Attenuation Variability in Porous Media: Effects on Phase Delay and Quality Factor

Abstract

Electromagnetic methods of surveying involve the propagation of time varying low frequency electromagnetic fields in and over the earth. This gives rise to a secondary electromagnetic field and a resultant field which is picked up by suitable receiving coil. This research work modelled electromagnetic method of survey using a Cathode Ray Oscilloscope and a signal generator. This work was aimed at relating the effects of phase delay and the quality factor of a propagating signal to some properties of the homogeneous medium, like porosity (compaction), permeability and hydraulic conductivity. River bed sand was used as the sample, it was washed, oven dried, sieved into different grain sizes and the porosity was determined. Each sample was packed in a square box and connected to a signal generator and an oscilloscope. Two sinusoidal waves of the same frequency, but different amplitudes were sent from a signal generator and the measurement was taken at different frequencies. Graphs of frequency were drawn each against phase delay and Q – factor. Graphs of porosity were drawn each against phase delay and Q – factor. In conclusion, we observed that the porosity of a material increased with the decrease in the mixture of its grain size and signals were more attenuated at lower frequencies but as the frequency of the input signal was increased, the material became more permeable to the passage of the input signal.

Keywords: porosity, attenuation coefficient, phase delay, quality factor and electromagnetism