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Liquid crystals, which have high dielectric anisotropy even in the terahertz region and are easily controllable for dielectric permittivity by applying an electric field, have become increasingly attractive in recent years. The non-radiative dielectric (NRD) waveguide has a structure in which a dielectric line is sandwiched between two metal plates and by replacing the dielectric part with liquid crystal, a low loss liquid crystal-loaded NRD waveguide type terahertz phase shifter can be obtained. However, since the thickness of the liquid crystal layer is several hundred micrometers, it has a response time of as long as several hundred seconds when the driving voltage is removed. It is necessary to devise improvements for practical application. By inserting two polyethylene terephthalate (PET) films and reducing the thickness of the liquid crystal layer, the decay time was improved well, but the phase change was significantly reduced. In this study, we report improving both decay time and phase change with aligned nanofiber/liquid crystal complex. In addition, we demonstrate liquid crystal-load phase shifter, which has 360&deg, phase change and the response time below one second.

Homogenous alignment of smectic liquid crystal is demonstrated by applying bidirectional shear with controlled amplitude and frequency. For shear amplitudes smaller than 10 μm and at the frequency of 100Hz, the smectic layer was found to align in the direction of shear. The quality of alignment was evaluated from the contrast ratio obtained when the sample was placed between crossed polarizers and set at 0° and 45° to the transmission axes. A monotonic increase in the alignment quality was found with increasing shear amplitude.

Non-radiative dielectric (NRD) waveguides are known as a type of transmission line with advantages such as the restriction of undesired radiation at curved sections and discontinuities. A new type of terahertz phase shifter which uses liquid crystal as the dielectric material in an NRD waveguide is presented for the first time. The phase change is very large but the decay time is extremely long. By inserting a PET sheet into a nematic liquid crystal-loaded NRD waveguide, the thickness of the liquid crystal layer is reduced. Although the phase change decreases, the decay time is greatly improved, and the availability of the partial use of nematic liquid crystal in the dielectric material of an NRD waveguide is confirmed. By comparing dielectric response results of the ordinary sandwiched cells with the experimental results of nematic liquid crystal-loaded NRD waveguides, it is confirmed that the response time does not depend on the kind of device.

The authors report continue tuning of the lasing wavelength in cholesteric liquid crystals (ChLCs) by an applied electrical fields. Although the pitch length and the corresponding lasing wavelength is sensible to external fields, only a discrete shift in the pitch is observed in the conventional cell configuration where the helix axis is lying the cell-normal direction, since the molecules are anchored to a single direction at the substrate interfaces. In this study, continuous wavelength tuning is achieved by laying the helix in the cell-plane direction, mitigating the effects of anchoring: this alignment is attained simply by applying an electric field while cooling the sample from the isotropic state, in a planarly rubbed sandwich cell. We also show that the tuning characteristics as that predicted based on calculations using the elastic theory.

We study optical properties of nanoimprinted gratings infiltrated with liquid crystal (LC). One-dimensional grating of a line-spacing pattern is used as a distributed feedback cavity. After filling LC into the trenches of the grating, the LC molecules align along the trench of grating and it shows uniform planar alignment. By optical pumping, laser emission occurs and the laser wavelength can be tuned by temperature control or application of voltage. We also demonstrate control of diffraction intensities from a two-dimensional grating using LC molecular reorientation in micro space.

We have demonstrated lasing in cholesteric liquid crystals (CLCs) of various thicknesses oriented by acoustic streaming. Although alignment control of CLC molecules in a thick cell is difficult, acoustic streaming can change the CLC alignment from a focal conic state to a planar state by molecular flow. The molecular reorientation leads to making a large uniform CLC layer that can function as a laser cavity. Therefore, laser action cannot be observed in the untreated thick cells because of the focal conic state, while a sharp emission appears from the thick cells treated by acoustic streaming. Furthermore, lasing wavelength shifts with a small wavelength interval are realized using a large cavity.

The Propagation characteristics of a shear horizontal (SH) wave in a trilayer structure having a viscous fluid layer is analyzed from a numerical analysis. Acoustic phase changes under application of electric fields in a nematic liquid crystal cell are measured using the SH wave. The acoustic phase advances with increasing the applied electric field. This result corresponds with the viscosity change based on a molecular reorientation of the liquid crystal. In dynamic response measurement, the response times in the phase and the optical measurements are different, because the measured area of the acoustic phase is only the vicinity of the glass surface.

