Hello Adel,
Polyethylene is IR transparent but it looks like the gel is blocking the IR energy from the skin to TMP006. Gel could also be creating an unwanted thermal insulation from the skin causing low ambient temperature change rate.
We have conducted a few experiments to measure the skin temperature using TMP006 but it did not involve using any gel like substances. To be able to assist you soon, it would be of help if you could provide us pictures of the setup. If you do not wish to disclose the details in this public forum please email me (abhishekmuppiri@ti.com).
Best Regards,
Abhi Muppiri
Applications Engineer
MHR- Sensing Products
Texas Instruments
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