Back to Departmental Colloquium: Fall 2006
Departmental Colloquium
Date: Thursday, Nov 9, 2006
Time: 4:15PM
Location: JWB 335
Cancelled
Vasundara V. Varadan
Microwave and Optics Laboratory for Imaging & Characterization, University of Arkansas
Title |
The Emperor's Metamaterial Cloak? |
Abstract |
Metamaterials with strong dispersion that can be tailored, magnetic properties from engineered structures, negative permittivity and/or permeability and negative refractive index opened up an exciting research field less than a decade ago when Veselago’s long forgotten paper on negative property electromagnetic materials was rediscovered. Applications such as super lenses that can overcome the diffraction barrier, near field focusing, flat lenses and the ability to ‘cloak’ or hide objects give rise to visions of a 21st century emperor’s new clothes. This seminar is on experimental studies of metamaterials fabricated with printed circuit board and LTCC techniques and explores some of the intriguing applications that have been proposed for metamaterials. A brief introduction will be given on a free space, focused microwave beam measurement system that mimics free field conditions on a table top and permits the use of small samples. Some well known and less well known experimental results on the microwave properties (5-110 GHz) of such materials will be presented. The current debate regarding the allowed sign of the imaginary part of complex electromagnetic properties in a no gain material will be discussed in the context of causality and energy conservation. Kramer-Kronig reconstruction of the imaginary part using just experimental data for the real part and vice versa will be shown. The measured anomalous dispersion of the complex permittivity and permeability is fitted with resonance models and it is shown that the properties are analytic functions in the upper half frequency plane and that the singularities are in the lower half plane even if the imaginary part is negative. It is also shown that the material is a net loss system independent of the sign of the imaginary parts for metamaterials and other biisotropic and bianisotropic materials described by both permittivity and permeability, independent of the constitutive model. Some recent experimental demonstrations of cloaking by a metamaterial as proposed by Milton and Nicorovici (2006) and earlier Nicorovici, McPhedran & Milton (1994) will help us conclude if indeed metamaterials will be used to stitch the emperor’s new cloak. –> |