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Design007-Jun2018

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JUNE 2018 I DESIGN007 MAGAZINE 55 ing time of a curing material. For example, if the product quickly becomes touch dry, it may not be suitable for stencil printing as the cured product may block the screen. In most cases, a minimum amount of material must be applied for thermal interface and gap filling applica- tions to ensure maximum heat transfer. For a thermal interface, the layer must achieve uni- form coverage over the entire interface; and when using a gap filler, the material must be applied while ensuring that all air is expelled, as air is a poor conductor of heat and may cause additional hotspots. If an encapsulation resin is deemed to be the best choice, it is likely that the entire PCB will need to be covered. The amount of resin applied will have to strike a balance between achieving the desired protection level and min- imising any weight and volume gains contrib- uted by the resin. Hopefully, the foregoing has provided a useful introduction to thermal management materials. Look out for my next contribution, where I will continue exploring thermal man- agement. DESIGN007 Jade Bridges is global technical support manager for Electrolube Ltd. Superconductors contain tiny tornadoes of supercur- rent, called vortex filaments, that create resistance when they move. This affects the way superconductors carry a current. But a magnet-controlled "switch" in superconductor configuration provides unprecedented flexibility in man- aging the location of vortex filaments, altering the proper- ties of the superconductor, according to a new paper in Nature Nanotechnology. "We work on superconductors and how to make them better for applications," said Boldizsár Jankó, professor in the Department of Physics at the University of Notre Dame and co-corresponding author on the paper. "One of the major problems in superconductor technology is that most of them have these filaments, these tiny tornadoes of supercurrent. When these move, then you have resistance." The collaborators' solution overlays the superconductor with an artificial spin ice consisting of an array of interacting nanoscale bar magnets. Rearranging the magnetic orientations of those nano-bar magnets results in a real-time rearrange- ment of the pinning on the superconduct- ing site. This makes possible multiple, reversible spin cycle configurations for the vortices. Spin is a particle's natural, angu- lar momentum. "The main discovery here is our ability to reconfigure these spinning sites reversibly and instead of having just one spin cycle configuration for the vortices, we now have many, and we can switch them back and forth," Jankó said. Because the control of the quantum fluxes is difficult to visualize in an experiment, simulations were required to successfully reproduce the results, said Xiaoyu Ma, a doctoral student in the Department of Physics who con- ducted the computer simulation in the study and is the co-first author on the paper. The simulations allowed researchers to see the detailed processes involved. "The number of vortex configurations that we can realize is huge, and we can design and locally reconfigure them site by site," Ma said. "This has never been realized before." Designing a Better Superconductor with Geometric Frustration

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