Shear horizontal surface waves on piezoelectric ceramic with layered structure

This paper presents theoretical and experimental results describing the propagation of SH (shear, horizontal) surface waves on a piezoelectric ceramic with a surface layer of different polarization than that in the substrate. An analytical formula for the group velocity of the SH surface waves is developed. The velocity of impulses of the SH surface waves is determined experimentally. Further, the theoretical results are compared to the experimental values.     

On the existence of localized shear horizontal acoustic waves in a piezoelectric plate with two semi-infinite same/different coatings

In this paper, the existence theorem of localized shear horizontal acoustic waves in a piezoelectric plate with two semi-infinite same/different coatings is established. Some properties of the waves in the waveguide structures are also discussed. The results show that the waveguides have some advantages and provide more choice for the designs of acoustic devices.     

Shear horizontal surface acoustic waves in semi-infinite piezoelectrics/metal superlattices

In this paper, an analytical method is presented for the study of shear horizontal surface acoustic waves in semi-infinite piezoelectrics/metal superlattices. The results show that the high electromechanical coupling coefficient and wide usable frequency range can be obtained in these superlattices.     

Shear surface acoustic waves in the stratified structure piezoelectric—High-temperature granular superconductor

The interaction of a Gulyaev-Bluestain surface wave with a granular high-temperature superconducting (HTSC) medium has been investigated. For piezoelectrics of symmetry 4mm and 6mm, dispersion equations have been derived that describe the characteristics of surface acoustic waves (SAWs). The temperature dependences of the SAW attenuation and phase have been calculated forZnO andBa ₂Si₂TiO₃ crystals. It is shown that at temperatures higher than the critical temperature an attenuation jump and a phase shift are observed. The effect intensifies with increase in the electromechanical coupling coefficient and with decrease in the thickness of the HTSC film. For theBa ₂Si₂TiO₃ crystal the attenuation jump and phase shift are11 dB/cm and38 deg/cm, respectively, at a frequency of820 MHz. The results obtained can also be generalized for periodic HTSC structures and can be used to design frequency-selective devices and fast-response bolometric photodetectors. Tomsk State University of Control Systems and Radioelectronics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 49–52, April, 1999.     

Resonant generation of surface acoustic waves between moving and stationary piezoelectric crystals

The propagation of surface acoustic waves in a system composed of two piezoelectric crystals moving with respect to each other and separated by a vacuum gap is considered. The waves are localized on different sides of the gap and coupled only through the electrostatic interaction. It is shown that when the velocity of the relative motion of crystals is close to some value, there occurs a wave instability resulting in a resonant generation of these surface waves. The rate of growth of Bleustein-Gulyaev waves in piezoelectric crystals of 6mm symmetry class is determined analytically.     

Angular control of acoustic waves oblique incidence by phononic crystals based on Dirac cones at the Brillouin zone boundary

This study investigated the angular control of incident acoustic waves for total transmission and reversed reflection using phononic crystals (PnCs). The Dirac point appears at the Brillouin zone boundary. The position of the Dirac point regularly changes with the length–width ratio of rubber rods, which makes the transmission angle adjustable. These structures could be applied to an acoustical 0 or π phase modulator by adjusting the number of layers of PnCs (even or odd). The angular control in the reflection domain can be achieved by adding a meta-surface at the boundary of the PnC.     

Temperature-stable orientations in LGS and LGN piezoelectric crystals for surface acoustic waves

The temperature characteristics of surface acoustic waves (SAW) propagating in LGS and LGN crystals are numerically analyzed. The optimal orientations that correspond to the zero value of the first-order temperature coefficient of delay (TCD) for SAW propagating in these crystals are considered. The second-order TCD for SAW is calculated for a wide range of operating temperatures. It is shown that the temperature dependences of the material constants of LGS and LGN crystals are strongly nonlinear. The characteristics of SAW propagating in a structure that consists of an isotropic layer overlying an LGS or LGN piezoelectric crystal are numerically calculated. It is shown that, in the presence of a thin aluminum layer of a certain thickness on the crystal surface, in some cases it is possible to extend the operating temperature range within which the TCD for SAW is equal to zero.     

Excitation of seismoacoustic waves by a harmonic force source acting at the boundary of a liquid layer and an elastic halfspace

A problem on the excitation of seismoacoustic waves in a system of a homogeneous isotropic elastic halfspace covered with a liquid layer is solved in the case of action of a source of point harmonic force on the surface of an elastic medium. Integral expressions are obtained for the radiation powers averaged over a wave period for longitudinal and transverse waves in a solid. Mode excitation is analyzed in detail. Expressions describing parts of the mode powers radiated into a liquid layer and an elastic medium are obtained. Numerical analysis of radiation powers is conducted for spherical longitudinal and transverse waves as well as for the radiation powers of seismoacoustic modes in a solid halfspace and a liquid layer. It is determined that in the conditions characteristic of bottom rocks in the case, where the basin depth is several times and more larger than the sound’s wavelength, about 2/3 of the total power is radiated into a liquid.     

Nonlinear interaction between acoustic and orientation waves in liquid crystals

Taking incompressibility of the medium into account is shown to lead to nonlinear coupling between acoustic and orientation waves in a nematic liquid crystal. Equations for three-wave resonant interaction are derived and the regime of nonlinear excitation of orientation waves in the course of propagation of a powerful high frequency acoustic wave in a liquid crystal is investigated.Branch of the Institute of Machine Management, Russian Academy of Sciences, Nizhny Novgorod. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, Nos. 1–2, pp. 146–152, January–February, 1995.     

Ion acoustic waves excited by boundary sheaths

Low frequency signals applied to a grid immersed in a plasma excite ion acoustic waves at the plasma boundaries simulataneous with those excited at the grid. A mechanism is suggested which involves the “direct coupled signal”.     

