Kenneth L. Dudley

Towards cost-efficient EMI shielding materials using carbon nanostructure-based nanocomposites

Using a combination of dispersing low-cost carbon nanofibers and a small quantity of carbon nanotubes within the polystyrene matrix, we have demonstrated the formation of a novel nanocomposite with superior microstructure and improved electromagnetic interference (EMI) shielding characteristic. This nanocomposite is very promising for use as an effective and practical EMI shielding material owing to its high shielding effectiveness, light weight, low cost, and easy processability.

The fabrication and electrical properties of carbon nanofibre?polystyrene composites

Carbon nanofibre?polystyrene (PS) composites were fabricated by ultrasonic dispersion in a solution followed by spraying to cast films. These films were then hot-pressed to form thicker structures. Direct current conductivity measurement results show that the conductivity of the composite reaches 2.6 ? 10?5?S?m?1 at 3?wt% carbon nanofibre loading, which is an increase of ten orders of magnitude over the pure PS matrix, indicating that the composite is electrically conductive at a very low nanofibre loading. The dielectric properties of carbon nanofibre?PS composites were investigated at room temperature within the Ku-band (frequency range: 12.4?18?GHz). The results reveal that the dielectric constants of the composites are slightly dependent on the frequency but increase rapidly with increasing carbon nanofibre loading in the composite. The experimental data show that the dielectric constant of carbon nanofibre?PS composite can reach more than 80 at a frequency of 15?GHz.

Electrical Conductivity and Electromagnetic Interference Shielding of Multi-walled Carbon Nanotube Filled Polymer Composites

Multi-walled carbon nanotube (MWNT) filled polystyrene (PS) composites were synthesized for electromagnetic interference (EMI) shielding applications. SEM images of composites showed the formation of the conducting networks through MWNTs within the PS matrix. The measured DC conductivity of composites increased with increasing MWNT loading, showing a typical percolation behavior. EMI shielding characteristics of MWNT-PS composites were investigated in the frequency range of 8.2–12.4 GHz (X-band). It was observed that the shielding effectiveness (SE) of such composite increased with the increase of MWNT loading. The SE of the composite containing 7 wt% MWNTs could reach more than 26 dB in the measured frequency region.

Open Circuit Resonant (SansEC) Sensor for Composite Damage Detection and Diagnosis in Aircraft Lightning Environments

Composite materials are increasingly used in modern aircraft for reducing weight, improving fuel efficiency, and enhancing the overall design, performance, and manufacturability of airborne vehicles. Materials such as fiberglass reinforced composites (FRC) and carbon-fiber-reinforced polymers (CFRP) are being used to great advantage in airframes, wings, engine nacelles, turbine blades, fairings, fuselage and empennage structures, control surfaces and coverings. However, the potential damage from the direct and indirect effects of lightning strikes is of increased concern to aircraft designers and operators. When a lightning strike occurs, the points of attachment and detachment on the aircraft surface must be found by visual inspection, and then assessed for damage by maintenance personnel to ensure continued safe flight operations. In this paper, a new method and system for aircraft in-situ damage detection and diagnosis are presented. The method and system are based on open circuit (SansEC) sensor technology developed at NASA Langley Research Center. SansEC (Sans Electric Connection) sensor technology is a new technical framework for designing, powering, and interrogating sensors to detect damage in composite materials. Damage in composite material is generally associated with a localized change in material permittivity and/or conductivity. These changes are sensed using SansEC. Unique electrical signatures are used for damage detection and diagnosis. NASA LaRC has both experimentally and theoretically demonstrated that SansEC sensors can be effectively used for in-situ composite damage detection.

An investigation of EME as a potential cause of fuel tank ignition

NASA researchers were tasked to study the potential for radio signals to excite an aircraft fuel quantity indication system (FQIS) enough to cause arcing, sparking or excessive heating within a fuel tank. Computational techniques were used to determine the threat from external high intensity radiated field transmitters nearby, such as shipboard and airborne radar systems. Experimental methods were used to determine the threat from portable electronic devices (PEDs) carried aboard by passengers. To support this work, unique electromagnetic coupling measurements were performed on a retired Boeing 747 aircraft, and new test and analysis methods were developed that may be applied to other FQIS designs as well as other aircraft electronic systems.

The use of transmission line impedance measurements to determine electromagnetic comparability of FQIS wiring installations

Impedance measurements of a fuel quantity indication system (FQIS) were used to compare the electrical properties of a simulated FQIS installation to those of an actual installation. The fuel tank wiring and fuel probes from a Boeing 747 were removed from a retired airplane and installed in the reverberation chamber. The NASA installation was intended to electrically simulate the aircraft installation. A series of impedance measurements were taken on both installations in order to compare the input impedance values for each installation. A unique combination of statistics and the Smith Chart were used to compare the installations. This paper describes the methodology used in the data acquisition process, and the statistics of the installations are compared in the complex domain.

RF coupling into the fuel tank of a large transport aircraft from intentionally transmitting PEDS in the passenger cabin

An investigation was performed to study the potential for RF power radiated from portable electronic devices (PEDs) to create an arcing/sparking event within the fuel tank of a large transport aircraft. This paper describes the experimental methods used for measuring RF coupling to the fuel tank and fuel quantity indication system (FQIS) wiring from PED sources located in the passenger cabin. To allow comparison of voltage/current data obtained in a laboratory chamber FQIS installation to an actual aircraft FQIS installation, aircraft fuel tank RF reverberation characteristics were also measured. Results from the measurements, along with a survey of threats from typical intentional transmitting PEDs are presented. The resulting worst-case power coupled onto fuel tank FQIS wiring is derived. The same approach can be applied to measure RF coupling into various other aircraft systems.

Fabrication and Characterization of High Temperature Resin/Carbon Nanofiller Composites

As part of ongoing efforts to develop multifunctional advanced composites, blends of PETI-330 with multi-walled carbon nanotubes (MWCNTs) and carbon nanofibers (CNF) were prepared and characterized. The effect of nanofiller loading level on melt viscosity was determined. The resulting powders were characterized for degree of mixing, thermal, and rheological properties. Select samples were scaled up for processing and continuous strands of nanocomposites were extruded. Based on the characterization results, samples containing 10 and 15 wt% MWCNT and 30 and 40 wt% CNF were scaled up to ∼300 g and used to fabricate moldings 10.2 cm × 15.2 cm × 0.32 cm in size. The moldings were fabricated by injecting the mixtures at 260–280 °C into a stainless steel tool followed by curing for 1 h at 371 °C. The tool was designed to impart substantial shear during the injection process in an attempt to achieve some alignment of nanofillers in the flow direction. Moldings were obtained that were subsequently characterized for thermal, mechanical, electrical and EMI shielding properties. The degree of dispersion and alignment of nanofillers were investigated using high-resolution scanning electron microscopy. Preparation and preliminary characterization of PETI-330/MWCNT and PETI-330/CNF composites will be discussed.