V.I. Ponomarenko – Dr.Sc.(Phys.-Math.), Professor, 
Department of Experimental Physics, V.I. Vernadsky Crimean Federal University (Simferopol) E-mail: vponom@gmail.com

I.M. Lagunov – Senior Lecturer, 
Department of Experimental Physics, V.I. Vernadsky Crimean Federal University (Simferopol)
E-mail: lagunov.igor@gmail.com

Various film structures are widely used in electromagnetic wave absorbers (EWS) in the technique of ultrahigh frequencies, equipment of anechoic chambers. Over time, on such coatings there are various defects: cracks, islet detachment, sticking of side materials, etc. In cases where the coating is applied to moving objects, exposed to air flow, precipitation, ambient temperature drop, degradation of the coating increases and changes occur in the material, leading to deterioration of the main characteristics of the EWS – power reflection coefficient (CO) in the operating wavelength range. We have carried out the modeling of the effect of defects in the form of cracks on the frequency dependence of CO-EWS, which is the main purpose of the article. Currently, the scientific literature does not provide any assessment of the impact of cracks on the characteristics of EWS. 

The simulation is carried out for two types of EWS – dielectric layer and magnetic layer located on a metal mirror. In this case, it is assumed that in the absence of cracks, EWSs are ideal, that is, have a CO equal to zero, and the crack system has a periodic character with a period, both along the axis x and along the axis y. A plane electromagnetic wave of length , polarized along the axis y, falls on the considered structure along the axis z . The variable parameters are wavelength , crack width  and crack spacing l .

It is assumed that the parameter p  l is small compared to one.

The article shows that the investigated structure with small cracks can be considered as a homogeneous layer with effective material

               constants ef and ef calculated by formulas   ef   2 1 ,   ef   2 1, applying the calculation to the formula for

                                                                                                                  l                                 l

                                                                                                                    2d           

          the reflection coefficient to the power of a single-layer coating: itg                  0 .

                                                                                                                                   

The results of numerical calculations obtained dispersion characteristics: the real and imaginary parts of the dielectric constant of an ideal non-magnetic layer  ,  and a layer with cracks at p  0.02 ef , ef ; real and imaginary parts of the magnetic permeability of the ideal magnetic layer  ,  , and a layer with cracks at p  0.02 ef , ef . It follows from the obtained dispersion characteristics that for a non-magnetic layer, the presence of cracks leads to a decrease in the real and imaginary components of the effective dielectric permeability compared to the ideal layer without cracks, and this decrease is greater the longer the wavelength. The effect of cracks on the magnetic permeability of the magnetic radioabsorbing layer leads to an increase in the real part of the magnetic permeability at  6 cm and a decrease in the imaginary part in the entire wave range, compared with the ideal layer.

It is shown that the influence of gaps leads to an increase in the reflection coefficient of the power up 0.08…0.10 with an increase in the ratio of the crack width to the period from zero to 0.02. For non-magnetic sew uncoordinated the influence of the gaps increases with increasing wavelength, whereas for magnetic sew it decreases.

The results of the work can be used to assess the impact on the characteristics of EWS defects such as cracks that have arisen under the influence of climatic and mechanical factors.

1. Li W., Chen M., Zeng Zh., Jin H., Pei Y., Zhang Zh. Broadband composite radar absorbing structures with resistive frequency selective surface: Optimal design, manufacturing and characterization. Composites Science and Technology. 2017. V. 145. P. 10−14.
2. Alimin B.F. Sovremennye razrabotki poglotitelei elektromagnitnykh voln i radiopogloshchayushchikh materialov. Zarubezhnaya radioelektronika. 1989. № 2. S. 75−82. (In Russian).
3. Bulanov N.M., Vorobei V.V. Tekhnologiya raketnykh i aerokosmicheskikh konstruktsii iz kompozitsionnykh materialov. M.: MGTU. 1998. 516 s. (In Russian).
4. Ponomarenko V.I., Mirovitskii D.I. Opredelenie parametrov soglasuyushchikh sloev v mnogosloinykh strukturakh. Radiotekhnika. 1988. T. 43. № 12. S. 58−60. (In Russian).
5. Budagyan I.F., Mirovitskii D.I., Ponomarenko V.I. Reshenie transtsendentnykh uravnenii, voznikayushchikh v zadachakh elektrodinamiki, putem svedeniya k differentsialnym. Radiotekhnika. 1983. T. 38. № 2. S. 66−69. (In Russian).
6. Smit Ya., Vein KH. Ferrity. M.: Izd-vo inostrannoi literatury. 1962. 286 s. (In Russian).
7. Rytov S.M. Elektromagnitnye svoistva melkosloistoi sredy. ZhETF. 1955. T. 29. № 5. S. 605−611. (In Russian).