598 research outputs found

    Analysis and Modeling of the Forces Exerted on the Cookware in Induction Heating Applications

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    We present a semianalytical model for calculating the forces exerted on cookware in domestic induction heating applications. The developed model is based on the Maxwell''s stress tensor and is also based on the existing semianalytic expressions of the electromagnetic fields in planar induction heating systems, which are expressed in terms of Fourier-Bessel series. Taking advantage of the axial symmetry of usual domestic induction heating systems, the flux of the vertical component of the Maxwell''s stress tensor is analytically integrated and the vertical force is obtained. The proposed model captures both eddy currents and magnetization that occurs in typical ferromagnetic cookware. The model is verified by means of two-dimensional Finite Element simulations and also is tested by means of measurements of the change of the weight experimented by cookware due to the forces during the heating process

    Self-adaptive overtemperature protection materials for safety-centric domestic induction heating applications

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    Security aspects in the household sphere have become a major concern in modern societies. In particular, regardless of the technology used, users increasingly appreciate a protection system to prevent material damage in the case of human errors or distractions during the cooking process. This paper presents a sensorless method for detecting and limiting overtemperature, unique to induction cooktops, based on their specific features, such as automatic pot detection and load power factor estimation. The protection system exploits the change in the load material properties at certain temperatures, the effect of which may be enhanced by arranging a multilayer structure comprising a low Curie temperature alloy and an aluminum layer. The proposed multilayer load exhibits two differentiated states: a normal state, where the cookware is efficiently heated, and a protection state, above the safety temperature, where the power factor abruptly decreases, limiting the overheating and making the state easily detectable by the cooktop. This method of overtemperature self-protection uses the electronics of conventional induction cooktops; therefore, no other sensors or systems are required, reducing its complexity and costs. Simulation and experimental results are provided for several cookware designs, thereby proving the feasibility of this proposal

    Index to NASA Tech Briefs, January - June 1967

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    Technological innovations for January-June 1967, abstracts and subject inde

    Stretching the limits of dynamic range, shielding effectiveness, and multiband frequency response

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    In this dissertation, an RF MEMS variable capacitor suitable for applications requiring ultrawide capacitive tuning ranges is reported. The device uses an electrostatically tunable liquid dielectric interface to continuously vary the capacitance without the use of any moving parts. As compared to existing MEMS varactors in literature, this device has an extremely simple design that can be implemented using simple fabrication methods that do not necessitate the use of clean room equipment. In addition, this varactor is particularly suited for incorporating a wide range of liquid dielectric materials for specific tuning ratio requirements. Additionally, the shielding effectiveness performance of graphene-doped ABS thin films is investigated. The use of graphene as a replacement for metal fillers in composite EMI shielding materials is quickly becoming a widely-investigated field in the electromagnetic compatibility community. By replacing conventional metal-based shielding methods with graphene-doped polymers, low-weight, field-use temporary shielding enclosures can be implemented that do not suffer from mechanical unreliability and corrosion/oxidation like a traditional metal enclosure. While the performance of composite EMI shielding materials has not yet surpassed metals, the advantages of polymer-based shielding methods could find usage in a variety of applications. Finally, mutliband pre-fractal antennas fabricated via 3D printing are reported. These devices are the first to incorporate the advantages of 3D printing (rapid prototyping, fabrication of complex geometries otherwise unobtainable) with the advantages of self-similar antennas (increased gain and multiband performance) in a single device. The Sierpinski tetrahedron-based antenna design was both computationally modeled and physically realized to illustrate its potential as a solution to enable true multiband communication platforms

    Topological Photonics

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    Topological photonics is a rapidly emerging field of research in which geometrical and topological ideas are exploited to design and control the behavior of light. Drawing inspiration from the discovery of the quantum Hall effects and topological insulators in condensed matter, recent advances have shown how to engineer analogous effects also for photons, leading to remarkable phenomena such as the robust unidirectional propagation of light, which hold great promise for applications. Thanks to the flexibility and diversity of photonics systems, this field is also opening up new opportunities to realize exotic topological models and to probe and exploit topological effects in new ways. This article reviews experimental and theoretical developments in topological photonics across a wide range of experimental platforms, including photonic crystals, waveguides, metamaterials, cavities, optomechanics, silicon photonics, and circuit QED. A discussion of how changing the dimensionality and symmetries of photonics systems has allowed for the realization of different topological phases is offered, and progress in understanding the interplay of topology with non-Hermitian effects, such as dissipation, is reviewed. As an exciting perspective, topological photonics can be combined with optical nonlinearities, leading toward new collective phenomena and novel strongly correlated states of light, such as an analog of the fractional quantum Hall effect.Comment: 87 pages, 30 figures, published versio

