Calibration of the open-flat coil-based tunnel diode oscillator technique (OFC magnetometer) for quantitative extraction of physical characteristics of superconductive state
Sg. Gevorgyan et al., Calibration of the open-flat coil-based tunnel diode oscillator technique (OFC magnetometer) for quantitative extraction of physical characteristics of superconductive state, PHYSICA C, 366(1), 2001, pp. 6-12
We are developing a flat coil-based tunnel diode oscillator technique, whic
h can be used for detection of changes of distances with similar to1 Angstr
om absolute and similar to 10(-6) relative resolution. It is also an excell
ent radio frequency Q-meter for detection of changes similar to 10(-9) W of
absorption in small-volume specimens. We are using it for high-resolution
study of various weakly expressed peculiarities of the superconductive stat
e in thin plate-like HTS (in particular, the peculiarities of vortex motion
, allowing determination of some material parameters). But, for correct ext
raction of physical characteristics by this sensitive technique there is ne
ed to calibrate properly both the shifts in resonant frequency (inductance
change) and the amplitude (Q-factor change) for the technique. The problem
here is much complicated compared with a solenoid coil-based traditional te
chnique. In this report we discuss only the method of calibration of coil's
resonant frequency change (testing field's configuration change) with copp
er plates, allowing correct transfer of the measured shifts of frequency to
changes of distance from the coil face. The results show an exponential de
crease of the sensitivity with a distance from the coil. The data allow est
imating the optimal sizes for the samples for a given coil design. For such
samples the frequency shifts are proportional to the sample area. The data
shows also the imperfections of the used flat coil's design causing some d
ecrease of sensitivity in a current technique. We discuss ways to make such
a perspective technique much better. (C) 2001 Elsevier Science B.V. All ri
ghts reserved.