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PP Principle

The permittivity probe works as a mutual impedance probe in quadrupole configuration: An AC-current of adjustable frequency and amplitude is injected into the comet surface medium through the two transmitter electrodes. The current generates a potential distribution inside the medium, which is monitored by two sensitive receiver electrodes. The observed potential difference is influenced by the electrical properties of the material inside the half-sphere underneath the Lander, defined by the distance of the used transmitter electrodes. Measuring the current, the potential difference and the phase difference between the injected current and the resulting potential variation gives the permittivity of the material inside the half sphere as a function of  frequency.

For water ice the dielectric constant and conductivity change drastically in the frequency range between 100Hz and 10 kHz, depending on the purity of the ice and its temperature. See the three pictures below: potential distribution in the surrounding of the lander, the change of the properties as a function of sphere size and therefore depth and the typical dependence of the dielectric constant and conductivity of water ice a a function of frequency and temperature.