The acoustic phase of a shear horizontal (SH) wave propagating into a nematic liquid crystal cell is measured. To investigate the acoustic phase depending on the director angle of a liquid crystal, the two SH wave devices having different initial molecular orientations are fabricated. The acoustic phase change of the SH wave devices is measured for various applied electric fields. The numerical analyses are also performed by considering director distribution in the nematic liquid crystal layer. The experimental acoustic phase changes are well accorded with the calculated shear stresses as a viscous resistance.

Mechanical vibration distributions of freely suspended ferroelectric liquid crystal films with various thicknesses in the range from 15 nm to 12 µm induced by applying a sinusoidal electric field are observed using a laser Doppler vibrometer. Mechanical resonance profiles of the freely suspended film are represented in the form of mechanical vibration distributions. Resonance frequency increases with the number of mechanical resonance modes. Surface tension is calculated from the number of mechanical resonance modes and the resonance frequency. The surface tension is not constant and is proportional to the thickness of the freely suspended film below 1.2 µm.

The dynamic responses of an acoustic phase to liquid crystal (LC) molecular reorientation in a shear horizontal (SH) wave device with an LC cell are measured by applying a voltage. The optical responses are also observed in order to determine the molecular director distributions in the device. The response of acoustic phase by removing the applied voltage is three orders of magnitude faster than the optical response. To investigate the effective viscosity acting on the SH wave propagation, the dynamic changes in the director distribution are calculated. Using the calculated director distribution, we obtain the effective viscosity acting on the SH wave propagation, which coincides qualitatively with the measured acoustic phase change.

The influence of spontaneous polarization on the active driving of V-shaped switching ferroelectric liquid crystals is discussed. Two ferroelectric liquid crystals with a high spontaneous polarization (200 nC/cm2) and a low spontaneous polarization (7 nC/cm2) are used in this study. The field-effect transistor used as an active switch and a storage capacitor is set parallel to a liquid crystal cell. In a high-spontaneous-polarization material, cell voltage increases, while the transistor is in the on-state. After the application of external driving voltage, cell voltage decreases owing to the discharging of the storage capacitor due to the changes induced by spontaneous polarization. On the other hand, in a low-spontaneous-polarization material, the decrease in cell voltage after the application of external driving voltage is very small. The low-spontaneous-polarization material, compared with the high-spontaneous-polarization material, is advantageous for controlling light intensity by active driving.

A nematic liquid crystal director orientation in a vicinity of a glass/liquid-crystal interface is investigated in relation to an acoustic phase change of a shear horizontal (SH) wave propagating in a cell structure. The relationships between phase change and electric field applied to the liquid crystal layer are given for various layer thicknesses. The numerical analysis of wave penetration in the liquid crystal cell is performed by considering distribution profiles of liquid crystal direction in relation to shear stress at the glass/liquid-crystal interface. The experimental acoustic phase changes are well consistent with the calculated shear stresses as flow resistance. The acoustic phase is strongly dependent on viscosity distribution and particle velocity in the liquid crystal layer.

In support of the application of liquid crystals to adaptive devices such as variable delay lines in the microwave and millimeter band, the complex permittivities and response times of five different nematic liquid crystals after voltage application were measured. We measured both the real part of the relative permittivity, when the long axis of the liquid crystal molecule is parallel to the high-frequency electric field, and the relative permittivity when it is perpendicular to the high-frequency electric field. The values and were measured. In the range from 10 kHz to 13 MHz, the capacitance and conductance of a liquid crystal cell sandwiched between ITO glass plates processed by rubbing were directly measured. For 100 MHz to 40 GHz, we propose the new cutback method, in which two coaxial tubes with different lengths are filled with the liquid crystal and the dielectric properties are measured on the basis of their respective group delay and transmission loss. Dielectric relaxation is verified in the low frequency range. In particular, in the range from 3 to 40 GHz, dielectric properties are shown for a continuous change of frequency. It is found that and are kept almost constant regardless of the frequency, taking values of approximately 3 and 2.5, respectively. , which is the difference between the permittivities in two orientations, exhibits a large variation, from 0.4 to 0.8, depending on the material, which provides crucial data for selecting the optimal material. The response time was measured by placing the liquid crystal cell between two polarizers with the polarizing directions set parallel. The light from a He-Ne laser (632.8 nm) is directed onto the liquid crystal cell, and the transmitted light is detected by a photodiode. Assuming that the liquid crystal is used in an adaptive device, the speed of operation is investigated. Based on the measurement results for two different nematic liquid crystals, the design of a variable delay line for 20, 30, and 40 GHz is considered, and a principle of liquid crystal material selection is presented. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 86(8): 49–60, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10130

