New metallic mesh designing with high electromagnetic shielding

Transcription

1 MATEC Web o Conerences 189, (018) MEAMT New metallic mesh designing with high electromagnetic shielding Longjia Qiu 1,,*, Li Li 1,, Zhieng Pan 1,, Bin Zhu 1,, Xiangbing Sun 1,, and Wei Yan 1, 1 Electro-Optical Equipment Research Institute o AVIC, Luoyang,47105, China Science and Technology on Electro-optic Control Laboratory, China Abstract. Metallic mesh is an important technic approach to realize the stealth o the electro-optical radar. This paper demonstrates the designing thoughts o metallic mesh, and in the conclusion, this paper achieves the integrated design method by analysing electromagnetic shielding, permeability and so on. By using this method, a metallic mesh designing with high electromagnetic shielding is designed, which will make the aircrat gain better stealth eect in combat. 1 Introduction The ighter is an important weapon to implement long-range precision strike, and it must have good penetration resistance and survivability. As an important electro-optical detection equipment or aircrat penetration, electro-optical radar is also an important scattering source or aircrat exposed to the outer surace o aircrat, so it is necessary to take stealth measures to reduce its RCS. The way to realize the stealth optical window is usually three kinds: one is to use the absorbing material in the structure surace o the optical window, the other is to change the shape design o the optical window structure, and the third is to adopt the metallic mesh to the optical window to shield the radar wave rom the optical window. The metallic mesh can shield the electromagnetic waves rom the optical window, because o its submillimetre scale cycle and micron magnitude line width, it shows dierent diraction characteristics when the electromagnetic waves at dierent wavelengths are incident. In the microwave band, the electromagnetic wavelength is longer than the mesh cycle, the metallic mesh at this time is the sub wavelength structure, and the posterior diraction plays the leading role, most o the electromagnetic waves are relected, the metallic mesh has electromagnetic shielding characteristics; In the inrared and visible wavelengths, the electromagnetic wave is less than the mesh cycle, the metallic mesh at this time is the macroscopic structure, the orward diraction plays a leading role, most o the electromagnetic wave transmission to the metallic mesh presents light properties. When a metallic mesh with a high requency iltering unction o electromagnetic wave is loaded on the optical window, the optical window is still transparent to the visible and inrared light, but or the length o the microwave and the radio wave, the optical window is equivalent to the metallization process, which realizes the isolation o electromagnetic waves inside and * Corresponding author: cubitcubit@16.com The Authors, published by EDP Sciences. This is an open access article distributed under the terms o the Creative Commons Attribution License 4.0 (

2 MATEC Web o Conerences 189, (018) MEAMT outside the optical window. To prevent external electromagnetic intererence and internal electromagnetic leakage, especially when the optical window with metallic mesh is loaded on the aircrat with shape conormal, the strong relection cavity eect or optical window on the radar band can be avoid, which achieve a signiicant reduction o radar signature signal. The main advantages o metallic mesh requency iltering technology or optical window electromagnetic shielding are: by selecting the appropriate mesh cycle and linewidth, and controlling the resonant requency o the electromagnetic wave, a wide-band electromagnetic shielding with a wavelength greater than millimetre wave can be achieved, and the millimetre wave can be passed through but only shielded rom the microwave band [1], and the same control may be achieved to the light transmission band. At the same time through the visible and inrared bands, can also only through the visible band and shielding inrared band []. Design technology or stealthy optical window with metallic mesh.1 Analysis o electromagnetic shielding characteristics or metallic mesh When the electromagnetic ield that changes over time is exposed to the surace o the conductive body, in which the induced current will be produced, this induced current will produce a new electromagnetic ield, the new electromagnetic ield is in the opposite direction with and the original one, and oset the original electromagnetic ield changes, this phenomenon is Faraday electromagnetic induction phenomenon. It indicates that the conductive shielding body has the ability o attenuation the electromagnetic wave intensity [3]. The equivalent circuit method is proposed by Ulrich to analyse the photoelectric properties o metallic mesh, a metallic mesh ilm can be equivalent to the circuit which composed by electrical impedance (inductance, capacitance, resistance). It indicates that the metallic mesh is a highly eicient and transparent conductive ilm [4], as shown in igure 1. Fig. 1. Metallic mesh diagram. In this paper, the integral equation is constructed by using the metallic mesh ilm with periodic array element, the spectral domain Galerkin method is used as the basic analysis method, the transmission coeicient and the relection coeicient o the metallic mesh are calculated by the moment method, and the electromagnetic shielding eiciency is obtained. Because o the surace resistance o metallic mesh, the spectral domain equation o the ideal conductor is modiied, and the theoretical analysis and experimental study are carried out on this basis [5]. In ree space, when the thickness o the metallic mesh is much smaller than the line width, and the line width is much smaller than the line cycle, when T<<a,a<<g, the

