by Janice Hamilton
The next time you visit a hospital and want to use a cellular phone, ask someone where you can do it safely. Making a call in the corridor could affect hospital equipment -- IV pumps, for example -- on a patient at the other end of the hall, or in a nearby room. Concordia researchers are trying to identify where cellular phones can be safely used, and where they should be prohibited.
Associate Professors of Electrical and Computer Engineering Christopher Trueman and Robert Paknys are studying the electromagnetic fields given off by cellular phones for the McGill University Biomedical Engineering Group on Electromagnetic Compatibility. This group is looking at electromagnetic interference from television transmitters, police radios and cellular phones that disrupts medical devices like monitors and infusion pumps. While some malfunctions are just inconvenient, others can be life-threatening.
Trueman, Paknys and post-doctoral fellow Junsheng Zhao are finding that the fields given off by a cellular phone tend to reflect off the brick side walls of hospital corridors. As you move away from the phone's antenna, the field strength drops off, then becomes fairly constant. The field also passes through walls into patients' rooms -- although this is not surprising, since cellular phones are designed to transmit between buildings.
"This suggests that hospital corridors might not be safe locations in which to operate cellular phones," Trueman said. "We want to make realistic mathematical models of hospital corridors, and do calculations to find out where it might be safe for people to operate their phones."
While the contract with McGill just started this winter, Trueman has been on contract for six years with the federal government's Communications Research Centre in Ottawa. He is trying to find out whether the calculations manufacturers use to test cellular phones are in line with what really happens. Beacause of the complexity of measurement, performance is generally calculated in the design stage, though the final design is measured before manufacturing.
Every commercial cellular phone model is slightly different, so Trueman designed a basic handset for his studies. He studied the handset by itself, then put it next to heads -- actually hollow cubes and spheres, filled with a sugar, salt and water mixture that has the electrical properties of brain matter. The presence of the head affects the patterns of the field.
First, he and graduate student Boris Lorkovic looked at the electromagnetic fields far from the handset. These are the fields at the receiver's end, and must be strong enough to ensure good-quality transmission. The observed measurements of these "far" fields matches the mathematical models he used. This suggests that calculations used in industry to ensure a cell phone will work satisfactorily are sufficiently accurate.
Trueman also studies the electromagnetic fields near the handset and antenna. These "near" fields -- the ones the sender is exposed to -- must be low enough to comply with safety regulations. "It's hard to get close without changing the fields, but using a three-dimensional probe, we've been successful at getting cleaner measurements," he said, adding that these measurements and two different calculation methods produce similar results, "so this boosts my confidence."
The next step uses a model head that is specially designed for electromagnetic studies. This "phantom head," nicknamed Yorick, underwent a CAT scan at the Royal Victoria Hospital; then student Najma Khalili went through the resulting 116 cross-sections and developed a detailed mathematical model of it. Using data from the Internet, she did the same thing for cross-sections of a cadaver head. Now, Trueman is working out and comparing calculations and measurements of far fields and near fields obtained with the phantom head. "We want to ensure both measurements and calculations are accurate," he said.