  In this Letter, we propose and experimentally demonstrate a simple method to
provide additional in-formation by conductivity measurements of soils. The AC
electrical conductance of the soil is measured while it is exposed to a
periodic vibration. The vibration-induced density fluctuation implies a
corresponding conductivity fluctuation that can be seen as combination
frequency components, the sum and the difference of the mean AC frequency and
the double of vibration frequency, in the current response. The method is
demonstrated by measurements on clayey and sandy soils.
