Hi J_P
I think that the magnetic field is not involved in the phenomenon, not directly, the unshielded TR coil it shows that it is involved a change in static E-field or dielectric change, perhaps the key is a perfect balance between a signal from an E-field amplifier and a signal from a RX coil drived by an unshielded TR coil, but two signals that have to do with the aerial E-field. My reflection on Mineoro sensor, If I remember well the gold sheet is very near to antenna or other similar device that is polarized with 27V and this is a sort of capacitor. The polarization acts as a filter for signals less that 27V. The gold is involved not for ions but more simply for its reliability over time (not oxide).
Best regards
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