Prof. Jean-Charles Bolomey
Supelec, Electromagnetic Research Department
University Paris-Sud XI
Jean-Charles Bolomey is currently an Emeritus Professor at Paris-Sud University. He graduated from the Ecole Supérieure d’Electricité (Supelec) in 1963, received his Ph.D. degree from Paris-Sud University in 1971, and became a Professor at this University in 1976. His research has been conducted in the Electromagnetic Research Department of the Laboratoire des Signaux et Systèmes, a joint unit of Supelec and the National Center for Scientific Research (CNRS).
Since 1981, his research contributions have been devoted to Near-Field techniques in a broad sense, including antenna measurement, EMC testing as well as Industrial-Scientific-Medical (ISM) applications. These contributions have largely concerned measurement techniques and have been deliberately oriented toward innovative technology transfer and valorization. Jean-Charles Bolomey has more particularly promoted the modulated probe array technology, demonstrating its unrivaled potential for rapid Near-Field scanning. He has co-authored with Professor F.Gardiol a reference book on principles and applications of the Modulated Scattering Technique (MST). He is holder of numerous patents covering various MST-based probe array arrangements for microwave sensing and imaging systems. In 1986, under the impulse of the National Agency for Valorization (ANVAR) and of the CNRS, Professor Bolomey founded the Société d’Applications Technologiques de l’Imagerie Micro-Onde (SATIMO), which is now considered as a leading company in the field of antenna measurement. He has been also involved in industrial applications of microwave heating as a Chairman of the Microwave Group of Electricité de France (EDF) and was appointed as a consultant by the Délégation Générale de l’Armement (DGA) in the field of High Power Microwave (HPM) metrology. He has also actively contributed to several cooperative European Programs ranging from medical hyperthermia to industrial process tomography and has contributed to various prototype transfer and evaluation procedures in these areas. Recently, his research was related to RF dosimetry and rapid SAR measurements for wireless communication devices. Professor Bolomey his now continuing his research on load-modulated scattering antennas, and, more particularly, novel sensing applications of RFID technology. He is also contributing as a member of several Scientific Advisory Boards of European Institutions (Chalmers University, Queen Mary London University) and startup companies.
Jean-Charles Bolomey has received several awards, including the Blondel Medal of the Société des Electriciens et des Electroniciens (SEE) in 1976, the Général Ferrié Award of the French Academy of Sciences in 1984, and the Best Paper Award of the European Microwave Conference (EuMC) in 1983. In 1994, he has granted the Schlumberger Stitching Fund Award for his contribution to inverse scattering techniques in microwave imagery. In 2001, he has received the Distinguished Achievement Award of the Antenna Measurement Technique Association (AMTA) for his pioneering activity in the field of modulated probe arrays, and in 2007, elected as Edmond S. Gillespie Fellow for AMTA. He received the 2004 Medal of the French URSI Chapter. He has obtained the 2006 H.A. Wheeler Best Application Prize Paper Award of the IEEE AP-Society for his co-authored paper on “Spherical Near-Field Facility for Characterizing Random Emissions”. Professor Bolomey is Fellow of the Institution of Electrical and Electronic Engineers (IEEE) and received the Grade Emeritus of SEE in 1995.
Scattering by Load-Modulated Antennas: Background and Sensing Applications
While transmitting and receiving properties of antennas are fully formulated and well understood, scattering issues remain more mysterious, even if they have been extensively exploited for a while in the antenna engineer practice for shaping radiation patterns, adjusting input impedances, or for characterization purposes. This presentation is more specifically focused on modulated scattering-based systems, which have been successfully developed during the last decades. Operating an antenna in a scattering mode allows avoiding any RF front-end, resulting in very simple and compact passive or battery-assisted transponders. These advantages are now widely exploited in low-cost RFID tags, as well as in low-invasive MST (Modulated Scatterer Technique) probes for EM-field measurements.
This presentation consists of two major parts. The first one consists of a short tutorial review of the minimum engineering background required for a comprehensive approach to modulated scattering systems. Small antennas will be more particularly considered because low-invasiveness and high spatial resolution constitute significant advantages in many sensing applications. The power budget, a key issue for such systems, is derived from a very simple reciprocity-based formulation. The advantage of this analytical formulation is to apply, whatever the distance, for arbitrarily complex scenarios. In addition, the influence of various parameters can be clearly identified, paving the way for optimizing the antenna design in terms of global system performance. Examples of both active and passive scatterers illustrate the efficiency of this approach.
The second part is more speculative and aims to identify transfer opportunities between RFID’s and MST technologies for sensing applications. As compared to existing MST probes, passive RFID tags offer, at a glance, the indisputable advantage of being modulated from their own, without any wire or fiber. However, they may suffer autonomy/life time limitations and are constrained by standard regulations in terms of frequency range and power level. Furthermore, they exhibit specific technical difficulties, such as non-linearity of the IC chips loading the antenna. Various solutions to these drawbacks are addressed. Focusing on the case of systems involving arrays of modulated scatterers for its growing relevance in rapid imaging and wireless sensing (e.g. antenna measurement, industrial testing, medical diagnostic…), it is explained how the architecture of MST systems has conceptually changed during the last decades, primarily to face the critical sensitivity issue. Extrapolating such an evolution suggests promising solutions based on either RFID-derived or breakthrough technologies. To conclude, it is remembered that, while microwaves suffer no competition in the field of communications, they are loosing this comfortable privilege for Industrial Scientific Medical (ISM) applications where they must compete with many other efficient and already well-established modalities. In this competition, new modulated scattering technologies are reasonably expected contributing to valorize the specific advantages already recognized to RF- and microwave-based sensing modalities.
