Can minimum separation criteria ensure electromagnetic compatibility in hospitals? An experimental study

Electromagnetic interference (EMI) from radiofrequency (RF) sources can cause medical device malfunction. It has been proposed that such EMI be minimized by only operating sources of given RF powers when sufficiently separated from medical devices of given immunities. Such minimum separation criteria are estimated assuming free-space propagation, which is only valid in the ideal case. Yet proposed medical device EMC standards will require that minimum-separation criteria be listed in equipment manuals accompanying all new medical devices. It is essential that the practical utility of such minimum-separation criteria be evaluated. Fields due to an 800-MHz-type cellphone were measured in various rooms and corridors within an urban hospital, having both new (gyprock) and old (clay-block) wings. Data obtained from a calibrated antenna attached to a spectrum analyzer were repeatedly measured and averaged. Results were compared to those predicted by free-space propagation. Free-space predictions tended to overestimate measured fields in gyprock rooms and along corridors of both gyprock and clay-block construction. However, the free-space model tended to underestimate field levels predicted in clay-block rooms and in below-ground corridors. Usage of separation criteria to ensure EMC appeared useful in gyprock rooms and hospital corridors, but less so in rooms with clay-block walls or in below-ground sections of the hospital. This suggested that the latter regions should be considered as being special zones where side-by-side operation of RF sources and medical devices would require more conservative management (e.g., restriction or special approval of particular source or medical device).