A Doppler Radar for Measuring Irregularities in Rolled Sheet Material

This 9-Gc system used a microwave signal reflected from the surface of a rotating roll of paper or plastic film to detect irregularities in the outer layers of the rolled material. The microwave package comprised a klystron oscillator, silicon dector crystal, and flared wave-guide horn antenna. A standard laboratory oscilloscope was used as the ``receiver'' and display system. Examples of materials tested were: kraft paper, cellophane, polypropylene and polyethylene film. The cellulosic materials absorbed more energy and gave weaker reflections than the polyolefins. The minimum detectable surface ``ripples'' were 0.010 inch high. A simple radar of this sort is useful for the noncontacting monitoring of moving surfaces. It has been used to detect surface motion through heavy protective windows.