Preface
The extent of measurements centered on electromagnetism largely exceeds traditional characterization of the electromagnetic fields. It can apply to domains as varied as nanotechnologies, telecommunications, meteorology, geolocalization, radioastronomy, health, biology, etc.
Measurement must follow the evolution of technologies. Note, for example, the strong development of radio and optical techniques. It is necessary to learn how to characterize these waves, which are increasingly powerful and propagate in increasingly complex media. These controlled waves also become a formidable tool for measurement, making it possible to consider high performance measurements giving time, distance, spectroscopic characterization, etc.
Regarding the multiplicity of controlled radio transmissions added to the different multiple sources that we call electromagnetic noises, there are naturally, increasingly pressing safety environment requirements, applied as standards and increasingly severe thresholds resulting in the development of more precise metrology in electromagnetism and methods of continuously improved measurements.
Measurement has a societal requirement that leads to the establishment and respect of recommendations and standards, which are intended for the information of companies and also to preserve public health. Specialists must encourage the development of a true metrological culture. This culture must give professionals and citizens the ability to properly analyze the very high quantity of data currently provided.
Science and measurement techniques in electromagnetism are very broad fields, as our electromagnetic environment covers all frequencies and wavelengths through distances from nanometers to light-years (described in Chapter 1). During the writing of this book we had to make some choices to limit the extent of this volume, while considering multiple facets of the topic. Thus we sweep the entire electromagnetic spectrum, from several hertz to terahertz; with optics, we consider distances ranging from nanometers to light-years; before extending towards the various measurement techniques using electromagnetic waves for various applications.
Chapter 2 written by Lalouat et al. concerns measurement to control electromagnetic waves using a near-field scanning optical microscope. The development of nanotechnologies and particularly nanophotonics involves new tools working within the nanometric scale. Optical near field techniques opens an interesting avenue for measurement within the nanometric scale, but also for controlling the electromagnetic field within nanometric dimensions and at last for designing new optical functions.
Visibility, the possibility of seeing at a certain distance is necessary in many fields such as meteorology, optical wireless communications, road safety or maritime, etc. Measurement of visibility, determined by the atmosphere transparency is described by Sizun and Al Naboulsi. In Chapter 3 they describe the measuring instruments dedicated to this determination — such as the transmissiometer and the diffusiometer — as well as the applicability covered by these visibility measurements.
Low coherence interferometry, discussed in Chapter 4 by Chapeleau et al., enables the measurement of phase and chromatic dispersion. This interferometric technique finds applications in the characterization of standard optical fibers, microstructured fibers and doped fibers, Bragg networks and optical planar circuits. In addition to the optical characteristics of the analyzed objects, interferometry makes it possible to reach, by rebuilding, other parameters such as the local temperature or deformation fields.
All the observations in millimeter-length, submillimeter waves and THz provide significant information for the study of atmospheric chemistry (ground, planets), astrochemistry (molecular clouds, star formation, study of galaxies, comets) and cosmology. In Chapter 5, Gérard Beaudin presents the new instrumental techniques for passive remote sensing at submillimeter waves and THz, which made it possible to obtain observations never achieved until now. The future significant projects for astronomy, aeronomy and planet exploration, will profit advantageously from these new technological developments.
In-situ measurements of the electromagnetic fields remain a difficult problem and it was necessary to give a reliable metrology that is accepted by all. In Chapter 6 Favennec develops exposimetry, i.e. techniques to measure human exposure to the electromagnetic field. Measurement of the fields lies within the scope of the field level checks with respect to the limitations of the field levels imposed on the territory.
For radiomobile communications, the propagation wave channel depends on the environment which is urban, rural, mountainous, etc. In Chapters 7 and 8, Sizun et al. present radiomobile measurement techniques, with particular focus on method choices according to the applications concerned and the need for analysis and modeling. Among the useful techniques specific to mobility, we see measurements in narrow band, impulse response measurements, angles of arrival and rates of transmission measurements.
With the explosion of mobile telephony into the world, dosimetry of the radio wave interactions with biological tissues has made significant progress in recent years. However, direct measurement of the absorptive powers of human tissues is limited by the heterogenity of tissues and the intrusive aspect of this approach. Taking account of significant progress in the field of electromagnetic simulators, a hybrid approach associating measurements and simulation was developed by Joe Wiart and Man Faï Wong (Chapter 9) and is applied to the dosimetry of the interactions in the head of portable telephones users. This hybrid approach, nevertheless, remains confronted with the variability of morphology and the representativeness of the digital models used.
Electromagnetic compatibility measurement of the electronic systems is fundamental. In Chapter 10, Besnier et al. gives a progress report on the current stakes of this type of measurement at the time when it plays an increasingly significant role in the development and homologation of electronic systems, whose complexity is increasing in a number of industrial products. The principles, the characteristics and the limits of certain current procedures are presented while emphasizing measurements of radiated emissivity and radiated immunity. The development of two recent measurement methods are presented because they offer new prospects for the electromagnetic measurement of compatibility: reverberating room with mode mixing and measurement in the near-field.
Chapter 11 written by Ismaël Cognard covers high precision pulsar timing in centimetric radioastronomy. This chapter presents instrumentations specific to 1.4 GHz for ultra-precise timing of radio impulses. A review of the techniques used to reach precise details of timing of a few hundred nanoseconds is proposed, accompanied by results obtained from Nançay's radio telescope.
In radioastronomy, interferometry appears as a new technique of observation. Thus, in Chapter 12, Zarka presents long baseline decameter interferometry. The Jupiter observations carried out simultaneously at Nançay and in Holland (700 km away), confirm this feasibility and the reliability of the suggested method.
We are quite conscious that this book on science and measurement techniques in electromagnetism does not cover all the fields and in particular that of quantum metrology; however it does enable us to form a well informed opinion about the variety of techniques and the methods available:
– to measure the characteristics of electromagnetic waves, in terms of local field, power and phase for a broad field of frequencies;
– for the metrology of physical quantity such as distance, time, optical range, etc., using the properties of electromagnetic waves;
– to find new approaches for new requirements for electromagnetic measurements in complex structured media such as biologic tissues.