Electromagnetic Measurements in the Near Field (2nd Edition)
This book is devoted to the specific problems of electromagnetic field (EMF) measurements in the near field and to the analysis of the main factors which impede accuracy in these measurements. It focuses on careful and accurate design of systems to measure in the near field, based on a thorough understanding of the fundamental engineering principles and on an analysis of the likely system errors. Beginning with a short introduction to electromagnetic fields with an emphasis on the near field, it then presents methods of EMF measurements in near field conditions. It details the factors limiting measurement accuracy including internal ones (thermal stability, frequency response, dynamic characteristics, susceptibility) and external ones (field integration, mutual couplings between a probe and primary and secondary EMF sources, directional pattern deformations). It continues with a discussion on how to gauge the parameters declared by an EMF meter manufacturer and simple methods for testing these parameters. It also details how designers of measuring equipment can reconsider the near field when designing and testing, as well as how users can exploit the knowledge within the book to ensure their tests and results contain the most accurate measurements possible. The SciTech Publishing Series on Electromagnetic Compatibility provides a continuously growing body of knowledge in the latest development and best practices in electromagnetic compatibility engineering. This series provides specialist and non-specialist professionals and students practical knowledge that is thoroughly grounded in relevant theory.
Inspec keywords: electric potential; electric field measurement; electromagnetic fields
Other keywords: photonic EMF measurement; directional pattern synthesis; electromagnetic measurement; magnetic field measurement; power density measurement; near field; electric field measurement; far field
Subjects: General electrical engineering topics; Conference proceedings; Electrostatics; Steady-state electromagnetic fields; electromagnetic induction; Electrostatics, magnetostatics
- Book DOI: 10.1049/SBEW042E
- Chapter DOI: 10.1049/SBEW042E
- ISBN: 9781891121067
- e-ISBN: 9781613531068
- Format: PDF
-
Front Matter
- + Show details - Hide details
-
p.
(1)
-
1 Introduction
- + Show details - Hide details
-
p.
1
–9
(9)
This book is concerned with near-field measurements and in this chapter, we would like to set the context of why this is necessary from a human point-of-view and introduce the field magnitudes that are important. The degradation of the natural electromagnetic environment is the forgotten price that must be paid for our inconsiderate enthusiasm for industrial revolution. As a result, we are reaching a situation in which spending for the protection of the environment must sometimes exceed the investment in the systems causing the degradation.
-
2 The Near Field and the Far Field
- + Show details - Hide details
-
p.
11
–25
(15)
The essential information for practical metrology is presented in this chapter, including a brief summary of the near-field properties as well as the basic equations and formulas related to fields generated by simple radiation sources.
-
3 EMF Measurement Methods
- + Show details - Hide details
-
p.
27
–49
(23)
From the point of view of antenna performance evaluation, it is essential to measure the strength of E or H components near the antenna. This then makes it possible to find the current or the charge distribution along the antenna. With this as a basis, it is possible to find the radiation pattern of the antenna and its input impedance. The measurement of E, H, or S in the near field (with the phase information conserved) permits us, with some complex calculations, to find the antenna's radiation pattern in the far field. From the point of view of shielding, absorbing, or EMF attenuating materials investigations, the E, H, and S measurements are sufficient as well.
-
4 Electric Field Measurement
- + Show details - Hide details
-
p.
51
–88
(38)
The basic method of electric field measurement, over a wide frequency range, involves the use of charge induction phenomenon in a body illuminated by the field. As shown in Fig. 4.1 is the electromotive force (emf) eE induced by the electric component of the EMF generated by an arbitrary source in a symmetrical dipole antenna of total length 2h.
-
5 Magnetic Field Measurement
- + Show details - Hide details
-
p.
89
–111
(23)
This chapter discusses properties of the probes for RF magnetic field measurements and in particular, the factors limiting the measurement accuracy. Our considerations are limited to a probe consisting of a circular loop antenna loaded with a detector of a shaped frequency response. However, the majority of results are fully applicable for Hall-cell probes, magneto-optic probes, those with a magneto-diode, and for other designs, especially when considering averaging of the measured field upon the surface of the measuring antenna (probe). Many of the considerations are similar in character to those presented in Chapter 4, and some are concerned with the magnetic field measurement specificity.
-
6 Power Density Measurement
- + Show details - Hide details
-
p.
113
–131
(19)
Widely applied methods of electromagnetic power density measurement were presented and analyzed in this chapter. The considerations have a purely theoretical character, and they are concerned with the field relationships only. The source of the measurement accuracy limitation, by way of E- or H-field measurement (method error), was demonstrated, and the magnitude of the error for different combinations of sources and measuring probes was estimated. Then, a certain accuracy improvement, as a result of simultaneous E- and H-field measurement, and a calculation of an arithmetic or geometric mean was proposed.
-
7 Directional Pattern Synthesis
- + Show details - Hide details
-
p.
133
–149
(17)
When radio communication or propagation problems are discussed, an idealized understanding of the expression linear or circular (or, more accurately, elliptical) polarization is usually used. At the same time, in order to simplify any complicated problems, it is forgotten that even a linearly polarized wave propagating near the surface of a lossy medium changes its polarization to an elliptical one that is applied to measure the equivalent conductivity of the medium. In the case of multi-path propagation of a circularly (elliptically) polarized wave as a result of multi-path interference, a spatial rotation of the polarization plane may be observed. Thus, it may be called quasi-spherical or quasi-spheroidal polarization. Usually, such a situation occurs in the neighborhood of a complicated system of radiators (primary and secondary) when they are excited with an FM modulated signal or, for instance, as a result of changes in phase differences of the rays coming to a point of observation, due to frequency changes or Doppler effect.
-
8 Other Factors Limiting Measurement Accuracy
- + Show details - Hide details
-
p.
151
–181
(31)
This chapter has briefly discussed, among others topics, the influence of thermal drift on the probe parameters, the role of its dynamic characteristics, deformation of the measured field by a person performing the measurements and by the meter, resonant phenomena, and others. At the end of the chapter, an example based on the uncertainty budget estimation of EMF measurement will be presented.
-
9 Photonic EMF Measurements
- + Show details - Hide details
-
p.
183
–206
(24)
Until now, the dominating technique for EMF measurement was to use an antenna (mainly a dipole or a loop) loaded with a detector (a diode or, more rarely, a thermocouple) and transfer the DC voltage from the probe to an indicator (in the case of the most popular designs of two piece meters) through a high-resistance (transparent) transmission line (Fig. 9.1a). The most important inconvenience of this technique is the vanishing of phase information that is (sometimes) indispensable; similarly, the spectral information is lost as well. Although the latter is usually unnecessary, especially where wideband measurements are of concern, we will see in our further considerations that it is possible and advantageous to perform wideband measurements using spectral information as well.
-
10 Final Comments
- + Show details - Hide details
-
p.
207
–213
(7)
This book discusses EMF measurement possibilities in the near field, especially for human safety and environmental protection purposes. Field measurement technical problems in the near field are similar or identical to those in the more widely understood area of electromagnetic compatibility. Some differences between the far and the near field were emphasized, especially those essential to measurements performed in the near field. EMF measurement methods in the near field were presented, and details were provided about factors limiting accuracy of the electric and magnetic-field and power-density measurement in the near field using small electric and small geometric antennas. The influence of external factors, which are important to estimation accuracy, was outlined, and new measuring possibilities, based mainly on the development of photonic techniques, were briefly presented.
-
Back Matter
- + Show details - Hide details
-
p.
215
(1)