The electrical properties of soil at frequencies up to 100 megacycles per second; with a note on the resistivity of ground in the United Kingdom

Previous papers have described the use of a laboratory method for investigating the electrical properties of soil under alternating-current conditions at frequencies ranging from 50 c./sec. up to 10 Mc./sec. The measurements have now been extended to 100 Mc./sec., and the results are described in the present paper. Substantially the same method has been used, but in order to provide an overlap with the previous work, the present measurements cover the frequency range of 1 to 100 Mc./sec. Check measurements carried out on small fixed resistors indicate that the overall accuracy at the highest frequencies is better than 20 per cent. As a result of this work it may now be stated that for normal samples of surface soil taken from the National Physical Laboratory, the conductivity is of the order of 108 e.s.u. at all frequencies up to 1 Mc./sec., rising to rather less than twice this value at 100 Mc./sec. Over the same frequency range, the dielectric constant decreases from about 105 at a frequency of 50 c./sec. to about 15 at 100 Mc./sec. An appendix to the paper draws attention to the electrical-resistivity maps of England and Wales and of Southern Scotland, recently published by the British Electrical and Allied Industries Research Association. These maps indicate in coloured form the apparent resistivity of the ground for a depth of 500 ft. A comparison is made between the values so indicated and those obtained by the author in previously described measurements on samples of soil obtained from various sites in England and Wales.