118 research outputs found

    The Impact of Multistability on Hysteresis Arising in Linear and Nonlinear Systems

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    Hysteresis is typically depicted as a looping behaviour in a system's input-output graph. This looping behaviour relates to multiple stable equilibria (that is, multi-stability) in the system. This work examines some necessary stability conditions for linear and nonlinear ordinary differential equations to exhibit hysteresis. Examples and simulations are presented supporting this. Additionally, the shape of hysteresis loops due to different types of multi-stability (e.g. continuum of equilibria or isolated equilibria) are described.Comment: 33 pages, 38 figures, submitted for peer revie

    Aeronautical Engineering: A Continuing Bibliography with Indexes (supplement 194)

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    This bibliography lists 369 reports, articles and other documents introduced into the NASA scientific and technical information system in November 1985

    Surface and inter-phase analysis of Composite Materials using Electromagnetic Techniques based on SQUID Sensors

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    In this thesis an electromagnetic characterization and a non-destructive evaluation of new advanced composite materials, Carbon Fiber Reinforced Polymers (CFRP) and Fiber-Glass Aluminium (FGA) laminates, using an eddy-current technique based on HTS dc-SQUID (Superconductive QUantum Interference Device) magnetometer is proposed. The main goal of this thesis is to propose a prototype based on a superconducting sensor, such as SQUID, to guarantee a more accuracy in the quality control at research level of the composite materials employed in the aeronautical applications. A briefly introduction about the superconductivity, a complete description of the SQUID properties and its basic working principles have been reported. Moreover, an overview of the most widely used non destructive technique employed in several industrial and research fields have been described. Particular attention is given to the eddy current testing and the technical improvement obtained using SQUID in NDE. The attention has been focused on two particular application, that are the main topics of this thesis. The first concerns with the investigation of the damage due to impact loading on the composites materials, and the second is the study of the corrosion process on the metallic surface. The electrical and mechanical properties of the tested advanced composite materials, such as Carbon Fiber Reinforced Polymers (CFRPs) and Fiber-glass Aluminium (FGA) laminates are investigated. The experimental results concern the non-destructive evaluation of impact loading on the CFRPs and FGA composites, by means of the electromagnetic techniques; the investigation of the electromechanical effect in the CFRPs using the SQUID based prototype and the AFM analyses; and the study of corrosion activity of the metallic surface using magnetic field measurement

    magnetization processes in permalloy overlays on magnetic bubble devices.

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    Using colloid techniques domain structure has been studied in several overlay components used in contemporary bubble devices. In isolated elements the demagnetized state is generally simple, containing a small number of domains. The influence of anisotropy on domain structure is demonstrated. Elements initially respond to applied fields by reversible domain boundary movement but in each case it has been found that partial saturation and hysteresis occur once the applied field exceeds a critical value, H(_s). This causes the formation of remanent states with 'magnetization buckling' similar to that found in larger samples of thin-film permalloy. The relationship between and element geometry and thickness and the formation of buckled states by a rotating field were investigated. Such states may adversely affect the operation of a bubble device. The approach to partial saturation in a simple bar has been modelled on the basis of a curved domain wall and approximate values for the saturation field calculated. The external field profile of the bar has also been obtained. Domain structure in various connected chevron columns (bubble detectors) was also studied. In contrast to isolated elements the initial 'zero-field' state in these components is generally one of saturation. This state can be broken by components of applied field parallel or perpendicular to the column and again magnetization buckling is involved. Magnetoresistance changes related to the buckled state were measured and found to be consistent with the colloid observations. These observations can be used to explain the characteristic magnetoresistance signal of a chevron column in a rotating field

    Aeronautical Engineering: A continuing bibliography (supplement 158)

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    This bibliography lists 499 reports, articles and other documents introduced into the NASA scientific and technical information system in January 1983

    A Study of Magnetic Materials Based Upon the Organic Acceptor 7,7,8,8-Tetracyanoquinodimethane

