A double coil method for simultaneous measurement of electrical and magnetic properties of spherical sample

We have been studying a method for simultaneously measuring the electrical and magnetic properties of spherical sample (SRPM method). In the SRPM method, the differences in the impedance of a circular coil with a sample and an identical one without a sample are vectorially measured, and the values are compared with the one calculated by the formulae including the sample parameters. Then the properties are simultaneously estimated by finding their agreements. As the sample is inserted into the coil and pulled out of the coil alternately, the properties obtained by this method often contain the large error caused by the deviation from ideal condition of the position the sample and the coil. For the improvement of such situation, a method using double coils is proposed. The spherical sample is coaxially placed on the center of both coils, and the connections of the two coils can be switched to pass the current through the coils in the same direction or in opposite directions. A new formulae for obtaining the difference in the impedance of the coil is derived to apply to such conditions. In order to confirm the validity of these formulae, the conductivity estimated by the SRPM method and the DC four-probe method were compared. They are within 1.8%