Thaddeus Schroeder

Temperature stable Hall effect sensors

Magnetic field sensors are needed for high-accuracy position, angle, force, strain, torque, and current flow measurements. Molecular beam epitaxy was used to grow tellurium-doped indium-gallium antimonide thin films. Hall effect sensors made from these films have been studied for their magnetic sensitivity and thermal stability. For a range of alloy composition near In/sub 0.8/Ga/sub 0.2/Sb and n-type doping levels near 2/spl times/10/sup 17/ cm/sup -3/, high magnetic sensitivity from -40/spl deg/C to +200/spl deg/C was found with a resolution of better than /spl plusmn/0.5% over the entire temperature range.

High accuracy magnetic position encoder concept

Position sensors based on the detection of magnetic flux densities by Hall sensors or magnetoresistors are used in automotive applications for crankshaft and camshaft position sensing, which is needed for engine control. The paper identifies the limitations of traditional designs, which introduce an angular error between the position signal pulse and the actual location of the corresponding triggering feature on the sensor target wheel. It proposes a solution ensuring that the position signal pulse coincides with a point of symmetry in the triggering target-wheel feature, thus eliminating the angular error. Two interesting implementations are described in the paper. One of them is analyzed in full detail, and a methodology for its design is provided. In particular, specific design rules are derived which link some of the design parameters to relevant dimensional specifications. These rules are established on the basis of a geometrical method developed for this particular type of problem which necessitates the calculation of flux densities in a few specific locations, namely where the sensing elements are located. The overall approach, including these design rules, is validated by finite element analysis as well as by experimental data,.

Magnetic velocity sensors

Variable-reluctance devices sense variations in flux linkage while semiconductors read variations in local flux density. The authors show how recognizing this fundamental difference leads to markedly different sensor design approaches, and propose new configurations with improved performance. The analysis of the sensors is based on a general theory developed for these sensors. The magnetic field computations use the finite-element method, which is particularly well suited to this problem involving complex airgap configurations and a need for the calculation of local flux densities and flux linkages.<<ETX>>

Microstructure and magnetic properties of CO2 laser surface melted Nd-Fe-B magnets

Abstract The near-surface microstructure and magnetic properties of permanent magnets produced from hot-pressed melt-spun ribbons of a Nd 0.13 Fe 0.81 B 0.06 alloy were modified by CO 2 laser beam melting. Self-quenching of the molten surface layer at an average cooling rate of ≈10 4 K/s resulted in a stratified structure consisting of a zone of large columnar grains between thinner layers of equiaxed grains. The resolidified material was comprised mostly of the magnetically hard Nd 2 Fe 14 B phase dispersed interdendritically among primary α-Fe dendrites. A small volume fraction of a fcc Nd-rich phase was also present. A solidification texture in the columnar zone resulted in alignment of the c -axis of the Nd 2 Fe 14 B phase, the direction of easiest magnetization, parallel to the surface of the sample. The magnetic properties of the resolidified layer were anisotropic. The magnetization was oriented parallel to the surface, in accordance with the preferred orientation of the Nd 2 Fe 14 B phase. Low coercivity in all directions (≈140Oe) was attributed to the relatively large grain size of the Nd 2 Fe 14 B phase and also to the amount of ferrite present.

An ion-drag air mass-flow sensor for automotive applications

An air-flow meter, developed primarily for the measurement of air intake into an internal combustion engine, is described. The well-known process of corona ion deflection in a gas flow together with proper electrode geometry and a detection scheme provides the conceptual basis for a humidity-insensitive ionic air-flow sensor. Output characteristics of the sensor, such as response time and range of operation, are discussed and compared to those of a production hot-wire meter of the type that is currently used with electronic fuel injection systems. Unlike the hot-wire transducer, the proposed sensor is shown to allow for bidirectional measurement of the air flow. The transient response time of the ionic sensor is shorter than that of the hot-wire transducer.<<ETX>>

Laser surface heating of Nd-Fe-B, Nd-Fe-Co-B, and BaO-6Fe2O3 permanent magnets

Abstract Hot-pressed Nd-Fe-B, epoxy-bonded Nd-Fe-Co-B, and BaO-6Fe 2 O 3 (ferrite) permanent magnets are heated by scanning their surfaces with an argon ion laser beam. The laser heating response of each magnet material is examined by measuring the depth of the heat-affected zone as a function of beam power and scan rate. An analytic heat transfer model is used to provide a convenient description of the laser surface heating process. The temperature distribution in the magnets is calculated to estimate the depth of the heat-affected zone as defined by the position of the Curie temperature isotherm. Agreement is good among the calculated and measured depths for all three permanent magnet materials.

MAGNECODE : LASER BEAM ENCODING OF PERMANENT MAGNETS FOR AUTOMOTIVE POSITION AND SPEED SENSORS

MAGNECODE uses laser surface heating to pattern permanent magnets for position sensor applications. Thermal and magnetic models provide good predictions of the geometry of the laser heated regions and the resulting spatial variations in the magnetic field. Important design factors are discussed and a comparison with other magnetic sensor technologies is given.

Power processor fed induction motor for simulation of internal combustion engine

A high performance electric drive system was developed to simulate the operating characteristics of automotive internal combust1on eng1nes. The torque-speed profiles of various types of automotive engines are stored on a printed circu1t card, thus allowing a particular engine to be selected simply by pushing a button. Th1s system has been used for both production testing and engineering analysis of automatic transmissions. The method of generating the torque-speed curves and the basic feedback control system are described.