Acoustical Properties of Anisotropic Materials

Several acoustic properties of anisotropic media have been investigated by the pulsed ultrasonic method and the results analyzed in terms of plane waves traveling through an infinite medium. Single crystals of ammonium dihydrogen phosphate (ADP) and potassium dihydrogen phosphate (KDP) were the subjects of this study and in each case velocity measurements were used to compute a complete set of elastic moduli. Coupling between modes which results in the simultaneous generation of two modes by a transducer and in the transfer of energy between modes during a reflection was studied. The phenomenon of acoustical birefringence in ADP was particularly investigated and it was found that all of the three modes with wave normals in the 45° direction in the yz plane are propagated in different directions making non‐zero angles with the wave normals. A case in which the anisotropic property of the medium causes anomalous beam spreading is reported and the circumstances leading to this condition are discussed.