F. Ares-Pena

Genetic algorithms in the design and optimization of antenna array patterns

This paper demonstrates the application of genetic algorithms (GAs) in array pattern synthesis. GAs have the ability to escape from local minima and maxima and are ideally suited for problems where the number of variables is very high. We present three examples: two for linear arrays and one involving linear and planar arrays.

A SIMPLE ALTERNATIVE FOR BEAM RECONFIGURATION OF ARRAY ANTENNAS

An innovative method for antenna arrays beam configuration is presented. In the proposed method, every element of the array is connected to its feed through a switch, so that it can be active or passive, depending on the switch position. Pattern reconfigurability is achieved by appropriately switching on or off the array elements. The optimal configuration of the switches for each of the radiated patterns, as well the common voltages of the active elements, is calculated by using a genetic algorithm. For each configuration, the currents in the driven and parasitic elements are determined, via their self and mutual impedances, by inversion of the impedance matrix. In the presented examples, the method has been applied to both linear and planar arrays of parallel dipoles that switch the power pattern from a pencil to a flat-topped beam (linear array) or to a footprint pattern (planar array). † Also with University of California, Los Angeles, USA 228 Ares, Franceschetti, and Rodriguez

GSM radiation triggers seizures and increases cerebral c-Fos positivity in rats pretreated with subconvulsive doses of picrotoxin

This study investigated the effects of mobile-phone-type radiation on the cerebral activity of seizure-prone animals. When rats transformed into an experimental model of seizure-proneness by acute subconvulsive doses of picrotoxin were exposed to 2 h GSM-modulated 900 MHz radiation at an intensity similar to that emitted by mobile phones, they suffered seizures and the levels of the neuronal activity marker c-Fos in neocortex, paleocortex, hippocampus and thalamus increased markedly. Non-irradiated picrotoxin-treated rats did not suffer seizures, and their cerebral c-Fos counts were significantly lower. Radiation caused no such differences in rats that had not been pretreated with picrotoxin. We conclude that GSM-type radiation can induce seizures in rats following their facilitation by subconvulsive doses of picrotoxin, and that research should be pursued into the possibility that this kind of radiation may similarly affect brain function in human subjects with epileptic disorders.

A study of neurotoxic biomarkers, c-fos and GFAP after acute exposure to GSM radiation at 900 MHz in the picrotoxin model of rat brains.

The acute effects of microwave exposure from the Global System for Mobile Communication (GSM) were studied in rats, using 900MHz radiation at an intensity similar to mobile phone emissions. Acute subconvulsive doses of picrotoxin were then administered to the rats and an experimental model of seizure-proneness was created from the data. Seventy-two adult male Sprague-Dawley rats underwent immunochemical testing of relevant anatomical areas to measure induction of the c-fos neuronal marker after 90min and 24h, and of the glial fibrillary acidic protein (GFAP) 72h after acute exposure to a 900MHz electromagnetic field (EMF). The experimental set-up facilitated measurement of absorbed power, from which the average specific absorption rate was calculated using the finite-difference time-domain (FDTD) 2h after exposure to EMF radiation at 1.45W/kg in picrotoxin-treated rats and 1.38W/kg in untreated rats. Ninety minutes after radiation high levels of c-fos expression were recorded in the neocortex and paleocortex along with low hippocampus activation in picrotoxin treated animals. Most brain areas, except the limbic cortical region, showed important increases in neuronal activation 24h after picrotoxin and radiation. Three days after picrotoxin treatment, radiation effects were still apparent in the neocortex, dentate gyrus and CA3, but a significant decrease in activity was noted in the piriform and entorhinal cortex. During this time, glial reactivity increased with every seizure in irradiated, picrotoxin-treated brain regions. Our results reveal that c-fos and glial markers were triggered by the combined stress of non-thermal irradiation and the toxic effect of picrotoxin on cerebral tissues.

Rapid Method for Finding Faulty Elements in Antenna Arrays Using Far Field Pattern Samples

A simple and fast technique that allows a diagnosis of faulty elements in antenna arrays, that only needs to consider a small number of samples of its degraded far-field pattern is described. The method tabulates patterns radiated by the array with 1 faulty element only. Then, the pattern corresponding to the configuration of failed/unfailed elements under test is calculated using the error-free pattern and the patterns with 1 faulty element. The configuration with the lowest difference between the calculated and the degraded patterns is selected. Comparison of the performance of this method using an exhaustive search and a genetic algorithm for an equispaced linear array of 100 lambda/2-dipoles is shown. Mutual coupling as well as noise/measurement errors in the pattern samples were considered in the numerical analysis.

Fast Array Thinning using Global Optimization Methods

A simple and fast method to accelerate the global optimization approaches used in array thinning is described. This method tabulates the contribution of every array element to the far-field pattern in order to improve the numerical efficiency of the optimization algorithm employed. Experiments using our proposal alongside with a genetic algorithm reduce the search computation time about 90%.

