We're currently trying to build a portable temperature sensor for the purposes of estimating human core temperature. This is a bit of an engineering problem (more to do with choice of materials than choice of IC), but it does involve electronics and related issues like heat transfer, so I feel it's relevant enough to this board. Please correct me if I'm wrong in this regard.
Since the device is portable and must be in contact for extended periods of time, invasive (rectal, esophageal) or cumbersome (axillary, in-ear/tympanic) methods of measurement are infeasible, leaving skin temperature as the next best alternative, since core temperature can normally be fairly well estimated from these values given certain constraints, such as known position on the body, shielding from environmental effects and so on. Contactless detection via infrared is unworkable since the uncertainty is greater than ±0.5°C, which is outside the acceptable range for clinical significance (i.e. the uncertainty needed in order to diagnose issues such as fever). Thus, the sensor needs to be in direct contact with the skin.
However, this creates further issues, the most pressing of which is the immediate cooling of the skin upon contact with the sensor, which will invariably be the temperature of the environment rather than the skin. While the skin will eventually return to its previous temperature, it normally takes around 20-30 minutes for this to happen. This is considered too long for our purposes. While insulation has reduced the difficulties caused by the sensor module's different thermal conductivity "permanently" reducing the skin temperature near the module, the additional thermal mass has not helped with stabilization times. As can be seen in the above articles, this has been approached in different ways - for instance, using a thermocouple and feedback-controlled heater adjusted for skin temperature to detect whenever temperature flux is zero (and thus whenever the sensor has the same temperature as the skin). This has a faster response since less heat will travel out of the skin, creating a lower discrepancy that needs stabilizing - however, the energy and power requirements of the heater are outside the scope of the battery and will quickly drain it, making this unsuitable for portable use.
Would anyone know of any way to get a good response time (<10 minutes at the very least... 2-5 minutes as a rough estimate perhaps) for such a device while keeping within clinical significance parameters of <±0.5°C - either by active (but low power) or passive (perhaps by superior thermal insulation) means?