Luis Castañer

A Miniaturized Two Axis Sun Sensor for Attitude Control of Nano-Satellites

This paper describes the design, fabrication, characterization, and satellite integration of a miniaturized two axis sun sensor which has been used in the attitude control system of the Spanish nano-satellite NANOSAT-1B. This device is made of four silicon photodiodes monolithically integrated in a crystalline silicon substrate, protected by a transparent cover glass assembled on the same silicon die against space radiation damage. The sensor fabrication combines standard silicon processing technology with a high performance solar cell fabrication process. The sensor, including electronics and mechanical and electrical interfacing with the satellite, has a small size (3 cm × 3 cm) and low weight (24 gr.), with a sun field-of-view greater than ±60° with an angle accuracy better than 0.15°. Three of these sensors have already been integrated in the NANOSAT-1B platform that has been successfully launched in July 2009.

Pull-in time–energy product of electrostatic actuators: comparison of experiments with simulation

Measurements of voltage and current transients of a scaled model of an electrostatic microactuator have been performed. Experiments were made at a variety of values of the actuation source resistance, and the effects on the pull-in time and on the energy consumed in a switching event were analysed. It is concluded that the pull-in time remains sensibly constant until source resistance values are reached corresponding more closely to current-controlled than to voltage-controlled actuation. Furthermore, the energy consumed per switching event monotonically decreases with increasing source resistance. There is an optimum source resistance at which a minimum can be found for the product of pull-in time and energy in agreement with earlier theoretical predictions. The experimental results are quantitatively compared with Saber simulations incorporating an analog hardware description language model for the actuator.

Tracking Control System Using an Incident Radiation Angle Microsensor

For some industrial applications, an accurate estimation of a light source position is needed. That is the case for a heliostat, a device that projects sunlight onto a focus hundreds of meters away from its aiming point. In this paper, we present a novel sensor design for generating an alignment error signal. Included is a detailed study of its response, which shows that certain geometrical design parameters are necessary to achieve desired accuracy. This sensor has been implemented using microelectromechanical system techniques to achieve a robust structure at low cost and it has been successfully applied to sun-tracking systems. Experimental results obtained in field tests are included

Tracking system for solar power plants

In this paper a sun tracking system is presented. The main component of this system is a solar sensor. It is a light source position sensor. The sensor is made using MEMS technology to increase the sensitivity of the sensor and reduce manufacture cost. An algorithm is also designed to implement the control system considering all the different meteorological conditions. Two scale models has been made to test the complete system, that is, as much as the sensor as the algorithm. The scale models are based in real applications where the sensor can be incorporated, as they are heliostats and photovoltaic cells. The experimental results are successful and show the robustness and high precision of the system

Colloidal crystals by electrospraying polystyrene nanofluids

This work introduces the electrospray technique as a suitable option to fabricate large-scale colloidal nanostructures, including colloidal crystals, in just a few minutes. It is shown that by changing the deposition conditions, different metamaterials can be fabricated: from scattered monolayers of polystyrene nanospheres to self-assembled three-dimensional ordered nanolayers having colloidal crystal properties. The electrospray technique overcomes the main problems encountered by top-down fabrication approaches, largely simplifying the experimental setup. Polystyrene nanospheres, with 360-nm diameter, were typically electrosprayed using off-the-shelf nanofluids. Several parameters of the setup and deposition conditions were explored, namely the distance between electrodes, nanofluid conductivity, applied voltage, and deposition rate. Layers thicker than 20 μm and area of 1 cm2 were typically produced, showing several domains of tens of microns wide with dislocations in between, but no cracks. The applied voltage was in the range of 10 kV, and the conductivity of the colloidal solution was in the range of 3 to 4 mS. Besides the morphology of the layers, the quality was also assessed by means of optical reflectance measurements showing an 80% reflectivity peak in the vicinity of 950-nm wavelength.

Wettability increase by "corona" ionization

Experiments showing an increase in the wettability of a hydrophobic surface when using corona air ionization are shown. Photoluminiscence observations support the predictions of charge accumulation at the triple line and confirm previous experiments. In all of the experiments, the contact angle was in the saturation regime at a value smaller than that predicted by the condition of a zero value for the solid-liquid surface tension. The PDMS did not show any deterioration due to the corona exposure under the experimental conditions used. The contact angle is shown to increase with humidity.

A fast low-cost solar cell spectral response measurement system with accuracy indicator

A novel automated spectral measurement system is presented. Special attention has been focused on the design in order to obtain rapid measurement facilities, minimize hardware and simplify serial communications between the different subsystems involved, resulting in a low-cost measurement system. It is controlled by an HP-9000 computer, through a fully menu-driven interface, and the primary measurement instrument is an HP-4142B modular source-monitor. A new indicator of measurement accuracy is defined, implemented and displayed in real time. This automated system has been employed intensively to study characteristics of different solar cell types in order to optimize their fabrication process. As such this automated measurement system is clearly useful for both research and fabrication.

Principles of solar cell operation

The two steps in photovoltaic energy conversion in solar cells are described using the ideal solar cell, the Shockley solar cell equation, and the Boltzmann constant. Also described are solar cell characteristics in practice; the quantum efficiency of a solar cell; the optical properties of solar cells, including antireflection properties, transmission, and light trapping; typical solar cell structures, including the p–n junction, uniform emitter and base, diffused emitter, heterojunction cells, p–i–n structure, and series resistance.

Sub-Bandgap External Quantum Efficiency in Ti Implanted Si Heterojunction with Intrinsic Thin Layer Cells

In this work we present the manufacturing processes and results obtained from the characterization of heterojunction with intrinsic thin layer solar cells that include a heavily Ti ion implanted Si absorbing layer. The cells exhibit external circuit photocurrent at photon energies well below the Si bandgap. We discuss the origin of this below-bandgap photocurrent and the modifications in the hydrogenated amorphous intrinsic Si layer thickness to increase the open-circuit voltage.

Simulation of flow sensors for home appliances

Hot-wire flow meters are currently usual as flow sensing devices. In this work, we explain the procedure used to simulate a water flow sensor for home appliances. The proposed system is composed of a thermally activated subsystem and an electronic subsystem which provides feedback and output read-out. The complete system has been fabricated, and the measurements corroborate the simulation procedure.