The nematic liquid-crystal director-orientation in the vicinity of the interface between a liquid-crystal layer and a glass substrate is evaluated in various orientations under an applied electric field, using shear horizontal (SH) wave propagation. The measured acoustic phase delay is related to numerical analysis of the propagation characteristics of the SH wave in a trilayer structure containing a nematic liquid-crystal layer (4-cyano-4′-pentylbiphenyl: 5CB) between two glass plates. This technique using SH wave propagation in a liquid-crystal cell is promising for evaluating the nematic liquid-crystal director angle in the vicinity of the interface.

Mechanical vibration characteristics of a freely suspended film of ferroelectric liquid crystal are investigated via measurements of the transmitted and reflected lights. The frequency spectrum of the mechanical vibration induced by applying electric field has several peaks corresponding to a resonance phenomenon. The mechanical vibration induced by irradiating an ultrasound in air has harmonic components in addition to the fundamental component of the carrier wave frequency of the ultrasound. The mechanical vibration is also observed under irradiation of ultrasound in the form of pulsed RF or amplitude-modulation (AM). The frequency components correspond to the eigenmodes of the resonance vibration. An AM ultrasound is demodulated by using the freely suspended film.

We report the spectral broadening of selective reflection (SR) with higher response speed in cholesteric liquid crystals (ChLCs). A planarly aligned ChLC was applied with an in-plane electric field with an inhomogeneous intensity in the cell-depth direction by using common interdigitated electrodes and selecting the cell gap and the interval between electrodes. The electric field normal to the helix increased the helical pitch of the ChLC, while the inhomogeneous field intensity caused the spatial distribution of the helical pitch in the cell-depth direction, increasing the SR band width from 100 to 300 nm with the response time of 3 ms.

We report fast electro-optic response independent of cell thickness in cholesteric liquid crystals (ChLCs). Usually, an electric field normal to the helix axis of ChLCs induces two fast and one slow response components: helical elongation (slow one), helical deformation (fast one), and flexoelectric effect (fast one). In this study, we found that a planarly aligned ChLC applied with an in-plane electric field exhibited only fast response components because the glass substrates suppressed the motion of the helical elongation. Furthermore, we demonstrated complete separation of the remaining fast components by using dielectric measurement system. Consequently, we were able to analyze dynamics of the helical deformation in detail, in which response times exhibited quadratic dependence on the helical pitch and no dependence on the cell thickness.

An electrorheology (ER) effect of a ferroelectric liquid crystal (FLC) is described on the basis in numerical analysis and experiment. Propagation characteristics of a shear-horizontal (SH) wave in a liquid crystal layer between a piezoelectric ceramic thin plate and a glass thin plate is numerically analyzed. The phase velocity of the SH wave depends predominantly on the viscosity of the FLC. The ER effect is measured using a SH wave device under the construction of delay line oscillator. The observed DC electric field dependence of oscillation frequency under the use of a helical structure of FLC is related to the observed microscopic result. This method has the advantage of simplicity and a small amount of liquid sample for evaluating the ER effect of the FLC.

The light diffraction properties of a shorter periodical domain, which is caused by an elastic wave propagating along one of two glass plates composing a liquid crystal cell, are described. The shorter periodical domain is controllable for the application of an electric field to the liquid crystal cell. The response time of the disappearance of the shorter periodical domain decreases with increasing the applied voltage. On the other hand, the response time of the domain formation is independent of the applied voltage. These response times agree quantitatively with those of the birefringence electrooptic effect. The domain disappearance by applying the voltage to the liquid crystal indicates the Freedericksz transition.

