Abstract
The effects of spring and magnetic field distortions on the output voltage of an electromagnetic moving-coil geophone were studied theoretically and experimentally. Spring distortion is caused by vibrations of large amplitudes. Magnetic distortion is due to the nonuniformity of the magnetic flux through the moving coil. The perturbation method was employed to solve the nonlinear vibration equation. The calculated vibration velocity was then combined with the magnetic flux analysis to study the combined effects of spring and magnetic distortions on the moving-coil geophone. It was found that the third harmonic in geophone output is dominated by spring distortion while the second harmonic is caused primarily by magnetic distortion. The behaviours of geophone output predicted by the mathematical model were verified by experiments in which the coil was wound unevenly and the magnetic flux was kept constant.
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