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    The study of organic based materials is a flourishing area of interest as the physical/chemical properties of the compound can be tuned through functionalisation or simple chemical changes to the organic component. This thesis will focus on the magnetic behaviour of metal-organic magnetic materials where a variety of techniques will be used to study the magnetism such as bulk magnetometry and muon spin relaxation. As well as the magnetic properties, some comments will be made on the chemical properties such as molecular structure. The thesis begins with an overview of the theory of magnetism and details regarding experimental techniques. Ni(TCNQ)2_2 is a recently discovered non-solvated metal organic magnet that was reported to show ferromagnetic behaviour below 20 K where there was evidence of a glassy magnetic component. This thesis reports the synthesis of both a protio and deutero form of the material where upon deuteration of the TCNQ molecule, a shift in critical temperature (TCT_{\rm C}) was observed to a higher temperature by approximately 15%. Diffraction experiments were conducted to attempt to provide information on the atomic structure however this proved unsuccessful. Magnetometry experiments showed a ferromagnetic transition at approximately 20 K in the deuterated and 17 K in the protonated materials where at low temperatures the sample appeared to be a three-dimensional magnetically order material. Muon spin relaxation studies were conducted on the deuterated sample which showed two peaks within the dynamical relaxation in zero-field; one associated with the transition and a low temperature (5 K) spin freezing effect where it is believed there are interactions between magnetic clusters that enter a quasi-static regime. It may be possible that the glassy component and the ferromagnetic behaviour of the material are not due to the same exchange mechanism or magnetic interactions. KTCNQ is a compound that undergoes a spin-Peierls transition, TSPT_{\rm SP}, at approximately 400 K where below this temperature there is a dimerisation of the TCNQ radical spins that couple antiferromagnetically and the system goes from a conductive to insulating state. In an attempt to tune the TCNQ-TCNQ interactions different materials were synthesised where the protons on the TCNQ ring were substituted for fluorine and bromine atoms. On substitution of the protons with other elements a dramatic shift in Tsp was observed where for the fluorine based compounds TSPT_{\rm SP} = 150 K and the KTCNQ-Br2_2 compound showed no evidence of a transition. Both KTCNQ-H4_4 and KTCNQ-F4_4 were studied further using muon spin relaxation where the transition is clearly modelled using a stretched exponential where an increase in electronic fluctuation rate is shown by a gradual move from an exponential to Gaussian relaxation. At low temperatures the relaxation again changes and within the KTCNQ-F4_4 sample 2 F-μ+\mu^+-F states are observed. Another controversial organic based magnet is Ni2_2TCNQ which was first synthesised in 2007. Here a study of a similar material is reported where the TCNQ has been swapped for TCNQF4_4 and the magnetic properties are shown to be a result of nickel nanoparticles trapped within a metal-organic or purely organic based matrix. The room temperature ferromagnetism is not strictly due to only the bulk Ni particles as this would result in a blocking temperature below 20 K and so the matrix is shown to play an important role. The size of the Ni nanoparticles was shown to be tuneable when using different solvents within the reaction, generally use of chlori- nated solvents lead to rapid decomposition of the starting material, Ni(COD)2_2 and lead to larger nanoparticles, however use of a nitrile based solvent led to Ni clusters that were approximately 1 nm in size and dispersed within the matrix. A novel scaling of the magnetisation curves as a function of field showed that once the ferromagnetic component had been subtracted the matrix or Ni based clusters show an antiferromagnetic ground state at low temperature. The final chapter describes an investigation of the starting material, Ni(COD)2_2 which was studied using a SQUID magnetometer where it was shown that there was a high level of magnetic impurities, which was attributed to small Ni clusters that showed a similar scaling relationship of the magnetisation as for the Ni2TCNQF4_4 based material. This demonstrates the inappropriate nature of Ni(COD)2_2 as a starting material for metal-organic based magnetic compounds

    The Development of Unique Focal Planes for High-Resolution Suborbital and Ground-Based Exploration

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    abstract: The development of new Ultra-Violet/Visible/IR range (UV/Vis/IR) astronomical instrumentation that use novel approaches for imaging and increase the accessibility of observing time for more research groups is essential for rapid innovation within the community. Unique focal planes that are rapid-prototyped, low cost, and provide high resolution are key. In this dissertation the emergent designs of three unique focal planes are discussed. These focal planes were each designed for a different astronomical platform: suborbital balloon, suborbital rocket, and ground-based observatory. The balloon-based payload is a hexapod-actuated focal plane that uses tip-tilt motion to increase angular resolution through the removal of jitter – known as the HExapod Resolution-Enhancement SYstem (HERESY), the suborbital rocket imaging payload is a Jet Propulsion Laboratory (JPL) delta-doped charge-coupled device (CCD) packaged to survive the rigors of launch and image far-ultra-violet (FUV) spectra, and the ground-based observatory payload is a star centroid tracking modification to the balloon version of HERESY for the tip-tilt correction of atmospheric turbulence. The design, construction, verification, and validation of each focal plane payload is discussed in detail. For HERESY’s balloon implementation, pointing error data from the Stratospheric Terahertz Observatory (STO) Antarctic balloon mission was used to form an experimental lab test setup to demonstrate the hexapod can eliminate jitter in flight-like conditions. For the suborbital rocket focal plane, a harsh set of unit-level tests to ensure the payload could survive launch and space conditions, as well as the characterization and optimization of the JPL detector, are detailed. Finally, a modification of co-mounting a fast-read detector to the HERESY focal plane, for use on ground-based observatories, intended to reduce atmospherically induced tip-tilt error through the centroid tracking of bright natural guidestars, is described.Dissertation/ThesisDoctoral Dissertation Exploration Systems Design 201

