C. Reig

Magnetic Field Sensors Based on Giant Magnetoresistance (GMR) Technology: Applications in Electrical Current Sensing.

The 2007 Nobel Prize in Physics can be understood as a global recognition to the rapid development of the Giant Magnetoresistance (GMR), from both the physics and engineering points of view. Behind the utilization of GMR structures as read heads for massive storage magnetic hard disks, important applications as solid state magnetic sensors have emerged. Low cost, compatibility with standard CMOS technologies and high sensitivity are common advantages of these sensors. This way, they have been successfully applied in a lot different environments. In this work, we are trying to collect the Spanish contributions to the progress of the research related to the GMR based sensors covering, among other subjects, the applications, the sensor design, the modelling and the electronic interfaces, focusing on electrical current sensing applications.

Full Wheatstone Bridge Spin-Valve Based Sensors for IC Currents Monitoring

Full Wheatstone bridge spin-valve-based electrical current sensors at the IC level are presented. Prototypes with different geometrical parameters have been designed, fabricated and fully characterized. DC characterization has been carried out, for measurement of insertion losses, linearity, voltage offset and sensitivity. Current ranges from 10 muA to 100 mA can be covered with these sensors with excellent linearity and sensitivities above 1 mV/(VmiddotmA) . AC characteristics have also been analyzed and bandwidths exceeding 100 kHz are demonstrated. Moreover, the temperature coefficients have been extracted in the range of -20degC to +60degC. In order to highlight the design properties, dependence of the sensors performance with external magnetic perturbations and self-heating have also been measured and quantified. The associated errors are in the range of 1%-2% of the full scale.

FDTD analysis of E-sectoral horn antennas for broad-band applications

The finite-difference time-domain (FDTD) method is applied to study the performance of E-plane sectoral horn antennas designed for broad-band applications. These antennas (proposed for 6-18 GHz phased arrays) have a large bandwidth, and they are easily array integrated. These antennas have a highly complicated geometry that is modeled using a polygonal approximation in the curved boundaries. Perfect matched layers (PMLs) combined with first-order absorbing boundaries are employed to simulate the free-space environment in the FDTD mesh.

Modeling of Magnetoresistive-Based Electrical Current Sensors: A Technological Approach

The utilization of modeling tools can, in many cases, help us in the design and final prototyping of any sort of sensors. In this paper, we describe a finite-element method (FEM) model applied to a hybrid technology involving a full Wheatstone bridge spin-valve-based electrical current sensor. After validating the model against experimental results, we focus our studies on geometrical aspects of the sensor configuration, in order to detect possible deviations that may have occurred during the fabrication process. In this regard, the characteristics of the behavior of the sensor depending on lateral displacements and inclination are included. Moreover, the frequency response of the sensor is also analyzed, thus enlarging the scope of the model.

Growth and characterisation of MnTe crystals

We report on the low temperature growth of MnTe crystals by means of travelling solution methods. Two different processes are considered; a classical THM process using a low temperature presynthesised MnTe ingot, and a modified THM process, in which an increasing length of solvent zone collects the tellurium that was added to the stoichiometric charge to decrease the reaction temperature. Ingots from the two methods are analysed by means of scanning electron microscopy, X-ray diffractometry, resistivity, susceptibility and optical absorption measurements.

Integration of GMR Sensors with Different Technologies

Less than thirty years after the giant magnetoresistance (GMR) effect was described, GMR sensors are the preferred choice in many applications demanding the measurement of low magnetic fields in small volumes. This rapid deployment from theoretical basis to market and state-of-the-art applications can be explained by the combination of excellent inherent properties with the feasibility of fabrication, allowing the real integration with many other standard technologies. In this paper, we present a review focusing on how this capability of integration has allowed the improvement of the inherent capabilities and, therefore, the range of application of GMR sensors. After briefly describing the phenomenological basis, we deal on the benefits of low temperature deposition techniques regarding the integration of GMR sensors with flexible (plastic) substrates and pre-processed CMOS chips. In this way, the limit of detection can be improved by means of bettering the sensitivity or reducing the noise. We also report on novel fields of application of GMR sensors by the recapitulation of a number of cases of success of their integration with different heterogeneous complementary elements. We finally describe three fully functional systems, two of them in the bio-technology world, as the proof of how the integrability has been instrumental in the meteoric development of GMR sensors and their applications.

Dual Printed Antenna for Wi-Fi Applications

A dual-frequency compact printed antenna for Wi-Fi (IEEE 802.11x at 2.45 and 5.5 GHz) applications is presented. The design is successfully optimized using a finite-difference time-domain (FDTD)-algorithm-based procedure. Some prototypes have been fabricated and measured, displaying a very good performance.

Electrical Isolators Based on Tunneling Magnetoresistance Technology

An analog isolator device, based on linear magnetic tunnel junctions is presented. Elemental single structures and full Wheatstone bridge devices are designed, fabricated and tested. In addition, the ranges of functionality of the devices are analyzed, mainly in terms of linearity, signal reconstruction and frequency response.

Wireless Sensor Network for Soil Moisture Applications

The development of a wireless sensor network for soil moisture measurements, in a wide reference area of 10 x 10 km2, is described in this work. Some automatic measurement stations were strategically placed following soil homogeneity and land uses criteria. These stations include acquisition, conditioning and communication systems. The electronics are operated by a solar panel fed battery, in order to allow them to operate autonomously. The collected data are then transmitted by radio links, with link ranges up to 8 km. A standard PC is used to control the whole network and store the data. This computer also allows accessing the data via Internet for its subsequent analysis. Even though the specific application was the characterization of a reference area, in order to use it in campaigns of calibration and validation of the space mission SMOS (Soil Moisture and Ocean Salinity), the system is easily extensible to other climatic measurements as well as for other zones of interest.

Yagi-Like Printed Antennas for Wireless Sensor Networks

In this work, two alternative printed antennas for wireless sensor networks applications in the ISM band are presented. The antennas are based on the well- known Yagi-Uda antenna and the principal difference between them is on the printed dipole design; in only one face of the substrate or in both faces. The design has been performed by using an in house developed code based on FDTD algorithm. In the design process, we have focused on the optimization of the bandwidth and the directivity. Finally, some prototypes with different number of dipoles have been fabricated and measured. The good agreement between simulated and experimental results demonstrates the validity of the simulations. The radiation parameters show the potentiality of these antennas for increasing the distance of communication in wireless networks.