3 MATEC Web o Conerences 189, (018) MEAMT shielding eect or the vertical incident radar waves, metallic mesh has normalized admittance: y a g ln(sin ) ( ) In equation (1), is normalized resonant requency. Because the mesh cycle g is approximately equal to the wavelength o the resonant wave, 0 1, =g/λ, λ is the wavelength o radar signal. At present, the requency range o radar signal is rom 0.05~40GHz, the range o requency domain is widely. Generally, the commonly used radar signal wavelength is 16.7mm~150mm, the mesh period studied in this paper is 00 μ m ~400 μ m, so when λ > >g, the normalized admittance is approximately: g a y ln(sin ) g () The transmittance o the metallic mesh with vertical incident wave is: 4y T(0,0) 1 4y For GHz ~18GHz Radar bands,, the equation (3) can be approximated as: T 4g a ( 0,0) ln(sin ) The shielding actor (DB) is: S 10log10 T 0 g From the above we can see that: Electromagnetic shielding eectiveness decreases with cycle g and increases with line width a; The metallic mesh cycle g has a signiicant eect on the electromagnetic shielding coeicient, and the eect o line width a is less. (1) (3) (4) (5). Analysis o the light transmittance characteristics or the metallic mesh In the optical requency range, the metallic mesh eects as a diraction grating, producing multistage diraction or the incident light, and the transmittance o the mesh is equivalent to the sum o the total transmittance o each diraction sequence, which can be approximated as [6]: () (6) For IR imaging applications, only the level 0 o the diraction sequence is eective, while the other levels have less inluence on imaging than the level 0, which can be negligible. It is usually possible to use scalar diraction theory to analyze the attenuation o optical system transmittance, while the point diusion unction applied to metallic mesh can be expressed by the square modulus o the pupil unction with Fourier transorm, which 3

4 MATEC Web o Conerences 189, (018) MEAMT ignoring the inluence o the optical path dierence, and the transmittance or the pupil unction o the optical system is as ollows: x x x x t( x, y) [ rect(, )** ( x ng, y mg)] rect(, ) g a g a Ng Ng m n (7) In equation (7): ** represents two-d convolution; N is the number o mesh irradiated by the incident light; n, m is integer sequence (...,-,-1,0,1,,...). ); rect (x, y) is two-d rectangular transmittance unction. I the diraction kernel area o the metallic mesh is assumed to be a circle which area is (Ng), then the radiation distribution o the point diusion unction or the optical system o metallic mesh is as ollows: I(, ) x y n( g a) sin c g a4 g g4 Ng m sin c ( y g m( g a) Ng n sin c sin c ( x ) g g (8) Use θx, θy replace the cosine angle o the diraction light with the x, y axes, λ is wavelength: sin( x) sin c( x) x (9) When, The peak value o the complex diraction sequence generated by the incident light through the metallic mesh is equal to the peak value o the point diusion unction o the optical system without the mesh, then any sequence o the diraction sequence, it takes the ratio o the energy or the occupied point diusion unction is: 4 E( n, m) g a n( g a ) m( g a ) sin c sin c 4 E ps g g g With metallic mesh, the energy ratio o the center level 0 is: T 0 E E (0,0) g a g The duty ratio o metallic mesh is in square relationship with (). From the above deduction we can see that: The transmittance increases with the cycle g, and decreases with the line width a increase; The cycle g has a greater impact on the transmittance, and the line width a eect is less. 3 Design o a new high electromagnetic shielding metallic mesh (10) (11) 4

