In a recently published report, Sen and Das [5] proposed a frequency tunable low-cost microwave absorber to obtain tunable absorption spectra. In this paper, we justify that the proposed device is not an absorber. It is observed that the total absorption rates merely reach 2% and 14.85% for the air gaps of 3.5 mm and 7.5 mm, respectively, when the co- and cross-polarization reflections are taken into account in the reported device. Obviously, The original authors erroneously consider a polarization converter as an absorber, and the obvious errors can be found in their paper.
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doi:10.1364/OE.26.001681
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5. Sen, G. and S. Das, "Frequency tunable low cost microwave absorber for EMI/EMC application," Progress In Electromagnetics Research Letters, Vol. 74, 47-52, 2018.
doi:10.2528/PIERL17120601
6. Liu, X. B., J. S. Zhang, W. Li, R. Lu, L. M. Li, Z. Xu, and A. X. Zhang, "Three-band polarization converter based on reflective metasurface," IEEE Antennas Wireless Propag. Lett., Vol. 16, 924-927, 2017.
doi:10.1109/LAWP.2016.2614686
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doi:10.1063/1.4868076
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