tailieunhanh - Acoustic Waves Part 7

Tham khảo tài liệu 'acoustic waves part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Shear Elastic Wave Refraction on a Gap between Piezoelectric Crystals with Uniform Relative Motion 169 The first refraction branch with wave number k2 we arrange to name as a usual branch as for it the waves in a moving crystal represent waves of a direct propagation irrespective of a choice of system of reference. Really if using 1 to compare phases of oscillations of a wave in passing exp rkxX-Qf and laboratory system of reference exp rkxX-roi for frequency of a wave in passing system of reference it is not difficult to receive expression Q ra-k 2V . 19 It shows Doppler shift of frequency of a wave and at substitution k2 from 18 determines always positive values of frequencies Q Q k2 ro 1 Psinat -1. On the contrary at the substitution in 19 k2- we receive Q- Q k2- -ro Psinaf-1 -1 and for the second refraction branch we have Q- 0 whereas ro 0. Thus in case of this refraction branch the waves refracted in a moving crystal are in relation to the crystal waves with the reversed wave front but are perceived in laboratory system of reference as waves of direct distribution. Therefore it is possible to name a refraction branch k2- as a reverse refraction branch. As against known results Fisher 1983 Brysev et al 1998 Fink et al 2000 the phenomenon of conjugation of wave front examined by us has of a purely kinematic origin. It is caused by drift action of a medium moving at a transonic velocity along the wave incident from the immobile crystal which exhaustively compensates the reverse propagation of a refracted wave relative to the crystal and eventually provides its spatial synchronism by means of electrical fields induced via the gap with waves that are true of direct propagation in the immobile piezoelectric crystal. On Fig. 4 5 solid lines show typical refraction curves of direct propagating waves which are described by the ends of wave vectors k2 from 18 at change of a direction of a vector wave normal n2 in a plane of incidence. They correspond to two .