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Safety of multi-channel stimulation implants: a single blocking capacitor per channel is not sufficient after single-fault failure.

An electrical fault in an implanted device that causes direct current to flow between electrodes will cause electrolysis, harmful unless it is very small. As a precaution, designers have for years put capacitors in series with pairs of electrodes to “block DC”. In this paper, we showed for the first time that this method of protection is actually far from safe in multichannel stimulators. As most stimulators are multichannel (e.g. retina, cochlear, etc), their designers (who mostly work in companies) must be more clever; they must appreciate the subtlety of possible failures that could destroy neural tissue in patients.