A new type of metallic electromagnetic structure has been developed that is characterized by having high surface impedance. Although it is made of continuous metal, and conducts dc currents, it does not conduct ac currents within a forbidden frequency band. Unlike normal conductors, this new surface does not support propagating surface waves, and its image currents are not phase reversed. The geometry is analogous to a corrugated metal surface in which the corrugations have been folded up into lumped-circuit elements, and distributed in a two-dimensional lattice. The surface can be described using solid-state band theory concepts, even though the periodicity is much less than the free-space wavelength. This unique material is applicable to a variety of electromagnetic problems, including new kinds of low-profile antennas.

/pdf/high-impedance-electromagnetic-surfaces-with-a-forbidden-3vtu72a5an.pdf

High-impedance electromagnetic surfaces with a forbidden frequency band

Herschel was launched on 14 May 2009, and is now an operational ESA space observatory o ering unprecedented observational capabilities in the far-infrared and submillimetre spectral range 55 671 m. Herschel carries a 3.5 metre diameter passively cooled Cassegrain telescope, which is the largest of its kind and utilises a novel silicon carbide technology. The science payload comprises three instruments: two direct detection cameras/medium resolution spectrometers, PACS and SPIRE, and a very high-resolution heterodyne spectrometer, HIFI, whose focal plane units are housed inside a superfluid helium cryostat. Herschel is an observatory facility operated in partnership among ESA, the instrument consortia, and NASA. The mission lifetime is determined by the cryostat hold time. Nominally approximately 20,000 hours will be available for astronomy, 32% is guaranteed time and the remainder is open to the worldwide general astronomical community through a standard competitive proposal procedure.

/pdf/herschel-space-observatory-an-esa-facility-for-far-infrared-3pdcouv7zo.pdf

Herschel Space Observatory - An ESA facility for far-infrared and submillimetre astronomy

The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

Transformation optics describes the capability to design the path of light waves almost at will through the use of metamaterials that control effective materials properties on a subwavelength scale. In this review, the physics and applications of transformation optics are discussed.

Transformation optics and metamaterials

Science and technologies based on terahertz frequency electromagnetic radiation (100 GHz–30 THz) have developed rapidly over the last 30 years. For most of the 20th Century, terahertz radiation, then referred to as sub-millimeter wave or far-infrared radiation, was mainly utilized by astronomers and some spectroscopists. Following the development of laser based terahertz time-domain spectroscopy in the 1980s and 1990s the field of THz science and technology expanded rapidly, to the extent that it now touches many areas from fundamental science to 'real world' applications. For example THz radiation is being used to optimize materials for new solar cells, and may also be a key technology for the next generation of airport security scanners. While the field was emerging it was possible to keep track of all new developments, however now the field has grown so much that it is increasingly difficult to follow the diverse range of new discoveries and applications that are appearing. At this point in time, when the field of THz science and technology is moving from an emerging to a more established and interdisciplinary field, it is apt to present a roadmap to help identify the breadth and future directions of the field. The aim of this roadmap is to present a snapshot of the present state of THz science and technology in 2017, and provide an opinion on the challenges and opportunities that the future holds. To be able to achieve this aim, we have invited a group of international experts to write 18 sections that cover most of the key areas of THz science and technology. We hope that The 2017 Roadmap on THz science and technology will prove to be a useful resource by providing a wide ranging introduction to the capabilities of THz radiation for those outside or just entering the field as well as providing perspective and breadth for those who are well established. We also feel that this review should serve as a useful guide for government and funding agencies.

https://iopscience.iop.org/article/10.1088/1361-6463/50/4/043001/pdf

The 2017 terahertz science and technology roadmap

Comparison of Diversity Gains of Wideband Antennas Measured in Anechoic and Reverberation Chambers

With the increase in complexity of objects in electromagnetic problem, designs are often involves several design parameters that elongate the design process. In some cases one might use some intuitive thinking to ease the design process or at least to obtain the initial design in a short time. When the structure includes or requires periodic surfaces, full wave analysis is a time consuming process. However, if the periodic surface can be replaced by simple homogeneous surface the design process will be faster. After that one can use the actual periodic surface that replace the simple surface and with little tuning one would get the actual design. Recently, such concept is used to analyze soft and hard surfaces [1] that are realized by corrugated surfaces or conducting strip loaded surfaces using Asymptotic Corrugation Bounday Condition (ACBC) [2] or Asymptotic Strips Boundary Conditions (ASBC) [3]. Lately, soft and hard surfaces are simulated using a much simpler boundary referred to as PEC/PMC [4]. The concept of this boundary condition is that the corrugated or strips surfaces that achieve soft or hard conditions is replaced by the PEC/PMC, which consists of a strip of PEC beside another one of PMC in a periodic form with a period p approaching zero. Such a boundary condition is tested successfully in the design of horn antennas [5].

Electromagnetic scattering from circular cylinders with PEC/PMC boundaries

Measurements of receiver sensitivity of mobile terminals in Rayleigh fading by using reverberation chamber

The new microstrip gap waveguide supports a quasi-TEM mode in the air by the use of artificial magnetic conductors which force the field to travel in the air rather than in the substrate. This paper presents an evaluation of losses by measuring the Q-factor of a resonator made in this technology, made using a mushroom-type EBG surface. Losses are crucial when using printed circuits to feed slot antennas, thereby motivating this work. Comparisons with standard microstrip lines will be provided, showing promising results.

http://publications.lib.chalmers.se/records/fulltext/163388/local_163388.pdf

Evaluation of losses in microstrip gap waveguide for slot antennas applications

This contribution discusses the relationship between the number of degrees of freedom (DoF) and the maximum directivity for an arbitrary set of sources enclosed by a given spherical surface. In particular, it is shown that the number of DoF is equal to twice the maximum directivity. This provides a directivity limitation for arbitrarily sized antennas, thus, extending the validity of the known formulas for electrically large and electrically small antennas.

Per-Simon Kildal

Papers

Comparison of Diversity Gains of Wideband Antennas Measured in Anechoic and Reverberation Chambers

Electromagnetic scattering from circular cylinders with PEC/PMC boundaries

Measurements of receiver sensitivity of mobile terminals in Rayleigh fading by using reverberation chamber

Evaluation of losses in microstrip gap waveguide for slot antennas applications

Degrees of freedom of the field and maximum directivity