A method is provided for measuring the flow rate of a medium in a volume subjected to a magnetic field. The method allows eutectic powder of alumina and a rare earth aluminate compound to stand at a temperature of 1300-1700 C. The electrically conductive first supporting layer is configured as a sheet having slotted voids in a first direction. Other examples of suitable plants include Balsamorhiza sagittata, Helianthella uniflora, and Tragopogon dubius.