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Bar-Cohen : Biomimetics: Biologically Inspired Technologies DK3163_c012 Final Proof page 321 21.9.2005 11:54pm

Multifunctional Materials 321

8

4

Dielectric constant 0

−4
Experiment (E parallel)
Experiement (E perp.)
Theoret. model
−8
11 13 15 17 19 21
GHz
Figure 12.10 (See color insert following page 302) (Top) Coiled wire architecture integrated with structural
Kevlar fibers by braiding. Braids woven and laminated into composite plates. (Bottom) EM characterization of the
braided and woven composite showing typical plasmon media response when aligned parallel to the polarization of
the EM radiation. Normal (nonplasma) dielectric response is observed when aligned in the perpendicular direction.

from 11 to 21 GHz, whereupon at around 18 GHz, the dielectric constant passes through zero. This
dispersion relation follows the characteristic trend of the thin straight wire arrays studied previously.
Between the plasma frequency and the upper limit of our frequency sweep, the dielectric constant of
the composite array approaches unity. Since the index of refraction of the material is the square of the
dielectric constant, we may also conclude that the index approaches unity.

12.2.1.4 Controlling the Effective Magnetic Permeability

Following Pendry et al. (1999), Smith et al. (2000a,b), and Shelby et al. (2001), we have shown that
the effective magnetic permeability, m, of free space can be rendered negative over a certain
frequency range by suitably integrating the so called split-ring-resonators, as shown in Figure
12.11. The structure, however, cannot be integrated into a thin composite panel. To remedy this
fundamental barrier, we considered collapsing the rings into nested folded plates, as shown in