[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 ~1010­106 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.

Compact liquid analyzer based on a resonator with a lateral excitation electric field.

A compact hardware-software complex for measuring the electrical and mechanical parameters of a liquid based on a piezoelectric resonator with a lateral exciting electric field has been developed. It is shown that the modulus of the electrical impedance of the resonator near the resonant frequency decreases monotonically with an increase in conductivity of the contacting liquid. The obtained dependences can be used as calibration curves for measuring conductivity in the range of 100-10,000 µS/cm. A method for the simultaneous determination of the modulus of elasticity, viscosity, and permittivity of a liquid using the electromechanical equivalent scheme was developed and tested on a mixture "water - glycerol" with the different glycerol content.

Microbial acoustic sensor test-system based on a piezoelectric resonator with a lateral electric field for kanamycin detection in liquid.

A microbial test-system for real-time determination of low/residual concentrations of kanamycin in a liquid without the need for special labels is presented. The main element of the system was a piezoelectric resonator excited by a lateral electric field based on an X-cut lithium niobate plate 0.5 mm thick with two rectangular electrodes on one side. On the other side of the resonator, there was a 1.5 ml liquid container. As a sensory element we used Escherichia coli B-878 microbial cells, which are sensitive to kanamycin. For measurement 1 ml of this cells suspension was placed in a liquid container and then the test liquid in the amount of 2 µl containing kanamycin was added. The change in the real part of the electrical impedance of the resonator before and after the test liquid addition was used as an analytical signal which indicated the presence of kanamycin. The lower limit of determination of kanamycin turned out to be 1.0 µg/ml with an analysis time of 10 min. The test-system allows to detect kanamycin in the presence of such antibiotic as ampicillin and polymixin.

Influence of the conductivity of a liquid contacting with a lateral electric field excited resonator based on PZT ceramics on its characteristics.

The influence of the conductivity of a liquid contacting with a piezoelectric resonator with a lateral electric field based on a PZT piezoceramic plate was experimentally and theoretically investigated. In this resonator the shear component of the mechanical displacement, which does not lead to radiation losses upon contact with the liquid, was prevalent. The frequency dependences of the real and imaginary parts of the electrical impedance of the resonator in the frequency range 50-300 kHz showed the presence of three resonances at frequencies of 68.7, 97.8 and 264 kHz with the values of the electro-mechanical coupling coefficient of 12.2%, 14.7% and 6.5%, respectively. The quality factor of each resonance in contact with the liquid turned out to be significantly higher than the quality factor of the resonator with a longitudinal acoustic wave based on lithium niobate. The dependences of the maximum value of the real part of the electrical impedance of such a resonator on the conductivity of the liquid for each resonance were obtained. This experimental data turned out to be in a good agreement with theoretical results obtained by using the method of equivalent circuit.

Effect of the conductivity of a thin film located near the acoustic delay line on the characteristics of propagating SH0 wave.

The results of the study of the influence of the conductivity of a thin film located with a certain gap above the acoustic delay line on the characteristics of propagating acoustic wave with a quasi-shear-horizontal polarization (SH0) are presented. The delay line was made of Y-X lithium niobate plate with a thickness of 200 µm containing two interdigital transducers for exciting and receiving SH0 wave. The operating frequency range of the delay line was equal to 2.6-3.8 MHz. The 1 mm thick glass plate with a film of the given conductivity applied on one plate's side was placed above this delay line with the some air gap. The change in the phase of output signal of the delay line was measured at the various values of the width of this gap. As films with the various values of the conductivity, tin dioxide films deposited on a glass plate by high-frequency reactive magnetron sputtering in the oxygen-argon mixture were used. It has been shown that the velocity of SH0 wave propagating in the delay line under investigation depends on the film conductivity and the width of the gap between the delay line and conductive film. The dependences of the change in the SH0 wave velocity on a width of the gap between the surface of the delay line and conductive film were constructed, as well as on the film conductivity. The comparison of the experimental results with the theoretical data showed their good agreement.

The sensor for measuring the micro-displacements based on the piezoelectric resonator with lateral electric field.

