  This paper discusses the development and engineering of electrical
spectroscopy for simultaneous and non invasive measurement of electrical
resistivity and dielectric permittivity. A suitable quadrupolar probe is able
to perform measurements on a subsurface with inaccuracies below a fixed limit
(10%) in a bandwidth of low (LF) frequency (100kHz). The quadrupole probe
should be connected to an appropriate analogical digital converter (ADC) which
samples in phase and quadrature (IQ) or in uniform mode. If the quadrupole is
characterized by a galvanic contact with the surface, the inaccuracies in the
measurement of resistivity and permittivity, due to the IQ or uniform sampling
ADC, are analytically expressed. A large number of numerical simulations proves
that the performances of the probe depend on the selected sampler and that the
IQ is better compared to the uniform mode under the same operating conditions,
i.e. bit resolution and medium.
