A. M. Shikhabudinov

New method of parasitic mode suppression in lateral-field-excited piezoelectric resonator

A new method of parasitic mode suppression in piezoelectric resonators with transverse (lateral) electric field is described, which employs the partial coverage of electrodes by a damping layer. The potential of the proposed method is demonstrated for a resonator based on an X-cut lithium niobate plate. It is experimentally confirmed that an acoustic wave with transverse electric polarization exhibits stiffening, the degree of which depends on both the electromechanical coupling coefficient and the wave aperture

Biological sensor based on a lateral electric field-excited resonator

This paper describes a biological sensor based on a lateral electric field-excited resonator using an X-cut lithium niobate plate. Its potential was shown through the example of biological interaction between bacterial cells and specific bacteriophages. The detection was based on the analysis of the measured real and imaginary parts of electrical impedance for a resonator loaded by the biological suspension under study. It has been shown that the sensor is sensitive to specific interactions between bacterial cells and specific bacteriophages in a pure state as well as in the presence of extraneous microflora. The degree of electrical impedance variation resulting from the biological interaction depends on the numbers of phage particles and bacteria cells. The sensor may be used not only for the qualitative analysis of bacteria but also for their quantitative detection.

Obtaining phage mini-antibodies and using them for detection of microbial cells with an electroacoustic sensor

Phage mini-antibodies to bacterial cells of strain Azospirillum brasilense Sp245 were obtained, and the possibility of using them for detection of microbial cells with a lateral field excited piezoelectric resonator was studied. It has been found that the frequency dependences of the real and imaginary parts of electrical impedance of such a resonator loaded with a suspension of A. brasilense Sp245 cells with the mini-antibodies differ significantly from the dependences of the resonator with a control cell suspension without mini-anti-bodies. The limit of possible determination of the concentration of microbial cells is found to be 103 cells/mL upon interaction with mini-antibodies. It has been ascertained that detection of A. brasilense Sp245 cells with the aid of mini-antibodies is possible even in the presence of other cultures, for example, E. coli BL-Ril and A. brasilense Sp7. Therefore, it has been shown for the first time that detection of microbial cells with an electroacoustic sensor is feasible.

The study of piezoelectric lateral-electric-field-excited resonator

The piezoelectric lateral-electric-field-excited resonator based on an X-cut lithium niobate plate has been investigated. Two rectangular electrodes were applied on one side of the plate so that the lateral electric field components were parallel to the crystallographic Y-axis and excited the longitudinal wave in the gap between the electrodes. The region around the electrodes was covered with a special absorbing varnish to suppress the spurious oscillations. The effect of the absorbing coating width on the resonant frequency and Q-factor of the lateral field-excited resonator was studied in detail with the series and parallel resonances for different width of the gap between the electrodes. As a result, we found experimentally the parameter regions of pure resonances and the boundaries of value variation for resonance frequency, Q-factor, and effective electromechanical coupling coefficient.

Elastic and viscous properties of nanocomposite films based on low-density polyethylene

The physical properties of nanocomposite materials which contain nanoparticles of metals and their compounds stabilized within a polymeric dielectric matrix are currently being studied. These materials show a low acoustic impedance, resulting in their use as low-perturbing substrates for thin piezoelectric plates, as well as matching and damping layers for bulk acoustic wave devices. Mechanical properties of the materials which contain various Fe and Fe2O3 nanoparticle concentrations are experimentally defined in the paper. It has been shown that the acoustic impedance of the materials under study may be varied by more than 30% and 40% for longitudinal and shear acoustic waves, respectively, within the same technological procedure. The velocities of bulk longitudinal and shear acoustic waves can be purposefully changed by more than 40% and 29%, respectively.

Liquid sensor based on a piezoelectric lateral electric field-excited resonator

The influence of viscous and conducting liquid on the characteristics of a piezoelectric lateral electric field-excited resonator based on the X-cut lithium niobate plate has been investigated. It has been found that the contact of a free surface of such resonator with conducting or viscous liquid leads to the substantial variation of its electrical impedance/admittance. The analysis has shown the modulus of electrical impedance or admittance at any frequency near the parallel or series resonance to be a parameter unambiguously associated with the conductivity or the viscosity. This parameter is more sensitive to the variation of the liquid conductivity or viscosity as compared to the widely used for this purpose resonant frequency whose variation area is essentially smaller. By this means the liquid conductivity and viscosity affects unambiguously on the change of electrical impedance and admittance modulus whose measurement at a fixed frequency should present no problem in practice. Consequently, the lateral field excited resonator we have described may be employed as a liquid conductivity and viscosity meter with an appropriate graduation.

Determination of the spectrum of lytic activity of bacteriophages by the method of acoustic analysis

The changes in the electroacoustic parameters of a cell suspension due to the interaction between cells and bacteriophages were studied both in pure culture and in the presence of extraneous microflora. It was shown that the specific changes in the electroacoustic parameters of a cell suspension under the influence of bacteriophage occur only in the microbial cells that are sensitive to this bacteriophage. A sensor unit allowed us to distinguish the situation where bacterial cells are infected with specific bacteriophages of the control experiments from the situation without such infection. An approximate criterion for specific interactions between bacteriophages and cells in the suspension was developed. According to this criterion, the change in electrical impedance of a sensor unit must not be less than ~1%. The standard microbiological technique of sowing the cells infected with bacteriophages on solid nutrient media was used as a control. The possibility of using the method of electroacoustic analysis to determine the spectrum of lytic activity of bacteriophages has been shown for the first time. The results that we obtained can be used to develop a new express method for determining the sensitivity of microbial cells to bacteriophages.

The research of the piezoelectric crystal resonators with the lateral field excitation

The ways of the suppression of the undesired modes and Q-factor improvement in the lateral field excited resonators are demonstrated on the example of the lithium niobate crystal of X-cut. The values of resonance frequency and Q-factor for two crystallographic axes orientations of electric field were found by the measurements of the frequency dependencies of the real and imaginary parts of the electrical impedance.

Immunodetection of bacteriophages by a piezoelectric resonator with lateral electric field

It has been demonstrated that electroacoustic analysis with polyclonal antibodies can be used for bacteriophage detection. The frequency dependences of the real and imaginary parts of electrical impedance of a resonator with a viral suspension with antibodies were shown to be essentially different from the dependences of a resonator with control viral suspension without antibodies. It was shown that ΦAl-Sp59b bacteriophages were detected with the use of antibodies in the presence of foreign virus particles. The ΦAl-Sp59b bacteriophage content in the analyzed suspension was ~1010–106 phages/mL; the time of analysis was no more than 5 min. The optimally informative parameter for obtaining reliable information was the change in the real or imaginary part of electrical impedance at a fixed frequency near the resonance upon the addition of specific antibodies to the analyzed suspension. It was demonstrated that the interaction between bacteriophages and antibodies can be recorded, offering good prospects for the development of a biological sensor for liquid-phase identification and virus detection.

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.