Optical Presence Sensor
A solution to the problem is the reflective system.
In this system, the sensor and source are collocated in the same package, while a reflective target is positioned on the opposite side of the object pathway.
When shiny objects are being sensed, the photosensor may be overloaded by the direct reflection at close ranges.
The solution to this type of problem is often very simple: the optical path-is'canted at-a small-angle with respect to the pathway of the objects being sensed.
Optical presence sensor