Speakers
Description
A thermochromic liquid crystal film is used as a detector of heat variations occurring on the surface of a solid material, allowing its thermal diffusivity to be obtained in an experimental setup like the well- established Lock-in Infrared Thermography with punctual excitation [1]. A novel configuration is described, where the thermochromic sensor is in direct contact with a thin sheet of the material to be measured, onto which the intensity modulated laser beam is focused. In this way, this is a rear detection configuration [2]. The thermochromic film changes its visible color depending on the increase in temperature that the solid undergoes when exposed to a surface heat flux [3]. These variations are recorded with a convectional CCD optical camera, obtaining thousands of images over time, which are then handled by an algorithm that performs digital Lock-in processing [4] to recover the amplitude and phase-lag thermograms at the laser modulation frequency. These thermograms are then analyzed to obtain the thermal diffusivity of the solid using the slopes method for a thermally thin sheet [1]. We also describe the calibration of the thermochromic liquid crystal film to establish the relationship between absolute temperature value and the pure digital color component, as well as its subsequent use to measure the thermal diffusivity of five different reference sheets, ranging from good to poor heat diffusers, demonstrating the versatility of this inspection method over a wide series of materials.
[1] A. Mendioroz, R. Fuente-Dacal, E. Apiñaniz, A. Salazar, Rev. Sci. Instrum. 80, 074904 (2009). https://doi.org/10.1063/1.3176467
[2] C. Ibarra-Castanedo, J. R. Tarpani, X.P.V. Maldague, Eur. J. Phys. 34 S91 (2013). https://doi.org/10.1088/0143-0807/34/6/S91
[3] J. Stasiek, A. Stasiek, M. Jewartowski, M.W. Collins, Opt. Laser Technol. 38, 243 (2006). https://doi.org/10.1016/j.optlastec.2005.06.028
[4] E. Vargas, A. Bedoya, A. Borges, A. Calderón, O. Delgado, E. Marín, Software X 32, 102397 (2025). https://doi.org/10.1016/j.softx.2025.102397
