An optical frequency domain distributed strain sensor for determining the strain distribution along an optical fiber includes an optical source that provides a polarization controlled optical interrogation signal having a frequency that varies in a recurring linear manner. The interrogation signal is injected into a sensor fiber embedded within a composite structure that places the fiber under strain. A portion of the interrogation signal is backscattered from the sensing fiber as a consequence of the strain experienced by the fiber and is mixed with a reference signal to produce beat frequency signals. The frequency of the beat signals is directly related the to position of backscatter in the sensing fiber while the amplitude of each beat frequency signal is directly related to the integrated strain-induced birefringence up to the backscatter point. An in-line fiber polarizer and an associated controllable polarizer control the polarization state of the interrogation signal in the sensor fiber to provide zero point sensitivity compensation and controllable testing for ambiguous strain points.
A surface conforming sense antenna is integrated with the surface skin of an aircraft by removing a rectangular looped strip of a metallized exterior composite surface skin. The remaining interior metallized portion isolated from the exterior metallized section forms an antenna sense element. The inner metallized portion is connected to an ADF radio receiver to function as a sense antenna in conjunction with a loop antenna. The gap between the metallized inner portion of the exterior metallized section allows lightning energy to be discharged thereacross. The modification does not impose a weight penalty or a wind drag penalty and does not degrade lightning protection for the composite aircraft.
A method for detecting structural flaws in a structural member that includes plastic composite matrix material involves taking a quantity of matrix material that is substantially free of any non-optic glass fibers, molding the matrix material into a structural loadbearing member having a length and opposite end surfaces, placing a plurality of straight continuous spaced elongated fiber optic strands having the same length as the loadbearing member in the matrix material before molding, loading the structural member to exert stress and strain thereon, exposing one of the ends of the fiber optic strands to a source of light, viewing the opposite ends of the fiber optic strands to determine if light is being emitted therefrom by passing through the fiber optic strands, and making an evaluation of any structural flaws in the member by determining whether light from the light source has been fully transmitted through the fiber optic strands.
A method and apparatus for evaluation and inspection of a composite-repaired structure generates a frequency-varying electrical signal to test and evaluate the composite-repaired area. The electrical signal is converted into a mechanical signal and transmitted through the composite-repaired area of the structure. The transmitted mechanical signal is received and converted into an electrical signal for processing. The processed signal is compared with a baseline reference signal to determine whether the composite-repaired area is damaged or undamaged. The baseline reference signal is obtained at the time of the composite repair of the structure.
Threshold current may be determined and one or more bias sources may be programmed in a laser drive circuit. For example, a laser diode emits light along first and second optical paths. A polarizer is positioned in the first optical path between the laser diode and a first detector, which outputs a first detector signal corresponding to the measured optical power of polarized light. A second detector monitors light along the second optical path and provides a second detector signal. A bias compensation circuit receives the first and second detector signals and provides a bias current control signal, which is utilized to program a bias current source supplied to the laser diode. Additionally, multiple polarizer devices may be utilized e.g., a first polarizer in a first optical path aligned with the laser beam and a second polarizer in a second optical path aligned substantially orthogonal to the polarization of the laser beam.
A method and apparatus is disclosed for measuring an energy gap of a semiconductor material. The method contains the steps of analyzing a character of a reference semiconductor sample and setting an energy gap pixel value, estimating a transfer function between the pixel value, positioning the sample properly and imaging the spectrum to obtain a live image, storing the live image and scanning the respective pixel values along an x-axis of the image, sequentially comparing the respective pixel value and the energy gap pixel value, reading an x-coordinate of the pixel and converting the wavelength of the pixel to estimate the energy gap. The apparatus optically measures the energy gap and comprises a light source irradiating a light beam, a lens for focusing the light beam, a polychromator for irradiating the spectrum of light of the light beam to the sample, optical filters for evaluating a spectrum band of the polychromator into wavelength values, an image acquisition apparatus, an image signal processor, an energy gap detecting and displaying apparatus, and a computer for executing operation and control functions necessary to measure the energy gap by use of the image signal processor and the energy gap detecting and displaying apparatus.
