Specifying zones for cellular telephone operation in hospital hallways

Critical-care medical equipment can malfunction if exposed to radio-frequency (RF) fields greater than the equipment's immunity. For newly purchased equipment, such immunity levels are at least 3 V/m. Since fields near a 600-mW, 850-MHz cell phone can greatly exceed this immunity level, hospitals often restrict locations where cell phone usage is permitted, some even banning cellphone usage throughout the hospital. To clarify whether such restriction is appropriate, this paper employs geometrical optics to investigate field strengths in a patient room due to cell phone usage in an adjacent hallway. Cellular-usage zones are maximized when wall construction employs both shielding and absorber elements. Criteria are suggested for specifying zones where cellphone usage should be restricted.