Off-diagonal impedance in amorphous wires and application to linear magnetic sensors

The magnetic-field behaviour of the off-diagonal impedance in Co-based amorphous wires is investigated under the condition of sinusoidal (50 MHz) and pulsed (5 ns rising time) current excitations. For comparison, the field characteristics of the diagonal impedance are measured as well. In general, when an alternating current is applied to a magnetic wire the voltage signal is generated not only across the wire but also in the coil mounted on it. These voltages are related with the diagonal and off-diagonal impedances, respectively. It is demonstrated that these impedances have a different behaviour as a function of axial magnetic field: the former is symmetrical and the latter is antisymmetrical with a near linear portion within a certain field interval. In the case of the off-diagonal response, the dc bias current eliminating circular domains is necessary. The pulsed excitation that combines both high and low frequency harmonics produces the off-diagonal voltage response without additional bias current or field. This suits ideal for a practical sensor circuit design. The principles of operation of a linear magnetic sensor based on C-MOS transistor circuit are discussed.Comment: Accepted to IEEE Trans. Magn. (2004

Metal-to-glass ratio and the Magneto-Impedance of glass-covered CoFeBSi microwires at high frequencies

High frequency [1-500 MHz] measurements of the Magneto-Impedance (MI) of glass-covered Co$_{69.4}$Fe$_{3.7}$B$_{15.9}$Si$_{11}$ microwires are carried out with various metal-to-wire diameter ratios. A twin-peak, anhysteretic behaviour is observed as a function of magnetic field. A maximum in $\Delta Z/Z$ appears at different values of the frequency $f$, 125, 140 and 85 MHz with the corresponding diameter ratio $p$ = 0.80, 0.55 and 0.32. We describe the measurement technique and interpret our results with a thermodynamic model that leads to a clearer view of the effects of $p$ on the maximum value of MI and the anisotropy field.Comment: 5 pages and 6 figure

Magnetoelastic properties of iron-based amorphous wires

SIGLEAvailable from British Library Document Supply Centre- DSC:DX171703 / BLDSC - British Library Document Supply CentreGBUnited Kingdo

An investigation of the Matteucci effect on amorphous wires and its application to bend sensing

The study of wearable sensors for human biometrics has recently developed into an important research area due to its potential for personalised health monitoring. To measure bending parameters in humans such as joint movement or posture, several techniques have been proposed however, the majority of these suffer from poor accuracy, sensitivity and linearity. To overcome these limitations, this research aims to develop a novel flexible sensor for the measurement of bending by utilising the Matteucci effect on amorphous wires. The Matteucci effect occurs in all ferromagnetic wires but the advantages of amorphous wires are their superior soft magnetic and magnetoelastic properties and a Matteucci effect that is very sensitive to applied stresses like tensile and torsion. For these reasons a sensor based on Matteucci effect was investigated for use as a wearable bending sensor. Previous studies of the Matteucci effect have been interpreted in terms of simple phenomenological models using conveniently sized lengths of amorphous wire. In this work, the Matteucci effect has been characterised in short, sensor-compatible, wires. In addition, a thorough examination of the stress dependency of the Matteucci effect was also investigated as this is an area that has been neglected in the past. The main aim of this work was to study the effect of tensile and torsion stresses on the Matteucci effect in both highly positive magnetostrictive and nearly zero magnetostrictive amorphous wires. A measurement rig was specifically built to characterise the Matteucci effect for a range of magnetic field amplitudes, frequencies, torsions and axial stresses. The second major aim was to use this characterisation data to ascertain the optimum working parameters to design and construct a novel flexible bending sensor. In this work, the Matteucci effect in amorphous wires was found to be very sensitive to both axial and torsional applied stresses and dependent upon the sign of the magnetostriction. Insights gained here were used to develop the bend sensor in three steps. The initial prototype was a non-flexible strain sensor for measuring tensile stress and exhibited a very high gauge factor equal to 601± 30. The second step resulted in a strain sensor prototype utilising a flexible planar coil to magnetise the amorphous wire. The final step produced a bend sensor this time consisting of a flexible solenoid with greater magnetising capability. It resulted in a bend sensor IV with a high output voltage sensitivity of 5.62 ± 0.02 mV/cm which is the slope of the voltage due to curvature and excellent linearity (R2 = 0.98). In this case the sensor’s operating range was 1.11 rad to 2.49 rad with ± 0.003 rad uncertainty. This range is scalable and dependent on the sensor configuration. This work has demonstrated the feasibility of utilising the Matteucci effect as a bend sensor with a performance exceeding that found in many commercial sensors

ROBI’: A prototype mobile manipulator for agricultural applications

The design of ROBI', a prototype mobile manipulator for agricultural applications devised following low-cost, low-weight, simplicity, flexibility and modularity requirements, is presented in this work. The mechanical design and the selection of the main components of the motion control system, including sensors and in-wheel motors, is described. The kinematic and dynamic models of the robot are also derived, with the aim to support the design of a trajectory tracking system and to make a preliminary assessment of the design choices, as well. Finally, two simulations, one~specifically related to a realistic trajectory in an agricultural field, show the validity of these choices

Development of high sensitivity materials for applications in magneto-mechanical torque sensor

The Matteucci effect, which mainly manifests itself as the change of magnetization of a material with torsional stress, is currently of great technological interest because of the search for magnetic torque sensors. Magnetic torque sensors are important to future improvements of automobiles and industrial robots. It is well known that the magnetic state of a material depends on both the external magnetic field and external stress which causes strain and change in magnetization of the material. The former phenomenon has been well understood in both theory and application. However, the magnetic state dependence of stress is not adequately understood and the experimental data is of limited extent. In this project, the Matteucci effect in iron, cobalt, nickel and permalloy rods has been documented when they were in magnetic remanence status along the axis and nickel ring when they were in remanence status along the circumference. The effect of annealing on the magnetomechanical effect in nickel and the temperature dependence of the magnetomechanical sensitivity has also been examined. Factors related to the sensitivity at equilibrium condition have been theoretically developed. It is found in the experiments that the mechanism of magnetic domain wall movement plays an important role rather than the domain rotation. A higher sensitivity was found by domain wall movement mechanism than that by domain rotation mechanism. However, the domain wall movement will result in more hysteresis than domain wall rotation. The dynamic process of Matteucci effect of iron, cobalt, permally, especially as-fabricated and annealed nickel rods have been examined. A tentative explanation for the difference of these in terms of magnetic domain configuration and domain wall movement was given. As a result, another method of configuring and processing magnetic domains to get a linear magnetomechanical response other than that suggested by Garshelis, which was the basic method before the present studies, has been experimentally developed and theoretically analyzed. A higher sensitivity was obtained in nickel by employing this method than that by employing the method of Garshelis. The results suggest that magnetic domain configuration is very important in designing a high sensitivity magnetic torque sensor