An interaction between an elastic wave and a liquid crystal is investigated from the view point of evaluation of the elastic properties of the liquid crystal. A periodical stripe domain pattern is induced by an interaction between the elastic wave and the nematic liquid crystal, the pattern is observed by a polarizing microscope. In the numerical analysis of elastic wave propagation in a nematic liquid crystal cell, the 0th mode depends on the liquid crystal properties, on the other hand the 1st mode is influenced predominantly by the properties of two sheets of glasses composing the cell. The 0th and 1st mode phase velocities are estimated from the periodic length of the stripe domain pattern. The 0th mode phase velocity in the nematic liquid crystal cell strongly depends on the cell layer thickness. The phase velocity obtained from the observed result is in good agreement with the numerical analysis result.

Switching mechanism of thick cell of ferroelectric liquid crystals has been studied by means of light scattering measurement and polarizing microscope observation adopting stroboscopic technique. The transmitted light through the cell at the instant of polarity reversal of applied voltage has been diffracted by the formation of periodical stripe texture. This transient stripe texture has a tilt from the smectic layer. The period of the transient stripe texture is independent of temperature and depends on applied voltage. The oblique angle from smectic layer depends on applied voltage.

The microwave variable phase shifter of a coplanar waveguide using ferroelectric liquid crystal with float electrodes, which are used for applying a dc voltage to a liquid crystal layer, is discussed. We confirmed the performance of the phase shifter in the frequency range from 10 to 30 GHz and found that phase shift is proportional to the frequency of the microwave according to the theory. The measured phase shift increases with an increase in applied voltage. The response time of this phase shifter was less than 1 ms above 120 V and a very high speed variable phase shifter was achieved.

Nonlinear optical phenomena such as second harmonic generation (SHG) have been studied in various ferroelectric liquid crystals. SHG efficiency depends on the molecular structure of ferroelectric liquid crystal and can be controlled by applied voltage. Phase matching of SHG has been well realized in these ferroelectric liquid crystals. SHG in polymeric ferroelectric liquid crystals, ferroelectric liquid crystal-conducting polymer composites, thin ferroelectric liquid crystal films and liquid crystals which exhibit flexoelectric effect have also been discussed.

Aggregation states and transient light scattering in the chiral smectic C phase of a ferroelectric liquid crystalline polymer (FLCP) were studied. The smectic phase shows an interlayer spacing of 38-39.5 A, which is about 1.41 times the length of the side chain mesogenic group. The transient scattering mode was obtained by repeated voltage polarity reversal. A reversible transparent-opaque (light scattering) change was observed in the chiral smectic C state upon application of electric fields with low and high frequencies, respectiely. Both transparent and opaque states were maintained stably even when the electric field was turned off (bistable light swiching). A novel type of electro-optical effect based on light scattering was obtained for the FLCP in the chiral smectic C state.

Thin films prepared by mixing ferroelectric liquid crystal with conducting polymer whose main chains are composed of highly extended conjugated electron system exhibit novel ferroelectric and optical properties, which are strongly dependent on the combination of ferroelectric liquid crystal and conducting polymer and their concentration. Ferroelectric behavior appears in the system with low conducting polymer ratio. Dependence of dielectric constant and spontaneous polarization on the composite ratio has been explained by taking the microstructure of the composite films into consideration. Various electrooptical effects in these systems have also been found, which depends on the molecular structure of both ferroelectric liquid crystal and conducting polymer.

Well-aligned thin films of polymeric ferroelectric liquid crystal have been prepared by means of a spin-coating method. Several types of electro-optical effects and the optical second-harmonic generation in these films have been measured. The characteristics of spin-coated polymeric ferroelectric liquid crystal film with a free surface have been discussed in comparison with those of conventional sandwich cells. The influences of the glass plates on the PFLC are also discussed.

