Neural Network Characterization of Reflectarray Antennas

An efficient artificial neural network (ANN) approach for the modeling of reflectarray elementary components is introduced to improve the numerical efficiency of the different phases of the antenna design and optimization procedure, without loss in accuracy. The comparison between the results of the analysis of the entire reflectarray designed using the simplified ANN model or adopting a full-wave characterization of the unit cell finally proves the effectiveness of the proposed model

Enhanced RF Behavior Multi-Layer Thermal Insulation

Abstract This paper shows that it is possible to exploit the modulated metasurface concept to control the unwanted coupling between antennas that are installed on the same satellite. The metasurface is combined with a Multi-Layer thermal Insulation blanket to reduce its specular reflection by spreading the energy incoherently in the surrounding space. In the design, sub-wavelength radiating elements printed on thin substrate have been used to make the metasurface response azimuthally independent, and to keep the weight of blanket down. The comparison between simulations and measurements confirms the validity of the idea

Modified BMIA/CAG method for the electromagnetic analysis of large-scale problems of random rough surface scattering

An efficient technique based on two-dimensional Fast Fourier Transform (FFT) and linear interpolation is presented for the evaluation of the scattering by a rough terrain surface which is of interest in remote-sensing applications characterized by a very large correlation length. Such technique, where introduced in a BMIA/CAG method, can reduce the computation time appreciably

Efficient Analysis for the Design Refinement of Large Multilayered Printed Reflectarrays

In this paper, we present an efficient numerical technique for the analysis of a reflectarray and its design refinement by the characterization of the “actual” influence of each radiating element when embedded in the antenna structure. The method makes use of the MLayAIM, a fast full-wave formulation suitable for the analysis of electrically large multilayered printed arrays which have one or more planar metallizations and vertical conductors. The low numerical complexity of the analysis method allows the development of a recursive procedure that, starting from the equivalent currents relevant to each cell of the reflectarray when this is immersed in the actual antenna layout, calculates the real phase-shift introduced by each radiating element and corrects its dimensions to better fit the antenna requirements

Derivation of Clear-Air Turbulence Parameters from High-Resolution Radiosonde Data

The knowledge of atmospheric refractive-index structure constant (Cn2) profiles is fundamental to determine the intensity of turbulence, and hence the impact of the scintillation impairment on the signals propagating in the troposphere. However, their relation with atmospheric variables is not straightforward, and profiles based on statistical considerations are normally employed. This can be a shortcoming when performing simulations for which scintillation disturbances need to be consistent with the assumed atmospheric conditions. In order to overcome this limitation, this work describes a procedure to obtain an estimate of the refractive-index structure constant profile under given atmospheric conditions. The procedure is based on the application of the vertical gradient approach to high resolution radiosonde data. The fact that turbulence is confined to vertically thin layers is accounted for by identifying the turbulent layers through the analysis of the Richardson number profiles, and the value of the outer scale length is estimated using the Thorpe length calculated from potential temperature profile. The procedure is applied to high resolution radiosonde data from the SPARC Data Center and the obtained results are consistent with measured Cn2 profiles previously published in the literature

Etiopathological study of oral and oropharyngeal carcinoma

Background: Oral cancer is thought to be the sixth most common form of cancer causing upto 50% of all malignancies in parts of India and South-East Asia, and an increasing trend in oral cancer mortality have been observed in several countries. The aim of the study was to evaluate the etiological factors contributing to oral and oropharyngeal carcinomas and its association with histopathological findings.Methods: This one year duration study was carried out on 100 patients diagnosed as oral and oropharyngeal cancer attending the Department of Otorhinolaryngology and Head and Neck Surgery, Gajra Raja Medical College and J.A. Group of Hospitals, Gwalior, Madhya Pradesh, India.Results: 98% of the patients were histologically squamous cell carcinomas, with well differentiated carcinoma being the most common i.e. 59%. The etiological factors which were found to have statistically significant association in oral cancers were poor oral hygiene, tobacco chewing and pan chewing. Other factors like cigarette/bidi smoking, alcoholism were also common.Conclusions: Any irritation or ulceration in the mouth not attributed to a recognizable causal factor and not healing within four weeks, especially in presence of risk factors must be investigated for its malignant potential. There is a need for improvement in early detection of oral and oropharyngeal carcinomas, because in the initial stages, treatment is more effective and the morbidity is minimal. Keywords:

Development, Validation and Preliminary Experiments of a Measuring Technique for Eggs Aging Estimation Based on Pulse Phase Thermography

