Engineers are working on a new generation of robots for use in hazardous environments and may discover radio communications enhancements that will help police and emergency responders work more safely.

One lesson emergency workers quickly learned during the 9/11 attack in New York City was that their radio-controlled search robots did not work well in tunnels or under mounds of concrete and steel debris. In fact, there came a point — all too often, short of the robots’ intended destinations — where communications failed all together.

The same proved true of firefighters’ radios in similar circumstances.

Since then, the U.S. National Institute of Standards and Technology (NIST) has been researching ways to improve emergency worker communications.

According to NIST researcher, electronics engineer Kate Remsley, their breakthrough came as a result of carefully-controlled experiments in an abandoned silica mine in northern California. The tests revealed that there is a transmission frequency ‘sweet spot’ at which radio waves travel farthest in a given tunnel. And the exact frequency depends on the diameter of the tunnel.

Remsley notes that NIST researchers are also looking at the ways radio waves bounce off of different kinds of objects. The hope there is that they can create a radio system that can penetrate curving or intersecting tunnels more effectively.