Theoretical and experimental studies of the influence of a thin metal film on the characteristics of a piezoelectric resonator with a lateral electric field showed the possibility of creating a micro-displacement meter in the range of 10-300 µm. For the experiments, two resonators based on the plates of PZT piezoceramics with a thickness of 3.56 and 4.46 mm with resonant frequencies of ~96 and ~260 kHz for both resonators were used. It has been experimentally established that in both cases, with an increase in the width of the gap between the free side of the piezoelectric resonator and thin aluminum film, the frequency of the parallel resonance and maximum value of the real part of the electrical impedance increase and reach saturation. Besides, it has been shown that the relative change of these values with a change in the width of the gap in the range 10-300 µm increases with decreasing the thickness of the resonator. In this case, the frequency of the series resonance practically does not change. It has been also established that the sensitivity of the resonator to the presence of a conducting film at the resonant frequency of ~96 kHz is significantly higher in comparison with the resonant frequency of ~260 kHz. The experimental results are in the qualitative agreement with the theoretical data.

The effect of the conductivity of a film located near a piezoelectric resonator with a lateral electric field based on the PZT ceramics on its characteristics.

In this paper, we investigated theoretically and experimentally the effect of the conductivity of the film located in the immediate vicinity of the free side of a piezoelectric resonator based on the PZT ceramics on its characteristics. It is shown that with increasing the conductivity of the film at first the parallel resonant frequency does not change, then it decreases in a certain interval and after that remains practically constant. With increasing the width of the gap between the film and the resonator, the resonant frequency increases and reaches the saturation. At that the degree of the total frequency change decreases with decreasing the conductivity of the film. We also investigated the dependence of the maximum value of the real part of the electrical impedance on the film conductivity at the different values of the width of the gap between the film and the resonator. The dependences of the maximum value of the real part of the electrical impedance on the width of the gap between the film and the resonator are also obtained for different values of the film conductivity. A comparison of the theoretical and experimental data showed their good qualitative agreement.

The influence of viscous and conducting liquid on the characteristics of the slot acoustic wave.

The influence of the liquid with the different values of conductivity, permittivity, and viscosity on the characteristics of the slot mode in the structure consisting of delay line with propagating shear - horizontal acoustic wave of zero order (SH0) and upper piezoelectric plate separated by the air gap was experimentally investigated. The delay line made of the Y-X lithium niobate plate 0.2mm thick contained two interdigital transducers for the excitation and reception of acoustic wave in the frequency range of 2.6-3.8MHz. The upper plate represented the 0.5mm thick plate of Z-X lithium niobate. The excitation of the slot mode led to the appearance of the sharp resonant peaks on the frequency dependencies of insertion loss and phase of the output signal. It has been found that the depth and frequency of these peaks depend on the parameters of liquid contacting with the upper plate. The possibility of the use of the slot mode in the pointed structure for the identification of liquids with the different values of the conductivity, viscosity, and permittivity was shown. The qualitative explanations of the obtained experimental results are presented.

The influence of the metal film, placed close to the free side of the piezoelectric lateral electric field excited resonator, on its characteristics.

The influence of the width of the gap between the free side of the piezoelectric lateral electric field excited resonator and the metal film placed on the dielectric plate on the frequencies of the parallel and series resonances was experimentally and theoretically studied. The measurements were carried out in the temperature range of 14-45 °C. It has been shown that the change of the gap width from 0 up to 3.5 mm leads to the change of the parallel resonant frequency on 1.3% at the constant temperature. At the same conditions the change of the series resonant frequency does not exceed 0.07%. Theoretical analysis quantitatively confirmed the experimental dependencies of the aforementioned frequencies on the gap width at the room temperature. At that the maximum difference between the theoretical and experimental values of the parallel and series resonant frequencies in all cases does not exceed 1.2%. The obtained results may be used as the basis for the development of the sensors for the measurement of the displacement in the interval of 0.2-2 mm in the temperature range of 15-45 °C.

The influence of the conducting film on the characteristics of the lateral electric field excited piezoelectric resonator.

