Tham khảo tài liệu 'the coming of materials science episode 10', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Functional Materials 295 tunable lasers and elaborate detectors. As Figure shows this level of multiplexing channels had become possible by 1995. Not only the number of messages that can pass along one fibre but also the speed of transmission has increased steadily over the past two decades according to Sato 2000 in Japan this speed has increased by about an order of magnitude per decade as a consequence of improved fibres and lasers and also improved networking hardware. . LIQUID CRYSTALS One is inclined to think of materials as being solids when editing an encyclopedia of materials some years ago I found it required an effort of imagination to include articles on various aspects of water and on inks. Yet one of the most important families of materials in the general area of consumer electronics are liquid crystals used in inexpensive displays for instance in digital watches and calculators. They have a fascinating history as well as deep physics. Liquid crystals come in several varieties for the sake of simplified illustration one can describe them as collections of long molecules tending statistically to lie along a specific direction there are three types nematic cholesteric and smectic with an increasing measure of order in that sequence and the variation of degree of alignment as the temperature changes is akin to the behaviour of spins in ferromagnets or of atomic order in certain alloys. The definite history of these curious materials goes back to 1888 when a botanist-cum-chemist Friedrich Reinitzer sent some cholesteric esters to a molecular physicist Otto Lehmann. 1890 1910 1930 1950 1970 1990 2010 2030 2050 Year Figure . Chronology of message capacity showing exponential increase with time. The number of voice channels transmitted per fibre increases rapidly with frequency of the signalling medium. The three right-hand side points refer to optical-fibre transmission after MacChesney and DiGiovanni 1991 with added point . 296 The Coming of .
