DENVER--Engineers from the National Institute of Standards and Technology have spent the last two years radio mapping large buildings and placing transmitters in old buildings before their implosion to study how waves behave inside buildings—both intact and demolished.

The idea is to help improve communications capabilities of first responders, who often lose signals in shielded or complex environments such as the basements and elevator shafts of buildings. The NIST also wants to study ways to detect radio signals through the dense rubble of a building that has collapsed as a result of natural disasters or terrorist attacks.

“We’ve been going around the country looking for buildings that are being imploded and putting RF signals and transmitters in to measure the radio frequency,” Chris Holloway, NIST electrical engineer, told an APCO audience attending the session, “Propagation and Detection of Signals Before, During and After a Building Collapse.”

The project was hatched after terrorists took down the World Trade Center on Sept. 11, 2001, and became a program funded by the Justice of Homeland Security departments. So far, the team, which includes electrical engineers Holloway and Kate Remley, has found that radio waves behave in unpredictable ways inside buildings, and any small change to a building, such as Mylar window coverings, can dramatically change propagation characteristics of radio waves.

NIST researchers have generated a large set of public-domain data on differences in signal reception at emergency communications frequencies for different types of building environments. They hope the information can begin to improve the communication capabilities of first responders and even change the way buildings are constructed.

The old Washington Convention Center and Veteran’s Stadium in Philadelphia were among a series of buildings around the country that NIST used for radio propagation experiments. Typically, NIST places a set of battery-operated transmitters located in strong boxes at various locations in a building prior to demolition. The transmitters send signals near the frequency bands used by emergency personnel and mobile telephones. The strength of the signals are then monitored and mapped outside the building before, during and after the building is imploded.

The next series of tests will center on looking at triangulation methods to determine where an RF signal is originating from.

“The problems now is you might have a strong signal on one side of a building, but the person holding the phones might be on the other side of the building,” said Holloway.

In addition, the researchers hope to develop reliable, cost-effective tools that can be retrofitted to existing radio systems to assist emergency personnel in locating and perhaps communicating with rescuers and other survivors trapping in a building. Early findings also suggest that metal debris can boost a signal buried by a pile of rubble.

“The idea is that future radios could send out low power signals such as chirps,” said Holloway. “This is based on what is used in deep space communications.”

Valuable information is also being derived simply from where NIST has placed the test RF signals, said Holloway. This might be valuable for building construction and ad-hoc network scenarios, he said. For instance, a building might include small transmitters that won’t activate until the power fails to create a communications network.