Simulation of optically encoded multiplexing for parallel multipoint sensing.

Spectral emission/absorption-based sensors are commonly used to monitor explosives, narcotics, and other restricted materials in high-security zones such as airports. Monitoring a broad range of spectral wavelengths with high spectral resolution would increase the repertoire of chemicals that can be monitored. However, a portable unit will have limitations in meeting these requirements. Optical fibers can be employed for collecting and transmitting spectral signals from portable sensor heads (PSHs) to a sensitive central spectral analyzer. However, simultaneous detection by sensors in multiple PSHs needs to be differentiated for identifying individual PSHs. An optical encoding method is presented in this paper for use of a portable unit for highly sensitive measurement. The methodology is demonstrated through a simulation using MATLAB Simulink.

An absolute method for determination of misalignment of an immersion ultrasonic transducer.

An absolute methodology has been developed for quantification of misalignment of an ultrasonic transducer using a corner-cube retroreflector. The amplitude based and the time of flight (TOF) based C-scans of the reflector are obtained for various misalignments of the transducer. At zero degree orientation of the transducer, the vertical positions of the maximum amplitude and the minimum TOF in the C-scan coincide. At any other orientation of the transducer with the horizontal plane, there is a vertical shift in the position of the maximum amplitude with respect to the minimum TOF. The position of the minimum (TOF) remains the same irrespective of the orientation of the transducer and hence is used as a reference for any misalignment of the transducer. With the measurement of the vertical shift and the horizontal distance between the transducer and the vertex of the reflector, the misalignment of the transducer is quantified. Based on the methodology developed in the present study, retroreflectors are placed in the Indian 500MWe Prototype Fast Breeder Reactor for assessment of the orientation of the ultrasonic transducer prior to the under-sodium ultrasonic scanning for detection of any protrusion of the subassemblies.