Yuki Sato

Harvard University, Cambridge, Massachusetts, United States

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Publications (9)57.92 Total impact

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    ABSTRACT: We demonstrate an innovative multifunctional artificial material that combines exotic metamaterial properties and the environmentally responsive nature of phase change media. The tunable metamaterial is designed with the aid of two interwoven coordinate-transformation equations and implemented with a network of thin film resistors and vanadium dioxide ($VO_{2}$). The strong temperature dependence of $VO_{2}$ electrical conductivity results in a relevant modification of the resistor network behavior, and we provide experimental evidence for a reconfigurable metamaterial electric circuit (MMEC) that not only mimics a continuous medium but is also capable of responding to thermal stimulation through dynamic variation of its spatial anisotropy. Upon external temperature change the overall effective functionality of the material switches between a "truncated-cloak" and "concentrator" for electric currents. Possible applications may include adaptive matching resistor networks, multifunctional electronic devices, and equivalent artificial materials in the magnetic domain. Additionally, the proposed technology could also be relevant for thermal management of integrated circuits
    05/2014;
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    ABSTRACT: Spatial tailoring of the material constitutive properties is a well-known strategy to mold the local flow of given observables in different physical domains. Coordinate-transformation-based methods (e.g., transformation optics) offer a powerful and systematic approach to design anisotropic, spatially inhomogeneous artificial materials (metamaterials) capable of precisely manipulating wave-based (electromagnetic, acoustic, elastic) as well as diffusion-based (heat) phenomena in a desired fashion. However, as versatile as these approaches have been, most designs have thus far been limited to serving single-target functionalities in a given physical domain. Here, we present a step towards a “transformation multiphysics” framework that allows independent and simultaneous manipulation of multiple physical phenomena. As a proof of principle of this new scheme, we design and synthesize (in terms of realistic material constituents) a metamaterial shell that simultaneously behaves as a thermal concentrator and an electrical “invisibility cloak.” Our numerical results open up intriguing possibilities in the largely unexplored phase space of multifunctional metadevices, with a wide variety of potential applications to electrical, magnetic, acoustic, and thermal scenarios.
    Physical Review X 05/2014; 4(2):021025. · 8.39 Impact Factor
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    ABSTRACT: Spatial tailoring of the material constitutive properties is a well-known strategy to mold the local flow of given observables in different physical domains. Coordinate-transformation-based methods (e.g., transformation optics) offer a powerful and systematic approach to design anisotropic, spatially-inhomogeneous artificial materials ("metamaterials") capable of precisely manipulating wave-based (electromagnetic, acoustic, elastic) as well as diffusion-based (heat) phenomena in a desired fashion. Most studies available in the literature deal with the design of a single specific functionality in a given physical domain. We address here the simultaneous manipulation of multiple physical phenomena in independent fashions. As a proof of principle of this "transformation multiphysics" framework, we design and synthesize (in terms of realistic material constituents) a metamaterial shell that simultaneously behaves as a thermal concentrator and an electrical "invisibility cloak". Our numerical results open up intriguing possibilities in the largely unexplored phase space of multi-functional metastructures, with a wide variety of potential applications to electrical, magnetic, acoustic, and thermal scenarios.
    11/2013;
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    ABSTRACT: We have developed a heat shield based on a metamaterial engineering approach to shield a region from transient diffusive heat flow. The shield is designed with a multilayered structure to prescribe the appropriate spatial profile for heat capacity, density, and thermal conductivity of the effective medium. The heat shield was experimentally compared to other isotropic materials.
    Applied Physics Letters 05/2013; 102(20). · 3.79 Impact Factor
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    Supradeep Narayana, Yuki Sato
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    ABSTRACT: Utilizing a multilayered composite approach, we have designed and constructed a new class of artificial materials for thermal conduction. We show that an engineered material can be utilized to control the diffusive heat flow in ways inconceivable with naturally occurring materials. By shielding, concentrating, and inverting heat current, we experimentally demonstrate the unique potential and the utility of guiding heat flux. Thermodynamics is a well-established discipline in sci-ence, and the concept of heat has been known for a long time. That often makes us forget how difficult it really is to manipulate heat flow in real life. Compared to the field of electric conduction armed with nonlinear solid-sate de-vices, heat conduction management is still in its infancy. The ability to precisely control heat current has significant implications beyond scientific curiosity, and can poten-tially lead