I. A. Borodina

Hybridization of acoustic waves in piezoelectric plates

The interaction (hybridization) of different types of acoustic waves of zero and higher orders propagating in lithium niobate piezoelectric plates is theoretically investigated. Different crystallographic orientations of the plates and different directions of wave propagation in them are considered. It is shown that, for an electrically free plate with the propagation direction along any of the crystallographic axes, the dispersion curves have intersection points and hybridization is absent. However, when the propagation direction slightly changes or when one of the plate surfaces is short-circuited, the dispersion curves separate and the waves become coupled. A quantitative coefficient characterizing the degree of wave hybridization with allowance for both mechanical and electric coupling is introduced. It is shown that the dependence of this coefficient on the product of the plate thickness by the wave frequency determines the extent of separation of the dispersion curves of interacting waves. The phenomenon under study is of both fundamental and practical interest, for example, in connection with the problem of an efficient excitation of nonpiezoactive acoustic waves in piezoelectric plates.

An acoustic method for the analysis of bacterial cells

The application of a biological electroacoustic sensor based on a lateral electric-field-excited piezoelectric resonator for the study of bacterial cells that interact with specific bacteriophages, mini-antibodies, and polyclonal antibodies was successfully demonstrated. The determined lower limit of microbialcell detection was approximately of 103 to 104 cells/mL for the duration of the assay of 10 min. The possibility of bacterial-cell detection via interaction with specific agents in the presence of extraneous microbiota was shown. The method allowed us to determine the spectrum of lytic activity of bacteriophages and the sensitivity of microbial cells to bacteriophages. The results of the study showed that application of a sensor piezoelectric lateral-field resonator is a promising technique for the detection and identification of microbial cells and determination of their phage resistance in microbiology, medicine, and veterinary medicine. Furthermore, the results of the experiments made it possible to understand the mechanisms of the processes that occur in a suspension of bacterial cells in the presence of various biological agents. The method also may provide useful information regarding biophysical mechanisms of interactions that occur in microbial populations.

The meter of microdisplacements based on piezoelectric lateral electric field excited resonator

At present the great interest of researchers is stimulated by piezoelectric lateral electric field excited resonators the electric field of which penetrates in contacting vacuum. The characteristics of resonator were studied at moving off its free side the glass plate with a strongly conductive film. It has been shown that parallel resonance frequency unambiguously ties with the gap width between resonator and conducting film. The series resonance frequency does not depend on the gap width but depends on the temperature. The resonators were made on plates of lithium niobate and PZT ceramics. The investigations showed the possibility of the development of the meter of microdisplacements with the temperature compensation on this basis. The ranges of measured displacements are equal 0-2 mm and 0-0.3 mm for resonators on lithium niobate and PZT ceramics, respectively. These devices may be used for continuous monitoring the deformation and crack opening displacement of various constructions.

Analysis of interaction of bacterial cells and bacteriophages in conducting suspensions with an acoustic sensor

The possibility of analyzing bacterial cells infected by a specific bacteriophage, using Escherichia coli as an example, with an acoustic sensor directly in suspensions with different initial electrical conductivities was studied. The analysis was based on measurement of the time dependence of phase and the complete loss of output sensor signals of fixed frequency before and after biological interaction of microbial cells and bacteriophages. The aforementioned sensor makes it possible to detect bacterial cells and assess their viability in conducting suspensions. It was shown that the conductivity of the buffer solution should not exceed 10 μS/cm and the minimum detectable concentration of microbial cells was ~104 cells/mL.

The plate acoustic wave sensor for detection of bacterial cells in liquid phase

The interactions “bacterial cells - bacteriophages”, “bacterial cells - antibodies” and “bacterial cells - mini-antibodies” directly in liquid phase were experimentally investigated with the help of acoustic sensor. The acoustic sensor under study represents two-channel delay line based on the plate of Y-X lithium niobate. One channel of delay line was electrically shorted, the second channel was electrically open. The liquid container was glued on plate surface between transducers of delay line. The dependencies of the change in phase and insertion loss on concentration of bacteriophages, antibodies, and mini-antibodies were obtained for both channels of delay line.

