It is commonly, although not universally, believed that all medical devices will be hardened to the threat of EMI from UHF sources in a few years. This belief stems in part from the fact that the electromagnetic interference susceptibility of electronic devices usually decreases with increasing source frequency. There is little specific data to support this for devices other than pacemakers, however. The existing guideline for minimum radiated electric field susceptibility limit for medical devices recommends a susceptibility threshold of not less than 7 v/m at 1 GHz. This value is applicable to sources modulated in accordance with report MDC-E 1385, but does not directly relate to the cw SPS power beam at 2.45 GHz. Devices, then, which meet the existing guideline, could conceivably fail in the region immediately outside the SPS receiving areas. Consideration should be given to the questions of the compatibility of the general class of medical electronic devices with the SPS power beam. An existing government agency, the Bureau of Medical Devices of the Food and Drug Administration, has responsibility for medical device standards. To avoid duplication of effort or conflicts, any future work regarding compatibility should be coordinated with this agency. 5. SPS INTERFERENCE TO INTEGRATED CIRCUITS Although the possibility of interference from microwave energy to integrated circuits has been recognized for some time, actual measurements of the effects are relatively sparse (Roe, 1975). Fortunately, a few measurements do exist that enable one to calculate the potential for interference to a few types of integrated circuits. The following will discuss the potential interference problems to three different types of integrated circuits. Interaction between microwave energy and integrated circuits can occur in various ways. Catastrophic failures have been produced in integrated circuits when the power coupled into the leads of the devices is of the order of 1 to 100 watts for 500 microseconds. These failures are typically due to bonding wire melting, metallization failure, and junction shorting. Nondestructive interaction, however, typically occurs at power levels that are orders of magnitude less than those necessary for catastrophic failure. This nondestructive interaction or interference is the subject of interest here. The predominate interference mechanism in integrated circuits is believed to be rectification of microwave energy by the various pn junctions found on all devices. This rectified current can inhibit or induce state changes or change the quiescent operating point of the device. Changes of the quiescent operating point can be
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