A New Fog Detection Technology by Using a Current (pA ∼nA) Path on the Interior Windshield of a Vehicle and Application 2008-01-0923

To detect fog on the interior windshield, a new kind of a sensor is introduced and uses the current which changes as a function of the amount of condensation, not an infrared light, temperature, and humidity. The sensor is called a current based fog sensor. An infrared based fog sensor has several limitations that fogging can only be measured on a particular spot of the windshield and a dirty windshield can lead to false triggers. A temperature & humidity based fog sensor has an erroneous possibility to detect fog formation because the dew-point temperature can be exactly calculated only under the stable condition in temperature and humidity. In fact, the temperature and humidity inside a vehicle are not stable in many cases. The current based fog sensor detects fog formation after fog is formed. At that time, the amount of fog is small and fog is not seen by the human eye. This means that the energy to remove fog on the interior windshield can be minimized. The sensing film of the current based fog sensor strongly connects water droplets one another for a stable current path. The current to flow through the surface is less than hundreds of nano-amperes because the surface resistance of the film is still high on the initial fog formation. The control device of the sensor easily measures the current corresponding to the level of moisture on the interior windshield. The current based fog sensor is independent on temperature and humidity. The reason that the sensor is applicable to a vehicle is shown in this paper. And it is proved through several experiments. We also show properties of the current based fog sensor.