The transient scattering mode (TSM) at the polarity reversal of applied field and the deformation of helicoidal structure (DHS) effect upon applying a stepwise field in polymeric ferroelectric liquid crystal have been studied. The response time of the TSM decreases with increasing applied field and increases with decreasing temperature. A stripe pattern parallel to the smectic layer has been observed at the instant of polarization reversal. This stripe pattern is similar to that of the helicoidal structure in the absence of field and has been maintained after removal of pulse field. A new type of bistable electrooptic effect has been demonstrated, in which the switching between the transparent state and the opaque state can be realized by application of pulse field.

This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Sadahito Uto, Hiroshi Moritake, Masanori Ozaki, Kent Skarp, and Bertil Helgee, Journal of Applied Physics 79, 4444 (1996) and may be found at https://doi.org/10.1063/1.361754., Thin films of a chiral side‐chain polymer with a ferroelectric phase were deposited on a substrate by spin coating. Electro‐optic switching in the films were observed by applying an external field using in‐plane electrodes. Characteristics of the switching are presented, together with an analysis of the switching dynamics that takes into account the inhomogenous field distribution in the active area.

The rotation of smectic layer in the antiferroelectric liquid crystals upon application of asymmetric voltage pulses has been observed. The influence of the cell configuration upon this layer rotation has been investigated. This layer rotation is not directly related with the interaction between liquid crystal molecules and the spacer at the liquid crystal-spacer interface. The rotation of smectic layer has been observed not only in a monodomain cell but also in a multidomain cell. This layer rotation has also been observed in ferroelectric liquid crystal as the same manner in antiferroelectric liquid crystals.

We investigated the possibility of practical applications using cholesteric liquid crystals (ChLCs) with Helfrich deformation, which causes the undulation of the helical structure. Usually, the Helfrich deformation is very unstable and can be obtained only in the transient state for a short time (< 10 s) under continuous field application. Here, we found that a ChLC polymerized with spatial pattern distribution exhibited high durability of the Helfrich deformation. Furthermore, we revealed molecular alignment of the Helfrich deformation by scanning electron microscope. Finally, we fabricated a switching device embedded with color-tunable reflection pixels to exhibit potential of reflective display application.

Poly (1,6-heptadiyne) derivatives substituted with long side chains containing mesogen units such as poly(bis(4-methoxy-4′-hexyloxybiphenyl)- dipropargyl malonate) (PMHBDPM) exhibit unique characteristics typical to both liquid crystal and conducting polymer. PMHBDPM exhibits smectic A phase in consistent with temperature dependence of X-ray diffraction. Two stages of electrochemical doping corresponding to the charge transfers between dopants and polymer main chain and also between dopants and the core of the mesogen unit in the side chain are observed. Diffusion coefficient of dopants also exhibits drastic change at the phase transition between smectic A phase and isotropic phase. These characteristics have been discussed in terms of molecular orientations of both polymer main chains and substituted side chains. Unique dielectric properties and X-ray diffraction characteristics have been observed in a mixture of PMHBDPM with ferroelectric liquid crystal of low molecular weight.

The highly efficient IR-modulation has been achieved using LC electro-optic elements. Experimental infrared modulator elements have been fabricated and demonstrated utilizing the transient light scattering effect of ferroelectric liquid crystal with asymmetric waveform voltage drive. The new elements performed 80%, 50%, 40% and 25% modulation degree in the 632.8nm, 2, 3-5 and 8-12 μm region. And we observed micro domain structure under the scattering state by a polarizing microscope to understand the mechanism of the domain switching. In addition, we evaluated properties of the scattering angular and temperature dependence quite important for the design of optics for the application in the infrared range.

The light scattering measurement and the polarized microscopic observation of field induced phase transition between antiferroelectric (AF) and ferroelectric (F) phases have been performed in a uniformly aligned cell. The light scattering is confirmed to be diffraction by the periodical change in refractive index in the stripe domains of AF and F phases. In F → AF phase transition, the nucleation of AF domain occurs at interfaces between liquid crystal and spacer edges and AF domain grows away from spacers. On the other hand, in AF → F phase transition, discrete F domains homogeneously appear and grow throughout the cell. The rotation of smectic layer is also observed under the application of an asymmetric voltage. This rotation is originated from the asymmetry of the polarity reversal of the applied voltage.

