A bomb has reduced a shopping mall to rubble, leaving rescue workers desperate to know if anyone inside is still alive. Thanks to a remarkable discovery at Bell Labs in New Jersey, they could one day find out simply by calling the cell phone of someone lying unconscious inside.
That is because the signal from a cell phone reveals two vital signs: a person's pulse and breathing rate. Better still, the person does not even have to answer the phone.
The Bell Labs engineers, led by the husband-and wife team of Victor Lubecke and Olga Boric-Lubecke, noticed that some of the microwaves transmitted by a cell phone's antenna bounce back to the phone from the user's chest, heart and lungs.
As those organs move, the frequency of the reflected radiation is Doppler shifted by a tiny amount. If the lung is expanding, the radiation bouncing off it is pushed closer together, slightly raising its frequency. A contracting lung lowers the frequency. The variation is tiny: one hertz in a billion.
Bell Labs - owned by Lucent Technologies Inc. - now plans to modify the mobile phone with a circuit that detects the Doppler shift in the reflected signal picked up by its antenna. The phone then sends this data on to the base station, where further processing extracts the user's vital signs. "We're talking about very low-frequency signals," Mr. Lubecke said. "They are easy to separate from a voice."
To pick up the reflected signals, the cell phone has to be held steady for a few seconds, Mr. Lubecke said. That is very likely what will happen if its owner is trapped or unconscious.
Doctors could also use the Bell Labs technology routinely to monitor a patient's heart or breathing - just by phoning the patient's mobile.
Mr. Lubecke has been working with James Lin of the University of Illinois in Chicago to test his ideas. The researchers used a radio with similar frequency and power to a typical mobile phone to demonstrate the effect in their lab. Now they are building a prototype detector.
Today's cell phone networks treat the interference information as unwanted noise and discard it. For the new system to work, the network will have to be modified to retain and interpret the signals, Mr. Lubeck said.
While the phone must be switched on, you do not have to answer it for the system to work: just making it ring generates enough of a signal to allow the heart and lung data to be piggybacked onto the signal that tells the caller your phone is ringing.
Some experts say the technology faces major challenges. Alan Preece, who investigates mobile phone health effects at the University of Bristol, said that the heartbeat signal would be so much weaker than the main signal that it risks being swamped.
If the Bell Labs discovery can be reliably exploited, it could also help you get remote diagnoses just by phoning your doctor. So while the jury is still out on cell phone safety, pending the results of a five year study by the World Health Organization, it looks like cell phones may have at least some potential health benefits on the horizon.
This article is excerpted from New Scientist, a weekly science and technology magazine based in London. Distributed by the New York Times Syndicate.