[2B3] Liquid crystal sensors for measurement of ultrasonic displacement
M Turvey, O Trushkevych and R S Edwards
University of Warwick, UK
Current ultrasonic wavefield measurement methods such as laser vibrometry or interferometry can be very time-consuming due to the need for point-by-point scanning. Liquid crystals have been proposed as acousto-optic sensors for ultrasound detection using acoustography or polymer-dispersed liquid crystals (PDLCs). However, limitations apply to their use through the need for polarisers and a water bath for acoustography and a sharp on-off characteristic for PDLCs. Sensors based on thermochromic liquid crystals (TLCs) are proposed here instead for wavefield imaging, where the heat generated by ultrasound being absorbed in the sensing layer results in a change in colour. The use of a colour scale can provide more detailed displacement information than PDLCs, while the output is still visual without the need for polarisers. A temperature change read-out can be extracted by comparing the colour displayed to a colour standard and converting it to temperature via a calibration curve. Possible applications could include initial measurements over large areas, transducer characterisation and condition monitoring via a smart paint. The visual nature of the sensor also makes it ideal for automation through the use of robotic vision.