to the development of thermal analogues of electronic transistors, rectifiers, and diodes. Here we show that an artificial material can be utilized to guide the heat flow in ways inconceivable with naturally occur-ring materials. We demonstrate this concept by engineer-ing a new class of artificial material for thermal conduction and experimentally shielding, concentrating, and inverting the applied heat flux. The results constitute a vivid dem-onstration of extreme heat flux control with artificial ma-terials and provide a conceptual insight that heat current, like electric and photonic current, should be viewed as a medium that can be manipulated, controlled, and processed. The ability to manipulate the path of energy propagation is a trait that distinguishes artificial materials from ordinary materials. In a solid material supporting heat current, the properties induced from artificially arranged thermal con-ductivities can be counterintuitive. Although some theo-retical work including the prediction of a thermal cloak has been carried out [1–3], such thermal ''meta''-materials have, so far, not been investigated experimentally. We first discuss the shielding operation and then proceed to con-centrating and inverting heat flux. See Fig. 1(a). When a block of material is placed between a heat source and a sink, a uniform temperature gradient is established across the material. Heat current flows from left to right as indicated by the arrows. Figure 1(b) depicts the same block with a hollow cylindrical shield inserted at the center. Here we require the exterior region to exhibit the same temperature profile as Fig. 1(a) without the shield, while the interior region now needs to have no temperature gradient. To gain control over the path of energy transport via thermal conduction, one needs to engineer an artificial material with prescribed anisotropy in its thermal conduc-tivity. One of the most practical ways to introduce such anisotropy is to build a stacked composite from macro-scopic layers of isotropic materials. Consider, for example, a composite made of alternating sheets of materials A and B. In a perpendicular direction, the two alternating con-ductances add in series, while they add in parallel in a transverse direction. Thus, the overall thermal conductivity of the effective medium becomes anisotropic, and the heat flux density vector changes direction as it propagates through the material. Building on this effect, one can design and assemble an artificial composite material that forces the heat flux to follow a particular path of interest. A concentric layered structure consisting of alternating layers of materials A and B of different homogeneous isotropic thermal conductivities A and B is depicted in Fig. 2(a). For the host background material, we use a 5% agar-water block with thermal conductivity h $ 0:56 W=ðmKÞ [4]. For the device to blend into the back-ground thermally and not perturb the external field profile, the thermal resistance of the host material should be close to the reduced average of those of the two
    Physical Review Letters 05/2012; 108(214303). · 7.73 Impact Factor
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    Supradeep Narayana, Yuki Sato
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    ABSTRACT: Utilizing a non-resonant graded material consisting of an array of artificially patterned superconducting and soft ferromagnetic elements, we construct a dc magnetic cloak. When an external dc magnetic field is applied, we find that the interior of the cloak is completely shielded while the exterior field remains unperturbed, as if the cloak and the cloaked region are just an empty space.
    Advanced Materials 11/2011; 24(1):71-4. · 14.83 Impact Factor
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    Supradeep Narayana, Yuki Sato
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    ABSTRACT: We report the observation of superfluid quantum interference in a compact, large-area matter-wave interferometer consisting of a multiple-turn interfering path in reciprocal geometry. Utilizing the Sagnac effect from Earth's rotation in conjunction with a phase shifter made of superfluid heat current, we demonstrate that such a scheme can be extended for sensitive rotation sensing as well as for general interferometry.
    Physical Review Letters 06/2011; 106(25):255301. · 7.73 Impact Factor
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    Supradeep Narayana, Yuki Sato
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    ABSTRACT: We report a new kind of experiment in which we take an array of nanoscale apertures that form a superfluid (4)He Josephson junction and apply quantum phase gradients directly along the array. We observe collective coherent behaviors from aperture elements, leading to quantum interference. Connections to superconducting and Bose-Einstein condensate Josephson junctions as well as phase coherence among the superfluid aperture array are discussed.
    Physical Review Letters 02/2011; 106(5):055302. · 7.73 Impact Factor
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    Supradeep Narayana, Yuki Sato
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    ABSTRACT: We report a direct observation of dynamical bifurcation between two plasma oscillation states of a superfluid Josephson junction. We excite the superfluid plasma resonance into a nonlinear regime by driving below the natural plasma frequency and observe a clear transition between two dynamical states. We also demonstrate bifurcation by changing the potential well with temperature variations.
    Physical Review Letters 11/2010; 105(20):205302. · 7.73 Impact Factor