Norm Stevens – Development of the Thermopile Detector

In the mid-60’s Norm Stevens developed an antimony-bismuth thermopile detector for an intrusion alarm concept for use in Vietnam.

I recall going down to the Detector Division to see a demo of the device he had set up in one of the halls in the building. It would alarm as we walked by. These kinds of devices are common today, but back then it was a new idea.

After the demo somebody in our Systems Group got the bright idea of using that detector for an IR radiometer (might have been Frank Malinowski, but I’m not sure).

We developed an instrument concept around it and came up with the first IR radiometer for the Mars 1969 mission (Mariners 6 and 7). That instrument and subsequent ones that flew on Missions to Venus, Mercury and Jupiter were very successful.

The detector itself was quite unique. The reticulated couples were deposited on an anodized piece of aluminum foil that was suspended over a piece of sapphire with a hole in it. The Al was then etched away leaving the thermopile elements suspended on a very thin layer of Al oxide (sapphire). The couples defining the active area of the detector were then coated with Bismuth smoke to increase the long wavelength absorption.

While this appeared to be a very fragile structure, not suitable for space environment, it was in fact quite robust. Courtney Manker, Norm’s partner in the project would clean the sapphire film with a single hair from a fine sable artist’s brush. He could easily puncture the film if he was not careful. We were all very dubious that the detectors would survive NASA’s vibe testing, but they survived nicely. I think because there was so little mass associated with the detector, G forces had little effect.

An interesting note on all of the IR radiometers using Norm’s detector was the use of the DC Restore concept (looking at space while DC restoring the electronics before viewing the scene). Frank Malinowski developed the technique and got a patent for it. The concept is in common use today and is in fact used on many SBRC instruments.

 

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