The device according to the invention provides a non-contacting
temperature sensing device incorporating micro-bolometric detectors as the suitable
infrared sensors for automotive applications. A first and second
infrared sensors each include an
active infrared sensing element and a temperature drift compensating element. A current bias is applied to the
active infrared sensing element as well as to the temperature drift compensating element, which is identical in structure with the
active infrared sensing element, and the
voltage outputs of these two elements pass through a
differential amplifier. The fluctuation in the substrate temperature or the ambient temperature affects the
active sensing element and the compensating element in the same way, thus it is cancelled out. Instead of using one spectral band of the
infrared radiation, as in the prior art, two
spectral bands are used resulting in a first and second
signal generated by the first and second infrared sensors. A ratio of the first and second signals is obtained. The ratio of the signals is
emissivity independent, so that the device of the present invention provides a more accurate measurement of temperature. The need to compensate for window
contamination is also eliminated by this
two band approach. The filtering elements for the two bands can be multi-layer thin film filters either coated on flat windows or on diffractive micro-lenses. The use of diffractive micro-lenses further reduces the size of the device, and eliminates the need for a separate optical lens.