Ultra-thin Absorbers

The absorbing panel, consisting of a lossy frequency selective surface over a thin grounded dielectric slab, despite its typical resonant behavior, is able to perform a very wideband absorption in a reduced thickness [1]. The absorbing structure allows obtaining remarkable performance (15 dB in the band from 7 GHz to 20 GHz) with an overall thickness of 5 mm only. This performance cannot be accomplished by lightweight configurations employing optimized Jaumann screen or by other commercially available non-magnetic multilayer structures with a thickness lower than 9-10 mm. Despite the intrinsic periodicity of the structure, its dimension can be reduced down to a 4 by 4 array preserving almost the same absorption performances, with respect to a PEC plate of the same dimensions.

Losses in the frequency selective surfaces are introduced by printing the periodic pattern through resistive inks and hence avoiding the typical soldering of a large number of lumped resistors. The use of resistive patterns provides a dramatically simpler and lightweight structure with respect to the design including a large number of lumped resistors. The effect of the surface resistance of the FSS and dielectric substrate characteristics on the input impedance of the absorber can be efficiently analyzed by means of a circuital model. The optimal value of surface resistance is affected both by substrate parameters (thickness and permittivity) and by FSS element shape [3].

The employment of vias results a good solution to enlarge and stabilize the bandwidth of the absorber for oblique TM polarization. The result is obtained by exploiting an additional resonance due to the plasma frequency of the wire medium formed by the vias array in the dielectric substrate [3,4].

Metallic High-Impedance Surfaces (HIS) can be employed to enhance the performance of commercial radar absorbers. By replacing the metallic ground plane with a thin HIS ground an additional absorbing peak can be obtained at low-frequency without substantially affect the overall thickness [5].

References:

[1] F. Costa, A. Monorchio, G. Manara, “Analysis and Design of Ultra Thin Electromagnetic Absorbers Comprising Resistively Loaded High Impedance Surfaces” IEEE Transaction on Antennas and Propagation vol. 58, no. 5, pp. 1551-1558, 2010.

[2] F. Costa, S. Genovesi, A. Monorchio, “On the Bandwidth of High-Impedance Frequency Selective Surfaces,” IEEE Antennas Wireless & Propagation Letters, vol. 8, pp. 1341-1344, 2009.

[3] O. Luukkonen, F. Costa, C. R. Simovski, A. Monorchio and S. A. Tretyakov, “A Thin Electromagnetic Absorber for Wide Incidence Angles and Both Polarizations” IEEE Transaction on Antennas and Propagation vol. 57, no. 10, 2009.

[4] O. Luukkonen, P. Alitalo, F. Costa, C. R. Simovski, A. Monorchio and S. A. Tretyakov, “Experimental verification of the suppression of spatial dispersion in artificial plasma” Applied Physics Letters, vol.96, no. 8, 22 February 2010.

[5] F. Costa, A. Monorchio, “A Multiband Electromagnetic Wave Absorber based on Reactive Impedance Ground Planes” IET Microwave Antennas & Propagation, vol. 4, no. 11, pp. 1720-1727, 2010.