Biomedical Engineering Reference
In-Depth Information
14.3.5.3 Power-flow density distribution
To further illustrate the transparent properties of the super-
resonant Ag-based CNP, we next show the power flow density, as
determined from (14.8), for the Case 1 and 3 excitations.The power
flow density is shown in the
xy
-plane in Fig. 14.16a and 14.16b,
respectively. Specifically, the quantity 10log
10
|
S
/
1(W/m
2
)
|
is used
to represent the normalized magnitude (color) of the power flow
density, while the arrows depict its direction. The corresponding
free-space results are shown in Fig. 14.16c and 14.16d. Although
the results for the EHD(s) in free space show an expected outward
propagating power flow density, those of the two excitation cases of
the active Ag-based CNP are rather interesting. Clearly, effects due
to the presence of the CNP are in evidence for the Case 1 excitation
in Fig. 14.16(a), two source-like spots exist for the power flow: one
on the negative
x
-axis and one at its center. The CNP is seen to
act like an effective EHD, which is located at its center. The second
effective source appears to be an image-like dipole whose presence
isinducedbythefieldsassociatedwiththeEHDandCNP.Thepower
flow originating from it is seen to cancel the power flow generated
by the effective dipole located at the center of the CNP. For the Case
3 excitation, only a single source-like spot is found, this being at the
center of the CNP. However, from the outside, it is clearly seen that
the entire four-EHD and Ag-based CNP system acts like an effective
sink; the arrows outside the CNP all point inwards to the center of
the CNP. This sink-like behavior confines the power from the EHDs
to this region, that is, this power never reaches the far-field region.
ThesepowerdensityresultscorrespondnicelytotheirreducedNRR
levelsreportedinFig.14.15.SimilarresultsasthoseinFig.14.16are
obtainedfor the Case 2 excitationof the CNP.
As noted above, the dips in the NRR reported here for the active
Ag-based CNPs can be interpreted as the active CNP cloaks of the
EHDs.
This result is effectively the spherical version of the cloaking
effects discussed in [57, 58] for coated cylinders. The non-
radiating states observed here can also be connected directly the
corresponding low-frequency antenna configuration [6] and to the
transparency/cloaking effects introduced by Alu and Engheta (see,
for instance [59-61]).
