SMP Research Seminar: Dr Oksana Trushkevych, University of Warwick

Dr Oksana Trushkevych, of the Department of Physics, University of Warwick, will be presenting a seminar on the research carried out by herself and colleague Rachel Edwards. All are welcome to attend.

PDLC Sensors For Ultrasonic Non-destructive Testing Abstract: In this talk I will focus on acousto-optic effects in polymer dispersed liquid crystal (PDLC) films. They show strong promise for fast large area ultrasound sensing and visualisation in a broad frequency range relevant to non-destructive testing, with large area, high speed and resolution, at low cost.

LCs are sensitive to a variety of external influences including acoustic (pressure) waves. They may be used as acoustic sensors, utilising acoustooptic effect. This has led to applications of thick aligned LC films for characterisation of acoustic (ultrasonic) emitters and for acoustic holography. Small samples could also be tested for defects, but the setups are complex and require immersion in a water bath. PDLC films with sufficiently large droplets have recently been shown to change optical properties in response to vibration at ultrasonic frequencies.

This opens interesting possibilities for sensing ultrasound without the need for a water bath or complex setups. We show fast visualisation of plate vibration patterns at high harmonics using a layer of PDLC on top of the plates. The frequency range in which the PDLC has been shown to be sensitive is very broad by ultrasound testing standards, and is at least 250kHz to 10MHz (limited by the excitation transducer frequency response). We also show that the absolute displacement of the vibrating plate at those frequencies, as referenced using laser interferometry, is of the order of 10nm and smaller, while the PDLC film thickness is orders of magnitude larger (100m). We share a vision of thin, flexible PDLC sensors that will be low cost, passive and offer simple fast imaging, with the potential for application directly to components as smart paints.

Host: Professor Helen Gleeson.