You have started a very interesting conversation. Another aspect to this subject is that the radiation given off by a source would have a characteristic bell curve with a distribution of frequencies that peak and the nominal temperature. In the case of a dog for example there is only a 2 degree C difference from human temperature. It would take a much more sophisticated sensor than the ones incorporated in a PIR to see the difference. There have however been some interesting idea put forth and you have the basis here for some good experiments.
Another good point. On the same concept I referenced above (shuttering), we used notch filters on top of an array of PIR elements to narrow our view to certain areas of the IR spectrum (both long and short waves) to create a number of detectors, which we used to detect specific gases (in our case measuring the absorption caused by the presence of gases instead of directly reading a warm body).
Another good point. On the same concept I referenced above (shuttering), we used notch filters on top of an array of PIR elements to narrow our view to certain areas of the IR spectrum (both long and short waves) to create a number of detectors, which we used to detect specific gases (in our case measuring the absorption caused by the presence of gases instead of directly reading a warm body).