5 MATEC Web o Conerences 189, (018) MEAMT Design o metallic mesh with dierent conigurations In order to meet the requirements o using, while maximizing the stealth eect o the aircrat, the irst thing in metallic mesh designing is to determine the transmittance to meet the requirements o indicators, on this basis, as ar as possible to obtain a higher electromagnetic shielding eiciency. Based on the typical square (igure ), hexagonal (igure 3) and circular metallic mesh (igure 4), this paper presents a new type o metallic mesh (igure 5), which improves the eiciency o electromagnetic shielding under the condition o keeping the light transmittance unchanged. In this paper, the comparative analysis o the metallic mesh coniguration is shown as ollows: Fig.. Square metallic mesh diagram. Fig. 3. Hexagonal metallic mesh diagram. Fig. 4. Circular metallic mesh diagram. Fig. 5. A new metallic mesh diagram. 3. Settings o simulation condition Electromagnetic shielding simulation conditions are setting as ollows: Optical material: plain glass; Optical swatch size:99mm 87mm 1mm; Radar wave requency:1ghz~18ghz. 3.3 Simulation results o electromagnetic shielding eectiveness or dierent conigurations o metallic mesh According to the above simulation condition, and adjusting the metallic mesh cycle, the inrared transmittance o each coniguration metallic mesh is equivalent, and the shielding perormance is simulated and compared, the results are shown in the ollowing table. 5

6 MATEC Web o Conerences 189, (018) MEAMT Table 1. Comparison o simulation results or electromagnetic shielding eectiveness with dierent conigurations o metallic mesh. Coniguration Transmittance Level 0 Transmittance Shielding Mean DB Shielding Maximum db Shielding Minimum db Square T square T square- 0 S square-mean S square-max S square-min Hexagonal T square T square- 0 S squaremean Circular T square T square- 0 S square-mean New coniguration S squaremax S square-max-.10 S squaremin+0.67 S square-min Tsquare T square- 0 Ssquaremean Ssquaremax+0.98 Ssquaremin It is shown rom the above table that the electromagnetic shielding eiciency is urther improved by the new type metallic mesh with the equivalent inrared transmission. 4 Summary In summary, it can be ound that the changes o metallic mesh cycle and line width parameters, the metallic mesh electromagnetic shielding eiciency and the impact o inrared transmittance is more signiicant, and the metallic mesh coniguration changes has less inluence or the metallic mesh electromagnetic shielding eiciency and inrared transmittance. In this paper, we proposed a new coniguration metallic mesh which has improved the eiciency o electromagnetic shielding compared with other typical metallic mesh, and it has the equivalent inrared transmittance with others. This new metallic mesh can make the aircrat gain better stealth eect in combat. Reerences 1. Analysis and design o transparent conductive coating and ilters. KOHIN M, WEIN S J, TRAYLOR J D, et al. Optical Engineering. (1993). Inrared thin ilms. SHIMSHOCK R P. Proceedings o SPIE the International Society or Optical Engineering. (1991) 3. Feng Xiaoguo, Fang Liang, Sun Lianchun. Design and abrication o metal grating ilm Structure [J]. Optics and precision Engineering, (005), 13(1): pp Gao Jinsong, Sun Lianchun, Zheng Xuanming. etc. Inrared transparent conductive metal grating ilm [J]. Optics Technology, (001), 7(6): pp Shen Zheneng, Feng Xiaoguo. Electrical inductive mesh ilm or electromagnetic shielding o inrared windows [J]. IR technology, (008), 8(30) : pp Fan Zhigang. Photoelectric test Technology [M]. Beijing electronic industry press, (004). 6