A method and apparatus are disclosed which allow for the detection of an object (14) by the generation of a radiated beam (18) and a subsequent reflection by the object (14) of a portion (20) thereof. The detection of particulate object material (16) due to a reflection of a portion (22) of the generated...http://www.google.com/patents/US5418359?utm_source=gb-gplus-sharePatent US5418359 - Method and apparatus for detecting objects with range-dependent blocking
