290 research outputs found

    Optimal Inverse Design of Magnetic Field Profiles in a Magnetically Shielded Cylinder

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    Magnetic shields that use both active and passive components to enable the generation of a tailored low-field environment are required for many applications in science, engineering, and medical imaging. Until now, accurate field nulling, or field generation, has only been possible over a small fraction of the overall volume of the shield. This is due to the interaction between the active field-generating components and the surrounding high-permeability passive shielding material. In this paper, we formulate the interaction between an arbitrary static current flow on a cylinder and an exterior closed high-permeability cylinder. We modify the Green’s function for the magnetic vector potential and match boundary conditions on the shield’s interior surface to calculate the total magnetic field generated by the system. We cast this formulation into an inverse optimization problem to design active–passive magnetic field shaping systems that accurately generate any physical static magnetic field in the interior of a closed cylindrical passive shield. We illustrate this method by designing hybrid systems that generate a range of magnetic field profiles to high accuracy over large interior volumes, and simulate them in real-world shields whose passive components have finite permeability, thickness, and axial entry holes. Our optimization procedure can be adapted to design active–passive magnetic field shaping systems that accurately generate any physical user-specified static magnetic field in the interior of a closed cylindrical shield of any length, enabling the development and miniaturization of systems that require accurate magnetic shielding and control

    Towards naturalistic scanning environments for wearable magnetoencephalography

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    Magnetoencephalography (MEG) is a neuroimaging technique that probes human brain function, by measuring the magnetic fields generated at the scalp by current flow in assemblies of neurons. A direct measure of neural activity, MEG offers high spatiotemporal resolution, but limitations imposed by superconducting sensor technologies impede its clinical utility. Specifically, neuromagnetic fields are up to a billion times smaller than that of the Earth, meaning MEG must be performed inside a magnetically shielded room (MSR), which is typically expensive, heavy, and difficult to site. Furthermore, current MEG systems employ superconducting quantum interference devices (SQUIDs) to detect these tiny magnetic fields, however, these sensors require cryogenic cooling with liquid helium. Consequently, scanners are bulky, expensive, and the SQUIDs must be arranged in a fixed, one-size-fits-all array. Any movement relative to the fixed sensors impacts data quality, meaning participant movement in MEG is severely restricted. The development of technology to enable a wearable MEG system allowing free participant movement would generate a step change for the field. Optically-pumped magnetometers (OPMs) are an alternative magnetic field detector recently developed with sufficient sensitivity for MEG measurements. Operating at body temperature, in a small and lightweight sensor package, OPMs offer the potential for a wearable MEG scanner that allows participant movement, with sensors mounted on the scalp in a helmet or cap. However, OPMs operate around a zero-field resonance, resulting in a narrow dynamic range that may be easily exceeded by movement of the sensor within a background magnetic field. Enabling a full range of participant motion during an OPM-MEG scan therefore presents a significant challenge, requiring precise control of the background magnetic field. This thesis describes the development of techniques to better control the magnetic environment for OPM-MEG. This includes greater reduction of background magnetic fields over a fixed region to minimise motion artefacts and facilitate larger movements, and the application of novel, multi-coil active magnetic shielding systems to enable flexibility in participant positioning within the MSR. We outline a new approach to map background magnetic fields more accurately, reducing the remnant magnetic field to <300 pT and yielding a five-fold reduction in motion artefact, to allow detection of a visual steady-state evoked response during continuous head motion. Employing state-of-the-art, triaxial OPMs alongside this precision magnetic field control technique, we map motor function during a handwriting task involving naturalistic head movements and investigate the advantages of triaxial sensitivity for MEG data analysis. Using multi-coil active magnetic shielding, we map motor function consistently in the same participant when seated and standing, and demonstrate the first OPM-MEG hyperscanning experiments. Finally, we outline how the integration of a multi-coil system into the walls of a lightweight MSR, when coupled with field control over a larger volume, provides an open scanning environment. In sum, these developments represent a significant step towards realising the full potential of OPM-MEG as a wearable functional neuroimaging technology

    Composite Films with Magnetic Nanorods: Fundamentals, Processing and Applications

