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Spectral dependence of reflectance and transmittance of heat mirrors such as TiO
2
/Ag-alloy/TiO
2
structure, base on the above design parameters, were simulated for different thickness of Ag-alloy layer. It is clear
from Fig. 5 and Fig. 6 that as the Ag-alloy layer thickness increases, the transmittance in the visible region (
T
vis
)
decreases while IR reflectance (
R
IR
) increases. An ideal heat mirror is such that it has
T
vis
=1.0 and
R
IR
=1.0. This
ideal behavior cannot be achieved in practice because when the Ag-alloy film thickness is changed, one of the two
T
vis
and
R
IR
increase while the other one decreases. Therefore, a compromise is needed. Ag-alloy film thickness in
the range of 20-25 nm seems to be a reasonable compromise as for this range of thickness; D/Alloy/D system have
values of greater than 65% for both
T
vis
and
R
IR
.(Fig. 7)
Conclusion
The feasibility study to use Ag-alloy thin film as an IR-reflected layer of heat mirror with D/A/D
structure was investigated by simulation technique. The optical constants of Ag-alloy and TiO
2
thin films with
a thickness of 30 nm which deposited on slide glasses by DC unbalanced magnetron sputtering were evaluated
by TFCalc. The optical constant of Ag-alloy thin film at 500 nm are
n
= 0.05 and
k
= 2.92 while TiO
2
thin film at
500 nm are
n
= 2.38 and
k
= 0. Spectral dependence of reflectance and transmittance of heat mirrors were
simulated for different thickness of Ag-alloy layer. The Ag-alloy layer thickness increases, the transmittance in the
visible region (
T
vis
) decreases while IR reflectance (
R
IR
) increases. As the result Ag-alloy thin film could
potentially serve as an IR-reflected layer in the system of the heat mirror with D/Alloy/D structure.
Acknowledgments
The financial support from the Energy Policy and Planning Office, Ministry of Energy, Thailand, is
gratefully acknowledged.
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