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

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

The increasing proliferation of advanced devices for UWB, 5G communication, micrometer-wave, and millimeter-wave communication demands an antenna which can handle huge data rates, provides high gain and stable radiation pattern as a panacea of most of the current wireless communication problems. Many different antenna designs have been proposed by the researchers but, Antipodal Vivaldi Antenna (AVA) has drawn the attention of most of the researchers because of its high gain, wide bandwidth, less radiation loss, and stable radiation pattern. Different methods are presented to make AVA more compact while maintaining the performance of an antenna to an acceptable level. These different methods are substrate choice, flare shape, slots, and feeding connectors. Also, AVA performance can be enhanced by incorporating corrugation, dielectric lens, patch in between two flares of AVA, balanced AVA (BAVA), metamaterial, computational intelligence (CI), and AVA array. The AVA performance enhancement techniques modify the electrical and physical properties of an antenna which in turn improves its performance. A large number of performance enhancement methods of AVA design have been proposed, however, no comprehensive study exists to categorize these performance enhancement techniques and outline their concepts, advantages, disadvantages, and applications. So, in this paper, we have attempted to outline all methods available for enhancing and optimizing the parameters of AVA. Additionally, to validate some of the important performance enhancement methods, they are incorporated in the basic conventional AVA design and further simulation results are obtained for the same which are in line with the surveyed literature. Each method is explained in detail by incorporating its key points, merits, and demerits. Moreover, illustrations from the literature are given to demonstrate improvement in the parameters as a result of applying a particular performance enhancement technique.

/pdf/a-survey-of-performance-enhancement-techniques-of-antipodal-gvdy1xils8.pdf

A Survey of Performance Enhancement Techniques of Antipodal Vivaldi Antenna

Novel methods of improving directivity and decreasing sidelobe radiation via the addition of an elliptical pseudoelement and irregularly spaced notches in the tapered slot antenna are presented in this paper. This antenna has been shown to be functional over the C, X, $\text{K}_{\mathrm {u}}$ , K, $\text{K}_{\mathrm {a}}$ , and portions of the $S$ - and $V$ -bands covering (2.5 to 57) GHz (22.8:1 bandwidth, defined where VSWR < 3). Minimum and maximum realized gains of 4 and 16 dB were achieved at 2.7 GHz and 29.8 GHz, respectively. The antenna offers directive radiation patterns with a half-power beamwidth under 40° for frequencies above 6 GHz and under 30° for frequencies above 32 GHz. As compared with other Vivaldi antennas reported in the past, the proposed design offers a larger bandwidth while providing higher peak gain and average gain. Good agreement was observed between simulation and measurements.

High-Gain Antipodal Vivaldi Antenna With Pseudoelement and Notched Tapered Slot Operating at (2.5 to 57) GHz

In recent decades, origami has been explored to aid in the design of engineering structures. These structures span multiple scales and have been demonstrated to be used towards various areas such as aerospace, metamaterial, biomedical, robotics, and architectural applications. Conventionally, origami or deployable structures have been actuated by hands, motors, or pneumatic actuators, which can result in heavy or bulky structures. On the other hand, active materials, which reconfigure in response to external stimulus, eliminate the need for external mechanical loads and bulky actuation systems. Thus, in recent years, active materials incorporated with deployable structures have shown promise for remote actuation of light weight, programmable origami. In this review, active materials such as shape memory polymers and alloys, hydrogels, liquid crystal elastomers, magnetic soft materials, and covalent adaptable network polymers, their actuation mechanisms, as well as how they have been utilized for active origami and where these structures are applicable is discussed. Additionally, the state-of-the-art fabrication methods to construct active origami are highlighted. The existing structural modeling strategies for origami, the constitutive models used to describe active materials, and the largest challenges and future directions for active origami research are summarized. This article is protected by copyright. All rights reserved.

Active Materials for Functional Origami.

Magnetically Actuated Reconfigurable Metamaterials as Conformal Electromagnetic Filters

Electromagnetic (EM) metamaterials with tailored properties are developed for wave manipulation, filtering, and cloaking for aerospace and defense applications. While traditional EM metamaterials exhibit fixed behaviors due to unchangeable material properties and geometries after fabrication, reconfigurable EM metamaterials allow for tunable performance through electrical/mechanical reconfiguration strategies. Traditional biasing circuit‐based electrical reconfiguration poses challenges due to complex circuit design, while motor‐driven mechanical reconfiguration can lead to bulky and tethered structures with restricted adaptability. Herein, magnetically actuated structurally reconfigurable EM metamaterials with enhanced adaptability/conformability to different geometries, showing merits of fast, reversible, and programmable shape morphing, are developed. Magnetic actuation enables metamaterial's mechanical reconfiguration between flat deployed, flat folded, curved deployed, and curved folded states for both conformal and freestanding 3D shape morphing. Locally, the EM metamaterials fold subwavelength units for tunable properties, switching between all‐pass and band‐stop behaviors upon structural reconfiguration. Globally, the structure can conform and morph to different curved surfaces. The structurally reconfigurable metamaterial also serves as a medium for customizable subwavelength units by rationally designing attached conductive patterns for varied filtering performances such as narrow‐band, dual‐band, and wide‐band filtering behaviors, illustrating the design flexibility and application versatility of the developed structurally reconfigurable EM metamaterial.

https://onlinelibrary.wiley.com/doi/pdfdirect/10.1002/aisy.202200106

Novel methods of improving directivity and decreasing sidelobe radiation via the addition of an elliptical pseudoelement and irregularly-spaced notches in the tapered slot antenna are presented in this paper. This antenna has been shown to be functional over the C, X, Ku, K., Ka, and portions of the Sand V bands covering 2.5 − 57 (22.8:1 bandwidth) GHz. Minimum and maximum realized gains of 5.2 and 15.2 dBi were achieved at 2.5 and 32 GHz., respectively. As compared to other Vivaldi antennas reported in the past, the proposed design offers a larger bandwidth while providing 3–4 dBi higher gain in the majority of the band.

Antipodal UWB Vivaldi Antenna with Pseudoelement and Notched Flares for 2.5-57 GHz Applications

A novel mechanically reconfigurable 8×11 slot array using accordion-like microactuators as an alternative to conventional electronically steered arrays is reported. The array scans 0° to –30° in elevation by simultaneously varying the inter-element spacing between sliding slot elements. To maintain low slidelobe levels, the radiating slots are designed to have nonuniform width. The array is fed by a single slotted waveguide from one side. The actuator provides continuous motion with a precision of 30  μ m (λ0/625) and is controlled via a printed circuit board (PCB) circuit. The accordion-like structure provides a uniform yet tunable spacing between each slot column, eliminating the need for costly and complex electronic scanning. This high precision approach reduces the system footprint, ensures high power handling capability, and ensures ease of integration in future applications. The structure, operating at 16 GHz, is fabricated using a laser-etching process and in-house additive manufacturing. Measurement results are congruent with simulations.

Mechanically Reconfigurable Slot Array Using Accordion-Like Microactuators

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Papers

High-Gain Antipodal Vivaldi Antenna With Pseudoelement and Notched Tapered Slot Operating at (2.5 to 57) GHz

Magnetically Actuated Reconfigurable Metamaterials as Conformal Electromagnetic Filters

Magnetically Actuated Reconfigurable Metamaterials as Conformal Electromagnetic Filters

Antipodal UWB Vivaldi Antenna with Pseudoelement and Notched Flares for 2.5-57 GHz Applications

Mechanically Reconfigurable Slot Array Using Accordion-Like Microactuators