How does double sheet detection work?

The ultrasonic transmitter transmits sound from the bottom to the product layer. The emitted signal makes the layer vibrate. As a result, a small sound wave is spread to the other side of the layer, which is analyzed by the ultrasonic receiver on the other side. In the case of superimposed layers (double layers), the signal is weakened so much that it barely reaches the receiver. Read more about the operation of double sheet detection sensors.