It is a problem that scientists and engineers have been grappling with since the aftermath of the September 11, 2001, terrorist attacks: How can emergency responders' communication tools be improved?
At ground zero in New York, first responders deployed search-and-rescue robots to help find survivors. The robots were supposed to be controlled via radio signals that never reached their targets.
"One of the things that became very clear was that the radio signals were lost rapidly between the transmitter, the robot and the person controlling the robot," electronics engineer Kate Remley said. "So, as a result, the robots were not able to go very far into the rubble pile to look for victims or for survivors."
From placing equipment inside soon-to-be-imploded buildings to testing a robot's ability to send audio and video in abandoned mines, Remley and other researchers at the National Institute of Standards and Technology are working to improve the devices that emergency workers rely on.
The institute conducts research in places that are notorious for rough emergency communications, from tunnels to collapsed buildings to oil refineries filled with metal that interferes with radio signals.
"We did some measurements in an old silica mine in northern California, where we deployed an urban search and rescue robot into the tunnel," Remley said.
"We monitored the radio wave communication, and we made note of where the signals failed, at what frequencies those signals failed and how far into the tunnel we could go before communication was lost. And we studied both the video that was being transmitted back from the robot and the control communications to the robot," she said.
The tunnel research revealed a "sweet spot": a particular frequency in mines, subways and tunnels where radio signals travel farthest. That may help researchers design wireless systems that are more likely to function in a disaster.
The sweet spot varies depending on a tunnel's dimensions. In a subway-sized tunnel, it is usually in the range of 400 megahertz to 1 gigahertz.
Creating "smarter" robots may also help improve disaster communications.
"A [smarter] robot will monitor its own received signal strength, so it will know when it is beginning to lose communication with its operator, and it will automatically deploy a little repeater [a device that can amplify and rebroadcast a radio signal] behind itself," Remley said.
"So it's a kind of artificial intelligence. The robot is saying, 'I know that I'm in a weak signal environment. I need to correct for that right away.' "
Not all of the research is done in difficult or dangerous places. The National Institute of Standards and Technology labs in Boulder, Colorado, have some intriguing facilities that also assist researchers in understanding how radio waves move.
One is the anechoic chamber, which means "without reflection." Remley said it is a very good facility for testing one transmitted signal and one received signal, because there are no reflections off the walls.
The campus also contains a reverberation chamber that creates the exact opposite effect.
"The idea here is, get as many reflections as possible," engineer Chris Holloway said.
"The magnetic fields bounce around inside this room. If we have a piece of wireless device [and] we want to see how it would work in environment X, Y, Z, we can come in here and change this environment, and it would give a researcher or engineer a very quick and dirty way of testing how a system might work," he said.
Researchers also put transmitters in buildings that were about to be imploded and measured their signals before, during and after the collapse. Then they tried to locate the equipment after the building was destroyed. Information from those tests could help find rescue workers with two-way radios and help pinpoint trapped survivors with cell phones.