Dependence of Levitation Force on Frequency of an Oscillating Magnetic   Levitation Field in a Bulk YBCO Superconductor
  The dependence of the magnetic field strength required for levitation of a melt textured, single domain YBCO superconductor disc on the frequency of the current generating the levitating magnetic field has been investigated. The magnetic field strength is found to be independent of frequency between 10 and 300 Hz. This required field strength is found to be in good experimental and theoretical[1] agreement with the field strength required to levitate the same superconductor with a non-oscillating magnetic field. Hysteretic losses within the superconductor predicted by Bean's critical-state model[2] were also calculated. The measured data rules out any significant Bean's model effects on the required levitation field strength within the measured frequency range. 
Hamilton Carter, Stephen Pate, George Goedecke
cond-mat.supr-con