RESUMEN
A review on planar printed structures that are based on Matryoshka-like geometries is presented. These structures use the well-known principle of Matryoshka dolls that are successively nested inside each other. The well-known advantages of the planar printed technology and of the meandered nested Matryoshka geometries are combined to generate miniaturized, multi-resonance, and/or wideband configurations. Both metal and complementary slot structures are considered. Closed and open configurations were analyzed. The working principles were explored in order to obtain physical insight into their behavior. Low-cost and single-layer applications as frequency-selective surfaces, filters, antennas, and sensors, in the microwave frequency region, were reviewed. Potential future research perspectives and new applications are then discussed.
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We demonstrate a concept for a large enhancement of the directivity and gain of readily available cm- and mm-wave antennas, i.e., without altering any property of the antenna design. Our concept exploits the high reflectivity of a Bragg reflector composed of three bilayers made of transparent materials. The cavity has a triangular aperture in order to resemble the idea of a horn-like, highly directive antenna. Importantly, we report gain enhancements of more than 400% in relation to the gain of the antenna without the Bragg structure, accompanied by a highly directive radiation pattern. The proposed structure is cost-effective and easy to fabricate with 3D-printing. Our results are presented for frequencies within the conventional WiFi frequencies, based on IEEE 802.11 standards, thus, enabling easily implementation by non-experts and needing only to be placed around the antenna to improve the directivity and gain of the signal.
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This work considers a base station equipped with an M-antenna uniform linear array and L users under line-of-sight conditions. As a result, one can derive an exact series expansion necessary to calculate the mean sum-rate channel capacity. This scenario leads to a mathematical problem where the joint probability density function (JPDF) of the eigenvalues of a Vandermonde matrix WWH are necessary, where W is the channel matrix. However, differently from the channel Rayleigh distributed, this joint PDF is not known in the literature. To circumvent this problem, we employ Taylor's series expansion and present a result where the moments of mn are computed. To calculate this quantity, we resort to the integer partition theory and present an exact expression for mn. Furthermore, we also find an upper bound for the mean sum-rate capacity through Jensen's inequality. All the results were validated by Monte Carlo numerical simulation.
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We report on the design of a low-profile integrated millimeter-wave antenna for efficient and broadband circularly polarized electromagnetic radiation. The designed antenna comprises a chiral dielectric metasurface built with a 2×2 arrangement of dielectric cylinders with slanted-slots at the center. A broadbeam high-gain with wide axial ratio (AR)<3 dB bandwidth was reached by pairing the electric and magnetic resonances of the dielectric cylinders and the slanted slots when excited by an elliptically polarized driven-patch antenna. This electric-magnetic pairing can be tuned by varying the cylinders diameter and the tilting and rotation angles of the slanted slots. The simulation results indicate impedance-matching bandwidths up to 22.6% (25.3-31.6 GHz) with 3-dB AR bandwidths of 11.6% (26.9-30.2 GHz), which in terms of compactness (0.95λ0×0.95λ0) and performance are superior to previous antenna designs. Since the simulations were performed by assuming materials and geometries easily implementable experimentally, it is hoped that circularly polarized antennas based on chiral metasurfaces can be integrated into 5G and satellite communications.
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Investigating the growth behavior of plant root systems as a function of soil water is considered an important information for the study of root physiology. A non-invasive tool based on electromagnetic wave transmittance in the microwave frequency range, operating close to 4.8 GHz, was developed using microstrip patch antennas to determine the volumetric moisture of soil in rhizoboxes. Antennas were placed on both sides of the rhizobox and, using a vector network analyzer, measured the S parameters. The dispersion parameter S21 (dB) was also used to show the effect of different soil types and temperature on the measurement. In addition, system sensitivity, reproducibility and repeatability were evaluated. The quantitative results of the soil moisture, measured in rhizoboxes, presented in this paper, demonstrate that the microwave technique using microstrip patch antennas is a reliable, non-invasive and accurate system, and has shown potentially promising applications for measurement of rhizobox-based root phenotyping.
Asunto(s)
Microondas , Suelo/química , Raíces de PlantasRESUMEN
Los efectos en salud de la radiación electromagnética ionizante son bien conocidos; sin embargo hay menos reconocimiento de los efectos en salud causados por exposición a radiación electromagnética no ionizante. La primera parte del presente trabajo se refiere a los efectos en salud de las radiaciones electromagnéticas no ionizantes, independiente de su origen, puesto que no hay diferencias apreciables entre los efectos producidos por los diversos tipos de radiación electromagnética no ionizante y por lo tanto, son también válidas para aquellas emitidas por la telefonía celular. Se describe una asociación estadísticamente significativa de varias enfermedades a radiación electromagnética de frecuencia baja (ELF) proveniente de tendidos o transformadores de alta tensión, radiación electromagnética ELF del tendido eléctrico domiciliario y de artefactos electrodomésticos, exposición ocupacional a radiación electromagnética principalmente ELF, y radiación electromagnética de radiofrecuencia (RF) proveniente de antenas de transmisión de televisión. A continuación se analizan los efectos ya demostrados de la telefonía celular (los teléfonos y sus antenas repetidoras). Luego se analizan los grados de certeza de un estudio del Estado de California (USA) para relacionar las diversas enfermedades causadas por radiación electromagnética no ionizante. Este estudio confirmó la alta o mediana probabilidad de una relación causa-efecto de la radiación electromagnética con las siguientes enfermedades: leucemia en adultos y niños, cáncer cerebral en adultos y niños, cáncer de mama femenino y masculino, abortos espontáneos, suicidio, enfermedad de Alzheimer, esclerosis lateral amiotrófica y enfermedades cardiovasculares incluyendo infarto del miocardio. Se describen cuales son estas enfermedades de acuerdo al origen de estas radiaciones y se analizan cuales pueden ser los mecanismos biológicos que determinan la génesis de éstas...
The health effects of ionizing electromagnetic radiation are well known; neverthless there exist less recognition on the health effects of exposure to non-ionizing electromagnetic radiation. The first part of the present report refers to health effects of non-ionizing electromagnetic radiation, independently of its origin, since there are not important differences among effects caused by the different kind of non-ionizing radiations, therefore, they are valid for those emmited by the mobile telephony. A statistically significant association is described among various diseases and extremely low frequency electromagnetic radiation (ELF) from high tension electric conductors or transformers, intradomiciliary electric lines or electrodomestic appliances, occupational exposure to electromagnetic fields, mainly ELF, and radiofrequency (RF) electromagnetic radiation from television transmission. Already demonstrated effects of mobile telephony (cellular telephones and their antenas). The degrees of certainty from a study of the State of California (USA) is analyzed to relate various diseases caused by non-ionizing radiation. This study confirmed high or moderate probability of a cause-effect relationship for adult and child leukemia, brain cancer in adults and children, female and male breast cancer, spontaneous abortions, suicide, Alzheimer disease, amiotrophic lateral sclerosis and cardiovascular diseases including myocardial infarction. Various diseases are related to the different origin of the radiation, and the biological mechanisms involved in disease generation are analyzed. Research performed in the USSR and afterwards in Russia on health effects of mobile telephony are summarized, these investigations originated the regulation in this country and afterwards in West Europe, and influenced the decisions of WHO on its carcinogenicity...