Shear Horizontal Wave Propagation Research Articles

Electrorheological Properties of Chiral Smectic-C Liquid Crystals Observed by Using Shear Horizontal Wave Propagation

An electrorheology (ER) effect of a chiral smectic- C (Sm- C *) liquid cyrstal is observed using a shear horizontal (SH) wave propagating in a liquid-crystal cell. Propagation loss and acoustic phase-delay in the liquid-crystal cell are measured and the propagation characteristics of the SH wave in the cell structure is numerically analyzed in the form of considering the stress tensor of Sm- C * phase. The experimental results are explained qualitatively in comparison with the numerical analysis results. A relative viscosity change under electric field is evaluated, which indicates that the ER effect in the Sm- C * liquid crystal is predominated by the orientations of the liquid-crystal directors and the Sm- C * layers. The present technique has the advantage of evaluating the ER properties without disturbing the Sm- C * layers.

Electrorheological Properties of Chiral Smectic-C Liquid Crystals Observed by Using Shear Horizontal Wave Propagation

An electrorheology (ER) effect of a chiral smectic- C (Sm- C *) liquid cyrstal is observed using a shear horizontal (SH) wave propagating in a liquid-crystal cell. Propagation loss and acoustic phase-delay in the liquid-crystal cell are measured and the propagation characteristics of the SH wave in the cell structure is numerically analyzed in the form of considering the stress tensor of Sm- C * phase. The experimental results are explained qualitatively in comparison with the numerical analysis results. A relative viscosity change under electric field is evaluated, which indicates that the ER effect in the Sm- C * liquid crystal is predominated by the orientations of the liquid-crystal directors and the Sm- C * layers. The present technique has the advantage of evaluating the ER properties without disturbing the Sm- C * layers.

Observation of orientation dependence of electrorheology effect in ferroelectric liquid crystal using shear horizontal wave

The electrorheology (ER) effect of ferroelectric liquid crystals is observed under shear-horizontal (SH) wave propagation. The ER effect is strongly dependent on the orientation direction of the liquid-crystal molecule. The apparent viscosity is evaluated through the numerical analysis result on the propagation characteristics of a SH wave in a trilayer structure including a ferroelectric liquid-crystal (Chisso, CS1014) layer between two glass plates. The ER effect is examined by the relation between the orientation of smectic layers and the propagation direction of the SH wave.

Viscosity Measurement of Nematic Liquid Crystal Using Shear Horizontal Wave Propagation in Liquid Crystal Cell

Propagation characteristics of a shear horizontal (SH) wave in a cell structure containing a nematic liquid crystal layer are described on the basis of numerical analysis and experimental results. The SH wave propagation is described by the numerical analysis result for the nematic liquid crystal as an anisotropic liquid, considering the director angle of the liquid crystal. The temperature dependence of effective viscosities of a typical nematic liquid crystal N-(p-methoxybenzylidene)-p'butylaniline)] (MBBA) is evaluated from the measurement of the phase velocity change of the SH wave in the liquid crystal cell.

Viscosity Measurement of Ferroelectric Liquid Crystal Using Shear Horizontal Wave Propagation in a Trilayer Structure

Propagation characteristics of a shear horizontal (SH) wave in a trilayer structure, having a viscous liquid layer between a piezoelectric ceramic plate and a glass plate, are described on the basis of numerical and experimental investigations. Viscosity dependences of mechanical displacement distributions and relationships between the fractional velocity change and the square root of viscosity are discussed. The viscosity is related to the acoustic phase delay, accompanied by the SH wave propagation, between two interdigital transducers on the SH wave device. The measured temperature dependence of viscosity of silicon oil is in good agreement with the numerical analysis result of the SH wave propagation. An electrorheology effect and the temperature dependence of the viscosity in a ferroelectric liquid crystal (FLC: CS1014) are also measured by this technique.

Computationally Efficient SH-Wave Modeling in Transversely Isotropic Media

Based on the description of shear horizontal (SH) wave propagation in arbitrarily oriented transversely isotropic media, radiation characteristics of ultrasonic transducers for this wave type are determined. The radiated wavefields are obtained by point source superposition, making use of an analytical relationship for the wave propagation direction as a function of the spatial coordinates. Approximate formulae are given for the radiation characteristics of circular and rectangular transducers in the far-field, which are in a form similar to the isotropic material case. Focusing on transversely isotropic weld metal specimens and unidirectional composites, numerical evaluation is performed for normal-incidence probes as well as for electromagnetic acoustic transducers.

