Calibrating the Potential Difference Vibrating Probe humming bird logo

Calibration of the SVET




Physical Description of Scanning Vibrating Electrode.

Wire Probe Construction
The 'wire probe' as it is called is a miniature spherical capacitor plate on the end of a short wire shaft. The wire shaft is insulated its entire length with the exception of its ball tip. The tip's fluffy platinum coating has large surface area and large capacitance. When it is vibrated in an electrical field, the field generates a small current in the probes capacitor plate which can be measured by the attached electronics. The two metal-bimorphs attached to the shaft allow the probe to be vibrated in the X and Y direction independently. The X- and Y-vibrational frequencies are different and currents generated in the probe tip can be resolved by lock-in amplifiers into separate X- and Y-currents (Ix and Iy). The ability of the X- and Y-currents to be resolved make this instrument a two-dimensional vibrating probe. The separate X- and Y- currents can be recombined to produce a total current in the XY-plane with an associated vector length and angle. (Figure modified from Kunkel, 1991).

Model of an Electrical-Potential Point-Source and a Scanning Vibrating Electrode.

Electrical Source Model
In order to calibrate the SVET one uses the fact that a known electrical current injected via a microelectrode will create a precisely known spherical potential field surrounding the orifice of the microelectrode. This field exhibits an equivalent potential drop along radii at equivalent distances from the orifice. This represents shells of equipotential which can be used to calibrate the probe vibrated in the appropriate direction on that spherical surface. Repeating this procedure in the X- and Y- directions away from the source provides separate X- and Y- calibrations as well as any corrections to either due to minor non-orthogonality of the X- and Y-vibration directions. (Figure modified from Kunkel, 1991).


If you have questions about calibrating the various probes or the University of Massachusetts Vibrating Probe Facility, email its PI, Joe Kunkel
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Page maintained by Joe Kunkel, joe@bio.umass.edu.
Copyright(c) 1996. Created: 96/04/21 Updated: 00/11/25