Near Field and Very-Near-Field Techniques: Current Status and Future Trends
The use of Near-Field (NF) techniques for antenna measurements is now well recognized in the antenna engineering practice. In the same time, Very-Near-Field (VNF) techniques are increasingly used for EMC applications. While such techniques suffered, during a long time, an apparent complexity resulting from the need of Near-to-Far Field transformation, recent advances in both software and equipment make them now fully accepted for their accuracy and flexibility. Indeed, Near-to-Far-Field transformations are now very efficiently achieved at moderate computational cost, even with regular PC’s. Furthermore, the major drawback of NF techniques, which consisted in the slowness of the measurement procedure, has been spectacularly overcome thanks to the use of probe arrays. Today, NF and VNF approaches appear as a very efficient way for obtaining, via computation, a maximum of information on intentional or non-intentional radiating system from a minimum number of measurements. Initially devoted to large antennas, NF techniques also constitute an attractive tool for rapid measurements on small antennas. More generally, as compared to direct measurement techniques involving long or compact ranges, they are much less space demanding and, consequently, they require smaller investments.
This presentation starts with briefly reviewing basic features of standard NF techniques based on a modal expansion of the radiated field. As an example, the test case of a base station antenna is considered. It is shown that, from a very limited number of NF data on a cylinder surface, it is possible, not only to calculate its radiation pattern in free-space, but also to check the compliance with reference levels or SAR basic restrictions in the close vicinity of the antenna, as well as to predict the field radiated, at any distance, in complex environments, thanks to appropriate codes. In a second time, inverse source algorithms are introduced. As compared to the modal expansion approach, these algorithms are relaxing some constraints on the number and distribution of sampling points, and those resulting from truncating the measurement surface. This last advantage is particularly interesting for VNF-based source modeling of unwanted radiation from electronic circuits or electrical components. However, they are more demanding in terms of computational effort, and suffer usual drawbacks of inverse problems. More prospectively, two other major aspects of NF and VNF techniques are considered. The first one is related to “phaseless” field or source reconstruction algorithms. Such algorithms are welcome when phase measurements are difficult (e.g. antennas in mm and sub-mm waves) or impossible (e.g. modulated signals of active antennas or spurious emissions for EMC applications). The second one deals with new generations of low-invasive sensors, which are currently developed. Their impact for VNF measurements is analyzed. To conclude, the extension of NF and VNF techniques to other applications such as medical diagnostic or industrial non-destructive testing is briefly presented.
Overview of Electromagnetic Scattering-Based Imaging Techniques
Making images consists in producing some footprints of a scene, allowing the human eye to view this scene. Intuitively, the footprint is supposed to show some kind of point-to-point correspondence between the scene and its image. Initially performed with natural light thanks to the human eye / brain combination, either alone or upgraded by means of optical instruments, the imaging procedures have been largely diversified during the last century. Such a diversification has been continuously stimulated by technological developments and led to consider new modalities to “see” objects escaping to human vision such as those buried in a medium opaque to the visible light. But penetrating opaque media usually requires operating at much larger than optical wavelengths, with the consequence that diffraction and scattering mechanisms, considered as second order perturbation in optical instruments, become first order effects decreasing image quality. For instance, the point-to-point correspondence between the observed object and its raw footprint is degraded or even may be apparently lost, requiring appropriate data processing. Many imaging systems dedicated to Industrial, Scientific, Security and Medical (IS2M) applications are based on electromagnetic waves, making them a convenient didactic support for a unified overview of scattering-based imaging techniques.
This presentation addresses two basic requirements for obtaining images of practical relevance. The first one is, evidently, that what one want to see is effectively visible. Such a visibility issue needs, beyond geometrical optics, entering into the details of scattering mechanisms. The second requirement is to be able to extract relevant images from measurements, by means of appropriate data acquisition and processing schemes. Setup geometry, number of measurement points, frequency band, measurement time, safety exposition standards, etc. constitute some examples of major experimental concerns, which, usually, must be optimized to comply with contradictory operational requirements. Processing techniques can be mainly categorized in linear and non-linear reconstructions. According to their complexity, which may vary in huge proportions, they can be implemented either in analogous or numerical ways, or by a combination of both.
Starting from well-known imaging modalities, such as optical 3D holography and X-Ray tomography, the imaging problem is considered under the more general inverse scattering point of view. After reviewing major setup geometries and related reconstruction algorithms, some guidelines to design an imaging system and optimize its performance are given. The selection of the operating frequency band is more particularly addressed, due to its decisive impact on image quality and system complexity. The case of microwaves will be more particularly developed from various viewpoints, including holography, tomography and Near-Field microscopy. Several examples of imaging systems dedicated to IS2M applications are presented to illustrate the current potential and limitations of such generalized imaging techniques. In conclusion, their expected evolution for the future is discussed.