Electric potential due to a ring electrode

Electrical sensors utilizing ring electrodes mounted on cylindrical rods have been used by several workers to measure the resistivity of marine sediments. As the resistivity of sediment is dependent upon the water content of the sediment, such measurements are extremely valuable for determining the density of sediments. Recently, ring electrodes have also been used in instrumentation to determine fluctuations in the marine sediment-seawater interface due to erosion or deposition. In the past, approximate formulas have been used to evaluate the response of the sensors. In this work, an exact formula is derived, and it is shown that the previous formulas are in error by up to 5%. Although this is not serious for most borehole logging applications, it is essential to use the exact formulas to interpret data from electromagnetic sediment level sensors