Advanced Carbon Fiber Composite Materials for Shielding and Antenna Applications

Due to the low weight, ease of fabrication, low cost, high stiffness, high thermal and electrical conductivity, advanced carbon fiber composite (CFC) material is one of the most desirable materials which have been considered recently in the aerospace, electronic, and infrastructure industry. This thesis examines the use of CFC materials for electromagnetic field shielding and antenna applications. Using a suitable electromagnetic model of composite materials, we evaluate the shielding effectiveness (SE) and other EM properties of composites paying attention to antenna design. Analytical and simulation results are compared with experimental data. Two kinds of composite materials are investigated, namely reinforced continuous carbon-fiber (RCCF) composites and carbon nanotube (CNT) composites. For analytical SE analysis of multilayer RCCF composites, the material shows anisotropic behavior along the direction of the fibers, and we employ the transmission matrix method in conjunction with the anisotropic properties of each layer. The shielding performance of composites is also experimentally investigated. In order to enhance the conductivity of an RCCF composite, a small volume fraction of multi-walled carbon nanotubes (MWCNTs) is added to the RCCF material. We investigate the SE of the proposed MWCNT “nanocomposite” over a wide frequency band up to 26.5 GHz. The effect of aspect ratio on shielding performance is addressed as well. The effective conductivity of the nanocomposites was determined over the frequency range of interest. The use of RCCF and single-walled carbon nanotube (SWCNT) composite is investigated for building antennas, by replacing the metal with CFC. We use an RCCF composite to build resonant and wideband antennas. The effect of the conductivity tensor of RCCF composite on the antenna performance is addressed. We also study the performance of a microstrip patch antenna with the ground plane made of RCCF composite. As one of the most highly-conductive composite materials, single wall carbon nanotube (SWCNT) buckypapers are used to build composite antennas. A new fabrication method is proposed to print arbitrarily-shaped full-composite SWCNT antenna on any type of substrate. Various types of SWCNT antennas are fabricated for different antenna applications, namely UHF-RFID, WLAN, UWB, and mm-wave applications. Good agreement is observed between simulation and experimental results for all the aforementioned composite antennas. Using the spectral domain method, the Green’s function is obtained for an infinitesimal HED on a dielectric slab over a CFC ground plane. Due to the high conductivity, CFCs are modeled using a surface impedance. The expressions for the electric field components are derived. The numerical integration details particularly dealing with low-converged tail of the integrand for fields at the air-dielectric interface are addressed. Numerical results based on this method compare well with results based on a time-domain finite integration technique. The effect of conductivity and anisotropy of the composite ground plane on electric field is investigated

Green's Function of a Dielectric Slab Grounded by Carbon Fiber Composite Materials

The exact solution is obtained for Green's function of an infinitesimal horizontal electric dipole on a dielectric slab backed by a ground plane of carbon fiber composite (CFC) material. We consider both reinforced continuous carbon fiber (RCCF) CFC and carbon nanotube (CNT) CFC. RCCF is modeled by an electrically anisotropic surface impedance tensor whereas CNT is modeled as isotropic. The spectral domain method is used and the asymptotic part of the integrand is treated by adding and subtracting that for a perfect electric conductor ground, leaving a rapidly-converging term for numerical integration. Numerical results based on this method compare well with results based on a time-domain finite integration technique. The effect of conductivity and anisotropy of the composite ground plane on electric field is investigated

Compact Multiband Planar Antenna for 2.4/3.5/5.2/5.8 GHz Wireless Applications

A low-profile planar monopole antenna is proposed to operate within WLAN and WiMax frequency bands. The antenna is composed three radiating elements together with an additional strip to control the antenna performance. An electromagnetic (EM) model of the proposed antenna is developed in CST Microwave Studio for numerical analysis and optimization. The principle of operation and parametric study on the antenna performance are provided. Two dual-band and triple-band antennas are fabricated and experimental results are presented

Performance of microstrip patch antenna on a reinforced carbon fiber composite ground plane

Using mass-produced multiwall carbon nanotubes (MWCNTs) from different providers, we have fabricated nanocomposites with high and nearly constant shielding effectiveness (SE) over a wide frequency range up to 26.5 GHz. The MWCNT weight fraction and sample thickness were lower than 10% and 2 mm, respectively. The fabrication process and percolation curves are described. A high dc conductivity of 239.1 S/m was achieved at an MWCNT loading of only 8% by weight. The effect of aspect ratio on shielding performance is addressed. By comparing the measured SE of the composite with predictions from a model of the measurement setup using Microwave Studio, the effective conductivity of the nanocomposite was determined. Since the thickness is very important for shielding analysis, the SE/unit thickness diagram was calculated by using the effective parameters of samples. The results were verified experimentally by measuring the SE of samples with different thicknesses

Carbon Nanotube Composites for Wideband Millimeter-Wave Antenna Applications

In this paper, we explore using carbon nanotube (CNT) composite material for wideband millimeter-wave antenna applications. An accurate electromagnetic model of the composite antenna is developed using Microwave Studio for numerical analysis. Good agreement between computed and measured results is shown for both copper and CNT antennas, and their performance is compared. The CNT antenna shows stable gain and radiation patterns over the 24 to 34 GHz frequency range. The dispersion characteristics of the CNT antenna show its suitability for wideband communication systems. Using a quarter-wave matched T-junction as feed network, a two-element CNT antenna array is realized and the performance is compared with a copper antenna. The housing effect on the performance of the CNT antenna is shown to be much lower than for the copper antenna

Multiwall Carbon Nanotube-Epoxy Composites With High Shielding Effectiveness for Aeronautic Applications

Using mass-produced multiwall carbon nanotubes (MWCNTs) from different providers, we have fabricated nanocomposites with high and nearly constant shielding effectiveness (SE) over a wide frequency range up to 26.5 GHz. The MWCNT weight fraction and sample thickness were lower than 10% and 2 mm, respectively. The fabrication process and percolation curves are described. A high dc conductivity of 239.1 S/m was achieved at an MWCNT loading of only 8% by weight. The effect of aspect ratio on shielding performance is addressed. By comparing the measured SE of the composite with predictions from a model of the measurement setup using Microwave Studio, the effective conductivity of the nanocomposite was determined. Since the thickness is very important for shielding analysis, the SE/unit thickness diagram was calculated by using the effective parameters of samples. The results were verified experimentally by measuring the SE of samples with different thicknesses