Proximity Sensing Technique using the Photothermal Effect.

A new optical method for the proximity sensing is proposed. The distance from the object surface to the sensor is measured by using the thermal wave generated by the light absorbed at the surface. The proposed method is useful for the surface with a high absorption coefficient. Moreover, the technique can be applied to the specular surface as well as the rough surface if the light is absorbed somewhat at the surface. A modified mirage technique was used for monitoring the amplitude and phase signals of the thermal wave. In the experiment, a black rubber plate and an aluminum mirror were used as the objects. The accuracies of measuring distance are discussed.