Defence Research Agency

About: Defence Research Agency is a based out in . It is known for research contribution in the topics: Synthetic aperture radar & Radar. The organization has 1211 authors who have published 1109 publications receiving 31542 citations.

Electrical measurement of silicon film and oxide thicknesses in partially depleted SOI technologies

Abstract: This paper discusses the electrical measurement of silicon film, gate oxide and buried oxide thicknesses in partially depleted SOI CMOS technologies. For the first time a technique is presented that allows extraction of all three thicknesses, as well as the average silicon film doping concentration, using static threshold voltage measurements only. All measurements and extraction procedures can easily be fully automated, making this method suitable for both accurate parameter extraction and process control. The results obtained with this new technique have been verified by SEM cross-section measurement and a comparison is made with other electrical techniques.

Composite-embedded highly birefringent optical fiber strain gauge with zero thermal-apparent strain

Abstract: We demonstrate temperature-insensitive strain measurement in a carbon fiber composite panel using a sensor based on broad-band interferometry in highly-birefringent optical fiber. The sensing element forms an unbalanced Fabry-Perot cavity in the measurement arm of a tandem interferometer. This is interrogated using an LED source and a scanning Michelson interferometer, producing three distinct interferograms, two of which relate to the group delay (GD) of the eigenmodes of the sensing element, the other providing a zero-OPD reference in the scanning interferometer. We measure the GD of each interferogram by dispersive Fourier-transform spectroscopy. Changes in strain and temperature in the measurement fiber affect the group delays of the sensing interferograms, but do not affect the zero-OPD interferograms, which is therefore used as the origin for group delay measurements. We determine a linear transformation relating the measured group delays to strain and temperature. Inverting this transformation then provides a means of recovering strain and temperature from measurements of group delay. We apply this technique to the simultaneous measurement of strain and temperature in the composite panel. Typical measurement errors are 7 microsecond(s) train and 0.7 K. The measured values are independent, and the strain values show no evidence of thermal-apparent strain.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Determination of Atomic Structure at Surfaces and Interfaces by High-Resolution Stem

Abstract: It is over 100 y since Lord Rayleigh first showed the differences between coherent and incoherent imaging in the light microscope, pointing out the advantages of the latter for resolution and image interpretation. The annular detector in the high-resolution STEM provides the same advantages for electrons, allowing incoherent imaging at atomic resolution, with image contrast strongly dependent on atomic number (Z). Since incoherent imaging has no phase problem, these Z-contrast images may be directly inverted to given the (projected) atomic positions. A maximum entropy method avoids false detail associated with direct deconvolution, and gives atomic coordinates to an accuracy of {+-}0.1{Angstrom}. Electron energy loss spectroscopy can provide valuable complementary information on light element bonding and the presence of impurities in specific atomic planes selected from the image. Together, these techniques have revealed some surprisingly complex interfacial structures. For surface studies, the 1.3{Angstrom} probe of the VG Microscopes HB603U STEM provides sufficient penetration and contrast to image single Pt and Rh atoms on {gamma}-alumina supports. Such images reveal preferred atomic configurations and allow possible surface adsorption sites to be deduced.

Modelling of Propagation in Outdoor Microcells at 62.4GHz

Abstract: Results of Line-of-Sight (LOS) and Non Line-of-Sight (NLOS) mobile radio propagation experiments made to characterise 62 GHz sub-urban microcell channels employing omnidirectional antennas are presented. Experimental results are compared with theoretical predictions obtained from an exhaustive ray tracing algorithm. NLOS results show a sharp drop in the mean signal level when the direct component is blocked. The model is found not to be able to predict the signal with accuracy in the shadow region, where reflections do have a major influence, and are responsible for any coverage in there.