Review of Progress in Quantitative Nondestructive Evaluation

Analysis of Microstrip Patch Antennas for Dielectric Measurement

Brunswick, ME

The microstrip patch antenna has been employed by Shimin [1] to measure the dielectric constant of thin slab materials. Although the applicability of the method in [1] is not restricted by the size of the material under test, the etching of the patch and the introduction of the ground plane on the material cannot be practical in many cases. A more practical approach based on the microstrip antenna is reported in [2] for the measurement of the dielectric constant of snow. The technique employs the antenna as an applicator. The antenna is brought to the close proximity or in contact with the surface of the material in order to cause interaction between the antenna’s near field and the object. The result is a change in the input impedance and the resonant frequency of the antenna. Similar to short antenna applicators [3], a patch antenna applicator can take measurements under resonant and off resonant conditions. However, at resonance, achieving accurate measurements are straight-forward. The technique can be applied to solids as well as to liquids with small or large losses. It can also be used in the thickness measurement of layered materials.