Non-linear dielectric spectrometer. (a) Equipment involved, (b) cylindrical flat electrodes tetrapolar cell, (c) low EEI impedance tetrapolar cell, and (d) tripolar cell. In (b) and (c) 1 and 4 correspond to outer electrodes, while 2 and 3 correspond to inner electrodes. In (d) 1 and 2 are connected together and the system acts as a tripolar analyzer, instead of a tetrapolar one. Numbers 1 to 4 correspond to the connections of the SI1287 unit depicted in (a).