Andreas Miaoudakis

Overall Uncertainty Estimation in Multiple Narrow-Band In Situ Electromagnetic Field Measurements

The possible adverse effects on human health of exposure to nonionizing electromagnetic fields have led international organizations and several countries to adopt exposure limits regarding public or occupational safety. To ensure compliance with these limits, specifically designed measurements with suitable instruments have to be performed. Since uncertainty is always present even when expensive instrumentation is employed, the final results from computations of the measured data deviate from the respective true values. The divergence depends on the instrumentation employed, the used methodology, or even the random effects, e.g., human factors or environmental conditions. In this paper, a method for evaluating total uncertainty when multiple narrow-band electromagnetic field measurements are performed is proposed. This is very common when exposure in residential areas is assessed.

On the Spatial Averaging of Multiple Narrowband Electromagnetic Field Measurements: Methods and Uncertainty Estimation

Methods of computational prediction can be used or specific measurements have to be performed for the estimation of human exposure to nonionizing electromagnetic fields at a certain place. According to the exposure standards, the predicted or the measured values have to be spatially averaged in an area representing the dimensions of the human body and compared with the adopted maximum permissible levels of exposure. In this paper, methods for spatial averaging nonionizing electromagnetic fields are discussed. Moreover, methods for estimating spatial average uncertainty of the total field strength values and of the summation of exposure quotients when narrowband measurements are performed in a multiple-frequency environment are proposed. Furthermore, since maximum field values have to be averaged according to the most widely accepted exposure standards, the traffic-dependent power level variation issue is also addressed. In particular, for GSM systems, an extrapolation method to the maximum possible field levels using data from real-time measurements when the frequency allocation per operator base station and the spatial distribution of the exposure sources are unknown is also proposed. Finally, an uncertainty estimation procedure associated to the extrapolated levels is presented.

On the uncertainty estimation of electromagnetic field measurements using field sensors: a general approach

One of the most common and popular practices on measuring the non-ionising electric and/or magnetic field strength employs field meters and the appropriate electric and/or magnetic field strength sensors. These measurements have to meet several requirements proposed by specific guidelines or standards. On the other hand, performing non-ionising exposure assessment using real measurement data can be a very difficult task due to instrumentation limits and uncertainties. In addition, each measuring technique, practice and recommendation has its own drawbacks. In this paper, a methodology for estimating the overall uncertainty for such measurements, including uncertainty estimation of spatial average values of electric or magnetic field strengths, is proposed. Estimating and reporting measurement uncertainty are of great importance, especially when the measured values are very close to the established limits of human exposure to non-ionising electromagnetic fields.

Evaluation of the electromagnetic fields exposure produced by WiMAX signals

Wireless networking technologies in recent years have witnessed important developments since the advantages benefit both data transmission service providers, and individuals or ordinary users. Ease of installation of a wireless network, led to the development of millions of Wi-Fi networks throughout the world. Nevertheless, Wi-Fi has certain drawbacks that inspired the implementation of a new technology called WiMAX. In 2003, the IEEE 802.16™ standard, also known as WiMAX (Worldwide Interoperability for Microwave Access) was adopted, in order to meet the requirements for broadband wireless access. The purpose of this paper is to study how the electromagnetic fields generated by WiMAX base stations can be evaluated in terms of exposure.

Electromagnetic exposure compliance estimation using narrowband directional measurements

The increased number of everyday applications that rely on wireless communication has drawn an attention to several concerns on the adverse health effects that prolonged or even short time exposure might have on humans. International organisations and countries have adopted guides and legislation for the public safety. They include reference levels (RLs) regarding field strength electromagnetic quantities. To check for RLs compliance in an environment with multiple transmitters of various types, analytical simulation models may be implemented provided that all the necessary information are available. Since this is not generally the case in the most practical situations, on-site measurements have to be performed. The necessary equipment for measurements of this type usually includes broadband field metres suitable to measure the field strength over the whole bandwidth of the field sensor used. These types of measurements have several drawbacks; to begin with, given that RLs are frequency depended, compliance evaluation can be misleading since no information is available regarding the measured spectrum distribution. Furthermore, in a multi-transmitter environment there is no way of distinguishing the contribution of a specific source to the overall field measured. Of course, this problem can be resolved using narrowband directional receiver antennas, yet there is always the need for a priori knowledge of the polarisation of the incident electromagnetic wave. In this work, the use of measurement schemes of this type is addressed. A method independent to the polarisation of the incident wave is proposed and a way to evaluate a single source contribution to the total field in a multi-transmitter environment and the polarisation of the measured incident wave is presented.

Self-powering wireless sensors in typical building environment

Electromagnetic Radiation found in a typical building today is an integral part of technology evolution. Electric power distribution networks are present in every building producing time variable magnetic and electric fields in a low frequency range (50 Hz - 100 KHz) commonly named as Extremely Low Frequencies (ELF). On the other hand wireless networks and other high frequency activity, in the range of Radio Frequencies (RF) 100 KHz up to 6 GHz produce ElectroMagnetic Fields (EMF) that radiate in the indoor environment. In this work the potential to take advantage of such electromagnetic pollution to provide power supply to micro-devices (such as wireless sensors) is examined. This is based in real EMF measurements in a typical office environment.

Electromagnetic field strength distribution in Wi-Fi signals covered areas: An experimental analysis of the variables that influence the exposure levels

The assessment of exposure to the radiation emitted by wireless devices need to take into account the complexity of WLAN networks and the quasi-stochastic nature of Wi-Fi signals. By analyzing only the maximum possible field strength and the traffic in such networks, one cannot accurately express the human exposure level. The type of transmitted information and the transmission protocol are factors that have significant influence on the field distribution in time and in amplitude. At the same transmission rate substantial differences may occur, depending on the traffic direction. All these aspects are analyzed here in different operating scenarios of WLAN devices within a network. The results of this paper show that the real electric field levels may vary between 15% and 80% of the maximum field strength - when measurements are made in the frequency domain only.

Measurements on Modern Wireless Communication Technologies and Estimation of Human Exposure

The evolution of wireless networking technologies in recent years leads to a faster, safer and more efficient knowledge transfer with the demand of growing up the volume of information handled. The ultimate aim of improving the living standards of citizens, requires a new foundation to evaluate and improve the existing to the present relevant measurement techniques and possibly the introduction of new ones. Also, new wireless information propagation models have to be proposed in the future and the old models have to be evaluated and modified for their improvement. This will be achieved by conducting reliable measurements and experimental tests. A key element of such measurements is the estimation of the present uncertainty. In this context, the purpose of this chapter is to study how the electromagnetic fields generated by modern wireless communication base stations can be measured and evaluated in terms of exposure.