MAGNETIC FIELD SENSOR UTILIZING MAGNETO IMPEDANCE IN THIN FILM MULTI-LAYERS

Since the discovery of the Magneto Impedance (MI) effect in 1994 there has been a global increase in the research devoted to understanding the effect. In certain magnetic materials, the impedance change, often referred to as the MI ratio, is in the range of 50 to 100% for an excitation current in the MHz frequency range for external magnetic fields of a few Oe. The use of thin film multilayer structures allows the increase of sensitivity and the reduction of size for MI effect to be integrated with micro magnetic sensor technologies. In the present work, we explain the origins of the MI effect and its versatile nature for the development of sub nano Tesla magnetic field sensors. The matrix like nature of the MI effect allows a variety of MI characteristics to be implemented in a thin film, which allows the structure to be tailored for maximum sensitivity in the chosen field sensing application. In the case of a simple transverse magnetic anisotropy, the diagonal components of the MI matrix are symmetric and the off diagonal components are anti-symmetric with respect to the dc longitudinal field. The asymmetry in the MI behaviour can be related to either a certain asymmetric arrangement of the dc magnetization (crossed an isotropy), or a contribution to the measured voltage due to the ac cross-magnetization process, which is represented as an off-diagonal component. These asymmetrical characteristics are useful in producing linear bi-directional field sensors without DC biasing. In attempt to find optimal film systems with respect to relative impedance change, sensitivity, linearity, operational frequency range, and dimensions, thin film multi-layers, consisting of a magnetic / conductor / magnetic material configuration were fabricated. Variations in magnetic compositions, geometries, structures and magnetic configurations (transverse, longitudinal or cross anisotropy) and additional insulations layers were produced. Planar coil thin film multi-layers were constructed to utilize the more magnetic complex asymmetric characteristics of the MI effect. An experimental configuration was developed in order to measure all components of the MI matrix within the thin films and standardise their sensitivity using the MI ratio. Two sub nano Tesla magnetic field sensors were developed during the course of this work based on the fabricated thin films. The first sensor concentrates on utilizing two asymmetrical Magneto Impedance (AMI) elements combined differentially. The sensor is driven by a sinusoidal current of 90 MHz biased with a dc bias current. For AMI film element of 5mm long, 40µm wide and having anisotropy angle of 45° the field detection resolution is in the magnitude of 1µ Oe for both ac and dc for fields of ~ 20e magnitude. The maximum response speed is in the order of 1MHz. The use of MI to the measurement low frequency fields such as bio-medical signals drove the design of the second sensor. Extensive research was undertaken to improve the phase noise of the oscillator and sensitivity of the detection mechanism using novel RF techniques to improve the sensitivity at high frequencies, and secondly a method to improve the low frequency sensitivity by AC biasing the MI element with a magnetic field. A thin film multilayer MI sensor was produced based on the measurement of the modulation of the incident reflected power due to an external AC magnetic field. Direct field measurement performance at 1kHz produced a resolution of 3.73 x 10-7 Oe. AC biased performance at 5kHz of a 20Hz field was a resolution of 5.27 x 10-6 Oe, and at 10Hz of 9.33 x 10-6 Oe. With continued improvement of the electronic components utilized in this novel method of Magneto Impedance sensor presented in this work, the possibility of measuring bio magnetic signals of the human body at room temperature becomes a distinct reality

THE DEVELOPMENT OF A NOVEL SUSPENSION ARM WITH 2-DIMENSIONAL ACTUATION, FOR USE IN ADVANCED HARD DISK DRIVES

As magnetic computer disks are developed to ever-greater data storage densities, the accuracy required for head positioning is moving beyond the accuracy provided by present technology using single-stage voice-coil motors in hard disk drives. This thesis details work to develop a novel active suspension arm with 2-dimensional actuation for use in advanced hard disk drives. The arm developed is capable of high-bandwidth data tracking as well as precision head flying height control motion. High-bandwidth data tracking is facilitated by the use of piezoelectric stack actuator, positioned closer to the head. The suspension arm is also capable of motion in the orthogonal axis. This motion represents active flying height control to maintain the correct altitude during drive operation. To characterise the suspension arm's structural dynamics, a high-resolution measurement system based on the optical beam deflection technique has been developed. This has enabled the accurate measurement of minute end-deflections of the suspension arm in 2-dimensions, to sub-nanometre resolution above noise. The design process of the suspension arm has led into the development of novel piezoelectric-actuated arms. In the work involving lead zirconate titanate (PZT) thick films as actuators, work in this thesis shows that reinforcing the films with fibre improves the overall actuation characteristics of the thick films. This discovery benefits applications such as structural health monitoring. The final suspension arm design has been adopted because it is simple in design, easier to integrate within current hard disk drive environment and easier to fabricate in mass. Closed-loop control algorithms based on proportional, integral and derivative (PID) controller techniques have been developed and implemented to demonstrate high bandwidths that have been achieved. The suspension arm developed presents an important solution in head-positioning technology in that it offers much higher bandwidths for data tracking and flying height control; both very essential in achieving even higher data storage densities on magnetic disks at much reduced head flying heights, compared to those in existing hard disk drives

