Analysis of Natural Vibrations of Round Flexing Membrane-Type Piezoelectric Transducers with an Arbitrary Dimension Ratio

The problem of natural vibrations of a round exing membrane-type piezoelectric transducer (piezoelectric plate) with an arbitrary dimension ratio is solved in the exact formulation using the finite element method for two variants of fastening the membrane (simply supported and rigidly fixed plate). The natural frequency spectra are analyzed in the resonance and antiresonance regimes. The displacement distributions over the plate surfaces are also analyzed and the dependences of the dynamic electromechanical coupling coefficient are investigated as functions of the geometric dimensions of the piezoelectric transducer, the plate material, and the piezoelectric ceramic composition. The optimum geometric dimensions of the transducer which ensure the maximum dynamic electromechanical coupling coefficient are determined and the value of the coefficient is estimated.     

A Unidirectional Hydroacoustic Receiver

Based on an asymmetric pressure-gradient sensor, which is a disk-shaped piezoelectric transducer installed at the end face of an acoustically stiff tubular cylindrical baffle, a hydroacoustic receiver with a cardioid-like unidirectional directivity pattern has been designed. Its purpose is to minimize the pattern backlobe level. The experimental prototype pattern has a backlobe level of 21 to 23% of the main lobe maximum. A theoretical expression has been derived for the backlobe level as a function of the wave dimensions of the cylindrical baffle. The theoretical backlobe levels agree with the experimental data. The feasibility of lowering the backlobe level down to 13–14% at realizable dimensions of the baffle and the piezoelectric transducer is demonstrated.     

The Hydrachnidae water mites of southwestern Siberia in relation to their participation in arbovirus circulation

The phenomenon of Hydrachnidae association with the tick-borne encephalitic viruses complex has been found out during the study of the role of the Hydrachnidae in the arboviruses circulation. We investigated the fauna, studied the quantity variation and trophic relations of these arthropods and blood-sucking Diptera. It was revealed no trophic relations between blood-sucking Diptera and mite species, where TBE strains were isolated from. On the basis of faunistic and virological study we suppose, that Hydroacarinae got an infection with the virus in the nymphal and imago stages, as well as larvae of mosquitos. Authors also note, that trophic relations between blood-sucking Diptera and chiggers (Trombidiidae) may be important in the arboviruses ecology.