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    This Dissertation is centered on studying the composite films with magnetic nanorods. In recent years, one-dimensional magnetic nanostructures, such as magnetic nanorods, chains of magnetic nanoparticles, and nanotubes filled with magnetic nanoparticles have caught great attentions due to the breadth of applications. Their unique magnetic and geometrical features open new avenues of studies in medicine, sensors, optofluidics, magnetic swimming, and microrheology. In particular, they offered great opportunities for design of multifunctional devices and for manufacturing of anisotropic nano- and microstructures with unprecedented magnetic and mechanical properties. However, the strategy for nanorod alignment in both Newtonian and complex fluids has not been developed and this remains the main challenge in materials engineering and processing. On the other hand, the basic understanding of the properties of the fabricated composite material is also lacking. These challenges and problems are addressed in this Dissertation. In chapter I, some basic concepts and common terminologies of ferromagnetism such as magnetic anisotropy, domain structure, etc. are introduced. The magnetic hysteresis for a single domain ferromagnetic nanoparticle is also explained. In chapter II, the magnetostatic problems for both single domain magnetic nanosphere and nanorod are solved. The interactions between both spherical nanoparticles and nanorods are also studied based on the solutions of magnetostatics. In chapter III, the synthesis of nickel and cobalt nanorods using electrochemical deposition method is described and various methods are applied to characterize the synthesized nanorods. In chapter IV, the strategies for the alignment of magnetic nanorods in Newtonian and complex fluids are developed. The nanorod alignment in complex fluids is found to be very tricky and deserves further study. In chapter V, the evaporation kinetics and viscosity change of a ceramic precursor (an example of complex fluid) is studied during the sol-gel processing. Together with chapter IV, they provide a basis for the fabrication of ceramic composites containing of magnetic nanorods. In chapter VI, the interactions between magnetic nanorods under magnetic field gradient are studied both theoretically and experimentally. This chapter provides a method of using field gradient to defeat repulsion between nanorods and achieve very high local concentration of nanorods. In chapter VII and VIII, the theory describing the property of composite film is proposed. The ferromagnetic resonance and heating properties of a single domain nanoparticle is studied in chapter VII. In chapter VIII, interactions of electromagnetic waves with magnetic nanocomposite films are discussed. We predict an unusual transmission, reflection, and absorption properties of these films and discuss the Faraday and Kerr effects as well

    Towards naturalistic scanning environments for wearable magnetoencephalography

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    Magnetoencephalography (MEG) is a neuroimaging technique that probes human brain function, by measuring the magnetic fields generated at the scalp by current flow in assemblies of neurons. A direct measure of neural activity, MEG offers high spatiotemporal resolution, but limitations imposed by superconducting sensor technologies impede its clinical utility. Specifically, neuromagnetic fields are up to a billion times smaller than that of the Earth, meaning MEG must be performed inside a magnetically shielded room (MSR), which is typically expensive, heavy, and difficult to site. Furthermore, current MEG systems employ superconducting quantum interference devices (SQUIDs) to detect these tiny magnetic fields, however, these sensors require cryogenic cooling with liquid helium. Consequently, scanners are bulky, expensive, and the SQUIDs must be arranged in a fixed, one-size-fits-all array. Any movement relative to the fixed sensors impacts data quality, meaning participant movement in MEG is severely restricted. The development of technology to enable a wearable MEG system allowing free participant movement would generate a step change for the field. Optically-pumped magnetometers (OPMs) are an alternative magnetic field detector recently developed with sufficient sensitivity for MEG measurements. Operating at body temperature, in a small and lightweight sensor package, OPMs offer the potential for a wearable MEG scanner that allows participant movement, with sensors mounted on the scalp in a helmet or cap. However, OPMs operate around a zero-field resonance, resulting in a narrow dynamic range that may be easily exceeded by movement of the sensor within a background magnetic field. Enabling a full range of participant motion during an OPM-MEG scan therefore presents a significant challenge, requiring precise control of the background magnetic field. This thesis describes the development of techniques to better control the magnetic environment for OPM-MEG. This includes greater reduction of background magnetic fields over a fixed region to minimise motion artefacts and facilitate larger movements, and the application of novel, multi-coil active magnetic shielding systems to enable flexibility in participant positioning within the MSR. We outline a new approach to map background magnetic fields more accurately, reducing the remnant magnetic field to <300 pT and yielding a five-fold reduction in motion artefact, to allow detection of a visual steady-state evoked response during continuous head motion. Employing state-of-the-art, triaxial OPMs alongside this precision magnetic field control technique, we map motor function during a handwriting task involving naturalistic head movements and investigate the advantages of triaxial sensitivity for MEG data analysis. Using multi-coil active magnetic shielding, we map motor function consistently in the same participant when seated and standing, and demonstrate the first OPM-MEG hyperscanning experiments. Finally, we outline how the integration of a multi-coil system into the walls of a lightweight MSR, when coupled with field control over a larger volume, provides an open scanning environment. In sum, these developments represent a significant step towards realising the full potential of OPM-MEG as a wearable functional neuroimaging technology