Assessment of the freshness of hen eggs destinated to human consumption is an extremely important goal for the modern food industry and sale chains, as eggs show a rapid natural aging which also depends on the storage conditions. Traditional techniques, such as candling and visual observation, have some practical limitations related to the subjective and qualitative nature of the analysis. The main objective of this paper is to propose a robust and automated approach, based on the use of pulsed phase thermography (PPT) and image processing, that can be used as an effective quality control tool to evaluate the freshness of eggs. As many studies show that the air chamber size is proportional to the egg freshness, the technique relies on the monitoring of the air chamber parameters to infer egg aging over time. The raw and phase infrared images are acquired and then post-processed by a dedicated algorithm which has been designed to automatically measure the size of the air chamber, in terms of normalized area and volume. The robustness of the method is firstly assessed through repeatability and reproducibility tests, which demonstrate that the uncertainty in the measure of the air chamber size never exceeds 5%. Then, an experimental campaign on a larger sample of 30 eggs, equally divided into three size categories (M, L, XL), is conducted. For each egg, the main sizes of the air chamber are measured with the proposed method and their evolution over time is investigated. Results have revealed, for all the egg categories, the existence of an analytic relationship and a high degree of correlation (R-2 > 0.95) between the geometric data of the air chamber and the weight loss, which is a well-known marker of egg aging

Testing of an adsorption chiller prototype for data center cooling.

The main objective of this study is to present a novel adsorption chiller prototype (designed and realized by the company Sorption Technologies GmbH) that is suitable for cooling of data center servers. This prototype has been designed to fit into commercially-available data center racks. This adsorption prototype has been designed to cool down the rack servers by means of liquid cooling. Furthermore, an air-cooler heat exchanger is also integrated into the adsorption machine to cool down the rest of the rack components (i.e., patch panels, HDD). This way, the adsorption system is able to cool down all rack components. Phase-change chambers are integrated into the adsorption modules for direct evaporation/condensation, removing the need of large vacuum valves and allowing to have a more simpler and compact vacuum system. This also means that the refrigerant distribution is completely done in liquid phase. The prototype is installed at the Department of Energy at the Politecnico di Milano and testing will be carried out using cooling water temperatures in the range 25 – 30 °C and hot water temperatures in the range 55 – 65 °C

Adsorption performance and thermodynamic analysis of SAPO-34 silicone composite foams for adsorption heat pump applications

Abstract In the present work, adsorption performances of an innovative composite adsorber, based on SAPO-34-silicone composite macro-cellular foams, are reported. The choice of a foamed structure was assessed to improve the water vapor access towards the embedded zeolite keeping good adsorption heat pump dynamic performance. Depending on zeolite amount used as filler, zeolite/silicone foams evidenced a soft and open cell configuration (low zeolite content) or rigid and closed one (high zeolite content). Morphological analysis evidenced that the cellular structure of the foam is homogeneous and well distributed along the foam cross section. Adsorption tests showed that the adsorbent foamed samples have very effective adsorption capabilities indicating that the porous structure of the filled pure zeolite was not obstructed. SAPO-34 filler contributed actively, with an efficiency above 90%, to the adsorption performances of the composite foam. Starting from experimental equilibrium data, a simple thermodynamic analysis based on energy balances was carried out for air conditioning application. Results of the analysis demonstrated that foam technology can guarantee cooling COP up to 7% higher than that estimated for the typical adsorber solution based on loose adsorbent grains inside an aluminum finned-flat tube heat exchanger, which is very promising for practical application in adsorption heat pumps

Modelling of a falling-film evaporator for adsorption chillers.

The objective of the present study was to develop a dynamic model to simulate a prototype falling-film evap-orator that is part of a single-bed adsorption chiller test bench located at the Department of Energy of the Politecnico di Milano. The model is based on the evaporator energy and mass balances and was calibrated and validated using experimental data coming from realistic operating conditions in a range of inlet chilled water temperatures (Tin,chw) from 15 to 25 °C. From the experimental data, it was obtained that the average overall heat transfer conductance (UA) was approximately 530 W/K for all temperatures during the quasi steady-state section of the process. A correlation to calculate the wetted surface through a variable called wettability factor (fwet) was developed from experimental data. The fwet factors were identified using the model and were in the range of 0.80 - 0.20 (Tin,chw= 15 °C) and 0.60 - 0.20 (Tin,chw= 25 °C). It was seen that, the higher the Tin,chw, the lower the fwet values. The UA and saturation temperature (Tref,sat) values from the model were in good accordance with experimental data during the quasi steady-state section of the process. Nevertheless, the final transition stage (i. e., a situation in which the evaporator's refrigerant pool is empty) required an additional hypothesis due to the uncertain process' dynamics. The mass and energy balances that are part of the hydrodynamics and heat transfer sections of the model use Nusselt's classic theory for falling-film