Longitudinal surface wave method

Potential methods of measurement for dilatation parameters are the damping of transverse and longitudinal surface waves and the damping of vibrating bubbles. For theory and measuring techniques see Wiistneck and Kretzschmar [47]. 

While capillary waves work at comparatively high frequencies, another type of surface waves, the longitudinal waves, can be generated with rather low frequencies so that both methods complement each other. Figure 4.16 shows the schematic of a setup for measuring the characteristics of longitudinal surface waves [201,202]. 

The influence of micellisation on the propagation of capillary waves has been discovered only for solutions of the nonionic surfactant - DePO. The determined values of Z2 are comparable with the results for solutions of DePB but they decrease monotonously with concentration. Therefore, the obtained results evidence that relations (5.284) and (5.285) describe the concentration dependence of the dynamic surface elasticity well. Hence, the method of transverse capillary waves can be used for studies of micellisation kinetics of surfactants with relatively low surface activity. For surfactants with higher surface activity where the formation and disintegration of micelles proceed slower the method of longitudinal surface waves can be used [102, 103]. The characteristics of longitudinal waves are more sensitive to the dynamic surface elasticity, and this allows one to study the micellisation kinetics under the condition... 

Fig. 2 shows the CFRP-sandwich specimen and the transducer mounted on the scanner. Fig. 23 presents a C-scan of the specimen as first interesting result. Only the defects visible from the outside are indicated. The distance between transducer and specimen was smaller than the focal length, so that the angle of incidence at the edge of the sound beam converts the longitudinal waves to Rayleigh-waves in the specimen. These waves provide a very sharp image of the surface. This method opens the possibility for a non-contact acoustic microscope. 

For exciting the surface waves the traditional method of transforming of the longitudinal wave by the plastic wedge is used. The scheme of surface waves excitation is shown in fig. 1. In particular, it is ascertained that the intensity of the excitation of the surface wave is determined by the position of the extreme point of the exit of the acoustic beam relatively to the front meniscus of the contact liquid. The investigations have shown, that under the... 

Capillary Ripples Surface or interfacial waves caused by perturbations of an interface. When the perturbations are caused by mechanical means (e.g., barrier motion), the transverse waves are known as capillary ripples or Laplace waves, and the longitudinal waves are known as Marangoni waves. The characteristics of these waves depend on the surface tension and the surface elasticity. This property forms the basis for the capillary wave method of determining surface or interfacial tension. 

The contact method can be used to obtain the complete set of stiffness constants for samples with much smaller dimensions. In this method [3,5], a piezoelectric ceramic transducer, bonded to one surface of the sample, generated a beam of pulsed 10 MHz elastic waves that was subsequently received by another transducer bonded to the opposite surface. The wave velocity was calculated from the transit time of the ultrasonic pulse measured on a gated time interval counter. Longitudinal and transverse waves were generated using two different types of transducers. 

The Fermi surface topology of cubic nitrides was first studied by Em and Switendick (1965) for TiN. Fig. 3.9 shows the cross-sections of the first three sheets of the TiN Fermi surface. Later, the Fermi surface was calculated by the KKR method and compared with the experimental data by Schadler, Weinberger, Klima and Neckel (1984), but no essential difference from the results by Ern and Switendick was found. Fig. 3.9 shows that the electrical conductivity of TiN is electronic in nature. This is evident from the position of the Fermi energy inside the metal states band. Other calculations of Fermi surfaces have been carried out by Fong and Cohen (1972) for NbN and by Ivashchenko (1984) for ZrN. The latter work also studied the relation between the Fermi surface topology and the phonon spectra. It is known that for longitudinal acoustic phonons there may be a decrease in frequency for the wave vectors q, at which the generalised susceptiblity x(q) reveals maxima. This situation may take place if the Fermi surface has lane-parallel parts. It has been shown that this is true for ZrN, and it may explain the appearance of phonon anomalies in ZrN. The presence of x(q) maxima also leads to an increase... 

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