Development of an Integrated Survey Vehicle for Measuring Pavement Surface Conditions at Highway Speeds, Volume I: Technical Report

DTFH61-85-C-00172The objective of this study was to develop an integrated survey vehicle for measuring pavement surface conditions at highway speeds. This was accomplished by determining the requirements and operating characteristics for such a system, preparing a design, and estimating initial and operating costs. This volume contains a review of the data and measurement needs for pavement condition surveys. The equipment available and under development for this purpose are identified with emphasis on measurements at highway speeds. Three potential survey vehicle designs are presented: the first uses off-the-shelf components, the second uses state-of-the-art components, while the third anticipates the addition of equipment still in development. The final design that was selected incorporates all three types of equipment. A complete, detailed design for the vehicle and the test equipment was prepared and each subpart discussed. Operating procedures for the survey vehicle are established and given in this report

Design and assessment of a low-frequency magnetic measurement system for eLISA

The primary purpose of this thesis is the design, development and validation of a system capable of measuring magnetic field with low-noise conditions at sub-millihertz frequencies. Such instrument is conceived as a part of a space mission concept for a gravitational-wave observatory called eLISA (evolved Laser Interferometer Space Antenna). In addition, the work of this thesis is also well-suited for use in magnetically sensitive fundamental physics experiments requiring long integration time, such as high-precision measurement of the weak equivalence principle using space atom interferometry. To this end, the baseline design of the instrument is also foreseen to monitor the environmental magnetic field in a proposed mission concept involving space atom-interferometric measurements, known as STE-QUEST (Space-Time Explorer and Quantum Equivalence Principle Space Test).El principal objetivo de esta tesis es el diseño, desarrollo y validación de un sistema capaz de medir campos magnéticos de bajo ruido a muy baja frecuencia (0.1\,mHz). Este instrumento es concebido como parte de una propuesta de misión espacial para un observatorio de ondas gravitacionales llamado eLISA (evolved Laser Interferometer Space Antenna). Además, el estudio de esta tesis es también de utilidad para experimentos de física fundamental especialmente sensibles a los campos magnéticos. En particular, aquellos que requieren tiempos de integración largos, como por ejemplo medidas de alta precisión del principio de equivalencia usando interferometría atómica en el espacio. En este contexto, está previsto que el sistema de medidas desarrollado en esta tesis forme también parte del la misión espacial STE-QUEST (Space-Time Explorer and Quantum Equivalence Principle Space Test). Diferentes tecnologías de sensores magnéticos (fluxgate, magnetoresitencias anisotrópicas, y magnetómetros atómicos) junto con técnicas apropiadas de reducción de ruido electrónico han sido estudiadas con el fin de evaluar si pueden ser usadas en misiones espaciales con exigentes requerimientos a baja frecuencia. Por otro lado, estas misiones requieren del control minucioso del ambiente magnético generado en el satélite. Esto es debido a que el instrumento principal puede operar correctamente y alcanzar su máximo rendimiento sólo si el entorno magnético se encuentra bajo unas determinadas condiciones. Por lo tanto, este trabajo también implica la investigación de las propiedades magnéticas del magnetómetro y su posible impacto sobre el experimento científico. Finalmente, otro problema potencial es la exactitud con la que el campo magnético puede ser estimado desde la posición del sensor hasta la región de interés donde se desea interpolar la medida. La elección de un método robusto para una determinada configuración de sensores es también parte de este trabajo. Aunque otros tópicos son cubiertos, los objetivos aquí mencionados son los principales temas cubiertos en esta tesis

Electron Beam Lithography patterning of superconducting and magnetic nanostructures for novel optical and spintronic devices

In this thesis novel, high-end superconducting and spintronic devices have been fabricated and characterized. In summary, the proposed work has been focused on the realization of nanowires, and more generally nanostructures, using the Electron Beam Lithography. Such a technology offers a powerful solution for nanofabrication able to conjugate spatial resolution, operation flexibility, and costs. Two main research fields has been explored: superconductive nanowires for advanced optical detection and nanostructures for magneto-resistance based devices