| 摘要 |
The primary field generated by a transmitting loop or coil energized with a AC current induces secondary currents within the body which in turn generate a secondary field. The secondary field is picked up by a pick-up loop or coil. A compensation coil is energized so that no voltage is induced in the pick-up coil when a reference body having the same resistivity is substituted for the body in which measurement are to be carried out. To compensate for body movements, the primary field can have a lower and a high freqency component. Since the high frequency components penetrate the body only to a predetermined depth (or not at all) the difference between the picked-up high or low frequencies signals is substantially independent of the distance between the object being measured and the measuring apparatus. Sectional views of larger areas of the body are generated by scanning sequentially with a plurality of transmitters spaced from each other and energized with phase-shifted currents and display of the corresponding picked-up signals on a cathode ray tube.
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