دانلود کتاب مایکروویو، موج میلی‌متری و کریستال‌های مایع تراهرتز

Liquid crystal, sometimes referred to as the fourth state of matter or mesophase, is a unique state of matter that has properties between those of conventional liquids and those of solid crystals. It has changed our vision of matter by shattering the three-state paradigm. Within a specific temperature range, liquid crystal materials do not change from crystals or solids directly to isotropic fluids when they melt but go through a series of thermodynamically stable intermediate mesophases.
For a long time, liquid crystals were merely scientific curiosity. A few ground-breaking discoveries in the 1960s led to the overwhelmingly ubiquitous LCD today. With more and more liquid crystal properties explored and exploited, liquid crystal quickly accelerates its momentum beyond the narrow niche of display.
Liquid crystal is inherently promising for electromagnetic applications because of its tunable electromagnetic anisotropy. Extensive and intensive researches have significantly advanced liquid crystal into one of the hot research frontiers for cutting-edge microwave, millimeter wave and terahertz technologies. With the arrival of 5G communications and the forthcoming 6G communications, liquid crystal has been anticipated to play a crucial role to meet the imperative need for compact, versatile and lightweight microwave and millimeter wave devices in portable devices and communication hubs. We have been witnessing soaring applications in the past two decades.
Although numerous papers have been published, to the best knowledge of the authors, this is the first ever interdisciplinary monograph on microwaves, millimeter waves and terahertz nematic liquid crystals.
This book opens with an introduction and elementary physics of generic liquid crystal, followed by a retrospective review of microwaves, millimeter waves and terahertz applications of nematic liquid crystals. Latest in-house research progress including synthesis of liquid crystal, measurement of dielectric properties, fabrica-tion of functional devices and a few representative advanced functional devices is then presented.
Chapter 1 gives an introduction to generic liquid crystals. First of all, the basic concept of liquid crystals is explained. Some well-known examples of liquid crystals are given to familiarize readers with first hand impression. Next, the history of liquid crystal is chronologically presented. Historical milestones and pioneers are high-lighted. After that, a systematic classification of liquid crystals is conducted. This chapter ends with a briefing of applications of liquid crystals based on the latest liter-ature survey, featuring only well-established, commercialized or even industrialized applications.
The performance of liquid crystal is dependent on a variety of internal and external factors. A crucial step in the industrial applications of liquid crystal is the theoretical understanding of the liquid crystal phases for controlling, predicting and even engi-neering liquid crystal properties. In Chap. 2, elements of the intricate interdisciplinary liquid crystal physics are briefed. Attention is focused on nematic liquid crystal. More importantly, in consistency with the featured applications of liquid crystal in microwave, millimeter wave and terahertz frequencies, electromagnetic properties critical for such electromagnetic applications as well as effect of electromagnetic fields on liquid crystals are given more concerns.
Chapter 3 begins with a brief introduction of the electromagnetic spectrum with intensified interest in microwave, millimeter wave and terahertz wave bands. An overview about applications of liquid crystal at microwave, millimeter wave and terahertz wave frequencies is next presented. The overview and the following topical reviews are based on a literature survey and the collected literatures. Finally, brief reviews on more specific topics are given.
Synthesis of novel nematic liquid crystal mixtures with high dielectric anisotropy, low dielectric loss, and low melting point for K-band application is presented in Chap. 4. The effect of molecular structure on dielectric properties is studied first, followed by a study on the temperature dependence of dielectric property and viscosity of liquid crystal. Forty-five intermediate liquid crystal compounds in 5 series with high dielectric anisotropy, and low melting point are then synthesized. Ultimately, seven new microwave nematic liquid crystal mixtures with different dielectric anisotropy are developed.
In Chap. 5, a new perturbation method of double-ridge waveguide resonator is proposed for microwave characterization of liquid crystals. It meets the requirements of accurately testing the dielectric anisotropy, dielectric tuning characteristics, dielec-tric loss and required working frequency band of the microwave nematic liquid crystal. This method provides valuable information for understanding microwave nematic liquid crystals and further research and development of microwave nematic liquid crystal materials.
Liquid crystal cell is one of the essential elements in reconfigurable microwave, millimeter wave and terahertz functional devices. In Chap. 6, a process for fabricating nematic liquid crystal cells for microwave, millimeter wave and terahertz functional devices is presented. It is based on a xenomorphic substrate and solves the packaging and uniformity issues of large and thick nematic liquid crystal layer.
Microwave phase shifters are one of the core components in electronic information systems and phased array radar systems. In Chap. 7, a miniature K-band microwave nematic liquid crystal-based phase shifter that can realize 360° phase shift in K-band is proposed.
A frequency tunable and pattern reconfigurable 1 × 4 phased array antenna is designed in Chap. 8. Numerical simulation proves that the antenna can dynamically adjust its operating frequency between 14.5 GHz and 16.4 GHz and continuously and dynamically control the beam direction between –20° and 20°.
In Chap. 9, nematic liquid crystal (NLC) is introduced to develop novel meta-materials, namely multifunctional digital metamaterials of arbitrary base. A proof-of-concept prototype consisting of a superstrate of quartz, an array of metallic patches, a substrate of NLC and a ground is proposed. The novel coding mech-anism has been proven through both numerical simulation and preliminary experi-ments. The potential of the novel metamaterial is demonstrated by two representative applications.