Anomalously Large Absorption of Electromagnetic Radiation …
7
G = G 1 −
T
2
1 e
−i4π h/λ 0
1 + G 1 e −i4π h/λ 0
,
(8)
where λ 0 = λ/
1 − (λ/2a) 2 —the wavelength in the waveguide, and a = 7.2 mm—
the size of the wide wall of the waveguide.
Knowing G and using (5), we calculated R for the shorting case.
Lines 1 and 2 in Fig. 2 correspond to the two extreme values of the power reflection
coefficient (with β = 1.3 and β = 1.8) for the case of the matched load.
Curves 3 and 4 correspond to the two theoretical values of R as a function of
frequency, calculated by (5) and (8) for the two extreme values of β (curve 3 for β
= 1.3, curve 4 for β = 1.8) for the case of shorting.
As shown in Fig. 2, the calculations for the case of shorting did not give satisfactory
agreement with the experimental results. The theoretical power reflection coefficients
(curves 3 and 4) are in 3÷5 times higher than obtained from the experiment (black
curve).
Moreover, the theoretical reflection coefficient in the shorting case decreases with
increasing frequency, which corresponds to the expected reduction of reflection with
frequency increasing.
In this case, λ 0 /4 increases and approaches the value of h, and equality with h
corresponds to a theoretical minimum of reflection.
4 Conclusion
Experimental data of the power reflection coefficient obtained for the gold film
thickness of 10 nm at a distance 1 mm from the shorting reflecting surface were
significantly less than that were calculated according to traditional theory in the
frequency band 26÷37.5 GHz.
Such a discrepancy was probably due to the absence of galvanic contact between
the gold film and the walls of the waveguide. This leads to the effect of an islet film
when there is no continuous conductivity over its entire surface. In this case, in the
calculations, it is necessary to take into account the reactive resistance introduced by
such kind of film.
The absorption was fixed on a level of 90% and almost not depended on frequency
that can significantly expand the ability to use such films in practice [4].
References
1. Saville P (2005) Review of radar absorbing materials. Tehnical Memorandum, DRDC Atlantic,
TM 2005-003, January 2005
2. Andreev VG, Vdovin VA, Voronov PS (2003) An experimental study of millimeter wave
absorption in thin metal films. Techn Phys Lett 29:953–955
7
G = G 1 −
T
2
1 e
−i4π h/λ 0
1 + G 1 e −i4π h/λ 0
,
(8)
where λ 0 = λ/
1 − (λ/2a) 2 —the wavelength in the waveguide, and a = 7.2 mm—
the size of the wide wall of the waveguide.
Knowing G and using (5), we calculated R for the shorting case.
Lines 1 and 2 in Fig. 2 correspond to the two extreme values of the power reflection
coefficient (with β = 1.3 and β = 1.8) for the case of the matched load.
Curves 3 and 4 correspond to the two theoretical values of R as a function of
frequency, calculated by (5) and (8) for the two extreme values of β (curve 3 for β
= 1.3, curve 4 for β = 1.8) for the case of shorting.
As shown in Fig. 2, the calculations for the case of shorting did not give satisfactory
agreement with the experimental results. The theoretical power reflection coefficients
(curves 3 and 4) are in 3÷5 times higher than obtained from the experiment (black
curve).
Moreover, the theoretical reflection coefficient in the shorting case decreases with
increasing frequency, which corresponds to the expected reduction of reflection with
frequency increasing.
In this case, λ 0 /4 increases and approaches the value of h, and equality with h
corresponds to a theoretical minimum of reflection.
4 Conclusion
Experimental data of the power reflection coefficient obtained for the gold film
thickness of 10 nm at a distance 1 mm from the shorting reflecting surface were
significantly less than that were calculated according to traditional theory in the
frequency band 26÷37.5 GHz.
Such a discrepancy was probably due to the absence of galvanic contact between
the gold film and the walls of the waveguide. This leads to the effect of an islet film
when there is no continuous conductivity over its entire surface. In this case, in the
calculations, it is necessary to take into account the reactive resistance introduced by
such kind of film.
The absorption was fixed on a level of 90% and almost not depended on frequency
that can significantly expand the ability to use such films in practice [4].
References
1. Saville P (2005) Review of radar absorbing materials. Tehnical Memorandum, DRDC Atlantic,
TM 2005-003, January 2005
2. Andreev VG, Vdovin VA, Voronov PS (2003) An experimental study of millimeter wave
absorption in thin metal films. Techn Phys Lett 29:953–955