Pepperl+Fuchs' ultrasonic sensors detect objects made from materials such as wood, metal, or plastic regardless of their shape or color. These objects can be solid, liquid, or in powdered form. The only requirement is that they are able to reflect sound waves back to the sensor. Some objects, however, could reduce the operating range. These include objects with a large, smooth, and slanted surface, or porous targets such as felt, wool, or foam rubber.