Evaluation of the measurement equipment for electromagnetic fields in the near-field and far-field zones

Abstract

Summary form only given. Almost all measurements for assessment of electromagnetic radiation effect on human health are practically made in the near-field and intermediate zones around the emitter. However, the equations of classic electrodynamics could not be used for calculating the electromagnetic radiation (EMR) in the above mentioned zones. Unfortunately, the equipment used for the radiofrequency (RF), and microwave ranges is most often calibrated only for power density measurements (for far-field zone). The use of such equipment in the near-field zone (without being calibrated for both electric and magnetic fields, separately) produces errors, which could not be easily evaluated. Sometimes the error may exceed in orders. A theoretical model for evaluation of equipment for nonselective measurements of EMR is presented using one calibrated only for the far-field zone, and used for all kind of measurements (including the near-fields). A model for assessment of the error in radiofrequency EMR measurements is developed on the basis of the apparatus' function of measuring equipment, and on the measured frequency range. The model affords an opportunity for the error's assessment in the near-field measurements with a calibration only for the far-field zone. A comparative evaluation of the errors from the measurements by different detector type (crystal and/or thermoresistor) has been performed using the proposed method. The crystal detector (calibrated for the far-field) gives an additional error of /spl plusmn/15%. The results of the comparison are shown as graphics. The model outlines once again the necessity of calibration in both homogeneous electric and/or magnetic fields.