One of the interesting things about infrared imaging is that materials that look completely opaque in visible light can behave very differently at other wavelengths.
I was curious whether the known MWIR transparency of some plastics would still work through a complete padded bubble envelope. With the bubbles, multiple layers, printing and adhesive, I wasn’t sure how much would actually make it through.
The experiment was recorded simultaneously in visible light and MWIR. The MWIR image was captured with an Indigo Systems Merlin camera, while a Ximea camera was used for the visible reference.
To make the result easy to recognize, I placed a sheet of A4 paper inside the envelope with the word BUG cut into it.
In the visible image the envelope is effectively opaque, while in the MWIR image enough radiation passes through the material for the hidden pattern inside to remain clearly visible.
The Merlin is a cooled InSb MWIR camera operating in roughly the 3–5 µm band. At these wavelengths the optical properties of a material can be very different from what we see with our eyes, so visible opacity does not necessarily tell us much about its infrared transmission.
The underlying transparency of some plastics in MWIR is well known, but I couldn’t find an example using a complete padded bubble envelope like this. The part I found interesting was whether the multiple layers and bubble structure would still allow enough spatial detail to see something hidden inside.
It was a simple experiment, but the result was better than I expected.
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