Oscillations, Waves, and Interactions - GWDG

Liquids: Formation of complexes and complex dynamics 373
Figure 4. Construction of a variable-path-length cell for measurements between 0.6 and
4.6 GHz [42]. 1, cavity for sample cell with thermostatic jacket (not shown); 2 and 3, hole for
inlet and outflow of sample; 4, sapphire rod serving as delay line and holding the piezoelectric
zinc oxide transducer layer on its rear face; 5, mount for 4; 6, spring clamped electrical
contact; 7, coaxial line; 8, plastic disc supporting the inner conductor of 7; 9, N-type
connector; 10, T-branch; 11, high precision ball-bush guide; 12, specially honed and lapped
bush; 13, bush; 14, piezo-translator; 15, backlash-free joint; 16, as 11; 17, finely honed and
lapped pin; 18, sliding carriage; 19, mounting plate; 20, finely polished reference plane; 21,
ball-and-socket joint; 22, adjustment device; 23, differential screws for sensitive adjustment
of the sapphire rod direction; 24, ball gudgeon preventing the sample cell from rotating; 25,
spring for the ball-and-socket joint 21; 26, thermostatic channels.
faces formed by piezoelectrical transducers [36]. In order to reduce diffraction losses
plano-concave [37] and biconcave devices [38,39] are also employed. As an illustration,
a detail drawing of a plano-concave cell is shown in Fig. 3. In many applications the
focussing effect of concavely shaped faces includes further favourable features, such
as a reduction of undesired effects from disturbances due to small changes in the
resonator adjustment on variation of temperature and superior mode spectrum as
compared to the biplanar cell.
In the upper frequency range (ν � 10 MHz) absolute α measurements are enabled
by transmitting pulse-modulated sonic waves through a cell of variable sample length.
The specimen cells mainly differ from one another by piezoelectric transmitter and
reciever unit and by their sample volume [40–42] which, because of the smaller wavelength,
may be much smaller at high frequencies. As an example the construction of
the variable-path-length cell for hypersonic measurements between 0.6 and 4.6 GHz
is presented in Fig. 4.