EMI Risk Assessment in a Hospital Ward With One and Two Roaming Wireless Transmitters

Abstract

To control electromagnetic interference, hospitals often specify that mobile transmitters may not be brought any closer than a minimum separation distance (MSD) to an electronic medical device. This paper investigates the risk that the field strength due to mobile transmitters exceeds the immunity level of a medical device. The spatial variation of the field strength can be characterized by the well-known Ricean probability distribution, using the Sabine method to evaluate the parameters. The mobility of transmitters is accounted for by assuming a function for the probability that a transmitter is present at each location throughout the hospital room. The risk of exceeding immunity is estimated with no restriction on the movement of mobile transmitters, and the reduction in risk is estimated when an MSD policy is enforced. Staff may not fully comply with the MSD, so the increase in risk with specified levels of non-compliance is found. It is shown that with some non-compliance the risk of exceeding immunity becomes constant with increasing MSD, and so specifying a larger MSD does not necessarily increase safety.

The New Localized Ray-Tracing-Maximum-Likelihood Method Estimates the Probability Distribution of the Field Strength

“…A question that arises is why, in the RTML method, we account only for the first order reflections everywhere in the room in determining E (1) M . The accuracy of the RTML method is at best equal to the accuracy of the cdf curve obtained by integrating the Ricean function whose parameters are determined using M field strength values within a local area.…”

“…Determining the electric field strength in indoor environments and at the ISM band frequencies or higher requires extravagantly large computational time if full-wave methods are used to solve Maxwell's equations. In some problems, such as electromagnetic interference (EMI) risk assessment studies [1], the location of the transmitter may vary, and thus the simulations must be repeated for many different source locations. Hence, even ray-tracing, from geometrical optics, may not satisfy a criterion for the computational speed.…”

“…The Nakagami, Weibul, Ricean, and Rayleigh distributions have been used to estimate the probability density function (pdf) of the electric field in indoor environments [2,3]. The Ricean function has been shown to accurately predict the cumulative distribution function (cdf) of the field in a room similar to that of this paper in [4][5][6].…”

Design of a 16‐element array antenna with a planar L‐shaped probe for a direction of arrival estimation of the unidentified broadband signal

“…In the L-band, a large number of signal sources are usually disposed in a narrow space of the indoor, interdevice interferences become a serious problem when the intensity of the signal sources are greater than the allowable value. [1][2][3] This issue is exacerbated when the strong strength of unidentified signals, such as intentional jammers or unauthorized radio broadcasts, disturbs other systems. To ensure trouble-free operation of the system, the direction of those unidentified signals must therefore be tracked, and their locations should be determined accurately.…”