Platinum and platinum/iridium electrode properties when used for extracochlear electrical stimulation of the totally deaf
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Little work has been reported which characterises the electrical behaviour of electrode materials used for extracochlear stimulation. Electrode properties were investigated to optimise preparation methods and facilitate the design of electrode driving circuitry. Electrode preparation techniques were developed in vitro, using a combination of electrochemical measurements and scanning electron microscopy. Electrochemical etching gave the lowest observed impedances. Four subjects were each temporarily implanted with two active extracochlear electrodes, one of pure platinum and another of electrochemically etched platinums/10 per cent iridium alloy impedance measurements were taken over a ten-day implantation period and were interpreted by a simple electrical model. Constant-current stimulation was perceptually more effective than voltage-controlled excitation for the same energy input. Stimulation dynamic ranges were measured and used to estimate design limits for practical stimulators. The effect of changing electrode diameters was studied in vitro and was related to the same model. The best in vitro analogue of the in vivo environment was found to be dilute isotonic saline.
KeywordsCochlear implant Electrical stimulation Electrode modelling Iridium Platinum
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