Search

This paper studies the influencing factors on the electromagnetic shielding of an inductive metallic mesh when the infrared transmission reduction of optical window caused by the mesh is less than 5%.The infrared transmission formulas of the inductive mesh are summarized,then,the electromagnetic field integral equation for the periodic structure of metallic mesh is built based on Galerkin's method in the spectral domain.The transmission and reflection coefficients are derived by the Moment of Method(MOM).After that,the electromagnetic shield effectiveness of the mesh is calculated and the effects of different line widths,periods,substrate materials,substrate thicknesses on the electromagnetic shielding of the transparent conductive optical window(with metallic mesh) are calculated and analyzed.Finally,metallic mesh samples with a line width of 12 μm,a period of 360 μm×360 μm and the surface resistance of 13 Ω,25 Ω are fabricated on a ZnS substrate by the laser direct writing figure,vacuum coating,et al..The electromagnetic shield effectiveness from 2 GHz to 18 GHz is tested by a free space method.Results indicate that the average electromagnetic shield effectiveness is more than 20 dB when the infrared transmission reduction caused by the metallic mesh is less than 2% in 8-10 μm.Experiments indicate that the optical and electrical performance of metallic mesh film is inconsistent.The main solution method is to select a thinner line width and smaller period and to reduce the surface resistance value of the mesh as low as possible at the same time.

According to the characteristics of semiconductor laser,beam plastic system of semiconductor laser is designed.First,the cylindrical lens is used to align and deflect the beam spread along the Y axis.Then the laser spread along X axis is aligned and expanded by the telescope system.Finally,transmitting laser beam is compressed using meniscus lens to realize beam shaping,reduce the beam divergence angle,improve the quality of the beam.Using ZEMAX software simulation system,the results show that the divergence angle of output beam along the X axis and the Y axis is 4.922 mrad after plastic,spot diameter is 1.2707mm,total length of plastic system is 65.6618mm,the maximum diameter of all element is 20.52mm.Both the quality of output beam and structure of the system are better than the similar products.

A Miniaturized-element Frequency Selective Surface(MEFSS) was fabricated based on the coupling mechanism between an inductive surface(metallic meshes)and a capacitive surface(wire patches).On the basis of the theory of the transmission line,the approximation formulas of the capacitance,the inductance were provided and the structural parameters of MEFSS were analyzed qualitatively.By using the vector modal matching method and the transmission characteristics of MEFSS with different geometry parameters and coupling layer electrical parameters were studied in this paper.Twelve lumped inductors and lumped capacitors were properly fabricated on the two side of a PI film by orthogonal arrangement,and the transmission characteristics of a MEFSS with a size of 240 mm×240 mm was tested by free space method.Results show that when the center frequency is 14.636 GHz,transmittance is-0.382 dB and the half transmittance bandwidth is 2.17 GHz at a TE 0° incidence.When the unit cell size is shorted,the center frequency drifts and the transmittance is decreased.The unit cell size is 0.125λ.When the unit cell size is fixed,the center frequency drifts as the increases of inductive widths,capacitance intervals and patch widths.Moreover,if the thickness of the coupling layer is increased by 0.4 mm,the center frequency lowly drifts by 1.4 GHz and transmittance is decreased by 2.6 dB.If the coupling layer relative permittivity is changed from 3.5 to 2,the center frequency highly drifts 2.8 GHz.It concludes that the FSS only with a size of 0.125 λ fabricated by coupling mechanism between inductive and capacitive surfaces is charaterized by miniaturization,wide pass-band and lower sensitive to the incident angle unit.

A centrifugal coating technology was researched to coating the uniform thickness photoresist on a concave spherical surface.Firstly,the critical factors affecting the uniform of photosensitive resist and the film forming force were investigated.Then,the centrifugal glue adhesive force during the flow state was analysed in the spherical photoresist spin coating down opening based on the hydrodynamic theory.A mathematical model to describe the relationship among the film thickness and centrifuge speed,viscosity of photoresist and the spin coating time was derived.Finally,in order to verify the correctness of the formula,some experiments of photoresist spin coating on the K9 glass concave sphere with a diameter of 120 mm,radius of 300 mm,vector height of 12.5 mm were performed.The experimental results certify that the proposed theory is consistent with the actual situation well.On the theoretical analysis,the uniform film thickness on the inner surface of an entire sphere can be obtained with the disalignment of photoresis pin coating axis and the main axis of electric engine.When the viscosity of photoresist is 1.1~1.9 Pa and the speed of main axis is 3 000-6 000/r·min-1,the uniform film thickness is 0.5~1 μm on a concave sphere.

On the basis of Y loop elements,a new method to set circular slots on the periodic element to improve the narrow bandwidth of a Frequency Selective Surface(FSS) structure was presented.The FSS structure was calculated by Galerkin's method in the spectral domain when the optimum radius was set to be 0.5 mm and the number of the circular slots to be 12,and the transmittance in the resonance frequency of 10 GHz has increased by 0.11 dB.The plane sample was fabricated by depositing coatings and a lithograph technology,and obtained measured values are in good agreement with the calculated values.The results show that the transmittance of this structure is about-0.62 dB at the resonance frequency,which has increased by 0.21 dB under the perpendicularity incidence compared with that of the Y loop without circular slot.Furthermore,the transmittances at TE 30°and 45°incidence are-0.66 dB and-0.81 dB,respectively,which has increased about 0.32dB and 0.27dB compared with those from the Y loop without circular slots.The bandwidth difference between the two structures is negligible,which are about 1 GHz and 0.8 GHz under TE 30°and 45°incidence,respectively.These results indicate that this method is an effective way to improve the transmittance of large periodic FSS structure at the resonance frequency.

In order to increase the second harmonic generation conversion efficiency,the periodic optical superlattice was sandwiched with nonpoled and nonlinear media with finite and variable width,which can bring about the significant modulation for the fundamental wave with changing the thickness of the additional media.It is found that: the conversion efficiency increases or reduces when the energy of fundamental wave increases or reduces;it can be enhanced significantly when transmission resonance(the rate of transmission obtains 1) takes place;compared with the conventional sample(the optical superlattice embedded in infinite and nonlinear media),the second harmonic generation conversion efficiency is enhanced 1.5 times at most;for the practical sample(the optical superlattice embedded in air),it can be enhanced 3.3 times at most.So the second harmonic generation conversion efficiency can be enhanced apparently by the transmission resonance.

The effective refractive index of finite one-dimensional photonic crystal(PC) was investigated.Firstly,the concept of a complex effective refractive index for the structure of finite periodic PC was introduced.Then the complex transmission coefficient was calculated by using the transfer matrix method.On this basis,analytical expression of the effective refractive index could be derived.Considered by the spatial structure of photonic crystal and the existence of photonic band-gap,the characteristics of photonic band-gap structure,the effective refractive index,optical thickness,physical thickness and the center wavelength were investigated.It is found that amplitude of oscillation for the effective refractive index can be effected by the ratio of refractive index of the basic periodic structure and the physical thickness of the basic periodic structure of PC;Center wavelength has no effect on the effective refractive index.