다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

Wave propagation and group velocity

Mie resonance-based dielectric metamaterials

We analyze the transmission and reflection data obtained through transfer matrix calculations on metamaterials of finite lengths, to determine their effective permittivity epsilon and permeability micro. Our study concerns metamaterial structures composed of periodic arrangements of wires, cut wires, split ring resonators (SRRs), closed SRRs, and both wires and SRRs. We find that the SRRs have a strong electric response, equivalent to that of cut wires, which dominates the behavior of left-handed materials (LHM). Analytical expressions for the effective parameters of the different structures are given, which can be used to explain the transmission characteristics of LHMs. Of particular relevance is the criterion introduced by our studies to identify if an experimental transmission peak is left or right handed.

Effective medium theory of left-handed materials

A new family of tunable microwave dielectrics with unparalleled performance at frequencies up to 125 GHz at room temperature has been created, using dimensionality to add and control a local ferroelectric instability in a system with exceptionally low dielectric loss. Tunable dielectric materials are valuable components for complex microwave circuitry, yet such materials tend to suffer losses when operated at microwave frequencies owing to intrinsic defects in their structures. Che-Hui Lee and colleagues have selected a family of dielectrics known to exhibit exceptionally low loss, and now show how these materials can be engineered to boost their tunability and attain levels of performance that rival all known tunable microwave dielectrics. The miniaturization and integration of frequency-agile microwave circuits—relevant to electronically tunable filters, antennas, resonators and phase shifters—with microelectronics offers tantalizing device possibilities, yet requires thin films whose dielectric constant at gigahertz frequencies can be tuned by applying a quasi-static electric field1. Appropriate systems such as BaxSr1−xTiO3 have a paraelectric–ferroelectric transition just below ambient temperature, providing high tunability1,2,3. Unfortunately, such films suffer significant losses arising from defects. Recognizing that progress is stymied by dielectric loss, we start with a system with exceptionally low loss—Srn+1TinO3n+1 phases4,5—in which (SrO)2 crystallographic shear6,7 planes provide an alternative to the formation of point defects for accommodating non-stoichiometry8,9. Here we report the experimental realization of a highly tunable ground state arising from the emergence of a local ferroelectric instability10 in biaxially strained Srn+1TinO3n+1 phases with n ≥ 3 at frequencies up to 125 GHz. In contrast to traditional methods of modifying ferroelectrics—doping1,2,3,11,12 or strain13,14,15,16—in this unique system an increase in the separation between the (SrO)2 planes, which can be achieved by changing n, bolsters the local ferroelectric instability. This new control parameter, n, can be exploited to achieve a figure of merit at room temperature that rivals all known tunable microwave dielectrics3.

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Exploiting dimensionality and defect mitigation to create tunable microwave dielectrics

Paraelectric BaSrTiO3 films deposited by sol-gel have been investigated from 1 kHz to 40 GHz using coplanar waveguides, resonators, and inter-digitated capacitances. At room temperature and without bias, the dielectric constant epsivr is around 300 and the loss tangent is 5times10-2. Tunability is 40% for a 40-V bias voltage. Analog phase-shifter circuits were subsequently fabricated in order to obtain a 360deg phase shift in the Ka-band with a moderate bias voltage. The lowest bias value was 17 V at 40 GHz, whereas 40 V were necessary at 30 GHz. For the latter condition, the insertion loss was -6dB. The best figure-of-merit of the phase shifters with a loading factor of 1.4 was 27deg/dB. These results show an improvement in terms of voltage-controlled tunability

A 360 $^{\circ}$ BST Phase Shifter With Moderate Bias Voltage at 30 GHz

We report on a negative-zero-positive metamaterial based on an omega-type microstructure with special attention on the nonvanishing group velocity for a zero refractive index. We first investigate the dispersion characteristics by full wave analysis, by stressing the necessary conditions of equality between the electric and magnetic plasma frequencies which are characteristic of the dispersion of the effective permittivity and permeability. Also, tuning of the gapless transition frequency between the left and right-handed dispersion branches was analyzed when the permittivity of the host substrate is changed. Last, we demonstrate experimentally the balanced composite character of the dispersion by frequency and angle-resolved transmission measurements, carried out at centimeter wavelengths on slabs and wedge-type prototypes, respectively.

