Biomedical Engineering Reference
In-Depth Information
(b)
(a)
Figure 5.4
(a)Schematicofanexperimentalsetuptodemonstratenegative
refraction. (b) Computed equi-frequency surfaces (EFS) for the (
+
1, S)
branch. The arrow refers to the direction of the refracted waves at 9.41
GHzunderanincidentangleat45
◦
.(c)Measuredelectricfieldintensityasa
function of the horizontal position of the circularly polarized horn receiver,
with or without (black) the chiral sample and alumina prisms at 9.41 GHz.
The two curves are normalized such that the magnitude of both peaks is
unity. The blue dashed line at horizontal position of
−
11 cm refers to the
spatial beam shift with respect to 0
◦
refracted angle.
in a polyurethane foam slab. The polyurethane foam slab is lossless
with
ε
≈
1. The sample slab contains 15
×
11 metallic helices,
each having 140 periods along helical axis (
z
-axis). Computed EFS
show that negative refraction can be achieved at both sides of the
polarization gap and we try to realize the negative refraction at
the lower edge of the gap. As the (
±
1,S) modes lie below the light
line, we excite the (
±
1,S) modes by prism coupling techniques [see
Fig. 5.4(a)], and the refractive angle is found by measuring the
spatial beam shift. Two isosceles right-angled triangular alumina
prisms (
ε
r
=
8.9) are placed so that they touch the sample slab
at both sides and a Gaussian beam is normally incident in
xz
-plane
to the air-prism interface from a linearly polarized horn emitter
(operating at 8.2-12.4 GHz with a gain factor of 24.6 dB), ensuring
an incident angle of 45
◦
from alumina to sample. The local field
intensity is measured by the LCP/RCP horn receiver as a function
of the horizontal position. The spatial shift of the outgoing beam is
found by measuring the peak position at the interface of prism. The
