B. D. Zaitsev

Investigation of acoustic waves in thin plates of lithium niobate and lithium tantalate

The general properties of fundamental antisymmetric A/sub 0/, symmetric S/sub 0/, and shear horizontal SH/sub 0/ acoustic waves propagating in thin piezoelectric plates have been theoretically investigated on samples of lithium niobate (LiNbO/sub 3/) and lithium tantalate (LiTaO/sub 3/). The results obtained will be useful for a proper development of various physical, chemical, and biological sensors and devices for signal processing based on plate acoustic waves.

Liquid level sensor using ultrasonic Lamb waves

This paper describes a novel, noninvasive method for measurement of liquid level in closed metal tanks that are under high pressure. It is based on the use of ultrasonic Lamb waves propagating along the tank wall. Contact with liquid substantially changes the characteristics of these waves and this can be used as an indicator of liquid presence. Theoretical analysis shows that the symmetric and antisymmetric Lamb wave modes, both fundamental and higher order, are sensitive to presence of the liquid. The optimal wave frequency depends on the thickness of the tank wall and wall material. A prototype level sensor based on this principle has been developed. It uses two pairs of wedge transducers to generate and detect Lamb waves propagating along the circumference of the gas tank. An operating frequency of 100 kHz is found to be optimal for use with tanks having a wall thickness of 30-50 mm. Prototype sensors developed under this program have been used successfully in oil fields in the far northern region of Russia.

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

Reflection of plate acoustic waves produced by a periodic array of mechanical load strips or grooves

The reflection of fundamental acoustic waves propagating in a thin piezoelectric plate by a periodic array of conducting strips of finite thickness or grooves has been theoretically and experimentally investigated. The analysis has shown that electrical shorting and mass loading affect the relationship of neighboring region impedances in a contrary manner. In some cases, these effects are comparable, and there exists a certain strip thickness for each piezoactive fundamental plate mode at which the reflection coefficient can become zero. A high efficiency of grooved reflector for plate acoustic waves was theoretically revealed. Experimental results for mass loading and grooved reflections, which have been obtained for an SH/sub 0/ wave propagating in the Y-X lithium niobate plate, are in a good agreement with the theory. They show a high efficiency of such reflectors and confirm the validity of using a model based on an equivalent circuit for the analysis of their operation. Investigations indicate that nearly 100% reflection of the SH/sub 0/ wave in the lithium niobate plate can be obtained with the use of a mass loading reflector containing 10 silver strips of thickness d/h=0.08 or a grooved reflector containing eight grooves of depth d/h=0.25. Here h is the plate thickness and d is the reflector thickness or depth.

New method of change in temperature coefficient delay of acoustic waves in thin piezoelectric plates

As is well-known, the development of highly effective and thermostable acoustic devices assumes using the acoustic waves with high coefficient of electromechanical coupling (K2) and low temperature coefficient of delay (TCD). At present, it also is well-known that fundamental shear horizontal (SH0) acoustic waves in thin piezoelectric plates possess significantly more electromechanical coupling compared to surface acoustic waves (SAW) in the same material. However, although the value of TCD of SH0 waves is insignificantly less than for SAW, this is not enough for development of thermostable devices. This paper suggests a new way of decreasing TCD of SH0 waves in piezoelectric plates at a high level of electromechanical coupling. This way assumes to use the structure containing the piezoelectric plate and liquid with the special dependence of permittivity on temperature. Theoretical and experimental investigation showed that, for SH0 wave in YX LiNbO3 plate at hf=700 m/s (h=plate thickness, f=wave frequency) the presence of butyl acetate can decrease the value of TCD by six times at K2=30%. In a whole the obtained results open the wide prospect of using SH0 wave in thin piezoelectric plate for development of highly effective and thermo-stable acoustic devices

Hybrid acoustic waves in thin potassium niobate plates

The present article seeks to theoretically predict an effect and namely, the resonant interaction between fundamental acoustic modes propagating in a thin piezoelectric plate. It has been theoretically shown that for certain crystallographic cuts and propagation directions the electrical shorting of one of the strong piezoelectric plate sides may result in a coupling between fundamental acoustic modes. For example, the hybrid mode is generated for a frequency of about 10 MHz by an antisymmetric wave A0 and a shear-horizontal wave SH0, which propagate along the X+15° direction in a metallized Y-cut 100-μm-thick potassium niobate plate.

The energy density and power flow of acoustic waves propagating in piezoelectric materials

It is shown that, for a plane bulk acoustic wave propagating in arbitrary piezoelectric media, the densities of mechanoelectrical and electromechanical energies are always equal in absolute value and have opposite signs. However, in general, the mechanoelectrical and electromechanical power flows of such a wave calculated by the traditional expression for the Poynting vector do not compensate each other, although the total density of these energies is always equal to zero. A discovered discrepancy based on the dissymmetry of piezoelectric constants with respect to the electrical and mechanical indexes may cause difficulties for calculation of important parameters for practical applications such as energy transport velocity of acoustic waves in piezoelectric materials.

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.

Miniature high efficiency transducers for use in ultrasonic flow meters

This paper describes development of a novel, high efficiency transducer for use in ultrasonic flow meters. It is based on conversion of energy between surface acoustic waves (SAWs) and bulk acoustic wave (BAWs). The transducer consists of thin plate of a suitable piezoelectric material whose SAW velocity is greater than velocity of BAW in the fluid. Under these conditions a surface wave traveling on the substrate radiates a bulk acoustic wave in the fluid. We show that with proper design efficient conversion of energy from SAW to BAW and vice versa can be obtained. For example. using lead zirconate titanate (PZT) as the piezoelectric material and water as the fluid, total conversion loss (SAW to BAW and back from BAW to SAW) of less than 3 dB has been obtained.

Anomalous resistoacoustic effect in a piezoelectric-conducting liquid structure

The presence of the anomalous resistoacoustic effect in the case of the propagation of a Bleustein-Gulyaev wave in a piezoelectric-conducting liquid structure is theoretically predicted. As the conductivity of the liquid increases, the wave velocity increases, reaches its maximum, and then decreases. The value of the positive variation of the wave velocity increases with decreasing dielectric constant of the liquid ɛlq and can reach 6% for potassium niobate at ɛlq=2.5. It is shown that there exists a critical value of the wave localization depth above which the anomalous resistoacoustic effect in such a structure is absent.