[2B2] Liquid crystal sensors for ultrasonic displacement measurements
M Turvey, R Edwards, O Trushkevych and D McKnight
University of Warwick, UK
Liquid crystals can be used as removable film sensors for the visualisation of ultrasonic fields. The standard method is laser vibrometry; however, this requires scanning across the surface. Previously, a polymer-dispersed liquid crystal film has been shown to allow for fast and low-cost mapping of ultrasonic field displacement. Here, it is shown that thermochromic liquid crystal (TLC) sensors that change colour with temperature can be similarly used to map displacement fields. TLCs absorb heat generated by the ultrasound field, which is observed as colour on the sensing film. Temperature maps can be extracted from optical photographs of the sensor and related to displacement and are benchmarked using interferometry and thermography of the sample. The speed and low cost of the sensor makes it ideal for initial measurements over large areas, condition monitoring and fast transducer characterisation. Additionally, the visual nature of the sensor makes it ideal for automation using robotic vision and intuitive understanding of beam paths for training purposes. The current sensors are most suitable for high-power ultrasound, about 1 W continuous wave and frequencies in the MHz range or higher, although they were demonstrated to work at frequencies as low as 40 kHz. Future work will enhance the sensitivity and frequency range.