The effect of a thin layer with the finite surface conductivity located near the lateral electric field excited resonator on its characteristics is studied theoretically and experimentally. It has been shown that for the fixed distance between the free side of the resonator and conducting layer with increasing the surface conductivity of the layer the resonant frequency of the parallel resonance remains initially practically constant, then sharply decreases in a certain range and then insignificantly changes. For the fixed value of the layer conductivity the parallel resonant frequency increases at the increase in the gap between the resonator and layer and then achieves the saturation. The maximum change in the frequency of the parallel resonance corresponds to a zero gap when the layer conductivity varies over the wide range is equal to ∼1%. The frequency of the series resonance decreases only by ∼0.08% due to the change in the layer conductivity. The obtained results may be useful for the development of the gas sensors based on the lateral electric field excited piezoelectric resonator conjugated to the gas sensitive film, the conductivity of which changes in the presence of the given gas.

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.

Gasoline sensor based on piezoelectric lateral electric field excited resonator.

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.

The acoustic sensor for rapid analysis of bacterial cells in the conductive suspensions.

The possibility of using the acoustic sensor on the basis of a two-channel delay line for rapid analysis of bacterial cells in the conductive suspensions was investigated. The dependencies of change in phase and insertion loss of output signal of the sensor on conductivity of buffer solution with various concentrations of cells due to a specific interaction "bacterial cells - mini-antibodies" for electrically open and electrically shorted channels of delay line were measured. It has been found that these changes have the most values for the electrically open channel. It has been also shown that the sensor rapidly responds to the specific interaction and the time stabilization of the phase and insertion loss of output signal is less than 10min.

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 3-4MHz with record values of Q-factor of ∼15,000 in both cases.

Array of piezoelectric lateral electric field excited resonators.

An array containing two resonators placed on X-cut lithium niobate plate has been experimentally investigated. The resonator's lateral electric field was directed along the Y-crystallographic axis. It has been shown that stable resonance exists for a longitudinal acoustic wave propagating along the X-axis in the area between the electrodes. A layer of special damping coating was deposited around the resonators and on the part of electrodes to suppress parasitic oscillations induced mainly by Lamb waves. Frequency dependences of the real and imaginary parts of electric impedance/admittance were measured for every resonator to find resonant frequency and Q-factor with series and parallel resonances. The optimal values of width of electrode coating for every resonator were revealed which provide good resonance quality. The measurements of parameter S12, which characterizes a degree of acoustical coupling between the resonators, have shown its value to be higher than 50dB in the absolute value in all the cases considered. This means that the resonators under study are entirely acoustically decoupled. Thus it has been demonstrated that the damping layer not only provides a sufficiently good quality of every resonator's resonance, but it also assures their entire acoustical decoupling.

High frequency shear horizontal plate acoustic wave devices.

It has been shown recently that shear horizontal acoustic waves propagating in piezoelectric plates whose thickness h is much less than the acoustic wavelength lambda possess a number of attractive properties for use in sensor and signal processing applications. In order to exploit the potential benefits of these waves, however, one needs to fabricate devices on very thin plates. We have developed a suitable fabrication method which can be used to realize devices on such thin plates. In this method, the device is first fabricated on a plate of normal thickness (approximately 500 microm) and the substrate is then lapped from the back side to reduce the thickness. The technique has been utilized to realize devices on plates of thickness less than 70 microm. A shear horizontal plate acoustic wave (SH-PAW) delay line of fundamental resonant frequency greater than 25 MHz and insertion loss less than 7 dB has been realized on a 60 microm thick Y--cut, X--propagation lithium niobate substrate. The device also shows strong response near the third harmonic frequency of 75 MHz.

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.

Characteristics of fundamental acoustic wave modes in thin piezoelectric plates.

The characteristics of the three lowest order plate waves (A(0), S(0), and SH(0)) propagating in piezoelectric plates whose thickness h is much less than the acoustic wavelength lambda are theoretically analyzed. It is found that these waves can provide much higher values of electromechanical coupling coefficient K(2) and lower values of temperature coefficient of delay (TCD) than is possible with surface acoustic waves (SAWs). For example, in 30Y-X lithium niobate, the SH(0) mode has K(2)=0.46 and TCD=55 ppm/degrees C. The corresponding values for SAW in the widely used, strong coupling material of 128Y-X lithium niobate are K(2)=0.053 and TCD=75 ppm/degrees C. Another important advantage of plate waves is that, unlike the case of SAWs, they can operate satisfactorily in contact with a liquid medium, thus making possible their use in liquid phase sensors.