Low cost broad spectrum liquid crystal thermal camera - Page 1
Forum section: electronics / general

author: Avaalon
author_rank: Newbie
timestamp: March 17, 2023, 03:22:05 pm
content: Hello. I did saw on Youtube guy building interesting design thermal camera using just black paint and sensor liquid crystal painted thin film:It's not as sensitive, fast and sharp as microbolometer camera but it's affordable. Most expensive part is germanium lens. Advantage I imagine here is that broad spectrum could be used for imaging since depending absorption properties of pigment, correct me if I'm wrong. Cheap liquid thermochromatic used for nail can be purchased here:https://www.aliexpress.com/item/1005005161458736.html?spm=a2g0o.productlist.main.63.a986ca70ZZs5L9&algo_pvid=90e824e1-2371-46c2-ad21-4c8cca9035d7&algo_exp_id=90e824e1-2371-46c2-ad21-4c8cca9035d7-31&pdp_ext_f=%7B%22sku_id%22%3A%2212000031926455910%22%7D&pdp_npi=3%40dis%21EUR%218.89%216.22%21%21%21%21%21%40211be54b16790660981713910d06eb%2112000031926455910%21sea%21LT%21924777360&curPageLogUid=ZtX8w76ZaUIMMaybe this type of camera could be improved by using different paint for blackest material vanta black aka vertically stacked carbon nanotubes? Would it have good absorption in the SWIR, MWIR, LWIR spectrum? Are there cheaper material thermal lenses that can be used? Would peltier cooling in camera improve sensitivity?

author: Fraser
author_rank: Super Contributor
timestamp: March 18, 2023, 07:27:27 am
content: I have experimented with this liquid crystal material and found sheets of Edmund Optics liquid crystal thermally sensitive sheets.The sheets of liquid crystal material are offered in different temperature ranges to suit a particular task. Those temperature ranges are relatively small.My findings were that the liquid crystal coating and liquid crystal sheets were too insensitive for use as a practical "thermal camera screen". Where the temperature sensitive sheets did offer some use was when laid over a PCB that offered a relatively uniform component height to the liquid crystal sheet. The hot components on the PCB quickly revealed themselves. The same can often be achieved by spraying a PCB with IPA or coating it with one of those Rosin Flux atomizers (I don't like either method though!)So in precis, Liquid Crystal thermal detection does work, but is very limited in performance. It is not a cheap material and a lens would be needed. Your money would be far better spent on a budget thermal camera. They have never before offered such excellent value for money. Even a simple 80x60 pixel thermal camera would be better than the Liquid Crystal based "thermal camera". Dare I say, a MLX90640 32x24 pixel camera would be more useful in terms of thermal sensitivity and temperature measurement !

author: Fraser
author_rank: Super Contributor
timestamp: March 18, 2023, 07:48:23 am
content: Regarding improving performance...Cooling the liquid crystal film works against sensitivity as the film reacts in a certain range of temperature and cooling it pushes the film further away from where it shows change. It does not improve the thermal sensitivity in any way.Making a more efficient "thermal collector" on the front face of the film would improve performance but thermal mass is your enemy so the film and any coating must be kept as thin as possible. The poor thermal sensitivity of the liquid crystal material will outweigh most/all improvements that could be used though.This film is so insensitive that in a camera application, being used as the detector, you need high energy scenes. Take a look at the Planck's Law to see what this means in everyday life.Fraser

author: Fraser
author_rank: Super Contributor
timestamp: March 18, 2023, 07:52:34 am
content: Past discussions.....https://www.eevblog.com/forum/thermal-imaging/using-a-liquid-crystal-impregnated-plastic-sheet-for-thermal-imaging/msg1098458/#msg1098458https://www.eevblog.com/forum/thermal-imaging/source-of-thermal-imaging-plastic-sheeting-is-lcrhallcrest-us-and-uk-family-owne/msg2177240/#msg2177240https://www.eevblog.com/forum/thermal-imaging/thermal-data-acquisition-using-nir/msg1096001/#msg1096001