    Design, fabrication, characterization and reliability study of CMOS-MEMS Lorentz-Force magnetometers

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    Tesi en modalitat de compendi de publicacionsToday, the most common form of mass-production semiconductor device fabrication is Complementary Metal-Oxide Semiconductor (CMOS) technology. The dedicated Integrated Circuit (IC) interfaces of commercial sensors are manufactured using this technology. The sensing elements are generally implemented using Micro-Electro-Mechanical-Systems (MEMS), which need to be manufactured using specialized micro-machining processes. Finally, the CMOS circuitry and the MEMS should ideally be combined in a single package. For some applications, integration of CMOS electronics and MEMS devices on a single chip (CMOS-MEMS) has the potential of reducing fabrication costs, size, parasitics and power consumption, compared to other integration approaches. Remarkably, a CMOS-MEMS device may be built with the back-end-of-line (BEOL) layers of the CMOS process. But, despite its advantages, this particular approach has proven to be very challenging given the current lack of commercial products in the market. The main objective of this Thesis is to prove that a high-performance MEMS, sealed and packaged in a standard package, may be accurately modeled and manufactured using the BEOL layers of a CMOS process in a reliable way. To attain this, the first highly reliable novel CMOS-MEMS Lorentz Force Magnetometer (LFM) was successfully designed, modeled, manufactured, characterized and subjected to several reliability tests, obtaining a comparable or superior performance to the typical solid-state magnetometers used in current smartphones. A novel technique to avoid magnetic offsets, the main drawback of LFMs, was presented and its performance confirmed experimentally. Initially, the issues encountered in the manufacturing process of MEMS using the BEOL layers of the CMOS process were discouraging. Vapor HF release of MEMS structures using the BEOL of CMOS wafers resulted in undesirable damaging effects that may lead to the conclusion that this manufacturing approach is not feasible. However, design techniques and workarounds for dealing with the observed issues were devised, tested and implemented in the design of the LFM presented in this Thesis, showing a clear path to successfully fabricate different MEMS devices using the BEOL.Hoy en día, la forma más común de producción en masa es una tecnología llamada Complementary Metal-Oxide Semiconductor (CMOS). La interfaz de los circuitos integrados (IC) de sensores comerciales se fabrica usando, precisamente, esta tecnología. Actualmente es común que los sensores se implementen usando Sistemas Micro-Electro-Mecánicos (MEMS), que necesitan ser fabricados usando procesos especiales de micro-mecanizado. En un último paso, la circuitería CMOS y el MEMS se combinan en un único elemento, llamado package. En algunas aplicaciones, la integración de la electrónica CMOS y los dispositivos MEMS en un único chip (CMOS-MEMS) alberga el potencial de reducir los costes de fabricación, el tamaño, los parásitos y el consumo, al compararla con otras formas de integración. Resulta notable que un dispositivo CMOS-MEMS pueda ser construido con las capas del back-end-of-line (BEOL) de un proceso CMOS. Pero, a pesar de sus ventajas, este enfoque ha demostrado ser un gran desafío como demuestra la falta de productos comerciales en el mercado. El objetivo principal de esta Tesis es probar que un MEMS de altas prestaciones, sellado y empaquetado en un encapsulado estándar, puede ser correctamente modelado y fabricado de una manera fiable usando las capas del BEOL de un proceso CMOS. Para probar esto mismo, el primer magnetómetro CMOS-MEMS de fuerza de Lorentz (LFM) fue exitosamente diseñado, modelado, fabricado, caracterizado y sometido a varias pruebas de fiabilidad, obteniendo un rendimiento comparable o superior al de los típicos magnetómetros de estado sólido, los cuales son usados en móviles actuales. Cabe destacar que en esta Tesis se presenta una novedosa técnica con la que se evitan offsets magnéticos, el mayor inconveniente de los magnetómetros de fuerza Lorentz. Su efectividad fue confirmada experimentalmente. En los inicios, los problemas asociados al proceso de fabricación de MEMS usando las capas BEOL de obleas CMOS resultaba desalentador. Liberar estructuras MEMS hechas con obleas CMOS con vapor de HF producía efectos no deseados que bien podrían llevar a la conclusión de que este enfoque de fabricación no es viable. Sin embargo, se idearon y probaron técnicas de diseño especiales y soluciones ad-hoc para contrarrestar estos efectos no deseados. Se implementaron en el diseño del magnetómetro de Lorentz presentado en esta Tesis, arrojando excelentes resultados, lo cual despeja el camino hacia la fabricación de diferentes dispositivos MEMS usando las capas BEOL.Postprint (published version

    Aeronautical engineering, a continuing bibliography with indexes

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    This bibliography lists 823 reports, articles, and other documents introduced into the NASA scientific and technical information system in November 1984
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