Safe usage of RF sources in hospitals: Assessing EMI risk when using Minimal Separations

Abstract

Wireless (radio-frequency, RF) technology is expected to improve healthcare delivery and should reduce incidence of “mobile” medical errors. However, wireless usage
must not cause electromagnetic-interference (EMI) malfunction of critical-care medical-devices, which might threaten patient safety. To reduce such “EMI risks”, the current healthcare EMC standard (IEC 60601-1-2-2001) requires that new-equipment manuals state that RF-sources be operated no closer than triple-free-space minimal separations from critical-care medical devices. However, the ensuing EMI risk is unknown. We now propose a method to estimate this risk, the “minimal-separation risk” (MSR).

To estimate the minimum-separation risk in corridors, data was obtained from both measurements and simulations. For measurements, an RF source was operated at one end of a corridor (50m x 3m x 2m, clay-block walls, concrete floors and ceilings) and fields were sampled with a robot. A power law model was fitted to the data, the residual was computed, and its cumulative distribution was used to estimate the probability of an EMI malfunction at triple-free-space separations from medical devices of 3- and 10-V/m immunities. Simulation data was obtained using 3D geometrical-optics simulations of the same corridor used for measurements.

It was estimated that when a 600-mW, 1.9GHz source is operated at more than triplefree-space minimal separations (10V/m: 1.8m; 3V/m: 5.9m), then the EMI risk would be reduced to less than 5-8 % for 3-V/m equipment, and to less 0.03-0.7 % for 10V/m equipment, based on simulated and measured data respectively. However, enforcing such separations would be inconvenient to medical staff.

The value of the minimum-separation risk is that it provides a quantitative EMI risk measure, required for development of wireless policies in hospitals.