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Radio Frequency (RF) Traveling Wave Inspection Tool


OBJECTIVE: Develop a non-destructive Radio Frequency evaluation tool for aircraft specialty coatings. DESCRIPTION: Specialized aircraft coatings can degrade over time and impact desired performance. Currently, waveguide reflectometers are used as an RF point inspection tool for on aircraft measurements. Current reflectometers measure at normal incidence or 90 degrees to the surface which does not accurately predict the electrical performance of the material across the aircraft's surface. It is desirable to measure the interaction of the non-specular component or traveling wave to fully characterize the electrical performance of the coatings. A new RF hand held measurement device is desired that is capable of making true traveling wave measurements excited between 5 degrees and 20 degrees to the surface. The device should be able to determine the attenuation per unit length (i.e.: dB/in) of a surface wave that is excited on the surface of the aircraft. It is desirable to measure this performance across the frequency band of 2-18 GHz. It is acceptable to have multiple devices to cover this frequency band, but not more than four. A single broad-band probe is highly desirable. The probe will be used on fielded air vehicles and cannot damage the surface being measured. The device should pose no safety hazard to personnel or equipment and can be used in an aircraft fueled environment. It shall be capable of being approved for flight line operation. The surface will not typically be flat and therefore should conform to the surface being tested. Assume that the probe must accommodate surfaces from flat to a compound radius of curvature of 50 inches. Ability to support higher radii of curvature is desirable. The probe should fit within a 12"by 12"area on the aircraft. A smaller footprint is desirable. It is anticipated that the probe will work in conjunction with a government furnished vector network analyzer. The analyzer is a two port instrument and it is desirable that the probe not require additional ports, access to analyzer may be arranged. The probe shall not impact analyzer battery power more than 20%. A standalone device or one that utilizes special test equipment is acceptable. It is expected that this probe will be transportable and operable by a single technician. PHASE I: Perform research relevant to surface wave excitation, attenuation and understand the challenges and goals of this program. Use commercially available magnetic materials as required. Develop methods on how to measure surface wave attenuation provided by the application of coating. Perform trade studies on the various concepts and down-select an approach that will be prototyped in Phase II. PHASE II: Design and fabricate the probe identified in Phase I for performing measurements in a lab environment. Results obtained should be verified with other methods of characterizing material performance. Extraction of material permittivity and permeability using standard techniques and analytically determining the surface wave attenuation is acceptable. A method of moving the probe along the surface while collecting data at predetermined locations should be explored for feasibility and utility. PHASE III: A probe suitable for flight line field use shall be demonstrated. Must be suitable for use in a hazardous vapor environment defined by the National Electric Code, Class I, Division 2. Probe shall not require modification to the surface being inspected nor shall it damage a typical painted surface. REFERENCES: 1. Richmond, J.H., Peters, L., and Hill, R.A.,"Surface Waves on a Lossy Planar Ferrite Slab,"IEEE Trans. Antennas and Propagation, AF-35 (7), 1987. 2. Collin, R.E.,"Field Theory of Guided Waves,"2nd ed. IEEE Press, Piscataway NJ, 1991, pp. 712-718. 3. Klopfleisch, M. and Schellenberger, U.,"Experimental Determination of the Attenuation of Surface Electromagnetic Waves,"J. Appl. Phys., 70 (2), 1991.
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