Assessment of minimal-separation criteria in a 50-m corridor

In a hospital, portable radio frequency (RF) sources can cause field strengths in excess of immunity levels of some critical-care medical devices, unless appropriate minimal separations are maintained between sources and devices. This paper examines the risk of medical-device interference due to a 1900 MHz cell phone transmitting near one end of a 50-m hospital corridor. Detailed maps of corridor field strength are calculated, using geometrical optics, in planar cross-sections at various heights above the floor. For a device of given immunity, the interference risk is quantified from the ratio: (number of locations with immunity exceeded)/(total number of locations). Minimal-separation distances (separations ensuring that transmitter fields fall below a given device's immunity level) obtained assuming free-space propagation are compared to minimal separations specified in the current IEC standard for medical electromagnetic compatibility (EMC). It is concluded that using the separations of this standard effectively reduces the interference risk to zero.