Study of Electromagnetic Interference with Medical Engineering Equipment

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We had studied the Electromagnetic Interference (EMI) with the electrocardiograph (ECG) in case of using an electric scalpel, which is a recent problem in medical operation rooms and is a current issue Japanese Association for Operating Room Technology. We pointed out that the noise induced on the AC-line and the noise radiated from an electric scalpel to ECG can be measured by spectrum analyzer or oscilloscope. As a result, it proved that EMI occurs in a wide frequency range on the ECG electrode cord while an electric scalpel is being operated. And EMI on the ECG proved to be induced through the ECG electrode cord. The noise induced on the ECG electrode cord indicates a special performance curve in case of operation both for cutting and for coagulation. Therefore, we made a proposal for the way of suppressing EMI on the ECG.It is that a low-pass filter is added between the ECG electrode code and the ECG transmitter. We have noticed that the origin of EMI's noise on the ECG occurs in a much lower frequency than 1kHz. We inspected these articles and the characteristic- of electric performance curves which were determined to 1kHz for the cut-off frequency. We suggest an added filter's circuit which accommodates a clamp circuit and a limited circuit. Furthermore, the cut-off frequency should be given at the lower frequency from 200Hz through 1kHz, because the spectrum of physical signals of ECG is even lower than about 30Hz except DC.Therefore, they are much smaller than EMI level occurring at the same frequency. As a result, we proposed DSP filter, which has the real-time operation.