Research On Electromagnetic Interference Noise Diagnosis And Suppression Methods For Medical Electronic Equipment

A great deal of medical electronic equipment requires rectification as they emit excessive electromagnetic interference(EMI) noise and cannot reach the standards of YY 0505-2012. Multiple noise sources exist in Medical electronic equipment, however, the research on the identification methods of the noise source has not been sufficient.Therefore, the most severe challenge of removing the EMI faults within the medical electronic equipment will fall on the identification on the noise sources that lead to exceeding noise.Aimed at meeting the challenge mentioned above, the paper conducts research on the EMI noise diagnosis and suppression methods of medical electronic equipment. The specific details are as follows.Firstly, the models of both conducted EMI noise in the power lines of medical electronic equipment and the radiation noise whose radiating source is in the free space are deduced on the basis of fundamental theories. the EMI noise model in common-mode/differential-mode is established as well.Secondly, analyzing the mechanism of production of EMI noise from the noise sources of the medical electronic equipment, and thus reaching at the corresponding suppression methods of EMI noise; analyzing the mechanism of transient supply current,imperfect earth, crosstalk and capacity coupling that cause transmitting EMI noise and establishing the model of radiation noise mechanism for the DC power line, the digital control line, the sensor line and AC power line; on the basis of the model of EMI noise mechanism, suggesting the suppression methods of EMI noise specific to PCB circuit and system cables in the medical electronic equipment.Thirdly, putting forward the diagnosis methods of conducted EMI noise based on EMD algorithm; through decomposing EMD, separating a quantity of IMF from the measured transmitting noise of time-domain hybrid, getting the Hilbert components from conducting the Hilbert transformation at the separated IMF, filtering the main components,and comparing the time-frequency characteristics of the signal in EUT, thus confirming the sources of causing exceeding transmitting noise; designing the diagnosis test-bed for EMI noise. The three simulation experiments , which has successively separated the hybrid signal made up by 50 Hz, 30 Hz, 20 Hz and 10 Hz and has correctly identified the simulated noise sources at 400 KHz and 100 KHz, indicate that the methods can effectively separate the noise sources in different frequency and different waveform.Fourthly, studying the diagnosis methods of radiating EMI noise based on near-field search technology; finding out the noise sources that arouse exceeding radiation noise by near-field probe and spectrum analyzer; designing a near-field diagnosis test-bed,conducting a near-field diagnosis experiment at a circuit board that produces radiation noise of 50 MHz and recognizing crystal oscillator of 50 MHz and its output signal loop as the radiation source that causes exceeding radiation. The experiment indicates that the methods can conduct a quick and effective diagnosis to the problem of exceeding radiation noise.Fifthly, testing and verifying the methods in the paper through synthetic diagnosis and processing experiments of EMI noise by three medical electronic equipment. The equipment of the three experiments are tested to be beyond standards and the noise sources are fundamentally confirmed through analysis of noise mechanism. Experiment one and experiment two apply EMD algorithm to diagnose the transmitting noise within the two equipment and experiment three applies near-field search technology to diagnose noise the radiation noise, all of which have successively recognized the noise sources that cause exceeding noise and have designed effective suppression methods of EMI noise. At last,the three equipment reach the testing standards and respectively include surplus capacity of at least 13.18 dB?V, 13.69 dB?V, and 12.43 dB?V/m. The three experiments have fully validated the methods in the paper to be effective and practical in engineering.