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Monitoring Coaxial-Probe Contact Force for Dielectric Properties Measurement

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  2010 Pittsburgh, Pennsylvania, June 20 - June 23, 2010  1008526.(doi:10.13031/2013.29883)
Authors:   Stuart O Nelson
Keywords:   Contact force, coaxial probe, dielectric properties measurement, load cell, strain meter.

A means is described for measuring and monitoring the contact force applied to a material sample with an open-ended coaxial-line probe for purposes of measuring the dielectric properties of semisolid material samples such as fruit, vegetable and animal tissues. The equipment consists of a stainless steel sample cup, load cell and associated strain meter and an aluminum alignment sleeve to insure that the force acting on the sample is properly transferred to the load cell. The assembly (sample, sample cup, load cell and spacer, in the alignment sleeve) rests on a platform with position adjustable vertically to raise the assembly and provide contact of the sample with a rigidly mounted coaxial probe above the sample holder. The strain meter to which the load cell is connected displays the force between the probe and the sample to facilitate monitoring this contact force. Use of a consistent contact force helps to reduce the variation in results of dielectric properties measurements by this technique.

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