    NASA patent abstracts bibliography: A continuing bibliography. Section 1: Abstracts (supplement 32)

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    Abstracts are provided for 136 patents and patent applications entered into the NASA scientific and technical information system during the period July through December 1987. Each entry consists of a citation , an abstract, and in most cases, a key illustration selected from the patent or patent application

    Improved micro-contact resistance model that considers material deformation, electron transport and thin film characteristics

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    This paper reports on an improved analytic model forpredicting micro-contact resistance needed for designing microelectro-mechanical systems (MEMS) switches. The originalmodel had two primary considerations: 1) contact materialdeformation (i.e. elastic, plastic, or elastic-plastic) and 2) effectivecontact area radius. The model also assumed that individual aspotswere close together and that their interactions weredependent on each other which led to using the single effective aspotcontact area model. This single effective area model wasused to determine specific electron transport regions (i.e. ballistic,quasi-ballistic, or diffusive) by comparing the effective radius andthe mean free path of an electron. Using this model required thatmicro-switch contact materials be deposited, during devicefabrication, with processes ensuring low surface roughness values(i.e. sputtered films). Sputtered thin film electric contacts,however, do not behave like bulk materials and the effects of thinfilm contacts and spreading resistance must be considered. Theimproved micro-contact resistance model accounts for the twoprimary considerations above, as well as, using thin film,sputtered, electric contact

    Non-isothermal plasma treatment of organic and inorganic polymers

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    Increased understanding of plasma-polymer interactions is required to further the technological use of such processes, and elucidates heterogeneous physico-chemical reactions which occur under bombardment by complex combinations of energetic species. This thesis presents a systematic investigation into the effect of exposing organic and inorganic polymeric surfaces to controlled non-isothermal plasmas. Concurrently, a novel process is presented by which metal oxide gas barrier coatings are synthesized on polymer substrates by non- isothermal plasma treatment. Organic polymers exhibiting a range of structures were modified using non-isothermal plasmas at atmospheric and low pressure. The extent of atmospheric discharge oxygenation, measured by X-ray photoelectron spectroscopy (XPS), correlated with the polymers' ozonolysis rate constants. Surface physical disruption, studied using atomic force microscopy (AFM), after atmospheric discharge treatment was more pronounced than after low pressure plasma treatment. During low pressure oxygen plasma treatment, polymers containing phenyl groups were oxygenated to an extent which varied with the strength of π-π* valence band excitation in XPS C(1s) spectra of the untreated polymers, suggesting a dominance of reaction of plasma atomic oxygen at polymer radical sites excited by plasma vacuum ultraviolet radiation. The size of globules, observed by AFM, on the plasma modified surfaces correlated with the extent of surface chemical modification, inkeeping with a mechanism of chemically driven agglomeration of plasma oxidized low molecular weight polymer material. Oxygen plasma was more effective than water plasma in chemically modifying the surface of films of zirconium-normal-butoxide spin coated on polyester substrates, and the resulting optimized treatment produced a significant reduction in gas permeation of the substrate. XPS studies showed that oxygen plasma treatment of a polyphenylsilsesquioxane film on polyester film created a SiO(_2) layer less than 8 nm thin, which reduced O(_2) and Ar permeation of the coated film by 37.5 % and 31.6% respectively

    Terahertz response of microfluidic-jetted fabricated 3D flexible metamaterials

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    Conventional materials exhibit some restrictions on their electromagnetic properties. Especially in terahertz region, for example, materials that exhibit magnetic response are far less common in nature than materials that exhibit electric response. However, materials can be designed, namely artificial man-made metamaterials that exhibit electromagnetic properties that are not found in natural materials by adjusting, for example, the dielectric, magnetic or structural parameters of the constituent elements. This dissertation demonstrates the use of new fabrication techniques to construct metamaterials in THz range via a material deposition system. The metamaterials are fabricated by stacking alternative layers with conventional designs such as single ring- split ring resonators (SRR) and microstrips to form a 3D metamaterial structure. Conductive nano-particle Ag, Cu and semiconductor polymer fluids are used as structural mediums. The metamaterials are fabricated on polyimide substrate. Their flexible nature will be advantageous in future device innovations. In order to obtain electromagnetic resonance in the terahertz range, the dimensions of the single ring-SRR and microstrips are first approximated by analytical methods and then confirmed by numerical simulation. The fabricated metamaterials are then characterized in transmission mode using Time-domain THz Spectroscopy (THz-TDS) in the 0.1 to 2 THz range
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