Resistivity Measurement of a Small-Volume Sample Using Two Planar Disc Electrodes and a New Geometric Factor

In this work, we derive a new geometric factor in oblate spheroidal coordinates for conductivity or resistivity measurements using two planar disc electrodes based on the electromagnetic field theory and neglecting the electrode polarization effects. The experiments were conducted on saline solutions contained in a grounded metallic bath to validate the obtained values of the derived geometric factor. The effect of the polarization impedance at the electrodes is found to be negligible when using relatively nonpolarizable silver-silver chloride electrodes at a frequency of 3 kHz. Our experimental results also show that the resistivity values determined using both the new geometric factor and a commercial conductivity meter are in good agreement for small electrode radius, interelectrode spacing and depth of sample, therefore making it a promising technique for applications in microfluidics devices. The effects of current density and temperature on the measurement results are also presented.