunnels Beneath US Roads and Railways
2nd June 2026
Researchers in the US have recently demonstrated a new way to detect hidden underground tunnels by transmitting acoustic signals from beneath the target instead of above it.
Led by Mike Kass, PhD, a researcher at Oak Ridge National Laboratory (ORNL) in Tennessee, the team tested the new technique during a field experiment at the facility’s campus. They were able to identify concealed underground structures that threaten roads, railways, and other critical infrastructure.
Tunnel detection usually relies on signals sent downwards from the surface. Still, for the project, the team flipped the process and transmitted sound upward from below a tunnel to generate a distinctive subharmonic signal.