Abstract: Closely spaced conventional optical fibers are arranged in a grid placed between a first surface and a second surface. A penetrating impact onto the first surface results in a hole of a size proportional to the diameter and velocity of the impacting object. The size and shape of the debris plume that travels between the first and second surfaces is also proportional to the diameter and velocity of the impacting object. If the debris plume is sufficiently energetic, a number of the fibers in the grid are broken. The size and shape of the area defined by the broken fibers can be determined simply by determining which fibers are no longer transmitting light. Analytical methods are then used to relate the extent of the damaged area to the location of an MOD impact, the direction from which the impact occurred, and the size of the impacting object.

Abstract: A fiber optic sensor includes two reflective elements in series. The first reflective element is formed as a partially mirrored surface on the end of a single-mode optical fiber lead which is bonded into a ferrule. A sleeve is used to join the ferrule to a second ferrule which is turn is bonded to a length of single-mode optical fiber. The second reflective element is a partially mirrored surface on the cleaved end of the second fiber. The second fiber may be affixed to or embedded in a structure to be monitored and changes its optical path length in response to a condition of the structure. Light introduced into the sensor is reflected from the first or second reflective element and thus follows two optical paths. The path length difference between the two optical paths is twice the optical path length of the second fiber.

Abstract: Brillouin scattering spectrum analysis is used to measure strain, displacement, temperature or other physical quantities at any location along an optical fiber attached to a structure. The fiber can be interrogated with different pulse widths for coarse and fine scans. The fiber can also have multiple sensors, either formed in a single fiber or branching off from a backbone fiber, in which case other segments of the fiber can be used for temperature compensation.

Abstract: An interoferometric fiber optic sensing system uses three optical fibers. A sensing optical fiber is applied to a structure to be monitored to detect displacement or the like by changing its optical path length. A reference optical fiber has a fixed optical path length. An adjustable length optical fiber is controllably adjusted in its optical path length. The three optical fibers form optical paths whose light outputs are caused to interfere. The adjustable length optical fiber is adjusted until an interference fringe appears. The quantity to be detected is derived from the maximum of the interference fringe. Several sensing optical fibers can be multiplexed; by staggering their optical path lengths, their interference fringes can be separated sufficiently to resolve them.

Abstract: Brillouin scattering spectrum analysis is used to measure strain, displacement, temperature or other physical quantities at any location along an optical fiber attached to a structure. The fiber can be interrogated with different pulse widths for coarse and fine scans. The fiber can also have multiple sensors, either formed in a single fiber or branching off from a backbone fiber, in which case other segments of the fiber can be used for temperature compensation.

Abstract: An an improved process for surface modification of solid substrates, such as polymers and carbon-based materials, is disclosed. The preferred process comprises three steps: a first activation step wherein reactive hydrogen groups are formed in a surface layer of a polymeric or carbon-based material; a second silylation step wherein the reactive hydrogen groups are reacted with a silylating agent to form silicon-containing groups; and a third stabilization step wherein an upper portion of the activated, silylated layer is oxidatively converted to a silicon and oxygen enriched surface layer. The process can be performed using materials not having pre-existing reactive hydrogen groups or precursor groups. Modified materials according to the present invention have improved properties, such as erosion resistance and oxygen and water barrier properties, and are potentially useful in numerous industries, such as aerospace and packaging.

Abstract: This invention provides an improved process for surface modification of polymers, graphites and carbon-based composite materials, and improved surface-modified materials produced by the process. The preferred surface modification process of the present invention comprises the steps of: high dose single or multiple implantation of the substrate with energetic ions, including ions of at least one metal or semi-metal element able to form a stable, non-volatile oxide; and oxidative full or partial conversion of an upper portion of the implanted layer to a continuous, resistant oxide-enriched surface layer. The process may also comprise the additional implantation of a hardening non-metal element to participate in the formation of a glass-like surface layer or to form a carbonized, hardened sub-layer.

Abstract: A damage detection and evaluation system utilizes optical fibers to detect and assess damage to a structure. The optical fibers are intermittently etched in a controlled manner to weaken them so they fracture when a desired load is applied to the structure. Where visual inspection of the optical fibers is used to check for damage, a reference set of optical fibers is used. Where photodetection is used and minimal connections to the structure are required, one end of the optical fiber is made reflecting so an optical connection is only made to the other end. To further simplify the connection, a single input/output optical connection to a demultiplexing/multiplexing chip mounted on or within the structure is provided. Where orthogonal grids of fibers are not possible, the invention provides interdigitated optical fibers and volume backscattering to locate the position of the first fracture along the length of the optical fiber.