Search for leaky SAWs in crystals with the aid of acoustic axes for bulk waves

A new method to search for leaky surface acoustic waves (SAWs) in crystals is suggested. The method is based on the relationship explained in the paper between leaky wave branches and a specific type of bulk wave reflection problem in which two bulk waves propagate in the direction of an acoustic axis. The unique property of the method is the possibility to predict exact values of the propagation velocity in certain points on leaky wave branches without solving any boundary problem. The method under discussion has given the authors the chance to find a leaky wave branch on the X-cut of berlinite, in spite of the opinion in literature that leaky waves do not exist there. This leaky branch contains an isolated solution in the form of a SAW without leakage at 122.5° from the Y-axis. A similar leaky branch is also found in the X-cut of langasite. The coincidence of a degeneracy point on a leaky branch and a value determined by the use of an acoustic axis is demonstrated for rotated X-cuts of berlinite. Leaky wave branches related to acoustic axes are found for all three basic cuts of potassium niobate, a crystal distinguished by superstrong piezoelectric coupling. It is shown that quasilongitudinal leaky SAWs in dilithium tetraborate degenerate into the solution of the specific type of reflection problem mentioned above, when the piezoelectric constants of the crystal are decreased