Transformation of 5,5-diaryl-4,5-dihydro-1,2,4-oxadiazoles to 4-arylquinazolines

The transformation of 5,5-diaryl-4,5-dihydro-1,2,4-oxadiazoles to 4-arylquinazolines in boiling acetic anhydride via acyclic 1-acetyloxy-4-aryl-1,3-diaza-1,3-butadienes is described.     

Scattering by periodic cracks and theory of comb transducers

Combs are distributed ultrasonic transducers for the generation of Rayleigh waves in solids. Synchronously excited by subsequent comb teeth, the surface wave grows along its propagation path under the comb. Although sliding contact between the comb and a solid sample is frequently assumed, the mechanical coupling is not weak. This modifies the surface wave propagation conditions to such an extent that the Rayleigh wave no longer exists at the comb–sample interface. Instead, an interface mode propagates, collecting power from each subsequent comb tooth and delivering it to the comb edge to be eventually transformed into a Rayleigh wave outside the comb. Generation efficiency is evaluated for the optimized angle of incidence of the longitudinal wave onto the comb–sample interface.     

Analysis of comb transducers with sliding teeth

Ultrasonic comb transducer generates surface acoustic waves on an elastic substrate by periodic traction exerted by its vibrating periodic teeth on the substrate surface. In this paper, the comb teeth are actually sliding elastic spacers between an acoustic buffer and the substrate. The incident wave in acoustic buffer scatters on periodic spacers producing interface waves in the system which transform into Rayleigh waves at the transducer edges. The full-wave theory of interface wave generation is presented, concluded by efficiency estimation of transformation of the incident wave into the surface wave in the substrate and of the surface waves back to bulk waves in the acoustic buffer. Numerical examples presented for all aluminum substrate, buffer and teeth show the 11-teeth comb combined efficiency for generation and detection on the level of ?40 dB for optimized teeth height.     

Reversing multistrip coupler

A theory of a reversing multistrip coupler (RMSC) is presented based on a previously developed spectral theory of IDTs. It shows that the frequency dependence of the track-changing reflection of a SAW taking place in a RMSC, and the dependence of the reflection of the SAW from a periodic grating reflector are described by the same functions. The reflection of the SAW to the other channel is complete in a narrow frequency band of relative width (2/3) Δv/v if the RMSC is sufficiently long. Several expected applications of RMSCs are discussed, among them SAW dispersive filters, resonators, and low-loss filters.     

Wave generation and scattering by periodic baffle system in application to beam-forming analysis

Directional excitation and detection of sound in the periodic baffle system are analyzed using the method developed earlier in electrostatics. The phenomenon is exploited in phased array transducers applied in ultrasonography, nondestructive evaluation and testing. The nice feature of the applied method is that the matrices of the resulting system of the equations are relatively easy for computations and that the results satisfy exactly the energy conservation law. Illustrative numerical examples present the far-field wave-beam steering generated in a baffle system that may be considered as a model of a linear ultrasonic transducer array.     

Surface acoustic wave diffraction in spectral theory of interdigital transducers

A theory of interdigital transducer is presented that accounts for the surface acoustic wave diffraction. It is formulated with help of the Blotekjaer, Ingebrigtsen, and Skeie expansion method used earlier in the plane-wave theory. Now, the electric field is applied to the breaks in the strips making parts of them polarized with different potentials. This way the finite aperture width transducers are modeled residing within an infinite system of periodic strips. Closed expressions are derived for system working below the Bragg condition. The theory is open for further development accounting for elastic strips, pseudo surface, leaky or even surface skimming bulk waves, for any frequency range, including Bragg reflection exploited in surface wave resonators.