There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Probability Distributions.- Linear Models for Regression.- Linear Models for Classification.- Neural Networks.- Kernel Methods.- Sparse Kernel Machines.- Graphical Models.- Mixture Models and EM.- Approximate Inference.- Sampling Methods.- Continuous Latent Variables.- Sequential Data.- Combining Models.

Pattern Recognition and Machine Learning

The term photonic crystals appears because of the analogy between electron waves in crystals and the light waves in artificial periodic dielectric structures. During the recent years the investigation of one-, two-and three-dimensional periodic structures has attracted a widespread attention of the world optics community because of great potentiality of such structures in advanced applied optical fields. The interest in periodic structures has been stimulated by the fast development of semiconductor technology that now allows the fabrication of artificial structures, whose period is comparable with the wavelength of light in the visible and infrared ranges.

http://ieeexplore.ieee.org/iel5/6354/16969/00781867.pdf

Photonic crystals

The adoption of a reconfigurable intelligent surface (RIS) for downlink multi-user communication from a multi-antenna base station is investigated in this paper. We develop energy-efficient designs for both the transmit power allocation and the phase shifts of the surface reflecting elements subject to individual link budget guarantees for the mobile users. This leads to non-convex design optimization problems for which to tackle we propose two computationally affordable approaches, capitalizing on alternating maximization, gradient descent search, and sequential fractional programming. Specifically, one algorithm employs gradient descent for obtaining the RIS phase coefficients, and fractional programming for optimal transmit power allocation. Instead, the second algorithm employs sequential fractional programming for the optimization of the RIS phase shifts. In addition, a realistic power consumption model for RIS-based systems is presented, and the performance of the proposed methods is analyzed in a realistic outdoor environment. In particular, our results show that the proposed RIS-based resource allocation methods are able to provide up to 300% higher energy efficiency in comparison with the use of regular multi-antenna amplify-and-forward relaying.

Reconfigurable Intelligent Surfaces for Energy Efficiency in Wireless Communication

A 1-bit reconfigurable reflectarray antenna consisting of 10×10 elements is fabricated and measured for proof-of-principle in high-gain beam-scanning antenna designs. The element is reconfigured by a PIN diode. By controlling the biasing voltage on each PIN, beam scanning performance of the reflectarray is obtained. The measured results show that both the radiation patterns and gains can be improved by optimizing the reference phase of the aperture phase distribution. Good scan beams within ±50° range are obtained in the horizontal plane. Due to the small aperture size, large edge diffraction, low spillover efficiency, and specular reflection lead to reduced gain and lower aperture efficiency, as well as poor scanning performance in the vertical plane.

Experimental study of a 1-bit 10×10 reconfigurable reflectarray antenna

Microstrip reflectarrays combine the many favorable features of both reflectors and printed arrays, and create a new generation of high-gain antennas which has low-profile and low-mass features. In addition to these mechanical advantages, they are also quite suitable for applications requiring high-gain beam-scanning. On the other hand, radiometer antennas for earth remote sensing or radio astronomy are required to have two-dimensional beam-scanning capability, with high resolution, low loss, and low cross-polarization features; therefore a reflectarray can be a good choice for the beam-scanning antenna in these systems. Conventionally, the phase distribution on a reflectarray aperture is designed based on the phase compensation of a parabolic reflector. However, for beam-scanning applications these designs show a poor performance. Spherical reflectors on the other hand are quite suitable for wide-angle two-dimensional beam-scanning, and since reflectarray elements can provide any value of phase shift, one can design the reflectarray aperture based on the phase compensation of a comparable spherical reflector. The goal of this work is to study the feasibility of planar reflectarray antennas with spherical phase distribution for beam-scanning applications. First, analytical expressions are derived for the aperture phase distribution of spherical-phase reflectarrays. In the next stage, the restricted aperture approach is used to design spherical-phase reflectarray antennas, and numerical studies are performed to determine the optimal focal of these planar designs. It is revealed that the optimal focal is a function of the scanned beam direction, and the focal length is reduced as the scan angle increases. In addition the beam-scanning performance of the reflectarrays are compared with spherical reflectors with the same subtended angle, and it is shown that for moderately wide scan coverage, a similar performance can be realized with these planar arrays. Moreover, parametric studies on the taper effect of the illuminated aperture, the size of the corresponding sphere, and the scan range are conducted, to characterize the beam scanning performance of these antennas. These studies show that planar reflectarrays with spherical phase distribution can be a suitable choice for a beam scanning radiometer antenna in remote sensing or radio astronomy applications.

Planar reflectarray antennas with spherical phase distribution for two-dimensional beam-scanning

This paper presents an overview of various RFID tag fabrication methods and briefly describes the advantages and disadvantages of each method. The purpose of this paper is to provide the reader with the fabrication techniques that can be applied for RFID fabrication purposes for laboratory scale experiments. This paper will present the performance results of laboratory made RFID tags based on two fabrication methods (etching and screen printing) on multiple substrates (paper, thin transparent film, polyethylene terephthalate (PET), and fabrics). These results will prove the effectiveness of the presented methods for RFID tag fabrication purposes.

Survey of Laboratory Scale Fabrication Techniques for Passive UHF RFID Tags

Demand response (DR) has drawn much interest as the increasing active consumer participation in smart grid Buildings account for a large portion of energy consumption, while many integrated smart electric equipment, such as energy storage devices (ESD), electric vehicles (EVs) and photovoltaic (PV), provide more opportunities for end-users to develop building energy management (BEM) strategies In this paper, a mixed-integer linear programming (MILP) framework-based modeling of a BEM structure is provided, considering dynamic thermal characteristic of buildings Three different scenarios are evaluated and the fully BEM scenario considering dynamic thermal characteristic performs the best

Building energy management based on demand response strategy considering dynamic thermal characteristic

Sensitivity is an important parameter to evaluate the performance of RFID sensing antennas. In order to obtain high sensitivity, two different sensing mechanisms are selected for temperature monitoring. One utilizes the electrical properties of sensing materials, and the other utilizes the thermal properties of sensing materials. Water and high density polyethylene-Ba0.3Sr0.7TiO3 (HDPE-BST) are the ones with temperature dependent electrical properties. On the other hand, mercury and Polytetrafluoroethylene (PTFE) are selected for their distinct thermal expansion properties. To magnify the effects of the sensing materials on the antennas characteristics, two different antenna configurations are used. Patch antennas are designed for the materials with electrical properties, and cavity backed slot antennas are designed for easy integration with the sensing materials with thermal properties. All of the four designs are frequency reconfigurable sensing antennas. In this situation, frequency shift per temperatures (Δf/ΔT), realized gain, and realized gain bandwidth are used to evaluate the antenna sensitivity. Finally, measurement results show that 40 MHz/10°C frequency shift with 14 m read range is realized by a capacitively-loaded cavity backed slot sensing antenna using thermal properties of the PTFE material.

https://www.ursi.org/Proceedings/ProcGA14/papers/ursi_paper2621.pdf

Fan Yang

Papers

Experimental study of a 1-bit 10×10 reconfigurable reflectarray antenna

Planar reflectarray antennas with spherical phase distribution for two-dimensional beam-scanning

Survey of Laboratory Scale Fabrication Techniques for Passive UHF RFID Tags

Building energy management based on demand response strategy considering dynamic thermal characteristic

High-sensitivity RFID sensing antennas: From sensing mechanism selections to antennas structure designs