AN ENERGY MEASURING TECHNIQUE

摘要

1293794 Measuring impedance and current density; electro-medical apparatus F HOFFMANN-LA ROCHE & CO AG 21 Oct 1969 [21 Oct 1968] 29998/69 Headings G1U G1N [Also in Division H3] The impedance of or current density in a current conducting medium, 10, e.g. brain tissue or a solution, is measured by inserting into the medium a probe 11 whose head 13 carries spaced current electrodes 16, and adjusting the current I allowed to flow from the medium into one electrode and then from the other electrode back into the medium until it equals the current that would have flowed through the volume of the medium displaced by the head. In this condition the probe head introduces no disturbance into the medium, and from the magnitude of the current I and the known dimensions of the head the current density in the medium may be calculated. The impedance of the medium may also be determined since minute sensing electrodes 15 are provided to detect the voltage difference E between the current electrodes. The no-disturbance condition is arrived at by measuring the voltage difference Eoc when the current I = 0 and then increasing I until the voltage difference has been reduced to a predetermined fraction k of Eoc, k being a constant for all media, determined by calibrating the probe in a medium of known impedance. The cylindrical or cubical probe head 13 is of epoxy material and the current electrodes 16 of silver chloride are disposed at its two ends 14. The sensing electrodes 15 are positioned in the centres of the current electrodes, and the voltage difference between them is, after amplification (21), both indicated (211) and used to adjustably control (221) the current I.