SELF

14

S.B. Karavashkin and O.N. Karavashkina

To study the properties of the transverse wave revealed experimentally, we have carried out the experiments determining the regularities of this wave attenuation and phase delay in space. The results of this investigation are presented in Figures 8a and 8b.

Fig.8. Experimental plots of (a) amplitude A_m; (b) phase delay _d ; and (c) average velocity v of transverse acoustic wave propagation, with respect to a distance r between radiator and receiver

We can see from the plots A_m (r) and  _d (r) that the wave propagation pattern is clearly divided into two zones. The near field from 75 to 320 mm is characterised by fast decrease of the amplitude A_m with the distance and by the faster growing phase delay _d. In this field the amplitude vanishes periodically. At the points where it vanishes, the signal phase steps by 180^o, i.e. the wave process inversion takes place. The inversion points are shown in Fig. 8b by the vertical dotted lines. And we have indicated experimentally that as the distance between the radiator and receiver increases, the phase inversion can occur without the amplitude vanishing. If disregarding this inversion in our calculations, the phase delay increased with the distance quite smoothly and faster than in the far field. This is not the reason to say that in the near field the standing waves settle and the transverse wave has the reactive pattern, as it is conventional. The fact of inversion is not enough for it, since the phase delay with the distance growth was indicated quite clearly.