Ghosts in the Born images of a layer probed by acoustic waves

The Born inversion of time records of acoustic pulses reflected from a layer object gives rise to the images with ghost-like artifacts that make it difficult to pick out the exact thickness and composition of the object. The origin of these ghosts is explained herein and a means is proposed for their suppression.     

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.     

Transformation of modes of surface acoustic waves in strong KNbO3 and PKN piezoelectric crystals

We consider the transformation of a generalized surface acoustic wave (GSAW) into a Bleustein-Gulyaev (B-G) or Rayleigh wave in the yx and 90-yx-cuts of rhombic KNbO₃ and orthorhombic PKN crystals in the case of slight deviation of the wave vector from the direction of the pure-mode axis. We have numerically analyzed the characteristics of the GSAW, B-G wave, and Rayleigh wave in the KNbO₃ and PKN crystals with strong piezoelectric coupling. It is shown that the GSAW has a mainly transverse component of the mechanical shift in the region of the yx cut. In this case, the electromechanical coupling coefficient has an unprecedented high value. We have analyzed the dependence of the distribution of mechanical shifts and electric potential of the wave propagating into the crystal on the distance from the substrate surface on the open and metallized surfaces; we also consider the dependence of the GSAW velocity in these crystals with variation in the metal film thickness. N. I. Lobachevsky State University, Nizhny Novgorod, Russia. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 43, No. 5, pp. 445–451, September, 2000.     

Internal transverse fluctuation waves in a viscous liquid at a hard boundary

A liquid layer resting on a hard bottom and bounded by hard walls is considered. Analysis of the dispersion relation shows that both slowly decaying solitary waves and rapidly decaying periodic waves may arise inside the layer at the interface between stratified ～100-nm-thick near-surface regions of low-viscous liquids. Stratification is due to the orienting influence of the hard bottom and to fluctuation forces. The dispersion laws for the waves are characteristic of purely capillary waves in both a deep and shallow liquid.     

Phase separated composite films of liquid crystals

Phase separation of liquid crystals from a solution with polymers has long been studied and used to prepare polymer stabilized and polymer dispersed structures. They are formed by spatially isotropic phase separation. A new mode, in which the phase separation proceeds anisotropically, has recently been discovered. Known as phase separated composite films (PSCOF), the resultant structures are made of adjacent parallel layers of liquid crystal and solidified polymer. PSCOFs have been made with nematic, ferroelectric (FLC), and antiferroelectric (AFLC) liquid crystals. Liquid crystals in PSCOFs exhibit electro-optical properties not observed in devices prepared by conventional methods, polymer dispersion, or polymer stabilization methods. Devices incorporating FLCs possess grey scale and switch 100 times faster at low fields than conventional surface stabilized devices. This method makes it possible to prepare very flexible devices and devices with liquid crystal film thickness comparable to optical wavelengths with great ease.     

Reflection and refraction of acoustic waves at the boundary between a magnetoacoustic material and a dielectric

Reflection and refraction of longitudinal and transverse acoustic waves at a plane boundary between an antiferromagnet and a dielectric are studied. The antiferromagnet is assumed to have an easy-plane anisotropy and to be in the state near the orientational phase transition in the magnetic field. A possibility of controlling the angles of the wave-type transformation upon reflection and the refraction angles, as well as all four coefficients of the wave transformation upon reflection and refraction, by the magnetic field is demonstrated. Conditions for the formation of the critical angles of internal reflection and the effect of the magnetic field on their values are specified. A possibility of the radiation of a grazing wave into the material bulk in the vicinity of the phase transition is analyzed.     

Excitation of bulk elastic waves at the surfaces of piezoelectric crystals with 422,622 symmetry

The problem of exciting bulk elastic waves at the surface of a piezoelectric with symmetries 422,622 has been solved by a successive approximation method. In the approximation of a fixed electric field, created at the surface of the piezoelectric crystal by a two-electrode transducer, the distributions are found for the shear wave stress and the energy flux density in the far zone. The equivalent circuit parameters for a two-electrode radiator are determined taking account of the dynamic piezoelectric correction obtained in the second approximation. The equivalent circuit parameters and the transducer loss are treated for TeO₂ crystals. A realistic possibility of using surface transducers in the development of acousto-optic modulators in the s.h.f. region is shown. Tomsk State Academy of Control Systems and Radio Electronics. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 8–15, January, 1997.     

Surface excitation of hypersound in piezoelectric crystals by plane electromagnetic waves

The generation of hypersound at a free surface of a piezoelectric crystal by means of an incident plane electromagnetic wave is considered and the corresponding boundary problem is discussed in detail. The formula developed in this paper are quite general and can be applied to any piezoelectric crystal and any face orientation. As an important example, the excitation of sound waves at several quartz faces is treated numerically and the results are presented in diagrams showing directly the power conversion from the plane incident electromagnetic wave into the sound waves as function of the angle of incidence and of polarization directions.     

Predetermined control of turbulent boundary layer with a piezoelectric oscillator

With a piezoelectric(PZT) oscillator, the predetermined controls of the turbulent boundary layer(TBL) are effective in reducing the drag force. The stream-wise velocities in the TBL are accurately measured downstream of the oscillator driven by an adjustable power source. The mean velocity profiles in the inner and outer scales are reported and the skin friction stresses with different voltage parameters are compared. Reduction of integral spatial scales in the inner region below y+of 30 suggests that the oscillator at work breaks up the near-wall stream-wise vortices responsible for high skin friction. For the TBL at Reθof 2183, the controls with a frequency of 160 Hz are superior among our experiments and a relative drag reduction rate of 26.83% is exciting. Wavelet analyses provide a reason why the controls with this special frequency perform best.