Biomedical Engineering Reference
In-Depth Information
with different obstacles inserted inside the chiral channels. Light
blue regions of Fig. 5.13 highlight the presence of robust transport
inthechiralchannelforthefrequencyregioninsidethepolarization
gap. The first obstacle is an aluminum block (PEC block) measuring
6.6 mm
×
6.6 mm
×
2.5 mm, approximately the same as the
channel's cross-section. We can see that the forward transmission
(blue) is almost the same as that of the unblocked channel (black).
If a larger PEC block with nearly double the size is inserted, the
transmission (green) is only slightly decreased. The relative phase
of the PEC blocked channel shown in Fig. 5.13(b) is nearly the same
as that of the un-blocked channel, indicating that the polarizations
of the output wave do not change even the obstacleis present.
We did some FDTD simulations to demonstrate the robust
transport property of the chiral channel states. The simulated
geometry parameters are the same as those in the experiment and
an E
x
-polarized source at 9.9 GHz is used. The patterns within a
period of 2
a
are shown to highlight the salient features. Poynting
vector patterns without and with the small-size PEC slab are shown
in Fig. 1.14(a) and (b), respectively. Energy flux propagates up the
unblocked channel in a helical shape inside the LH chiral channel.
When the LH polarized wave encounters a slab inserted inside the
chiral channel, the reflection will change LH to RH polarization.
Howeve,thereflectedwavecannotpropagatebecauseofthe
absence of backward RH-guided mode. The only way for the flux
is to continue moving upward, resulting in the robust transport
phenomenon and hence high transmittance.
The behaviors of robust transport cannot be sustained outside
the band gap. Figure 5.13(b) illustrates that low transmission is
recorded from 9.4 to 9.7 GHz (blue and green curves), as the
EM wave is strongly reflected by the PEC blocks. The results of
relativephasebetweenSxandSy,plottedinFig.5.13(b),havelarger
fluctuationsthanthoseinsidethepolarizationgap,showingthatthe
polarization character is changed a lot after the obstacleis inserted.
For the case of a dielectric slab, the robust transport effect
can also be observed in the chiral channel. When an alumina
slab with the same size as the first PEC slab is inserted, the
transmissions remain high inside the polarization gap (see red
curves in Fig. 5.13). Note that the spectrum is slightly different from
