RF TRAVELING-WAVE SCANNING SYSTEM WITH A NONINVASIVE, BROADBAND PHOTONIC PROBE

ABSTRACT: The feasibility of developing a prototype traveling-wave scanning system based on non-metallic, broadband, optical-fiber-coupled microwave-field sensors that can be used for the test and evaluation of coatings applied to the surface of aircraft without damaging the coating layers is investigated. The concepts to be employed in performing the measurement of microwave surface waves will be explored and implemented through the design, development, and performance evaluation of four key system components: photonic, nonintrusive, microwave-field-sensitive probes; microwave traveling-wave signal launchers; a flexibly positionable sensor head; and a subsystem containing an optical source and optical-beam-conditioning elements. Construction of the photonic sensors will be all-dielectric, they will have dimensions much smaller than the wavelengths of the surface waves, and they will be held by the sensor-head mechanism so that they remain in close proximity to the surface of an aircraft, even during the scanning process. In this way, the characteristics of traveling waves may be extracted without disrupting their propagation and without contacting or damaging the coatings during in situ measurements. The four subsystem components will be combined to form a breadboard demonstration system based on a completely fiber-enclosed optical network. BENEFIT: The proposed aircraft-coating test system will provide accurate profiles of the material properties of coating layers, including attenuation constant, permittivity, and permeability, along a given scan path and over a broad measurement bandwidth. The outstanding resolution provided by the traveling-wave test system would make it possible to identify a wide range of both electrical and physical defects in coatings, and in particular ones that are too small to be detected by other test methods. Accurate test results provided by the coating-test system can initiate rapid and effective action to mitigate or repair the detected defects in the aircraft coating, eventually leading to reduction of the air vehicle"s service down time and extension of its life span. The comprehensive test solution to be provided by the traveling-wave measurement system should directly contribute to a significant reduction in the time and cost required to test aircraft coatings, and in particular ones that are applied on in-service aircraft, where only a few less-effective test methods are otherwise available. Commercially, Advanced Fiber Sensors would like its products to find use in the civilian aerospace sector, both for maintenance and the trouble-shooting of coating issues, and we also believe there should be additional application of the technology for companies that develop the coatings to be employed on aircraft. Beyond aerospace, there are also other industries that utilize coatings that could be characterized using the analysis of traveling microwave signals, including automotive, marine, and construction.