Enrique Tremps

Magnetic sensor for building structural vibrations.

This paper shows a new displacement-to-frequency transducer based on the variation of a coil inductance when a magnetic core is partially or completely inserted inside. This transducer is based on a Colpitts oscillator due its low manufacturing price, behavior and immunity to noise. A tank circuit with a configuration in parallel was used because it can be employed at lower frequencies and it enables it to make a direct analysis. The sensor has a dynamic range equal to the length of the coil. The cores can exchange sensors (coils with its ferromagnetic core) using the same electronic measuring system. In this way, with only an electronic circuit, the core sensor determines the measurement range. The obtained resolution is higher than 1/100,000, and the sensor also allows the measurement and knowing in real time the effect of vibration, thermal expansion, referred overload movements, etc.., that can occur in the structural elements of a building.

Anisotropic Magnetoresistive Study in Bilayer NiFe-NiO for Sensor Applications

Related with the detection of weak magnetic fields, the anisotropic magnetoresistive (AMR) effect is widely utilized in sensor applications. Exchange coupling between an antiferromagnet (AF) and the ferromagnet (FM) has been known as a significant parameter in the field sensitivity of magnetoresistance because of pinning effects on magnetic domain in FM layer by the bias field in AF. In this work we have studied the thermal evolution of the magnetization reversal processes in nanocrystalline exchange biased Ni80Fe20/Ni-O bilayers with large training effects and we report the anisotropic magnetoresistance ratio arising from field orientation in the bilayer.

Development of an Electrochemical Maltose Biosensor

In this work, electrochemical maltose biosensors based on mutants of the maltose binding protein (MBP) are developed. A rutheniumII complex (RuII), which is covalently attached to MBP, serves as an electrochemical reporter of MBP conformational changes. Biosensors were made through direct attachment of RuII complex modified MBP to gold electrode surfaces. The responses of some individual mutants were evaluated using square wave voltammetry. A maltose-dependent change in Faradic current and capacitance was observed. It is therefore demonstrated that biosensors using generically this family of bacterial periplasmic binding proteins (bPBP) can be made lending themselves to facile biorecognition element preparation and low cost electrochemical transduction.

Giant Magnetoimpedance in CoP Electrodeposited Films

In the last few years there has been increasing interest in CoP electrodeposited alloys due to their excellent properties as soft magnetic materials (low coercivity and high permeability) in addition to the giant magnetoimpedance that they exhibit. More recently magneto-impedance (MI) effect has also been reported on thin films obtained by sputtering techniques. Most of the studies performed on MI have been carried out on wires or ribbons, where the sensor shape was conditioned by its manufacturing process. However these limitations disappear on samples grown by sputtering or electrolysis where the geometry of sensors can be defined by using photolithographic techniques. In this work we have studied the giant magnetoimpedance in CoP films. The influence of the thickness of ferromagnetic material, conductive material, the frequency and intensity excitement and the geometric shape of the samples has been investigated.

Switched Reluctance Motors Control

A current controlled switched reluctance motor (SRM) drive for variable speed applications with efficiency optimization is presented. A robust, modular and flexible prototyping SRM drives is proposed. It is composed of a power electronic block, a driver board, a measurement and interface board and a DSP controller board. Firing angles are computed online, the turn-on is calculated by means of the Boses rule, and the turn-off is calculated using the general theory of the optimal turn-off angle proposed by Gribble. In steady state operation, tie initial selection of firing angles is fine-tuned by means of an algorithm that minimizes the input power of the drive. A 6/4 switched reluctance motor drive prototype was tested and the experimental results show an improvement in online efficiency, a good steady-state performance and no deterioration in the dynamic response. An efficiency comparison with a commercial vector-controlled induction motor drive of the same size is also included.

Building Functional Surfaces for Biosensors Development

Polyelectrolyte multilayers (PEM) built by layer-by-layer technique have been extensively studied over the last years, resulting in a wide variety of current and potential applications. This technique can be used to construct thin films with different functionalities, or to functionalize surfaces with substantial different properties of those of the underlying substrates. The multilayering process is achieved by the alternate adsorption of oppositely charged polyelectrolytes. In this work we get advantage of the protein resistant property of the Poly (l-lysine)-graft-(polyethyleneglycol) to create protein patterns. Proteins can be immobilized on a surface by unspecific physical adsorption, covalent binding or through specific interactions. The first protein used in this work was laccase, a copper-containing redox enzyme that catalyse the oxidation of a broad range of polyphenols and aromatic substrates, coupled to the reduction of O2 to H2O without need of cofactors. Applications of laccases have been reported in food, pulp, paper, and textile industry, and also in biosensor development. Some uses require the immobilization of the enzyme on solid supports by adsorption, covalent attachment, entrapment, etc, on several substrates. Especially for biosensor development, highly active, stable and reproducible immobilization of laccase is required.

Performance Optimization in Switched Reluctance Motor Drives

In this paper, switched reluctance motors (SRM) are proposed as an alternative for electric power assisted steering (EPAS) applications. A prototype machine has been developed as very attractive design for a steering electric motor, both from a cost and size perspective. A four-phase 8/6 SRM drive is designed for a rack type EPAS which should provide a maximum force of 10 kN. Two-dimension finite element analysis is used to validate the design.