    ΔE-Effect Magnetic Field Sensors

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    Many conceivable biomedical and diagnostic applications require the detection of small-amplitude and low-frequency magnetic fields. Against this background, a magnetometer concept is investigated in this work based on the magnetoelastic ΔE effect. The ΔE effect causes the resonance frequency of a magnetoelastic resonator to detune in the presence of a magnetic field, which can be read-out electrically with an additional piezoelectric phase. Various microelectromechanical resonators are experimentally analyzed in terms of the ΔE effect and signal-and-noise response. This response is highly complex because of the anisotropic and nonlinear coupled magnetic, mechanical, and electrical properties. Models are developed and extended where necessary to gain insights into the potentials and limits accompanying sensor design and operating parameters. Beyond the material and geometry parameters, we analyze the effect of different resonance modes, spatial property variations, and operating frequencies on sensitivity. Although a large ΔE effect is confirmed in the shear modulus, the sensitivity of classical cantilever resonators does not benefit from this effect. An approach utilizing surface acoustic shear-waves provides a solution and can detect small signals over a large bandwidth. Comprehensive analyses of the quality factor and piezoelectric material parameters indicate methods to increase sensitivity and signal-to-noise ratio significantly. First exchange-biased ΔE-effect sensors pave the way for compact setups and arrays with a large number of sensor elements. With an extended signal-and-noise model, specific requirements are identified that could improve the signal-to-noise ratio. The insights gained lead to a new concept that can circumvent previous limitations. With the results and models, important contributions are made to the understanding and development of ΔE-effect sensors with prospects for improvements in the future

    20th Space Simulation Conference: The Changing Testing Paradigm

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    The Institute of Environmental Sciences' Twentieth Space Simulation Conference, "The Changing Testing Paradigm" provided participants with a forum to acquire and exchange information on the state-of-the-art in space simulation, test technology, atomic oxygen, program/system testing, dynamics testing, contamination, and materials. The papers presented at this conference and the resulting discussions carried out the conference theme "The Changing Testing Paradigm.

    STEP: Satellite Test of the Equivalence Principle. Report on the phase A study

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    During Phase A, the STEP Study Team identified three types of experiments that can be accommodated on the STEP satellite within the mission constraints and whose performance is orders of magnitude better than any present or planned future experiment of the same kind on the ground. The scientific objectives of the STEP mission are to: test the Equivalence Principle to one part in 10(exp 17), six orders of magnitude better than has been achieved on the ground; search for a new interaction between quantum-mechanical spin and ordinary matter with a sensitivity of the mass-spin coupling constant g(sub p)g(sub s) = 6 x 10(exp -34) at a range of 1 mm, which represents a seven order-of-magnitude improvement over comparable ground-based measurements; and determine the constant of gravity G with a precision of one part in 10(exp 6) and to test the validity of the inverse square law with the same precision, both two orders of magnitude better than has been achieved on the ground

    Sixteenth Space Simulation Conference Confirming Spaceworthiness Into the Next Millennium

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    The conference provided participants with a forum to acquire and exchange information on the state of the art in space simulation, test technology, thermal simulation and protection, contamination, and techniques of test measurements

    Symmetrybreaking

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    NASA Tech Briefs, January 2008

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    Topics covered include: Induction Charge Detector with Multiple Sensing Stages; Generic Helicopter-Based Testbed for Surface Terrain Imaging Sensors; Robot Electronics Architecture; Optimized Geometry for Superconducting Sensing Coils; Sensing a Changing Chemical Mixture Using an Electronic Nose; Inertial Orientation Trackers with Drift Compensation; Microstrip Yagi Antenna with Dual Aperture-Coupled Feed; Patterned Ferroelectric Films for Tunable Microwave Devices; Micron-Accurate Laser Fresnel-Diffraction Ranging System; Efficient G(sup 4)FET-Based Logic Circuits; Web-Enabled Optoelectronic Particle-Fallout Monitor; SiO2/TiO2 Composite for Removing Hg from Combustion Exhaust; Lightweight Tanks for Storing Liquefied Natural Gas; Hybrid Wound Filaments for Greater Resistance to Impacts; Making High-Tensile-Strength Amalgam Components; Bonding by Hydroxide-Catalyzed Hydration and Dehydration; Balanced Flow Meters without Moving Parts; Deflection-Compensating Beam for Use inside a Cylinder; Four-Point-Latching Microactuator; Curved Piezoelectric Actuators for Stretching Optical Fibers; Tunable Optical Assembly with Vibration Dampening; Passive Porous Treatment for Reducing Flap Side-Edge Noise; Cylindrical Piezoelectric Fiber Composite Actuators; Patterning of Indium Tin Oxide Films; Gimballed Shoulders for Friction Stir Welding; Improved Thermal Modulator for Gas Chromatography; Nuclear-Spin Gyroscope Based on an Atomic Co-Magnetometer; Utilizing Ion-Mobility Data to Estimate Molecular Masses; Optical Displacement Sensor for Sub-Hertz Applications; Polarization/Spatial Combining of Laser-Diode Pump Beams; Spatial Combining of Laser-Diode Beams for Pumping an NPRO; Algorithm Optimally Orders Forward-Chaining Inference Rules; Project Integration Architecture; High Power Amplifier and Power Supply; Estimating Mixing Heights Using Microwave Temperature Profiler; and Multiple-Cone Sunshade for a Spaceborne Telescope
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