We introduce a technique for illumination optimization based on a projector–camera system applied to a multireflective three-dimensional (3-D) scene. Simple mapping would fail if the scene is nonplane since they would translate to incoherent mapping between the projector and the camera. The correspondence between the pixels on the projector and camera in multireflective 3-D scene was indirectly established by surface orientation measurement. Once the correspondence was established, the local light was adapted by using the iteration in order to obtain the optimal illumination intensities at different surface orientations. User intervention for judging the desirable image is required in the iteration stage since there is no absolute reference for comparison to which the object must appear. According to the feedback from the camera, the projector is to compensate for surface reflectance for the most part by modulating the projection brightness at each pixel to be inversely proportional to the brightness of the pixel under uniform light. The time required for this adaptive illumination can be shortened to the inspection stage of 40 ms as long as the inspected object does not change in orientation or location. This proposed technique aims to enhance the illumination capabilities and presents a more unified system than existing methods.
An ultrasonic hydrophone based on a dual polarization distributed Bragg reflector (DBR) fiber laser is described, and its application to detecting the vector medical ultrasound is demonstrated. The principle of the hydrophone is based on the detection of output beat frequency signal modulated by ultrasound. The amplitude, frequency and orientation of the ultrasound can be determined by the using the upper and lower sideband frequency. It has been found that the hydrophone has an orientation recognizable ability which the piezoelectric ultrasonic immersion transducer doesn’t have. It suggests that the type of hydrophone can provide an alternative to piezoelectric hydrophone technology.
Distributed Bragg Reflector (DBR) polarimetric optical fiber laser sensors have been attracting great interests due to harsh environment capability and high signal-to-noise ratio .We demonstrate directional force measurement technology using dual-polarization DBR optical fiber laser as a sensor. The influences of external force (bending, current and ultrasonic signal) could be analyzed by inducing a DFB polarimetric laser sensor to detect the beating signals shifts when the cavity is perturbed. We present the analysis of sensing mechanism on the DBR geometric construction and demodulation of directional information by separating the dual orthogonal polarization modes. With loading angles at 35°, 45°, 55°with 10° interval, the DBR laser sensor has shown orientation recognization ability corresponding to beating signals shifts, offering a potential for vector force directional detection.
The wavelength readout system reported in this paper is chiefly constructed of fiber Fabry-Perot tunable filter (FFP-TF),
data acquisition card and a virtual instrument with programmable NI Labview. By combining the dynamic scanning of
FFP-TF in C waveband (1520nm-1570nm) with 50nm free spectral range (FSR) and 4000 standard finesse value, the
wavelength of a tested laser diode (LD) could be detected accurately, while the spectrum is displayed on line with the
help of a virtual instrument to make the spectroscopy quick analysis possible. Furthermore, the scheme can also be
applied for wavelength interrogation in fiber Bragg grating (FBG) sensing system. Considering the practibility and
economical efficiency of such a system, it will be of great significance to adopt such a wavelength readout system in
fiber sensors used for construction, mining, aerospace,etc.
The paper reports results obtained from a field test site in structural monitoring-a "test-to-failure," measuring strain
using Fiber Bragg gratings (FBGs) sensor networks on a novel drilled concrete test pier in Huaihe river zone,Anhui
province,China. To undertake the study, FBG-based sensors were chosen ,metallic recoated ,steel-tube packaged , and
incorporated with steel rebars in this concrete structure. The sensors were interrogated using a compact system based on
wavelength-division multiplexing (WDM) and F-P scanning approach. Throughout the test, the FBG sensors were
continuously monitored, the incremental increases in the strain caused by boundary shear stress could be seen. The
sensors were able to follow the resulting induced changes in load of over a range in excess of 2.5M Newton just prior to
failure of the pier and representing extreme levels of strain for such a novel mechanical structure. The measurements
made with the FBG-based system were found to be in agreement with the changes expected in the structure, produced by
the self-balanced loading applied. The study has demonstrated the successful use of FBG sensor networks used in a test
of this root type pier foundation, consequently made assessment about the health and security of the highway bridge.