体内埋め込み型機能的電気刺激 (FES) システムにおける伝送誤り訂正回路の有効性

抄録

In the implantable functional electrical stimulation (FES) system, the electromagnetic induction was used to make the implanted stimulator be powered and controlled externally. This could lead to disturb transmitted stimulus data from the external unit to the implanted stimulator by environmental electromagnetic noise. As one of fail-safe methods to improve noise immunity, an application of the error detecting and correcting circuit to the implantable FES system was described. The term “noise immunity” meant the property of a system enabling it to reject influence of an external electromagnetic noise. The circuit was based on the Hamming coding, made high-speed error detection and correction feasible, and allowed hardware simplicity. An encoder and a decoder were incorporated into the prototype FES system. In the evaluation of the noise immunity capability, an electromagnetic noise generator, which was composed of a sinusoidal oscillator and a disturbance coil, was employed. The disturbance coil was moved coaxially and parallel close to the transmitting coil. Then, with varying frequency of sinusoidal wave of the oscillator, an attention was paid to the distance between the transmitting coil and the disturbance coil. The distance where the bit error rate of transmitted data was 2.5×10^-4 was measured in the cases with and without the error correcting circuit (ECC), respectively. The experimental results clearly showed that the system with the ECC was more insensitive to disturbance noise than that without the ECC. The ECC also worked effectively even in the cases of utilizing other electromagnetic disturbances, such as some electric appliances and a 430MHz-band radio ham transceiver. It was concluded that the reliability of transmitted stimulus data would be verified by using the ECC for the implantable FES system.