The Green-function transform and wave propagation

Fourier methods well known in signal processing are applied to three-dimensional wave propagation problems. The Fourier transform of the Green function, when written explicitly in terms of a real-valued spatial frequency, consists of homogeneous and inhomogeneous components. Both parts are necessary to result in a pure out-going wave that satisfies causality. The homogeneous component consists only of propagating waves, but the inhomogeneous component contains both evanescent and propagating terms. Thus we make a distinction between inhomogenous waves and evanescent waves. The evanescent component is completely contained in the region of the inhomogeneous component outside the k-space sphere. Further, propagating waves in the Weyl expansion contain both homogeneous and inhomogeneous components. The connection between the Whittaker and Weyl expansions is discussed. A list of relevant spherically symmetric Fourier transforms is given

Acoustic transmission of metadata in audio files using Sonic Quick Response Codes (SQRC)

With the advent of high-resolution recording and playback systems, a proportion of the ultrasonic frequency spectrum can potentially be utilized as a carrier for imperceptible data, which can be used to trigger events or to hold metadata in the form of, for example, an ISRC (International Standard Recording Code), a website URL or audio track liner notes. The Sonic Quick Response Code (SQRC) algorithm was previously proposed as a method for encoding inaudible acoustic metadata within a 96 kHz audio file in the 30-35 kHz range

S-band omnidirectional antenna for the SERT-C satellite

The program to design an S-band omnidirectional antenna system for the SERT-C spacecraft is discussed. The program involved the tasks of antenna analyses by computer techniques, scale model radiation pattern measurements of a number of antenna systems, full-scale RF measurements, and the recommended design, including detailed drawings. A number of antenna elements were considered: the cavity-backed spiral, quadrifilar helix, and crossed-dipoles were chosen for in-depth studies. The final design consisted of a two-element array of cavity-backed spirals mounted on opposite sides of spacecraft and fed in-phase through a hybrid junction. This antenna system meets the coverage requirement of having a gain of at least minus 10 dBi over 50 percent of a 4 pi steradian sphere with the solar panels in operation. This coverage level is increased if the ground station has the capability to change polarization

Polarized focused vortex beams: half-order phase vortices.

A theoretical treatment is presented for the focusing of polarized vortex beams, including the generation of Bessel beams. A combination of a phase vortex with arbitrary topological charge, and a polarization vortex of arbitrary order is considered. Results are given for both paraxial and high NA systems. Conditions for the presence of non-zero on-axis intensity are given. An interesting observation is that half-order phase vortices can exist, without the existence of any phase discontinuity. The behavior of Bessel beams with half-order phase vortices is investigated

Scanning Optical Microscopy of Semiconductor Materials and Devices

In the scanning optical microscope a focused light spot is used to illuminate the object and some property monitored as the spot is scanned relative to the object to build up an image. By monitoring different properties it is thus possible to use the scanning optical microscope in a wide range of imaging modes, which can be used to give much information concerning the structure and properties of semiconductor materials and devices. In the optical-beam induced current method the focused light spot generates electronic carriers in a semiconductor specimen, and the resultant current monitored. The technique can be used to study defects in semiconducting materials and to measure electronic properties. If instead the reflected light is monitored we can obtain images in which resolution, contrast and depth of focus are all improved relative to conventional optical microscopy. Using the confocal imaging mode surface topography of thick structures can be investigated. In the scanning optical microscope we gain all these advantages whilst avoiding the disadvantageous effects of an electron beam and the necessity for a vacuum environment

Pupil filters for generation of light sheets.

Pupil filters for cylindrical (two-dimensional) focusing with extended depth of field are investigated. An important application is in generating light sheets with uniform intensity. Filters for spherical (three-dimensional) focusing with a flat axial intensity, coupled with weak side lobes are also discussed

Development of autoclavable addition type polyimides

Two highly promising approaches to yield autoclavable addition-type polyimides were identified and evaluated in the program. Conditions were established for autoclave preparation of Hercules HMS graphite fiber reinforced composites in the temperature range of 473 K to 505 K under an applied pressure of 0.7 MN/m2 (100 psi) for time durations up to four hours. Upon oven postcure in air at 589 K, composite samples demonstrated high mechanical property retention at 561 K after isothermal aging in air for 1000 hours. Promise was shown for shorter term mechanical property retention at 589 K upon exposure in air at this temperature