Quality assessment of varistor ZnO structures by resonant ultrasound spectroscopy

摘要

Varistors are produced from ZnO cylindrically-shaped structures whose quality depends on varying technological conditions at stages of their shape forming and firing. Therefore, the varistors are tested at the final phase of production and faulty elements are excluded. We propose to test the quality of ZnO structures at an earlier stage of production to eliminate defective structures from further and expensive processing. The recommended method applies resonant ultrasound spectroscopy that meets the demand for limiting the costs introduced by an additional measurement procedure. This paper presents the prepared economical measurement system that can be used for this purpose. The proposed method measures one of the lowest resonant frequencies and dimensions of the tested specimen. The measured quantities enable the estimation of a parameter that is proportional to the sound velocity in the tested ZnO sample and gives information about the quality of the ZnO structure. Detailed experimental data obtained for two batches of ZnO structures, on purpose prepared in different ways, are analysed to confirm the usefulness of the applied procedure in industrial applications.