Abstract

Between 44,000 and 98,000 patients die each year in US hospitals due to medical errors which may be prevented by providing the medical staff with instant access to patient records using wireless technology. If the electric field intensity of a wireless transmitter is greater than the immunity level of an electronic medical device (EMD), the device may malfunction. The consequences of this electromagnetic interference (EMI) can be as serious as harm to the patient. This thesis presents a quantitative assessment of the risk of exceeding immunity (REI) and an analysis of some EMI control policies by developing methods for fast estimation of the probability distribution of the electromagnetic field strength in indoor environments accounting for the mobility of transmitters.

To determine the REI, ray-tracing, the Sabine method from acoustics, and the Ricean probability density function (pdf) are used. A commercial software is used to show that the presence of some furniture has negligible effect on the pdf of the field strength.

An approximation of the power in higher order reflections in ray-tracing is used to present the modified ray-tracing-Rice method, immensely increasing the computational speed with no loss of accuracy compared to the Ray-tracing-Rice method. The Ricean and Nakagami pdfs are compared. It is shown that determining the Nakagami parameters requires more computation with no improvement in accuracy hence the Nakagami distribution is not recommended in indoor propagation.

The two-wave with diffuse power theory is shown to be unreliable in estimating the pdf of the sum field of two fixed transmitters and reliable in the case of roaming transmitters. The Ricean function is then shown to approximate the pdf of the sum field of two roaming transmitters.

The presence-weighted risk of exceeding immunity (PWREI) is introduced accounting for the mobility of one and two transmitters which can be present at distances close to and far from the EMD. The PWREI is useful for large-scale decision-making processes where both low- and high-risk scenarios are considered, contrary to worst-case analyses where the transmitters are fixed at close distances. The PWREI accounts for a policy where the staff members carrying the transmitters are required to maintain a minimum separation distance (MSD) from the EMD, and a non-compliance possibility. The PWREI is applied to a hospital ward using transmitters radiating 100 mW at 2.45 GHz. With full compliance, any low level of PWREI can be reached by increasing the MSD. Assuming some non-compliance, there exists an optimal MSD at which the PWREI reaches the risk floor and remains constant for greater MSDs, suggesting that larger MSDs are not necessarily safer. The MSD suggested by the International Electrotechnical Committee is too conservative compared to the optimal MSD. A vertical separation between the transmitter and the EMD is useful and recommended for increasing the efficacy of the MSD policy.