Reconfigurable pixel antennas for communications

The explosive growth of wireless communications has brought new requirements in terms of compactness, mobility and multi-functionality that pushes antenna research. In this context, recon gurable antennas have gained a lot of attention due to their ability to adjust dynamically their frequency and radiation properties, providing multiple functionalities and being able to adapt themselves to a changing environment. A pixel antenna is a particular type of recon gurable antenna composed of a grid of metallic patches interconnected by RF-switches which can dynamically reshape its active surface. This capability provides pixel antennas with a recon guration level much higher than in other recon gurable architectures. Despite the outstanding recon guration capabilities of pixel antennas, there are important practical issues related to the performance-complexity balance that must be addressed before they can be implemented in commercial systems. This doctoral work focuses on the minimization of the pixel antenna complexity while maximizing its recon guration capabilities, contributing to the development of pixel antennas from a conceptual structure towards a practical recon gurable antenna architecture. First, the conceptualization of novel pixel geometries is addressed. It is shown that antenna complexity can be signi cantly reduced by using multiple-sized pixels. This multi-size technique allows to design pixel antennas with a number of switches one order of magnitude lower than in common pixel structures, while preserving high multiparameter recon gurability. A new conceptual architecture where the pixel surface acts as a parasitic layer is also proposed. The parasitic nature of the pixel layer leads to important advantages regarding the switch biasing and integration possibilities. Secondly, new pixel recon guration technologies are explored. After investigating the capabilities of semiconductors and RF-MEMS switches, micro uidic technology is proposed as a new technology to create and remove liquid metal pixels rather than interconnecting them. Thirdly, the full multi-parameter recon guration capabilities of pixel antennas is explored, which contrasts with the partial explorations available in the literature. The maximum achievable recon guration ranges (frequency range, beam-steering angular range and polarization modes) as well as the linkage between the di erent parameter under recon guration are studied. Finally, the performance of recon gurable antennas in beam-steering applications is analyzed. Figures-of-merit are derived to quantify radiation pattern recon gurability, enabling the evaluation of the performance of recon gurable antennas, pixel antennas and recon guration algorithms

Reconfigurable pixel antennas for communications

Premi extraordinari doctorat curs 2012-2013, àmbit Enginyeria de les TICThe explosive growth of wireless communications has brought new requirements in terms of compactness, mobility and multi-functionality that pushes antenna research. In this context, recon gurable antennas have gained a lot of attention due to their ability to adjust dynamically their frequency and radiation properties, providing multiple functionalities and being able to adapt themselves to a changing environment. A pixel antenna is a particular type of recon gurable antenna composed of a grid of metallic patches interconnected by RF-switches which can dynamically reshape its active surface. This capability provides pixel antennas with a recon guration level much higher than in other recon gurable architectures. Despite the outstanding recon guration capabilities of pixel antennas, there are important practical issues related to the performance-complexity balance that must be addressed before they can be implemented in commercial systems. This doctoral work focuses on the minimization of the pixel antenna complexity while maximizing its recon guration capabilities, contributing to the development of pixel antennas from a conceptual structure towards a practical recon gurable antenna architecture. First, the conceptualization of novel pixel geometries is addressed. It is shown that antenna complexity can be signi cantly reduced by using multiple-sized pixels. This multi-size technique allows to design pixel antennas with a number of switches one order of magnitude lower than in common pixel structures, while preserving high multiparameter recon gurability. A new conceptual architecture where the pixel surface acts as a parasitic layer is also proposed. The parasitic nature of the pixel layer leads to important advantages regarding the switch biasing and integration possibilities. Secondly, new pixel recon guration technologies are explored. After investigating the capabilities of semiconductors and RF-MEMS switches, micro uidic technology is proposed as a new technology to create and remove liquid metal pixels rather than interconnecting them. Thirdly, the full multi-parameter recon guration capabilities of pixel antennas is explored, which contrasts with the partial explorations available in the literature. The maximum achievable recon guration ranges (frequency range, beam-steering angular range and polarization modes) as well as the linkage between the di erent parameter under recon guration are studied. Finally, the performance of recon gurable antennas in beam-steering applications is analyzed. Figures-of-merit are derived to quantify radiation pattern recon gurability, enabling the evaluation of the performance of recon gurable antennas, pixel antennas and recon guration algorithms.Award-winningPostprint (published version

Improvements in CO2 Booster Architectures with Different Economizer Arrangements.