The Action of Pulse-Modulated GSM Radiation Increases Regional Changes in Brain Activity and c-Fos Expression in Cortical and Subcortical Areas in a Rat Model of Picrotoxin-Induced Seizure Proneness

The action of the pulse‐modulated GSM radiofrequency of mobile phones has been suggested as a physical phenomenon that might have biological effects on the mammalian central nervous system. In the present study, GSM‐exposed picrotoxin‐pretreated rats showed differences in clinical and EEG signs, and in c‐Fos expression in the brain, with respect to picrotoxin‐treated rats exposed to an equivalent dose of unmodulated radiation. Neither radiation treatment caused tissue heating, so thermal effects can be ruled out. The most marked effects of GSM radiation on c‐Fos expression in picrotoxin‐treated rats were observed in limbic structures, olfactory cortex areas and subcortical areas, the dentate gyrus, and the central lateral nucleus of the thalamic intralaminar nucleus group. Nonpicrotoxin‐treated animals exposed to unmodulated radiation showed the highest levels of neuronal c‐Fos expression in cortical areas. These results suggest a specific effect of the pulse modulation of GSM radiation on brain activity of a picrotoxin‐induced seizure‐proneness rat model and indicate that this mobile‐phone‐type radiation might induce regional changes in previous preexcitability conditions of neuronal activation.

EXPOSURE TO 2.45 GHz MICROWAVE RADIATION PROVOKES CEREBRAL CHANGES IN INDUCTION OF HSP-90 fi/fl HEAT SHOCK PROTEIN IN RAT

Physical agents such as non-ionizing continuous-wave 2.45GHz radiation may cause damage that alters cellular homeostasis and may trigger activation of the genes that encode heat shock proteins (HSP). We used Enzyme-Linked ImmunoSorbent Assay (ELISA) and immunohistochemistry to analyze the changes in levels of HSP-90 and its distribution in the brain of Sprague-Dawley rats, ninety minutes and twenty-four hours after acute (30min) continuous exposure to 2.45 GHz radiation in a the Gigahertz Transverse Electromagnetic (GTEM cell). In addition, we studied further indicators of neuronal insult: dark neurons, chromatin condensation and nucleus fragmentation, which were observed under optical conventional or fluorescence microscopy after DAPI staining. The cellular distribution of protein HSP-90 in the brain increased with each corresponding SAR (0.034 ± 3.10−3, 0.069 ± 5.10−3, 0.27 ± 21.10−3 W/kg), in hypothalamic nuclei, limbic cortex and somatosensorial cortex after exposure to the radiation. At twenty-four hours post-irradiation, levels of HSP-90 protein remained high in all hypothalamic nuclei for all SARs, and in the parietal cortex, except the limbic system, HSP-90 levels were lower than in non-irradiated rats, almost half the levels in rats exposed to the highest power radiation. Non-apoptotic cellular nuclei and a some dark neurons were found ninety minutes and twenty-four hours after maximal SAR exposure. The results suggest that acute exposure to electromagnetic fields triggered an imbalance in anatomical HSP90 levels but the anti-apoptotic mechanism is probably sufficient to compensate the non-ionizing stimulus. Further studies are required to determine the regional effects of chronic electromagnetic pollution on heat shock proteins and their involvement in neurological processes and neuronal damage.

An Experimental Set-Up for Measurement of the Power Absorbed from 900 MHz GSM Standing Waves by Small Animals, Illustrated by Application to Picrotoxin-Treated Rats

We describe an experimental set-up for exposure of small animals to radiofrequency standing waves that allows direct measurement of the power absorbed by the animal. Essentially, the setup consists of a metallic box containing an antenna and experimental animal immobilized in a methacrylate holder; a signal generator feeding the antenna; and a power meter. In addition, the box can also contain a video camera to record the animal’s behaviour, and a receiving antenna (connected externally to a power meter and a spectrum analyser) to detect undesired (external) radiation and possible harmonics of the radiating system. The absorbed power measurement trivially allows calculation of whole-body mean SAR from the animal’s weight; and assuming local SARs to be proportional to whole-body mean SAR, the latter can be used to adjust organ-specific SAR predictions obtained by simulation using a commercial FDTD program with a numerical phantom. The use of the system is illustrated by application to rats given subconvulsive doses of picrotoxin to induce a seizure-prone state analogous to epilepsy: levels of the neuronal activity marker c-Fos in the frontal and piriform cortex of picrotoxin-treated rats exposed to 900 MHz GSM radiation were twice as high as those of unexposed animals.

Analysis and synthesis of a printed array for satellite communication with moving vehicles

We describe a mobile communications antenna consisting of concentric rings of elliptically polarized circular patches. For certain sets of relative phases, optimization of geometry and excitation amplitudes by simulated annealing synthesizes a conical beam with a maximum at a desired /spl theta/ and satisfactory directivity within a desired /spl theta/ range. An example of a two-ring array 50 cm in diameter with directivity >3 dB between /spl theta/=35/spl deg/ and /spl theta/=50/spl deg/ is presented.