Eugeniusz Grudzinski

EMF probes calibration in a waveguide

This paper is devoted to an estimation of electromagnetic field probe calibration error, while the calibration is performed within a waveguide, due to the presence of conducting walls of the waveguide and their influence on the calibrated probes transmittance. The presented estimations and measurements are performed for symmetric dipole antennas of different slenderness ratios. However, the approach is applicable to any type of electromagnetic field (EMF) standard and design of field probes.

Methods of the standard EMF generation

The previous chapter referred to two calibration methods: the standard transmitting antenna method (STA) or standard field method, and standard receiving antenna method (SRA) or substitution method. Lets characterize them briefly. 1. The STA method is based upon EMF generation with the use of a transmitting antenna whose parameters (radiation pattern, efficiency) are known to a required accuracy and established either theoretically or experimentally. The EMF at an observation point is calculated taking into account the parameters of the antenna, its excitation, and the geometry of propagation. 2. The SRA method requires a receiving antenna of well-known parameters and a system that makes it possible to measure current in the antenna or the voltage at its input. The SRA is placed in an EMF generated by an arbitrary source and then replaced by an antenna (meter, probe, device) under test. Two assumptions are made in this procedure: the EMF is stable enough to not change during the replacement, the antenna under test is immersed in the same field as the SRA and makes identical EMF deformations to the SRA. In the previous discussions we took into account EMF standards with dipole or loop antennas. However, an almost identical approach may be adopted when other types of standards are in use. For instance, in guided wave standards, the EMF is established on the ground of excitation measurement of a system of known parameters, which is similar to the standard field method. In the case of different types of chambers the substitution method is more appropriate.

Accuracy analysis of the standards with horn antennas

The accuracy of the power gain and the effective area of the horn antenna are of primary importance for the class of the EMF standard in which the antenna is applied. Horn antenna work above 1 GHz frequency range. Horn antennas are usually fed from a waveguide; the simplest “horn antenna”is an open end of a waveguide. Possible estimation errors and measurements are discussed in this chapter.

Accuracy analysis of EMF standards with dipole antennas

The accuracy of H-field generation is consider in this chapter. In these considerations, only “internal” factors will be taken into account, i.e., location of a transmitting and a receiving antenna, excitation measurement error, electrical sizes of the loop antennas, and others. Because of the specificity of the standard, it is possible to neglect here any “external” factors limiting accuracy of the standard, such as the influence of ground conductivity, the presence of other conducting objects in the neighborhood of the standard, multipath propagation, or interference caused by external EMF. This simplification is acceptable because of the fact that the antennas are much smaller compared to the wavelength and, as a result, are much less sensitive to the factors mentioned. For the same reason, the H-field standards may work in a less rigorously controlled environment, with no screened or anechoic chambers.

Comparative analysis of the EMF standards

Previous chapters presented and partially analyzed factors limiting the accuracy of EMF standards with dipole antennas, whip antennas, loop antennas, directional antennas, and guided waves. Several examples of accuracy estimations of the standards designed and used by the authors were introduced. Now we will try to present several methods that may be used when an estimation of separate factors limiting accuracy may be evaluated and the ways an estimation of a standards accuracy may be verified. Although the role of the factors may be discussed without an unequivocal answer, intensive work has been done toward their full identification and evaluation. The first step here is the continuous care of the power sources, meters, directional couplers, and other auxiliary equipment. These devices must be stored in appropriate conditions that ensure their protection against electrical and mechanical failures, corrosion, and other unwanted damage that can degrade their electrical properties. Apart from this, the equipment should be subject to periodic testing and calibration. Some components, for instance, thermocouple heads or the diode detectors, may be tested and calibrated directly by their users. However, the most important devices must be calibrated in a specialized laboratory, for example, by the manufacturer or other authorized institution (as, for instance, with data shown in Tables 7.1a, 7.1b, and 7.2). Final results of the approaches, i.e., the accuracy of a standard, may be proven by a comparison with other devices. The comparisons may be performed within a single lab, with different standardization methods, or, much better, cross-comparison standards in different labs. The latter may be especially helpful in eliminating permanent errors that could neither be observed nor taken into account in a lab where they frequently appear in its routine measurements.

Analysis of Peculiarities of Determination of the Electromagnetic Field Parameters near Radiation Sources

Some peculiarities of determination of the electrical E and magnetic H components of field strength near the field source (in the inner zone) are considered in the report. It is shown that in such cases calculation methods do not take into account many factors that can essentially distort the calculation results.

Analysis of requirements and peculiarities of design of electromagnetic field sensors when using them for people life and health protection

Main requirements and peculiarities of design of sensors for measurement of man-made electrical and magnetic radiation are considered, taking into account national standards that regulate the acceptable levels of electromagnetic fields. This problem is analysed from the point of view of using such sensors for protection of human life and health. Some errors of electromagnetic field measurements are investigated