Design and test of 3 GHz, fundamental mode surface transverse wave resonators on quartz

Surface transverse wave (STW) resonators, based on the propagation of high velocity shear horizontal waves on Y-rotated quartz were designed, fabricated and tested. A model is presented to predict the resonant frequency of a 3-grating structure as a function of design parameters such as periodicities, metal thickness, and finger-to-gap ratio. Experimental devices have been fabricated by direct e-beam lithography with linewidth geometries in the range of 0.3-0.5 mum, and an operating frequency close to 3 GHz in fundamental mode. Two different designs using either a quasi synchronous structure (type 1) or a change of periodicity inside the cavity (type 2) were tested. The best experimental factor of merit is close to the best results already published for quartz STW resonators.

Viscosity Measurement of Ferroelectric Liquid Crystal Using Shear Horizontal Wave

The characteristics of shear horizontal (SH) wave propagation on a piezoelectric ceramic plate having the poling axis along the horizontal direction are described. The zeroth-order symmetrical (S0) mode has a nearly nondispersive property and an interdigital transducer (IDT) for the S0 mode under the configuration of no counter electrode on the opposite surface of the plate has a high electromechanical coupling constant k2 value exceeding 20% throughout the entire range of frequency times thickness (fd) values. The viscosity of a ferroelectric liquid crystal (FLC) is measured using the S0 mode SH wave device which has two acoustic wave channels. In the smectic phase of FLC, the viscosity in the direction perpendicular to the smectic layer plane is larger than that parallel to it. The difference in the viscosity between the two directions of FLC alignment is detected by measuring the acoustical phase delay difference between two acoustic wave channels.

Shear horizontal wave propagation in periodically layered composites

The transverse resonance approach to guided wave analysis is applied to shear horizontal (SH) wave propagation in periodically layered composites. It is found for SH waves that at high values of the guided wavevector /spl beta/, the wave energy is trapped in the slower of the two media and propagates accordingly at the slower wavespeed. At low values of /spl beta/, however, the modes demonstrate a clustering behavior, indicative of the underlying Floquet wave structure. The number of modes in a cluster is observed to correlate with the number of unit cells in the layered plate. New physical insights into the behavior of these systems are obtained by analyzing the partial waves of the guided SH modes in terms of Floquet waves. We show that the fast and slow shear waves in the periodically layered composite play an analogous role to the longitudinal and shear partial waves comprising Lamb waves in a homogeneous plate.

Small but finite amplitude waves in a two-layered incompressible elastic medium

Propagation of small but finite amplitude shear horizontal waves in a two-layered elastic plate of uniform thickness is considered. By employing a perturbation expansion it is shown that the wave field is governed asymptotically by a modified Korteweg-de Vries equation. Then the effects of nonlinear material properties on the propagation characteristics of the asymptotic waves are discussed. It is remarked that solitons may exist depending on the constitution of the layered media.

Liquid Viscosity Measurement Using SH Wave Propagation Characteristics on Piezoelectric Ceramic Thin Plate

Liquid viscosity measurement using shear horizontal (SH) wave propagation characteristics on a piezoelectric ceramic thin plate is described. The mode conversion loss associated with the compressional component U3 is zero, because the SH wave on the piezoelectric ceramic substrate poled along the horizontal axis has only the horizontal component U2, The IDT has a much larger electromechanical coupling factor for the S0 mode SH wave than that of the SH surface acoustic wave (SAW). The metal-coated condition of the liquid-loaded surface is essential for detecting the liquid viscosity. There exists a linear relationship between the fractional phase velocity change of the S0 mode and the square root of the liquid viscosity. The measured results on liquid viscosity using the S0 mode SH wave devices, for some concentrations of glycerol-water solutions, are in good agreement with the theoretical prediction.

Propagation of shear horizontal surface acoustic waves parallel to the grooves of a random grating

An elastic medium that occupies the region x3≳ζ(x1), where the surface-profile function ζ(x1) is assumed to be a stationary, stochastic process, is studied. The displacement field u(x;t) in this region is assumed to satisfy stress-free boundary conditions on the surface x3=ζ(x1). First the boundary conditions satisfied by the mean displacement field 〈u(x;t)〉 on the plane x3=0 are obtained, where the angle brackets 〈 〉 denote an average over the ensemble of realizations of ζ(x1). The results are then used to obtain the dispersion relation for surface acoustic waves of shear horizontal polarization propagating in the x2 direction, i.e., parallel to the grooves of the random grating defined by the surface-profile function ζ(x1). It is found that the surface acoustic waves of this polarization, which cannot exist on a planar, stress-free surface of an elastic medium, are trapped by the random roughness, but are bound to the surface for only a finite range of values of the wave number k2 characterizing their propagation in the x2 direction. The attenuation of these roughness-trapped surface acoustic waves is also determined.

