[1A2] Thermochromic liquid crystal sensors for ultrasonic displacement measurements
M Turvey, O Trushkevych, D J McKnight and R S Edwards
University of Warwick, UK
Liquid crystal films can be used as removable sensors for visualisation of ultrasonic fields. The standard method for visualisation is laser vibrometry; however, this can be time consuming due to scanning requirements.
Here, we show thermochromic liquid crystal (TLC) sensors for wavefield imaging. Heat generated by absorption of the ultrasound vibration is observed as a colour change. Temperature change in the sensor can be extracted from optical photographs and related to ultrasound displacement. Two visualisation tasks are shown. Firstly, the measurement of resonant modes of a flexural transducer will be presented, with interferometry and thermography used for benchmarking. Secondly, internal defect detection through visualisation of side-drilled holes in a metal block will be shown.
The speed and the low cost of the sensor make it ideal for initial measurements over large areas and for fast transducer characterisation. Additionally, the visual nature of the sensor allows for intuitive understanding of beam paths for training purposes. This generation of sensors are most suitable for high-power ultrasound, about 1-5 W continuous wave and frequencies in the MHz range. We have adapted them to work at frequencies as low as 40 kHz and future work will optimise them for lower powers.
Here, we show thermochromic liquid crystal (TLC) sensors for wavefield imaging. Heat generated by absorption of the ultrasound vibration is observed as a colour change. Temperature change in the sensor can be extracted from optical photographs and related to ultrasound displacement. Two visualisation tasks are shown. Firstly, the measurement of resonant modes of a flexural transducer will be presented, with interferometry and thermography used for benchmarking. Secondly, internal defect detection through visualisation of side-drilled holes in a metal block will be shown.
The speed and the low cost of the sensor make it ideal for initial measurements over large areas and for fast transducer characterisation. Additionally, the visual nature of the sensor allows for intuitive understanding of beam paths for training purposes. This generation of sensors are most suitable for high-power ultrasound, about 1-5 W continuous wave and frequencies in the MHz range. We have adapted them to work at frequencies as low as 40 kHz and future work will optimise them for lower powers.
