Testing immunity of active implantable medical devices to industrial magnetic field environments

The aim of this work is to develop a new method for testing the immunity of active implantable medical devices to low frequency industrial magnetic fields (between 50 Hz and 100 kHz) up to the high occupational exposure limits. It is based on an experimental approach using a specific test bench with the capability of reproducing real exposure situations and testing multiple orientations between the magnetic field and the device. The solution adopted was to combined 3 concentric Helmholtz coils on 3 perpendicular axes. The test bench was designed using a numerical simulation software. A good agreement between the numerical model and the test bench characterisation was observed. The determination of the interference threshold of a pacemaker in function of the frequency is given as an example. The experimental results show between 50 Hz and 400 Hz an interference threshold between the public and the occupational exposure limits. Above 400 Hz, no malfunction below the occupational high exposure limits was observed. The encountered malfunctions are completely reversible. It also appears that the occurrence of interference strongly depends on the magnetic field orientation. This new test method will be applied to several pacemakers and could be used or adapted for others active medical implants such as cardioverter defibrillator or neurostimulator.