Mechanisms of appearance of backward shear-horizontal waves in potassium niobate plates

摘要

The backward waves with opposite directions of energy transport and phase velocity are in the focus of current studies in physics. Besides they are of interest for possible technical applications. This type of wave motion was previously studied in acoustics mainly in the case of Lamb modes. Nevertheless, shear-horizontal (SH) plate modes, as known, can also be backward waves if the plates are piezoelectric. However, SH backward waves were never observed experimentally. The reason for that is a very narrow frequency range where these waves are found numerically in common piezoelectric materials like ZnO with a relative frequency range of only 2*10-5. As we have recently shown [J. Commun. Technol. Electron., November, 2016], the situation is opposite in the case of superstrong piezoelectric crystals of potassium niobate, for which the wide frequency ranges of the existence of backward waves occur in the X-cut plates, while they are absent in the Y-cut plates. The aim of the present work is to study quantitatively the possible mechanisms that affect the appearance of waves under consideration.