Laboratory Generation of Electricity from Earth's Rotation Through Its Own Magnetic Field

Earth rotates through the axisymmetric part of its own magnetic field, but a simple proof shows that it is impossible to use this to generate electricity in a conductor rotating with Earth. However, we previously showed theoretically that this proof contains an assumption that could be violated, and its conclusion circumvented (Chyba & Hand, Phys. Rev. Applied 6, 014017-1-18 (2016)). This requires using a soft magnetic material with topology satisfying a particular condition and having a low magnetic Reynolds number Rm. We realize these requirements with a cylindrical shell of MnZn ferrite. Controlling for thermoelectric and other confounding effects, we show that this system generates a continuous DC voltage and current of the (low) predicted magnitude. We test and verify other predictions of the theory: voltage and current peak when the cylindrical shell's long axis is orthogonal to both Earth's rotational velocity v and magnetic field; voltage and current go to zero when the entire apparatus (shell together with current leads and multimeters) is rotated 90^o to orient the shell parallel to v; voltage and current again reach a maximum but of opposite sign when the apparatus is rotated a further 90^o; an otherwise-identical solid MnZn cylinder generates 0 voltage at all orientations; and a high-Rm cylindrical shell produces 0 voltage. We also reproduce the effect at a second experimental location. Ways in which this effect might be scaled to generate higher voltage and current may now be investigated.