  A localized and strong RF magnetic field, created by a magnetic write head,
is used to examine the linear electrodynamic properties of a Nb superconducting
film. The complex reflection coefficient of the write head held in close
proximity to the films is measured as a function of sample temperature. A model
combining a magnetic circuit (magnetic write head inductively coupled to the
sample) and transmission line (microwave circuit) is given to interpret the
linear response measurement. Additionally, this reflection linear response
measurement can be used to determine the temperature dependence of the magnetic
penetration depth on a variety of superconductors.
