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Biomimetics - Biologically Inspired Technologies - Yoseph Bar Cohen Episode 2 Part 2

Tham khảo tài liệu 'biomimetics - biologically inspired technologies - yoseph bar cohen episode 2 part 2', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 312 Biomimetics Biologically Inspired Technologies 12.2.1 Electromagnetic Functionality Recent advances in electromagnetic EM metamaterials have provided an opportunity to change and tune the dielectric constant as well as the index of refraction of the material over a range of useful frequencies. Electromagnetic metamaterials are artificially structured media with unique and distinct EM properties that are not observed in naturally occurring materials. A variety of metamaterials with striking EM properties have been introduced most notably those with a negative refractive index NRI . NRI is associated with a medium of simultaneously negative electric permittivity e and the magnetic permeability m. There are no known conventional materials with such exceptional properties. Recently Smith et al. 2000a b at UCSD have produced a medium with effective e and m that are measured to be simultaneously negative. Later Smith et al. performed a Snell s law experiment on a similar metamaterial wedge sample and demonstrated the negative refraction of a microwave beam Shelby et al. 2001 . Thus they showed that their medium does indeed possess an NRI that is it is a negative index material NIM . Such a property has been hypothesized by Veselago who termed the medium left-handed Veselago 1968 . The work on controlling the dielectric constant and producing negative e and m has been discussed by Smith et al. Smith et al. 2002 2003 2004a b c Kolinko and Smith 2003 Pendry et al. 2003 . However until recently the NIMs produced have been experimental samples suitable only for proof-of-concept demonstrations. Based on the calculation of the effective EM properties of a medium containing periodically distributed very thin conducting wires and electric resonators the authors at UCSD have introduced into structural composites electromagnetic enhancements in the form of tunable index of refraction radio frequency RF absorption and when desired a negative index of refraction Starr et al. 2004