Ian Robert Mason

First imagery generated by near-field real-time aperture synthesis passive millimetre wave imagers at 94 GHz and 183 GHz

The first passive millimetre wave (PMMW) imagery is presented from two proof-of-concept aperture synthesis demonstrators, developed to investigate the use of aperture synthesis for personnel security screening and all weather flying at 94 GHz, and satellite based earth observation at 183 GHz [1]. Emission from point noise sources and discharge tubes are used to examine the coherence on system baselines and to measure the point spread functions, making comparisons with theory. Image quality is examined using near field aperture synthesis and G-matrix calibration imaging algorithms. The radiometric sensitivity is measured using the emission from absorbers at elevated temperatures acting as extended sources and compared with theory. Capabilities of the latest Field Programmable Gate Arrays (FPGA) technologies for aperture synthesis PMMW imaging in all-weather and security screening applications are examined.

Design issues for tunable filters for optical telecommunications

A summary is presented of some of the issues facing the developers of tunable filters for use in optical communication systems, including those exploiting acousto- optic, thermo-optic and electro-optic effects. The potential of electromechanically tuned variants is also assessed in relation to devices micromachined from silicon. Emphasis is given to electro-optically tuned devices, with experimental data presented for an example based on a nanophase polymer dispersed liquid crystal composite.

Measurements of aerospace materials and their interpretation for non-destructive testing

Millimetre and terahertz radiation penetration into materials enables non-destructive testing capabilities for the aerospace industry, either remotely using imaging technology or locally using microscope type diagnostics. This paper presents measurements made on Norcoat and Prosial, used in the aerospace industry for thermal insulation and on carbon fibre, used for its high strength weight ratio. Michelson interferometer measurements over the band 100 GHz to 1 THz, with a 30 GHz spectral resolution, are presented, together with images of a range of samples taken using a 35 GHz real-time imaging system. The measured optical properties of these materials are examined and used in modelling to predict signatures of failure modes in these materials when they are attached to cryogenic fuel tanks.

Progress in the realisation of frequency agile filters using nanoscopic polymer dispersed liquid crystals

Nano-phase polymer dispersed liquid crystal materials provide a way forward for the realisation of electro-optically tunable filters for use in the visible and near-infrared. Devices can be produced with little or no hysteresis effects.

Electro-optic effects in nanophase polymer dispersed liquid-crystal systems

Research into electro-optic effects in nanophase polymer dispersed liquid crystal (PDLC) materials has highlighted their potential as materials for a new class of tunable filters. The structures, based on UV cured phase separated composites, contain liquid crystal both as discrete nano-scale droplets, and as material dissolved in the polymeric host. The essential difference between these materials and more conventional PDLCs is the scale of the refractive index inhomogeneity which is considerably smaller than the wavelength of visible light. Based upon effective medium approximations, the composite thus acts as a single isotropic medium, whose average refractive index is dependent on the level of applied electric field. Tunable filters have been fabricated using the composite material for use in the visible spectral band.