V.2 No 1

13

Transversal acoustic wave in gas

4. Experimental results and their analysis

Two photographs of the experimental device are shown in Figures 6a and 6b: at the parallel and at normal orientation of the polarisation planes of radiator (the upper left device) and receiver (the upper right one).

a)                                                                              b)

Fig.6. General form of experimental set when polarisation planes of radiator and receiver are parallel (a) and normal (b) to each other

At the oscillograph screen (bottom right) you can see that when the signal source was turned by 90^o, the signal vanished. When the radiator turning more slowly, the sinusoid at the screen slowly diminished till the noise level, when the phase displaced by 90^o. And when it displaced by 180^o, the sinusoid increased up to maximum. In turning further, this pattern repeated. The diagrams _m() and A_m() in Figures 7a and 7b corroborate it. They were measured at the distances between the radiator and receiver equal to 99 mm (Fig. 7a) and 620 mm (Fig. 7b). As we will show further, these distances correspond to the near (Fresnel zone) and far fields (Fraunhofer zone).

Accurate to the error of the experiment, in both cases we can see that when the radiator turning by 180^o, the signal phase varied also by 180^o, and the amplitude had 8-form in the polarisation planes parallelism direction, as it is usual for a transversal wave.

Fig.7. Experimental diagrams of amplitude A_m and phase _m of transverse acoustic wave with respect to angle a between polarisation planes of radiator and receiver in induction zone (a) and in wave zone (b)

Comparing the obtained results for the near and far fields, we see that when passing to that far, the phase diagram sharpens, and the amplitude diagram smears. This is caused by the fact that the spurious reflection increasingly effects on the results of experiment as the distance between the radiator and receiver increases.

On the whole, the obtained results unambiguously evidence that the experimental device radiated and indicated the transversal wave in gas medium.