CO2 transcritical booster architectures are widely analyzed to be applied in centralized commercial refrigeration plants in consonance with the irrevocable phase-out of HFCs. Most of these analyses show the limitations of CO2 cycles in terms of energy e ciency, especially in warm countries. From the literature, several improvements have been proposed to raise the booster e ciency in high ambient temperatures. The use of economizers is an interesting technique to reduce the temperature after the gas cooler and to improve the energy e ciency of transcritical CO2 cycles. The economizer cools down the high pressure’s line of CO2 by evaporating the same refrigerant extracted from another point of the facility. Depending on the extraction point, some configurations are possible. In this work, di erent booster architectures with economizers have been analyzed and compared. From the results, the combination of the economizer with the additional compressor allows obtaining energy savings of up to 8.5% in warm countries and up to 4% in cold countries with regard to the flash-by-pass arrangement and reduce the volumetric displacement required of the MT compressors by up to 37%

Experimental determination of the optimum working conditions of a transcritical CO2 refrigeration plant with integrated mechanical subcooling

Subcooling methods for transcritical CO2 plants are being studied in order to improve their behavior. Among them, the Integrated Mechanical Subcooling system is one of the most promising owing that performs with high efficiency and it is a total-CO2 system. This work presents the experimental determination of the optimum working conditions of a transcritical CO2 plant working with an integrated mechanical subcooling system. The plant was tested at different pressure and subcooling conditions in order to optimize the COP of the plant and determine the optimal conditions for three ambient temperatures 25.0 °C, 30.4 °C and 35.1 °C and evaporation levels between −15.6 °C and −4.1 °C. Optimum operating conditions were determined and two correlations are proposed to determine the optimal pressure and subcooling as function the gas-cooler outlet temperature and the evaporation level

Multiplicación de especies silvestres mediterráneas para uso ornamental

Peer Reviewe

Thermodynamic Analysis of a CO2 Refrigeration Cycle with Integrated Mechanical Subcooling

Different alternatives are being studied nowadays in order to enhance the behavior of transcritical CO2 refrigeration plants. Among the most studied options, subcooling is one of the most analyzed methods in the last years, increasing cooling capacity and Coefficient Of Performance (COP), especially at high hot sink temperatures. A new cycle, called integrated mechanical subcooling cycle, has been developed, as a total-CO2 solution, to provide the subcooling in CO2 transcritical refrigeration cycles. It corresponds to a promising solution from the point of view of energy efficiency. The purpose of this work is to present, for the first time, thermodynamic analysis of a CO2 refrigeration cycle with integrated mechanical subcooling cycle from first and second law approaches. Using simplified models of the components, the optimum operating conditions, optimum gas-cooler pressure, and subcooling degree are determined in order to obtain the maximum COP. The main energy parameters of the system were analyzed for different evaporation levels and heat rejection temperatures. The exergy destruction was analyzed for each component, identifying the elements of the system that introduce more irreversibilities. It has been concluded that the new cycle could offer COP improvements from 11.7% to 15.9% in relation to single-stage cycles with internal heat exchanger (IHX) at 35 °C ambient temperature

Energy impact of the Internal Heat Exchanger in a horizontal freezing cabinet. Experimental evaluation with the R404A low-GWP alternatives R454C, R455A, R468A, R290 and R1270

