Design And Property Research Of Structure And Function Integration Carbon Fiber Composite With Controllable Shielding Effectiveness

With the development of wireless communication technology brings electromagnetic pollution to human beings and electromagnetic interference to sophisticated electronics.The use of stealth technology and special communication become important parts of national defense.Shielding products with high shielding effectiveness,good absorption loss,controllability and integration of structure and function become the research focus at this background.This paper focus on the design and manufacture of electromagnetic shielding products with the latest developing requirements,which can not only reduce electromagnetic pollution and interference,but also achieve variable shielding performance and integration of structure and function.Carbon fiber with good mechanical property and electrical conductivity was used as the functive.The anisotropy of carbon fiber and its products were used to achieve variable shielding performance.The shielding product can be divided into main body with aperture and rotatable unit.The conductivity,dielectric constant,shielding effectiveness and power constituent parts of carbon fiber felt based multilayer composite,carbon fiber felt-glass fiber felt based sandwich composite,carbon fiber yarn,carbon fiber unidirectional cloth and carbon fiber woven cloth based composites with different orientation angle were studied.Morphology analysis was used to study the microstructure.Carbonyl iron powder was used as the radio wave absorber.When orientation angle increased from 0°to 90°,strong axial conductive networkwas replaced by weak circular conductive network for carbon fiber felt,continuous unidirectional structure turned into discrete cross sections for carbon fiber yarn and orthogonal structure changed into linear structure for carbon fiber fabric.Carbonyl iron powder was evenly dispersed in carbon fiber felt based composites and concentrated distribution in carbon fiber cloth based composites.Electric conductivity and shielding effectiveness decreased when orientation increased from 0°to 90°.The variation scope of conductivity and shielding effectiveness of carbon fiber felt/epoxy resin composites were[30.1-147.2]Sm^-1 and[13.5-59.9]dB.For carbon fiber cloth/epoxy resin composites,these variation scopes were[0.07-4.2]Sm^-1 and[8.1-55.1]dB.Carbon fiber felt-glass fiber felt sandwich structure will increase the variation scope of shielding effectiveness by increasing the maximum value and decreasing the minimum value.The use of carbonyl iron powder decreased the variation scope and increased the absorption loss.With increase in orientation angle,reflected power decreased and absorbed power increase.For carbon fiber felt based composites,absorbed power could get maximum value when orientation angle was at specific value.For carbon fiber yarn based composites,absorbed power got maximum value and changed little when orientation angle was beyond specific value.Shielding effectiveness decreased when aperture was made in composites and rapidly decreased when the size of aperture was close to 1/4 wavelength.For sample with round aperture,shielding effectiveness decreased from 74.8dB to 17.5dB at 10GHz when diameter increased from 2.0mm to 10.0mm.For sample with square aperture,shielding effectiveness decreased from 67.5dB to 13.0dB at 10 GHz when side length increased from 2.0mm to 10.0mm.For sample with rectangular aperture with side length 12.0mm,the shielding effectiveness could become less than 5.0dB.For sample contain 6.0mm×12.0mm aperture and 7.5mm rotatable unit,the shielding effectiveness can be regulated continuously from about 35.0 dB to 75.0 dB.The shielding effectiveness variation scope can be regulated by the shape and size of aperture and the structure of rotatable units.The artificial circuits of carbon fiber felt and carbon fiber yarn were analyzed.Shielding models of multilayer structure and sandwich structure were made to calculate shielding effectiveness of sample with random orientation angle and match the tested value.Simulation software was used to simulate the shielding performance to guide the experiments.The advantages and disadvantages of different carbon fiber products were analyzed to build theoretical basis and production experience for the design and manufacture of carbon fiber based shielding composites with integration of structure and function.By contorting the orientation angle,carbon fiber based composites can get highest shielding effectiveness to prevent institution,get maximum value of absorbed power to reduce electromagnetic pollution and achieve variable shielding effectiveness to satisfy the developing requirements from military fields.