Immunity of medical electronic devices to electromagnetic field of cellular mobile phones

The growing use of hand held radio telephones has altered electromagnetic environ-ment quite strongly during the last ten years. The purpose of this research was to examine the environment in hospitals, where almost all electronics must function properly to ensure the safety of the patients. However, hand held phones assist personal in their work and advances safety indirectly. Therefore it is important to investigate the real interference position. This research project was performed in co-operation with the medical engineering center of Helsinki University Central Hospital, HUCH. In this research it was concen-trated in those public areas of hospitals, where visitors or visiting workers may walk without surveillance. HUCH engineers think that these areas are more critical than special departments, where medical personnel usually see device malfuntions. Only few device types performing medical operations are generally used in public areas. Such devices are infusion pumps, syringe pumps, infant incubators and cardi-otocographs. These device types were chosen as objects in this research project. In addition some ECG-recorders were tested, because they are often used in general departments for monitoring purposes. An insulin pump was also tested as an example of small battery operated apparatus. Most device models chosen as test objects are in general use in HUCH. The electromagnetic immunity of medical devices was tested using hand held mobile phones in the vicinity of medical devices, to find out the required distance to cause interference in the operation of the device. Furthermore immunity tests were per-formed with a transmitting test antenna in an anechoic chamber to find out the lowest field strength sufficient to disturb their operation. The test method was in accordance with the basic standard IEC 1000-4-3, and the test was performed with the test signal having the same kind of modulation as the real transmitting signal of the particular radiotelephone. Also, the common test modulations required in basic test standards were used for comparison purpose. The results from the different test methods were compared with each other, which helps in assessing the results of the immunity tests made according to different product or basic standards.