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Photo-induced coded-aperture imaging (PI-CAI) based on compressed sensing (CS) at 590 GHz using a WR-1.5 (500-750 GHz) vector network analyser is demonstrated. For a 256-pixel (16 × 16) frame, the acquisition time can be reduced by 40%, as compared with PI-CAI without CS, while maintaining high imaging quality. On the basis of this approach, it is envisioned that real-time (26 fps) THz imaging with 1000 pixels (32 × 32) can be realised using high-speed digital micromirror device chipsets and optimised data-acquisition software.

We report a novel and simple approach to realize terahertz (THz) dynamic two-dimensional (2D) beam steering and forming antennas, based on reconfigurable photo-induced Fresnel zone plates (PI-FZPs). The FZPs are formed by directly illuminating a high-resistivity silicon wafer with the desired patterns using a digital light processing (DLP) projector, without any circuit or device fabrication. At 750 GHz, the THz beam from a diagonal horn antenna has been steered two dimensionally over a range from approximately _12° to + 12° from the antenna boresight, by projecting different PI-FZP patterns. In addition, using PI-FZPs with different focal lengths, the THz beam size can be dynamically tuned. Both the beam steering and forming can be performed simultaneously without affecting the antenna performance, making this an enabling technology for emerging THz applications such as sensing, imaging, tracking, adaptive wireless communications and short-range high-speed interconnections.Index Terms-Photo-induced Fresnel zone plate (PI-FZP), 2Dbeam-steering, beam-forming, terahertz antenna.

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Osteoporosis or bone loss affects many people, particularly the aged women, and leads to disabling bone fractures. An early diagnosis could provide preventive management. However, available bone densitometry equipment are very expensive and not available widely in the Third World. The present work presents the design & development of an innovative low cost bone densitometer based on conventional X-ray equipment available widely. The main innovation is the incorporation of a stack of aluminium with varying thickness placed beside the limb of a patient while taking an X-ray image. Then the optical density of the bone area in the developed film is compared to that from the aluminium stack, which eliminates variations due to all other processing factors, and gives a measure of the bone density. A low cost device has been developed to measure the optical density of the X-ray film over a circular area of about 1cm to give an average reading, which is more appropriate than spot metering in this application. Preliminary measurements of a few human subjects using this equipment clearly indicate the differences obtained due to expected osteoporosis. Calibration with standard bone densitometry equipment could provide values in standard units. This low cost innovative method and equipment appears to provide a low cost alternative to the diagnosis of osteoporosis. DOI: http://dx.doi.org/10.3329/bjmp.v4i1.14693 Bangladesh Journal of Medical Physics Vol.4 No.1 2011 95-100

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