For flat objects it is very important that the tilt of the surface is not greater than half the opening angle. This is to ensure that radar beams reflected from the surface are reflected back into the sensor for proper detection. Round objects have the advantage that they are rotationally symmetric. This makes alignment much easier, as round objects always reflect something back to the sensor. Compared to a flat object with comparable size, the signal strength of the reflected beam is reduced.
Radar beams can penetrate certain materials (such as plastic panes). The covers do not require full transparency to be penetrated by radar beams. For example it is possible to look through black plastic sheets. A small portion of the radar beam will be reflected back to the sensor from the cover. Through a special teach-in-algorithm the sensor learns the profile of the reflection. It subsequently measures objects behind the cover, as if the cover is none-existent.
The radar sensor is also available in a configuration, where it operates similar to a light barrier. Via a special teach-in-algorithm the sensor learns the reflector position. After teaching the sensor monitors the reflector position. If an object breaks the line of sight between the sensor and reflector, the sensor output switches. The advantage of this configuration is that it is unnecessary for the object to reflect a signal back to the sensor. Therefore even randomly-shaped objects or radar absorbing objects can be reliably detected.