Shear horizontal elastic solitons in crystal plates

The effect of nonlinearity on the propagation of shear horizontal elastic waves in crystal plates is analysed in the framework of Maradudin's equations. It is demonstrated that in the plates it is possible to have propagation of bright and dark solitons of the shear horizontal polarization, and the influence of the plate properties on their parameters is studied. The condition to create dark solitons in the plates is obtained also.

Velocity of shear horizontal surface waves on an isotropic elastic cylinder with finite width

Theoretical and experimental results describing the propagation of shear horizontal (SH) surface waves on an isotropic elastic cylinder are presented. Analytical formulas for group velocities are developed. The velocity of impulses of the SH surface waves is determined experimentally. Subsequently, the experimental results are compared to the theoretical values. The measured velocity is close to the group velocity calculated according to our theory for cylinders of finite width. As yet, the existing theories consider only the propagtion of SH surface waves over the unlimited cylinders [I. A. Viktorov, Sov. Phys. Acoust. 20, 199 (1974) and L. M. Brekhovski, Sov. Phys. Acoust. 13, 541 (1967)].

Shear horizontal surface waves on an isotropic elastic cylinder

This paper comprises theoretical and practical results concerning the problem of propagation of surface shear horizontal (SH) waves on monolithic, elastic cylinders. It was proved that SH surface waves have a multimode structure and their pulses propagate with a velocity that tends asymptotically to the velocity v0 of the shear bulk waves for increasing frequency. On the other hand, the phase velocity vp of surface SH waves decreases asymptotically to the velocity v0, as a function of frequency. For the obtained theoretical formulas, numerical calculations were performed and are valid for homogeneous elastic cylinders. The experiment was carried out for glass cylinders. Satisfactory agreement between theoretical and experimental results was stated.

Influence of a layered polarization of piezoelectric ceramics on shear-horizontal surface-wave propagation

This paper presents the results of theoretical analysis concerning the propagation of shear-horizontal (SH) surface waves on a piezoelectric ceramic with a surface layer of piezoelectric properties different from those in the substrate. Phase velocity and amplitude distributions of the SH surface waves were calculated for the standard piezoelectric ceramic PZT-4. Some practical applications in acoustoelectronics are suggested.

Analysis of shear horizontal surface waves at the boundary between a piezoelectric crystal and a viscous fluid medium

Surface shear horizontal wave propagation at the boundary of a piezoelectric substrate with a viscous fluid is theoretically analyzed. The analytical solution clearly shows the dependence of the velocity change, the wave propagation loss, and the wave amplitude profile (thus the energy confinement near the surface), in terms of the liquid viscosity and density, the layer thickness, and the wave frequency. It is shown that the viscous fluid loading produces some guidance near the surface but also some damping of the wave. The propagation loss is due only to viscous coupling and not to a mode conversion and viscous coupling as is the case with Rayleigh surface acoustic waves (SAWs). Closed-form expressions are derived for the attenuation coefficient and the fractional velocity change (thus the frequency change) in terms of the piezoelectric crystal and viscous liquid parameters. The theory, applicable to both a Bleustein–Gulyaev (BG) wave and a surface skimming bulk wave (SSBW), indicates that surface shear waves could be used in the implementation of sensitive acoustic wave liquid-phase-based detectors, viscosity sensors, and/or biosensors. These sensors will not experience the high propagation loss associated with Rayleigh SAWs.

Propagation and Amplification of Shear-Horizontal Waves in Piezoelectric Plates

Propagation of shear horizontal waves in class C6v piezoelectric plates with polar (or sixfold) axis in the transverse horizontal direction is analyzed for various boundary conditions: faces electrically free, shorted, or coupled to a thin homogeneous semiconductor plate. The case considered is that of identical physical conditions at the opposite faces, which permits the symmetric and antisymmetric waves to be treated independently. Of the above waves, the lowest modes behave as transverse surface waves at high frequencies, and the higher modes retain their oscillatory behavior in the thickness direction. Numerical solutions are obtained for amplification and phase velocity in PZT under different boundary conditions, and it is shown that the phase velocity can also be strongly dependent on the drift velocity of carriers in the semiconductor. The shapes of the dispersion and amplification-frequency curves are also drift-dependent, especially in the vicinity of cutoff.