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

Planar reflectarray antennas with spherical phase distribution are studied in this paper. Analytical expressions are derived for the aperture phase distribution, and the restricted aperture approach is used to minimize the effects of spherical aberration. The optimal feed position is determined by means of a phase error analysis, and a planar reflectarray with 30 dB gain and 30 degrees elevation coverage is studied for two-dimensional beam-scanning. These studies show that planar reflectarrays with spherical phase distribution can be a suitable choice for high-gain two-dimensional beam-scanning applications.

Studies on planar reflectarrays with spherical-phase distribution for 2-D beam-scanning

Traditional gradient descent inversion for transient electromagnetic (TEM) data is time and memory comsuming because the derivative matrices need to be computed repeatly. In this paper, we apply the Supervised Descent Method (SDM) into pixel-based inversion for TEM data. This method is based on the concept of gradient learning. In an offline stage, the average descent direction can be learned from a set of training data; and in an online stage, data inversion can be achieved by the learned descent directions without computing the derivative matrices. Numerical tests verify that this algorithm converges faster and is also more efficient. Moreover, SDM offers a more convinient way to incorporate prior information into inversion that could improve the efficiency of data interpretation.

Application of Gradient Learning Scheme to Pixel-Based Inversion for Transient EM Data

A novel Ku -band pattern-reconfigurable array antenna is designed and experimentally tested, which is able to electronically form various radiation patterns, including a single pencil beam, dual beams, quad beams, and a single fan beam. It consists of 4 × 4 probe-fed O-slot patch elements. Two p-i-n diodes are integrated on the O-slot of each element, and by alternatively activating one of the p-i-n diodes, the direction of the excitation current is reversed. Hence, the element is able to generate two-phase states with 180° phase difference. In order to properly excite the elements, a stripline power dividing network with a waveguide feeding port is designed. Furthermore, an antenna prototype is fabricated and measured. The measured gain of the single pencil beam is 15.0 dBi at 12.5 GHz, and the measured 1 dB gain bandwidth is 9.6% (11.8–13.0 GHz). The simulations and measurements of various beam patterns agree very well, which successfully verify the dynamic pattern-reconfigurable capability of the proposed array design.

Design and Measurement of a Ku -Band Pattern-Reconfigurable Array Antenna Using 16 O-Slot Patch Elements With p-i-n Diodes

The design and simulations of a Ku-band 1-bit reconfigurable transmitarray is presented. The proposed element consists of two orthogonal H-shaped slots and a coupling microstrip transmission line. By controlling the two PIN diodes integrated on the transmission line, opposite ends of the receiving H-shaped slot are excited, thus achieving 1-bit quantized phase with 180° phase difference. The simulated insertion loss at both phase states is 1.6 dB. A 16×16 transmitarray with aperture size of 128 mm is designed and analyzed. Full-wave simulation results show a satisfactory performance with gain of 18.8 dBi and aperture efficiency of 23.0% at 12 GHz.

Design of a Ku-band 1-bit reconfigurable transmitarray with 16×16 slot coupled elements

This work summarizes our latest research progress on wire antennas near artificial complex ground planes. As a new generation of low gain antenna, they have the advantages of low profile and versatile radiation properties. Various antenna designs are discussed in this paper, including surface wave antennas, circularly polarized antennas, and antennas with reconfigurable radiation patterns. They exhibit good potential for applications in wireless communications.

Fan Yang

Papers

Studies on planar reflectarrays with spherical-phase distribution for 2-D beam-scanning

Application of Gradient Learning Scheme to Pixel-Based Inversion for Transient EM Data

Design and Measurement of a Ku -Band Pattern-Reconfigurable Array Antenna Using 16 O-Slot Patch Elements With p-i-n Diodes

Design of a Ku-band 1-bit reconfigurable transmitarray with 16×16 slot coupled elements

Wire antennas on artificial complex ground planes: a new generation of low gain antennas