By Josh Perry, Editor
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In a recent article from Advanced Thermal Solutions, Inc. (ATS), a leading-edge engineering company based in Norwood, Mass., the design for thermocouples was examined to create a sensor that would limit measurement errors at microscale.

Creating a micropipette thermocouple. (Advanced Thermal Solutions, Inc.)

“As an example, a thin film made of carbon nanotubes presents an extreme challenge, as the film is only 100 nm thick, or about 1/1000 of the diameter of an average human hair,” the article explained. “At this scale, the material has practically no thermal mass, so the temperature of the film can easily be affected by most temperature transducers.”

The article highlighted research into sensors using glass micropipettes as a base with tip diameters of only 2-30 micrometers. The micropipettes were created by heating a glass tube and pulling it apart to form a finely-tapered section. The micropipettes were filled with a tin-based soldering alloy and a beveler sharpened the tip.

A nickel film coated the outside of the micropipette and the nickel combined with the exposed tin at the tip to create the thermocouple junction. The sensors were calibrated in a water bath at temperatures of 21-40°C.

“Clearly these are not quite like the standard thermocouples that we use for standard thermal measurements,” the article noted, “and the setup and fabrication of the sensors is more involved. The payoff is sensors that have an extremely fast response time to temperature changes, only a few microseconds in air, as well as very little thermal influence on the samples they are testing, which is critical at the small scales.”

It concluded, “This approach may be excessive for most electronics thermal management purposes, but it does illustrate that even something as familiar as a thermocouple can be approached in many different ways. The sizes of these sensors allow them to make temperature measurements with pinpoint precision, and to identify very small heat sources and heat flow paths.”

To see how a standard thermocouple can be created in the lab, watch the video below: