Study On The Dielectric Property Of C_sf And Carbon Black

Tailoring the complex permittivity is important and difficult to dielectric absorbing materials. The broad frequency band absorption of the materials depends on good frequency response characteristic. Carbon fiber and carbon black are kinds of dielectric absorbing materials with high ε′, ε″and tanδ. So it's very important to study the dielectric properties and frequency response characteristic of carbon fiber and carbon black composites. However, the variable rule and characteristic of their complex permittivity have not been clearly recognized, because of the high military privacy and sensitization.The carbon black and short carbon fibers (C_sf) were introduced into different matrixes according to different ratios to prepare composites in this paper, and the complex permittivity of the samples containing carbon black or fibers with different length in 8.2¹2.4GHz were studied. The carbon black is imbedded in wax matrix and carbon fibers are imbedded in epoxy resin. The results show that the length and content of C_sf and the content of carbon black influence heavily the complex permittivity of composites. The conclusions are shown as the following:The better length offsets the shorter fibers as the content of C_sf increases. When the content of C_sf is 0.5wt% and 1wt%, the max value of complex permittivity is 5mm and 4mm composites individually. When the content is 1.5wt%, 2wt% and 3wt%, the max value of complex permittivity gradually turns to 3mm composites. And the composites containing C_sf has certain frequency characteristic.It concludes from the dielectric data of each length composites that the complex permittivity increases at first as the C_sf content increases, and decrease subsequently. That is to say there is a peak value to each C_sf length composites. When the C_sf lengths is below 4mm, it is considered the peak content is greater than 3wt%. When the lengths of C_sf is in 5mm～7mm, the peak content is around 0.7wt%.The ε′ and ε″ of composites containing 0.5～4mm C_sf can be effectively modeled by second order polynomials (ε′,ε″=am²+bm+c), the variables a, b, c are the coefficients, m is the fiber mass filling factor.The more content of carbon black, the better frequency characteristic of composites has. When the content of carbon black is up to 25wt%, the real part and frequency decreasing amount both decease rapidly. However, the imaginary part and...