Conformación de Superficies Reflectoras de Sistemas Dobles de Tipo Offset con Alimentadores descritos en Campo Próximo

This work discusses an iterative procedure of shaping offset dual-reflector antennas based on geometrical optics considering both far-field and near-field measurements of amplitude and phase from the feed horn. The surfaces synthesized will transform a known radiation field of a feed to a desired aperture distribution. This technique is applied for both circular and elliptical apertures and has the advantage to simplify the problem compared with existing techniques based on solving nonlinear differential equations. A MATLAB tool has been developed to implement the shaping algorithms. This procedure is applied for the design of a 1.1 m high-gain antenna for the ESA’s Solar Orbiter spacecraft. This antenna operating at X-band will manage high data rate and high efficiency communications with Earth stations.

Size, strain, and band offset engineering in GaAs(Sb)(N)-capped InAs quantum dots for 1.3 - 1.55 µm LEDs and LDs

The optical and structural properties of InAs/GaAs quantum dots (QD) are strongly modified through the use of a thin (~ 5 nm) GaAsSb(N) capping layer. In the case of GaAsSb-capped QDs, cross-sectional scanning tunnelling microscopy measurements show that the QD height can be controllably tuned through the Sb content up to ~ 14 % Sb. The increased QD height (together with the reduced strain) gives rise to a strong red shift and a large enhancement of the photoluminescence (PL) characteristics. This is due to improved carrier confinement and reduced sensitivity of the excitonic bandgap to QD size fluctuations within the ensemble. Moreover, the PL degradation with temperature is strongly reduced in the presence of Sb. Despite this, emission in the 1.5 !lm region with these structures is only achieved for high Sb contents and a type-II band alignment that degrades the PL. Adding small amounts of N to the GaAsSb capping layer allows to progressively reduce the QD-barrier conduction band offset. This different strategy to red shift the PL allows reaching 1.5 !lm with moderate Sb contents, keeping therefore a type-I alignment. Nevertheless, the PL emission is progressively degraded when the N content in the capping layer is increased

Control en modo corriente y tensión eficaz con lazo de offset para inversor monofásico embarcado en aviones adecuado para funcionamiento en paralelo y conexión trifásica

La incorporación de un lazo de tensión eficaz de (RMS) es una posibilidad atractiva para el control de inversores de potencia de una manera sencilla. Si se combina con un control en modo corriente usando una sonda de efecto Hall, el ruido de modo común de la etapa de potencia transmitido al control puede ser reducido, mejorando la distorsión armónica total (THD) y manteniendo la posibilidad de operación en paralelo. Además, al estar el control de tensión definido sobre baja frecuencia (DC), obtener una gran ganancia a la frecuencia de interés (0Hz) es sencilla con control basado en PI, lo cual garantiza una onda de tensión de salida a 400Hz sin error, a costa de un peor desempeño ante transitorios y ante cargas no lineales. Sin embargo, la implementación de una estrategia de control de esta naturaleza puede provocar la aparición de offset en la salida. Por otra parte, el esquema oculta la información de la fase de la onda de tensión de salida, necesaria para sincronizar tres módulos monofásicos en un montaje trifásico. En este artículo el diseño e implementación del sistema completo es abordado, resolviendo los inconvenientes mencionados mediante un tercer lazo analógico de control para el offset y un algoritmo de sincronización implementado en una FPGA.

Current Mode with RMS Voltage and Offset Control Loops for a Single-Phase Aircraft Inverter Suitable for Parallel and 3-Phase Operation Modes

Rms voltage regulation may be an attractive possibility for controlling power inverters. Combined with a Hall Effect sensor for current control, it keeps its parallel operation capability while increasing its noise immunity, which may lead to a reduction of the Total Harmonic Distortion (THD). Besides, as voltage regulation is designed in DC, a simple PI regulator can provide accurate voltage tracking. Nevertheless, this approach does not lack drawbacks. Its narrow voltage bandwidth makes transients last longer and it increases the voltage THD when feeding non-linear loads, such as rectifying stages. On the other hand, the implementation can fall into offset voltage error. Furthermore, the information of the output voltage phase is hidden for the control as well, making the synchronization of a 3-phase setup not trivial. This paper explains the concept, design and implementation of the whole control scheme, in an on board inverter able to run in parallel and within a 3-phase setup. Special attention is paid to solve the problems foreseen at implementation level: a third analog loop accounts for the offset level is added and a digital algorithm guarantees 3-phase voltage synchronization.

Rational conchoid and offset constructions: algorithms and implementation

This paper is framed within the problem of analyzing the rationality of the components of two classical geometric constructions, namely the offset and the conchoid to an algebraic plane curve and, in the affirmative case, the actual computation of parametrizations. We recall some of the basic definitions and main properties on offsets (see [13]), and conchoids (see [15]) as well as the algorithms for parametrizing their rational components (see [1] and [16], respectively). Moreover, we implement the basic ideas creating two packages in the computer algebra system Maple to analyze the rationality of conchoids and offset curves, as well as the corresponding help pages. In addition, we present a brief atlas where the offset and conchoids of several algebraic plane curves are obtained, their rationality analyzed, and parametrizations are provided using the created packages.

Heterojunction Band Offset Limitations on Open-Circuit Voltage in p-ZnTe/n-ZnSe Solar Cells

Limitations on the open-circuit voltage of p-ZnTe/n-ZnSe heterojunction solar cells are studied via current-voltage (I-V) measurements under solar concentration and at variable temperature. The open-circuit voltage reaches a maximum value of 1.95 V at 77 K and 199 suns. The open-circuit voltage shows good agreement with the calculated built-in potential of 2.00 V at 77 K. These results suggest that the open-circuit voltage is limited by heterojunction band offsets associated with the type-II heterojunction band lineup, rather than the bandgap energy of the ZnTe absorber material.