This last factor and the electrical characteristics of the probe coil are related to skin depth and the quality factor of the circuit in the ac bridge.
The real part k' of the magnetic susceptibility will affect the imaginary part of the impedance (self-induction) by increasing the magnetic energy within the probe coil. Simultaneously, k" will affect the coil resistance through different energy losses.
Let us look at the interaction between the core materials of the probe coil compared with the reference one; these two components of the ac bridge are mainly characterized by these two parameters: the change in the resistance of the wire in the probe coil and the inductance variation of the wire in the probe coil as presented by Garcia-Martin et al.
where [U.sub.D] is the emf detected by a ballistic galvanometer after reaching equilibrium (null detector on the ac bridge arms), [U.sub.G] is the sinusoidal oscillator excitation tension of the inductance ac bridge at low frequency, and [DELTA]L and [DELTA]R are, respectively, the inductance and resistance variation of the search probe coil impedance with the specimen inserted.
In the second part, we search the relationship between the wire parameters of the probe coil and the physical properties of the core-like sample in the coil axis.
A small probe coil, built with bubble levels attached, is placed in the superconductor's magnetic field at approximately the same radius and height as the moving coil.
The second test is between the superconductor (primary) and a secondary coil attached to the second probe station, but this probe coil is oriented at a right angle to measure the magnitude of the field.