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Bar-Cohen : Biomimetics: Biologically Inspired Technologies DK3163_c012 Final Proof page 319 21.9.2005 11:54pm

Multifunctional Materials 319

Frequency Dependence of the Effective Refractive Index
1.2

1
Refractive index 0.8 single

0.6
double 1:1
0.4
double 1:2
double 2:3
0.2

0
3 6 9 12 15 18 21 24
Frequency (GHz)

Figure 12.8 (Top) Frequency dependency of the effective refractive index for various coil geometries. Double
coils (bottom) can also be used to cancel the effect of chirality. However, they also modify the plasma frequency of
the medium as the effective inductance and capacitance per unit volume is changed.

denier nylon fiber. The core of the braid consists of one end of 1000 denier Kevlar fiber and three
ends of 420 denier nylon fiber. An illustration is provided in Figure 12.9 showing the constituents
of the braid architecture. Nylon is included in the braiding process since it will serve as the polymer
matrix of the final composite, although it may not be the optimal choice in terms of mechanical
strength of the resulting composite. Complete fiber wet-out can be a difficult processing challenge
in braided composite materials, due to the inherent tight packing of fibers in the braiding process.
We have initially addressed this issue by developing a commingled braid composite, which
integrates the eventual matrix phase as a thermoplastic fiber that is braided along with the structural

Table 12.1 Parameters for Simulating Various Coil Geometries in HFSS Electromagnetic
Simulations
Single Double 1:1 Double 1:2 Double 2:3
Outer cell Spacing (mm) 6.35 6.35 6.35 6.35
Cell height (mm) 1.1 1.1 1.1 1.1
Inner diameter (mm) 2.6 2.6 2.6 2.6
Inner cell Turns in one cell 1 1 2 3
Inner diameter (mm) — 2.2 2.2 2.2
Turns in one cell — 1 1 1
Wire thickness (mm) 0.1 0.1 0.1 0.1
Plasma frequency (GHz) 3.26 7.59 6.73 5.35