Biomedical Engineering Reference
In-Depth Information
Table 14.1
Minimum NRR values
for Case 1, 2, and 3 excitations
Case
NRR [dB]
Wavelength
λ
[nm]
1
−
12.7
594.9
2
−
25.8
593.2
3
−
27.1
593.2
distinctminimumNRRvalues,themaximumNRRinallcasesoccurs
atthesamewavelengthof502.1nmandhasapproximatelythesame
magnitude, around 62.5 dB. Table 14.1 summarizes the minimum
NRR values and the wavelengths at which they are attained in the
three excitation cases. The dips in the NRR values found in Fig.
14.15 can be said to correspond to non-radiating, or transparent,
orcloakedstates,wherethequantumemitters(EHD)areeffectively
cloaked orjammed to a far-field observer.
Although the active Ag-based CNP acts as a super-resonant CNP
at the wavelength of 502.1 nm, where the peak in the NRR in
Fig. 14.15 is observed, this is not so at the wavelengths found
in Table 14.1 at which the respective dips in NRR are found.
Nevertheless, it is interesting to observe how an active CNP, initially
designed to be super-resonant at a certain wavelength, can in fact
significantly suppress the EHD(s) radiation at another wavelength.
The fact that this suppression is indeed gain-assisted was
confirmed by examining the present CNP configuration in the cases
in which the silica nano-core is first lossless and then lossy (and
passive), although the material parameters of the silver nano-shell
remainedunchanged.Tothisend,weexpressedthesilicanano-core
permittivity as
ε
1
=
ε
1
−
j
ε
1
=
2.05
ε
0
(1
−
j
tan
δ
e
), where the loss
tangent is tan
δ
e
=
ε
1
/
(2.05
ε
0
), and examined the properties of the
resulting Ag-based CNP for four cases: 1) tan
δ
e
=
0, 2) tan
δ
e
=
0.01, 3) tan
δ
e
=
0.1 and 4) tan
δ
e
=
1. For all excitations: Cases, 1,
2, and 3, of the CNP, the case of a lossless silica nano-core provides
thelowestNRRvalues.FortheCase1excitation,theNRRreducesto
about11dB,whichiscomparabletotheactiveCNPdesign.However,
the two remaining passive cases result in a NRR value around -16
dB, which are still orders of magnitude above the minimum values
obtainedfor the corresponding active Ag-basedCNP.
