Comparison of Injected and Radiated EMC Testing of Active Implanted Cardiac Medical Devices at the Boundary Frequency of 450 MHz.

We compared testing via radiated vs. injected susceptibility methods specified in the ISO 14117 standard for electromagnetic compatibility of implantable cardiac medical devices. Injected testing is specified at and below 450 MHz and radiated testing is specified at and above this boundary frequency. Experimental and computational studies were performed to determine voltages induced in a model of an implant. The device under test (DUT) was a model with a metal case (5.0 x 4.5 x 3.4 cm high) containing a diode detector and a fiber optic link plus an insulated wire simulating a unipolar lead. We evaluated induced voltage in the model for radiated versus injected testing. The voltage from experimental measurements agreed with computed values within ±1.4 dB or less. Radiated testing with 12.25 Watts delivered to the dipole specified in the standard induced the same voltage as the injected test requirement (14 Vp-p). This is in strong contrast to the specified radiated test power of 120 mW or even the optional worst-case radiated test level of 8 Watts. Lateral displacement of the dipole by 2 cm changed the voltage induced in the DUT by 20% or less. For depth changes below saline surface from 5 mm to 10 mm voltage variations were 12.5%. There is poor agreement (by a factor of 9.9 or more) for radiated vs. injected testing at the border frequency of 450 MHz separating the two methods. Our computational model can also be used at other frequencies and for EMC studies of other types of active implants that use the ISO14117 standard's radiated test method, such as neuro-stimulators.