High resolution computations and measurements of potential EMI with models of medical implants and radiating sources

We used high resolution finite difference time domain (FDTD) computer modeling to evaluate the potential of cellular phones to cause interference in an implanted cardiac pacemaker-defibrillator. The model consists of a combination of an 835 MHz source which is either (1) a special boat-mounted cellular phone antenna (a sleeve dipole fed by a 3 W amplifier) or (2) a standard EMI test model of a cellular phone handset (a dipole antenna placed 8 mm from the victim). The victim is a simplified model of a pacemaker-defibrillator with one insulated sensing/stimulation lead in a torso simulator. The handset model and the victim conform to the AAMI PC69 standard for pacemaker-defibrillator EMI testing. We compare the EMI-induced voltage in the victim from the sleeve dipole source with the induced voltage from a cellular phone handset model. We to performed experiments using the actual antennas to compare with the computed results. We used a fiber-optically linked pacemaker-defibrillator simulator to measure the induced voltage at the junction between the lead and the box of the pacemaker-defibrillator model. Our conclusions are that the sleeve dipole at 15 cm, driven by a 3 W amplifier, is less capable of causing potential interference than the handset. The sleeve dipole, with its 3 W amplifier, produces 12.7 dB less induced voltage in the victim than the phone handset model driven with 0.6 W. Our results are validated, since measured values differed by 1.7 dB or less from computed values. This is well within the uncertainties of the measurements and computations.