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RF Material Property Characterization


OBJECTIVE: Develop a system capable of providing non-destructive evaluation (NDE) of composite, non-conductive materials in multi-layer stacks while simultaneously providing feedback on material thicknesses and RF material properties. DESCRIPTION: The Missile Defense Agency produces many composite materials in applications spanning the breadth of the agency. Composite structures and layups play an important role in a variety of sensor and weapon system platforms. Composite structures and layups are also an important part of Missile Defense targets. These composite layups include thermal protection systems, motor casings, etc. Flaws in target composites may either be structural (disbonds, inclusions, or voids) as well as RF (unexpected complex permittivity or permeability). Current methods of non-destructive evaluation for composites vary. Some, such as"tap"tests, rely on human training to identify issues. Other tests such as X-ray or ultrasonic testing can produce good data with respect to structural issues but cannot identify issues in material make-up resulting in unexpected RF performance characteristics. The goal is the development of an inexpensive and effective means of assessing for most structural issues while simultaneously checking material layer thickness and RF material properties. The RF material property measurement requirement is complicated by the need for RF material properties on each individual layer in contract to a composite"effective permittivity"for a material stack to enable high-fidelity modeling. Wavelengths of interest for RF material property extraction include S-X Bands. Structural voids and inclusions are of interest for sizes roughly larger than a nickel. The final NDE system should be fundamentally man-portable. By this, it is meant that the system should not require special equipment or multiple people to move. The system should not require any special protective gear to operate. PHASE I: Develop a concept system to perform NDE and material property characterization data collection of composite, non-conductive material stacks. The concept system should be able to identify inclusions and voids as a threshold and disbands as a goal. Further, the system should be able to identify RF material properties (permittivity and permeability) for individual layers in a multi-layer material stack. The system should also be able to identify material layer thicknesses for manufacturing verification. Demonstrate the performance of the system to perform all of these functions through modeling and simulation. PHASE II: Develop a prototype of the concept system. Perform bench testing of the system and proceed to development tests in the field. Re-package the design into a portable unit and perform field testing. PHASE III: Perform NDE on various composites as part of manufacturing processes. COMMERCIALIZATION: Composite materials are common in a wide variety of commercial applications including commercial aircraft.
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