Negative-zero-positive metamaterial with omega-type metal inclusions

The frequency dependence of the complex permittivity (e∗=e′-je″) of Ba0.5Sr0.5TiO3 0.3-μm-thick film is measured up to 110 GHz by using interdigitated capacitors and coplanar waveguides. It is shown that the temperature dependence (from 77 to 373 K) of microwave losses, measured at 20 GHz, is described by a tan(δ)-(e′)3/2 law. This result indicates distributed electromagnetic wave interactions with the local soft-phonon modes. This conclusion is further confirmed by the satisfactorily fit of the frequency dependence of the complex permittivity by a Cole–Cole function with an exponent β=0.6 and a characteristic time τ=0.21 ps.

Dispersion and loss of ferroelectric Ba0.5Sr0.5TiO3 thin films up to 110 GHz

3D stacking technologies are electrically studied to predict high speed data transmission for memory on logic applications. Maximal frequency of bandwidth for memory-processor and processor-BGA channels are extracted and compared for Face to Face and Face to Back 3D stacking and between an interposer technology. Using expected electrical specifications of Wide IO applications in terms of data rates, a roadmap is proposed in accordance to the integration density, carried out by the TSV density.

Evaluation of 3D interconnect routing and stacking strategy to optimize high speed signal transmission for memory on logic

OUR RESEARCH WORK DEALS WITH THE DEVELOPMENT OF NEW GAME-BASED LEARNING (GBL) ENVIRONMENTS. WE THINK THAT THE WAY OF ACQUIRING KNOWLEDGE DURING A LEARNING SESSION IS SIMILAR TO FOLLOWING AN ADVENTURE IN A ROLE-PLAYING GAME AND WE APPLY THE METAPHOR OF EXPLORING A VIRTUAL WORLD, WHERE EACH STUDENT EMBARKS ON A QUEST IN ORDER TO COLLECT KNOWLEDGE RELATED TO A LEARNING ACTIVITY. 
IN OUR UNIVERSITY, WE HAVE SET UP NUMBERS OF EXPERIMENTS WITH STUDENTS USING GBL ENVIRONMENTS. THEY REVEALED WEAKNESSES FOR SPECIFIC LEARNING ACTIVITIES. SOMETIMES, LEARNERS SEEM TO ACQUIRE A SKILL IN THE GAME, BUT THEY ARE NOT ABLE TO REUSE IT EASILY IN THE REAL WORLD. THIS IS PARTICULARLY THE CASE FOR SKILLS THAT REQUIRE CONCRETE MANIPULATION OF REAL OBJECTS TO BE ACQUIRED. GBL ENVIRONMENTS THUS LACK OF MEANS TO LEARN KNOW-HOW ASPECTS. SOME OF THE LEARNING PROCESSES INVOLVING REAL WORLD OBJECTS ARE VERY DIFFICULT TO REPRODUCE IN GBL ENVIRONMENTS AND THERE IS AN ESSENTIAL TECHNOLOGICAL ISSUE IN MIXING VIRTUAL AND REAL ASPECTS IN GBL ENVIRONMENTS. 
IN THIS ARTICLE, WE DESCRIBE THE POSSIBLE PROBLEMS THAT CAN APPEAR WHEN USING THIS MIXED APPROACH, GIVE HINTS ON HOW TO AVOID THEM AND ILLUSTRATE OUR PROPOSITION WITH EXAMPLES ISSUED FROM THE ELECTRONIC DOMAIN. WE FOCUS ON ISSUES LINKED TO THE TRANSITION BETWEEN VIRTUAL AND REAL WORLDS AND WE EXPLORE HOW NEW ELECTRONIC FEATURES CAN FACILITATE THIS MIXED APPROACH, WHERE IDENTIFICATION, LOCALISATION AND UPDATE OF THE USER MODELS ARE KEY ISSUES.

Grégory Houzet

Papers

A 360 $^{\circ}$ BST Phase Shifter With Moderate Bias Voltage at 30 GHz

Negative-zero-positive metamaterial with omega-type metal inclusions

Dispersion and loss of ferroelectric Ba0.5Sr0.5TiO3 thin films up to 110 GHz

Evaluation of 3D interconnect routing and stacking strategy to optimize high speed signal transmission for memory on logic

Mixed Reality Games