A. A. Teplykh

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.

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.

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.

The peculiarities of propagation of the backward acoustic waves in piezoelectric plates

The characteristics of backward acoustic waves in piezoelectric plates under different electrical boundary conditions were investigated. It has been shown that electrical shorting of the plate leads to increasing and decreasing the phase velocity for backward and forward branches, respectively. The peculiarities of the hybridization effect of backward waves were studied.

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.

Correspondence - Acoustic waves in a structure containing two piezoelectric plates separated by an air (vacuum) gap

This paper presents experimental results for the characteristics of acoustic waves propagating in a structure containing two parallel piezoelectric plates (I and II) separated by an air gap. Plate I, made of Y-X lithium niobate, contained two interdigital transducers that excited and received an acoustic wave with shear-horizontal polarization. Piezoelectric plate II, made of lithium niobate, was placed above and between the transducers, separated by a fixed gap. For its certain orientation, the amplitude-frequency characteristic showed sharply defined resonant attenuation peaks, which were situated at an equidistant separation from each other. The depth of the peaks was observed to decrease with a wider gap between the plates. It has been stated that these peaks are associated with the resonant reflections of a slot acoustic wave across the width of plate II. Experimentally determined phase velocities and electromechanical coupling coefficient for the slot wave in the structure under study are in a good agreement with theoretical values for various crystallographic orientations of plate II. A comparison between the experimental and theoretical results has allowed us to state two conditions for the slot wave to exist. The structures described may be employed for noncontact excitation of acoustic waves in the plates and for the development of various liquid, gas, and temperature sensors.

Gasoline sensor based on piezoelectric lateral electric field excited resonator

HIGHLIGHTSMeter for analysis of gasoline based on piezoelectric resonator with lateral electric field is developed.Maximal resistance of the electrical impedance of resonator is suitable parameter of sensor.Possibility of considering temperature of gasoline at its analyses is shown.Example of finding octane number of unknown sample of gasoline is shown. ABSTRACT It has been shown that by using piezoelectric lateral electric field excited resonators based on X – cut LiNbO3, one can determine the octane number of gasoline. The measured dependence of gasoline permittivity on its octane number has shown that there is an ambiguous connection between pointed parameters. We have demonstrated both theoretically and experimentally that the value of the real part of the electrical impedance on the frequency of parallel resonance uniquely associates with the octane number of gasoline contacting the free side of the resonator. At that the frequency of parallel resonance does not depend on permittivity/octane number of gasoline. An example of determination of the octane number of a mixture of two different samples of gasoline is given.

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.

Noncontact determination of thin films conductance by SH0 plate acoustic waves

The paper is devoted to the development of noncontact acoustic method of the determination of thin film conductance by using shear-horizontal zero order (SH0) acoustic waves in thin piezoelectric plates. The method is based on the registration of changes in velocity and attenuation of acoustic waves in a piezoelectric plate due to placing the structure “film under study–dielectric substrate” on the certain distance from the plate. The limits of measured values by the suggested method are determined. The theoretical data are compared with the experimental results.

Effect of a Liquid on the Characteristics of Antisymmetric Lamb Waves in Thin Piezoelectric Plates

The effect of a perfectly elastic nonviscous nonconducting liquid on the characteristics of a zero-order antisymmetric Lamb wave (the A0 wave) in a 128YX LiNbO3 plate, whose thickness is small compared to the wavelength, is studied both theoretically and experimentally. A method for calculating the velocity and attenuation of this wave depending on the value of the parameter hf (h is the plate thickness and f is the wave frequency) is proposed. In addition, the characteristics of an A0 wave in a piezoelectric plate that is in contact with two different perfectly elastic nonviscous nonconducting liquids on its two sides are investigated. A possibility for the development of a proximate analyzer of liquids on the basis of such a structure is indicated.