A new technique to monitor the electrode and lead failures in implantable microstimulators and sensors

The electrodes and wire lead failures are the main reasons of implantable system malfunction. The impedance change and fibrosis of the living tissue which is in contact with the electrode are also important parameters to monitor. Measuring the resistance of leads, electrode-tissue contact and the interelectrode tissue can be used to test the functionality of implanted electrodes and to deduce the state of the interelectrode tissue. This paper describes the feasibility of using an oscillator, the frequency of which is controlled by the above mentioned resistance, to test the electrode functionally as well as the state of the living tissue. The oscillation frequency is a digital signal which can be easily evaluated by the implant or the external controller. It is shown that this approach results in a very low-cost and practical solution. The oscillator has been designed using CMOS 1.2 μm technology parameters. This technique can be implemented in any implantable system to increase its reliability