Despite of the insignificant mass of these dust grains they have such a high velocity that the impact energy is capable to damage or destroy parts of spacecrafts. The sensitive area of one sensor is 100 x 100 mm 2 . Piezo-electric microphones are attached to the foil. When a particle hits the foil, they give signal that is proportional to impact momentum. Particle impact creates a cloud of free electrons and ions from the foil.
Energetic particles can penetrate the foil and create a plasma cloud also behind the foil.
These charges are collected by high voltage sense wires, which form dense wire grids below and above the metal foil. Combining the signals from the sense wires and the piezo-electric microphones one can determine the mass and velocity of impacting particle.