Surface-bonded single-mode optical fibre sensors have been used to monitor the interaction of ultrasonic S 0 Lamb waves with defects in carbon fibre composite plates. Lamb waves were initiated using Perspex-coupled piezoelectric transducers. The defects investigated comprised holes, regions of impact damage and delaminations. Holes could be identified by analysing direct S 0 reflections and impact damage by S 0 back-wall echo amplitude. Large delaminations gave a poor direct S 0 reflection. Evidence was found for mode conversion at centre plane delaminations.
We report a simple theory for the reduction of substrate modes in quasi-optical power-combining arrays. This qualitative theory predicts that detrimental substrate-mode effects can be greatly reduced through a judicious choice of the array unit cell size. Experimental evidence from quasi-optical tripler grids is presented to confirm the theory. Measured results show a dramatic improvement in the radiation pattern and effective radiated power of arrays with both grounded and ungrounded substrates.
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