Unique liquid crystalline behaviors have been observed in polyacetylene derivatives substituted with long side chains containing mesogen unit such as poly [5- (p- (trans -4′- n- octylcyclohexyl) phenoxy) -1- pentyne] (PPCH803A) with phenylcyclohexyl mesogenic moiety. Texture typical to smectic liquid crystal has been confirmed by optical microscopic observation. Smectic structure has also been confirmed by X-ray diffraction. Anisotropy of optical absorption spectrum consistent with X-ray diffraction has been observed, from which the band gap of PPCH803A has also been evaluated to be 2.7 eV. Dielectric constant of PPCH803A in the smectic phase (90-150°C) is about 2.8 and changes at phase transition temperature in step wise. The mixture of PPCH803A with ferroelectric liquid crystal of low molecular weight exhibits large dielectric constant and unique ferroelectric behavior in the temperature range of the smectic phase of PPCH803A.

Microwave and millimeter-wave devices including a liquid crystal (LC) are increasingly attractive for the use in adaptive and controllable devices. Various types of microwave phase shifters having an LC transmission line have been studied (e.g. microstripline, coplanar waveguide, and rectangular waveguide). In conventional microwave devices, the response time after removal of voltage is slow because the LC layer in the devices is usually thick. In this study, the time response of the LC permittivity is studied experimentally and theoretically. Experimentally measured response curves having two time constants for decay are examined by using Frank's continuum theory with and without the backflow effect.

The chiral smectic C phase of ferroelectric liquid crystals (FLCs) has a self-assembling helical structure which is regarded as a one-dimensional pseudo-photonic crystal. It is well known that a stopband of a FLC can be tuned in wavelength domain by changing temperature or electric field. We here have demonstrated an FLC stopband with independently tunable wavelength and bandwidth by controlling temperature and incident angle. At highly oblique incidence, the stopband does not have polarization dependence. Furthermore, the bandwidth at highly oblique incidence is much wider than that at normal incidence. The mechanism of the tunable stopband is clarified by considering the reflection at oblique incidence.

A striped domain pattern is induced in a nematic liquid-crystal cell under elastic wave propagation, which is changed to be optically uniform in the presence of a frequency-modulated elastic wave in the cell. Optical properties of the uniform domain pattern are investigated in terms of response time and contrast for optical switching. The generation of the uniform domain pattern leads to the advantages of controllable contrast ratio and non electrical switching.

Viscosity properties of liquids, liquid crystals, electrolyte solutions and ionic liquids using the shear horizaontal wave are investigated. The measured viscosities of glycerol/water solutions well agree with the reference values. Using orientation treatment and application of voltage, the electroviscosity effect of liquid crystal is confirmed by this method. Moreover, the relation between viscosity and ionic conductivity of ionic liquids, which followed Walden's rule is obtained.

Dielectric properties of TFMHPOBC, 3MC2PCPOPB and TFMHBOPP which indicate different phase sequences have been investigated as functions of temperature and dc bias field. In the antiferroelectric phase under no bias field, relaxations due to the soft mode and molecular rotation around the short axis are observed. The soft mode relaxation of TFMHBOPP does not decrease even in the transition from chiral smectic CA (Sm CA) phase to isotropic. Under dc bias field, a new relaxation is observed in the SmCA phase of TFMHPOBC and TFMHBOPP. The dielectric strength of this relaxation depends on the bias field, while the relaxation frequency is not affected by the dc bias field.

A detailed study of the dielectric and optical properties of the ferroelectric liquid crystal material (R)-4′-(3-methoxycarbonyl-2-propoxycarbonyl)phenyl 4-(4-(n-octyloxy)phenyl)benzoate (3MC2PCPOPB) has been carried out. It has been found that an anomalous temperature dependence of the dielectric constant in 3MC2PCPOPB is due to the antiferroelectric and ferrielectric properties. A T(temperature)-E(electric field) phase diagram has been obtained on the basis of the apparent tilt angle measurements. In a thin cell (< 3 μm), both ferroelectric and antiferroelectric domains are simultaneously observed over a wide temperature range, and the complete antiferroelectric phase does not appear even at low temperature. A characteristic texture in which boundary focal conics are aligned parallel to a smectic layer has been observed. The movement of the zig-zag defect line caused by the application of the voltage is also observed.

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.