The thermochromic nature of vanadium dioxide (VO2) has facilitated many promising applications for reconfigurable frequency selectivity. The phase-changing property of VO2 was used to realise a reconfigurable frequency-selective surface (FSS) capable of manipulating electromagnetic waves for different functionalities. Diffractive optical elements (DOE) are used for diffracting laser beams to form conductive FSS images on the VO2 wafer for frequency selectivity. The dipoles on the VO2 wafer generate a stop band response of 12 dB and 10 dB for unit cells of the single dipole and double dipole at 3.5 GHz, respectively. A 10 GHz FSS array is projected by DOE on the 2-inch VO2 wafer with a filtering effect of 13 dB at 9.5–10.5 GHz. This solution is used to design a radar cross-section (RCS) modification FSS with reflected waves of about 20 dB higher reflectivity in the backscattering direction than in the specular direction.
A miniaturised structural health monitoring device has been developed capable of measuring the absolute distance between close parallel surfaces using Fabry-Pérot interferometry with nm-scale sensitivity. This is achieved by fabricating turning mirrors on two opposite cores of a multi-core fibre to produce a probe with dimensions limited only be the fibre diameter. Two fabrication processes have been investigated: Focused ion beam milling, which has resulted in a sensor measurement accuracy, sensitivity and range of ±0.056 µm, ±0.006 µm and ∼16000 µm respectively; and ultrafast laser assisted etching of the cleaved fibre end, where a sensor measurement accuracy, sensitivity and range of ±0.065 µm, ±0.006 µm and ∼7500 µm have been demonstrated.
Ultrafast laser welding, hydroxide catalysis bonding (HCB) and adhesive bonding techniques were used to bond N-BK7 cubes to aluminum bases. Using a thermal chamber and polariscope, the stress induced birefringence was measured at temperatures from -50°C to +80°C. Adhesive samples made with different industrial assembly methods were compared for thermal birefringent behavior. An ultrafast laser welded sample was thermally cycled in increasing temperature ranges, surviving the test with reduced retardation, indicating fatigue. An HCB sample was thermally cycled like the laser welded sample, and had a linear birefringent relation to temperature initially, and failed by fatigue after a fracture event.
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