V.2 No 1

9

Transversal acoustic wave in gas

As a result of the carried out investigation, we determined that the electrostatic type of the construction whose shape is shown in Fig. 4a and 4b satisfies these requirements best.

Fig.4. General form of radiator/receiver of transverse acoustic wave: a) construction of the radiator/receiver; b) its front view as an assembly

In this construction, the radiator/receiver consisted of the glass-textolite base 1, upon which a plate of linoleum 2 was bonded to suppress a spurious radiation. In the plates the cuts were done to feed through them the terminals of the stationary copper armatures 3. A current-conducting membrane 5 served as the moveable armature. It was pulled with the help of the current-conducting plates 6 over the spacer 4 having two windows divided by the partition. The membrane cross section was made a little less than the related windows size, its two halves could oscillate pure transversely. The front view of the radiator as an assembly is shown in Fig. 4b. The windows size of the half-oscillator was chosen in the view of effective work in the band 6 – 10 kHz.

As we said above, to improve the radiator directivity, the radiator and receiver were placed into the trapezoidal trumpets having flat walls parallel to the wave polarisation plane. On the outside, the trumpets were additionally screened with the sound-absorbing material and screened from the electric background interference as well. The trumpet of the radiator was placed on the moveable base helping to vary the distance between the radiator and receiver and the angle between their polarisation planes.

2.3 The circuits providing the antiphase radiation/reception of an acoustic oscillations

In addition to the specially developed construction of the radiator/receiver calculated for the radiation/reception of the transversal acoustic wave, we have developed the special circuits supplying the power to the radiator and picking an antiphase signal over the transversal acoustic wave receiver. It facilitated to obtain more precise characteristics of the studied phenomenon.