The biological acoustic sensor to record the interactions of the microbial cells with the phage antibodies in conducting suspensions

The acoustic biological sensor for the analysis of the bacterial cells in conducting suspension was developed. The sensor represented the two channel delay line based on the piezoelectric plate of Y-X lithium niobate thick of 0.2mm. Two pairs of the interdigital transducers (IDT) for the excitation and reception of shear horizontal acoustic wave of zero order (SH0) in each channel were deposited by the method of photolithography. One channel of the delay line was electrically shorted by the deposition of thin aluminum film between IDTs. The second channel remained as electrically open. The liquid container with the volume of 5ml was fixed on the plate surface between IDTs by the glue, which did not cause the additional insertion loss. For the first time the influence of the conductivity of the cell suspension on the registration of the specific and nonspecific interactions of the bacterial cells with phage-antibodies (phage-Abs) was studied by means of the developed sensor. The dependencies of the change in insertion loss and phase of the output signal on the conductivity of the buffer solution at specific/nonspecific interactions for the electrically open and shorted channels of the delay line were obtained. It was shown that the sensor successfully registered the interactions of microbial cells with phage-Abs in the range of the conductivity of 2-20 μS/cm on the model samples A. brasilense Sp245 - specific phage-Abs. The sensor in the time regime of the operation fast reacted on the specific/nonspecific interaction and the time of the stabilization of the output parameters did not exceed 10min.

Use of mini-antibodies for detection of bacteriophages by the electroaucoustic analysis method

The possibility of detecting bacteriophages using phage mini-antibodies by the electroacoustic analysis method using bacteriophages FA1-59b was shown. It was found that the frequency dependence of the real and imaginary parts of the electrical impedance of a resonator with a suspension of phages and the appropriate antibodies significantly differs from that of the resonator with a control virus suspension without addition of mini-antibodies. The amount of FAl-Sp59b bacteriophage in the analyzed suspension varied from ~1010 to 106 phage/mL; the analysis did not take longer than 5 min. The change in the real or imaginary parts of the electrical impedance at the fixed frequency near the resonance after addition of specific mini-antibodies in the suspension appeared to be an optimal information parameter to obtain reliable information. These results may allow the development of a biological sensor to identify and quantify viruses in the liquid phase.

The acoustic sensor for bacterial cell detection in conductive suspensions

The influence of the conductivity of cell suspension on the registration of specific interactions of bacterial cells with antibodies, mini-antibodies, and bacteriophages with the help of acoustic sensor on the basis of a two-channel delay line was studied. The dependencies of change in output insertion loss and phase of sensor on conductivity of buffer solution at the specific and nonspecific interactions for electrically open and electrically shorted channels of delay line were measured. It was shown that sensor successfully registered the specific interactions with antibodies, bacteriophages, and mini-antibodies for the range of suspension conductivity of 2-50 μS/cm.

Composite lateral electric field excited piezoelectric resonator

The novel method of suppression of parasitic oscillations in lateral electric field excited piezoelectric resonator is suggested. Traditionally such resonator represents the piezoelectric plate with two electrodes on one side of the plate. The crystallographic orientation of the plate is selected so that the tangential components of electric field excite bulk acoustic wave with given polarization travelling along the normal to the plate sides. However at that the normal components of field excite the parasitic Lamb waves and bulk waves of other polarization which deteriorate the resonant properties of the resonator. In this work we suggest to separate the source of the HF electric field and resounded piezoelectric plate by air gap. In this case the tangential components of the field in piezoelectric plate do not practically weaken but normal components significantly decrease. This method is realized on the composite resonator having the structure “glass plate with rectangular electrodes - air gap - plate of 128 Y X lithium niobate.” It has been shown that there exist the optimal value of the width gap which ensure the good quality of series and parallel resonances in frequency range 3–4 MHz with record values of Q - factor of ∼15000 in both cases.

A composite piezoelectric resonator with a lateral electric field

A new method of suppressing parasitic oscillations in a piezoelectric resonator with excitation of the transverse electric field is proposed. The method is based on spatial separation of the high-frequency electric field of a source and the resonating piezoelectric plate by means of an air gap. In this case, the tangential components of field in the piezoelectric plate are practically not attenuated, while the normal components are significantly reduced. The method is implemented by means of a composite resonator consisting of a glass plate with rectangular electrodes, an air gap, and a plate of lithium niobate 1of 128 Y–X cut. It is shown that there is an optimal width of the air gap that provides a good quality of series and parallel resonance in a frequency range of 3–4 MHz with a maximum quality factor of ∼15000 in both cases.