This work analyses the influence of the Internal Heat Exchan ger (IHX) on the energy performance of a vapor compression cycle associated with a freezing cabinet using different R404A low-GWP alternatives. Among them, the refrigerants R454C (GPW100=146), R455A (GPW100=146), R468A (GPW100=146), R290 (GPW100=5) and R1270 (GPW100=1.8) have been tested in a horizontal freezing cabinet maintaining a product target temperature of -20°C at the heat rejection temperatures of 20, 30 and 40°C. The results from tests show that the use of the IHX reduces energy consumption in all scenarios without significantly increasing the compressor's discharge temperature. For a test period of 16 hours, the refrigerants that offer better reductions are R404A and R1270, followed by R455A, R290, R454C and R468A. The maximum energy saving is rated to 9.2% at the heat rejection temperature of 40°C, demonstrating that the enhancement of the IHX is better as higher the heat rejection conditions are.Funding for open access charge: CRUE-Universitat Jaume

Energy impact evaluation of different low-GWP alternatives to replace R134a in a beverage cooler. Experimental analysis and optimization for the pure refrigerants R152a, R1234yf, R290, R1270, R600a and R744

Due to the entry into force in 2014 of the European F-Gas Regulation n° 517/2014 and the subsequent Kigali amendment, the phase-out of the medium and high-GWP refrigerants has speeded up in all refrigeration fields. The effect on the plug-in or stand-alone systems has meant that other environmentally friendly refrigerants must replace the R134a with low or ultra-low GWP maintaining the same operating conditions and reducing the energy consumption. Extended examples of these fluids are the hydrocarbons R600a and R290 and the inorganic fluid R744 (CO2). However, there are other alternatives to the HFCs R152a and R1234yf or the hydrocarbon R1270 that have hardly been analysed and can make a positive contribution to this sector. Accordingly, this work aims to evaluate the behaviour of a commercial beverage cooler experimentally when it is optimised with six alternatives to the HFC R134a: R152a, R1234yf, R290, R1270, R600a and R744. Results demonstrated that fluids R290, R1270, R152a, R744 and R600a reduce the energy of R134a in 27.5%, 26.3%, 13.7%, 3.9% and 1.2%, respectively, while the use of R1234yf increases the energy usage to 4.1%.Funding for open access charge: CRUE-Universitat Jaume

Energy evaluation of a Low Temperature commercial refrigeration plant working with the new low-GWP blend R468A as drop-in of R404A

This work analyses experimentally the energy behaviour of a centralized commercial refrigeration plant designed to be used with R404A (GWP100=3,943) at low temperatures, when it is replaced with the new low-GWP refrigerant blend R468A (GPW100=148). The tests have been done at a selected product temperature of -20°C, Class III indoor conditions according to ISO 23953-2:2015 and 20, 30 and 40°C of heat sink temperature. The product has been kept at the requested temperature in whichever conditions tested. Respect to R404A, running with R468A presents an increase in compressor discharge temperature, greater compressión operation time, and a reduction in compressor electric comssumption that yields in a very similar total energy consumption of the refrigeration plant. So it has been proved that, from an operational point of view, R468A can be a R404A drop in replacement fluid. Also, it has been measured energy savings when an internal heat exchanger is placed

A3 and A2 refrigerants: Border determination and hunt for A2 low-GWP blends

In Press, Journal Pre-proofThe hunt for new refrigerant blends has been concentrated to locate A1 refrigerants. However, the investigation for A2 or A2L blends to replace hydrocarbons (A3) has not attracted attention yet, although these mixtures will allow to increase the maximum charge of refrigeration systems from 500 g to 1200 g. This paper extends Linteris’ et al. work to define, for first time, the frontier between A3 and A2 ASHRAE safety classifications with an approach that can avoid large experimental campaigns. Then, using the methodology, it determines the composition limits of possible A2 binary blends with hydrocarbons that have a GWP below 150. Only mixtures of hydrocarbons with A2 or A2L components meet the criteria, and the composition of the least flammable fluid is predominant. Proposed hypothesis, developed theoretically, should be completed in the future with experimentation, to quantify the energy performance of found blends.Funding for open access charge: CRUE-Universitat Jaume