摘要:

Nonlinear electroelastic equations, quadratic in the small field variables, are applied in the analysis of second harmonic generation of surface waves in piezoelectric solids. Preliminary to the treatment of the anisotropic piezoelectric case, the more tractable problems of the second harmonic generation and parametric excitation of surface waves in isotropic elastic solids are treated. In all instances the solutions asymptotically satisfy the nonlinear differential equations and boundary conditions on the surface of the semi‐infinite solid to a specified order in a small parameter. Since the equations are quadratic rather than cubic in the small field variables, only initial spatial rates of growth of the harmonically generated and parametrically excited waves are determined. Nevertheless, an extension of the analysis to enable the calculation of more than the aforementioned initial slopes is indicated. In the isotropic elastic case the solution for the second harmonic reveals, among other things, that the ratio of the dilatational to equivoluminal portions of the growing second harmonic is the same as in the input Rayleigh wave.

ISSN:0021-8979    

DOI:10.1063/1.1663047

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Acoustic surface waves propagating around a piezoelectric cylinder with metallic overlays are investigated. The piezoelectric core is assumed to possess the hexagonal symmetry, and the layer is electrically shorted. The dispersion equation is derived. Numerical results for the phase velocities, the displacement, and potential profiles are presented for different layer materials with various thicknesses. It is found that the thickness of the gold and chromium has a substantial effect on the dispersion, while in the case of aluminum layers little influence is observed. An asymptotic expansion for the dispersion equation is also derived and is found to yield results in good agreement with the exact solution.

ISSN:0021-8979    

DOI:10.1063/1.1663048

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The various growth morphologies of CdS films grown epitaxially on SrF2substrates were investigated by studying films grown at different supersaturations on smooth and intentionally pitted substrate surfaces. By correlating the growth conditions with photomicrographic and x‐ray topographic studies, cathodoluminescence, and low‐temperature uv excited edge emission we show that the hexagonal flat top is the equilibrium growth form produced by two‐dimensional nucleation. Using the same studies we show that the hexagonal pyramids are associated with an excess amount of cadmium, and that they could be formed by growth around a cadmium droplet. The cadmium droplets form when conditions exist which do not allow the cadmium adatoms sufficient time to diffuse to their equilibrium position.

ISSN:0021-8979    

DOI:10.1063/1.1663049

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Numerical techniques are presented for extending and implementing the Lagrangian analysis originated by Fowles, Williams, and Cowperthwaite. The analysis derives internal energy, specific volume, and stress and particle velocity histories from either stress or particle velocity records from a series of gages embedded in material undergoing uniaxial strain flow. The material may have an arbitrarily complex constitutive relation. The accuracy of the analysis for attenuating waves is studied by handling analytically derived stress and velocity histories. Waves with attenuation of 40–75% can be treated, depending upon the accuracy desired. The analysis is applied to waves measured in graphite, sandstone, asbestos phenolic composite, and porous alumina.

ISSN:0021-8979    

DOI:10.1063/1.1663050

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The scattering of Rayleigh surface waves into longitudinal volume waves has been carried out utilizing optical patterns imaged on photoconductive cadmium sulfide films. A 100‐MHz interdigital transducer was used to launch surface waves along the top face of a lithium niobate delay line. Imaging of an optical grating pattern onto a CdS film overlay produces photoconductive variations which interact with the fields associated with the surface wave. The optical pattern, a series of bars, will cause constructive interference of volume waves scattered normal to the surface when the grating periodicity is one wavelength of the surface wave. A theoretical calculation of this scattering efficiency is made and is found to be in excellent agreement with the experimental results. This device offers significant advantages over similar devices in that the scattering grating may be changed or translated quite readily.

ISSN:0021-8979    

DOI:10.1063/1.1663051

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

Elastic proton backscattering has been used to study the mechanism by which LiOH corrosion layers on LiH are converted to Li2O. The concentration‐vs‐depth profile was measured during vacuum anneals in the temperature range 200–280°C, over which the conversion rate varied by two orders of magnitude. Conversion was found to proceed via two reaction fronts, one advancing from the LiH&sngbnd;LiOH interface, the other from the surface. Both H2and H2O were evolved during the reaction. The results are interpreted in terms of H2O being formed at both reaction fronts, and then diffusing respectively to the LiH substrate and to the surface. Water reaching the LiH substrate then reacts to produce H2, while H2O at the surface is released. The conversion rate on the LiH substrate is related quantitatively to the static equilibrium pressure of H2O over a mixture of bulk LiOH and Li2O in the absence of LiH. Values for this thermodynamic quantity have been reported in the literature. From the analysis it is concluded that H2O formation at the reaction fronts is the rate‐determining step in the conversion. The activation energy for the conversion process is 31 kcal/mole.

ISSN:0021-8979    

DOI:10.1063/1.1663052

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

New improved materials for smectic liquid crystal storage displays are described which have the advantages of image generation at lower laser power, independence of image generation over a wider range of laser scanning speeds, improved contrast, and near ambient temperature (24°C) storage. The electric erase characteristics, laser writing speeds, and contrast are demonstrated to be dramatically dependent on both the smectic liquid crystal and added dopants. Local electric erase is observed only for smectic liquid crystals having a nematic phase or incipient nematic range. Better contrast and a wider range of laser writing speeds are obtained when dopants are added which are soluble in the isotropic phase and insoluble in the smectic phase. Enhanced contrast (higher scattering center density) obtained by adding certain dopants is considered to result from enhanced nucleation in the bulk and stabilization of singularities resulting therefrom by reduction of the associated core and strain energies.

ISSN:0021-8979    

DOI:10.1063/1.1663053

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

A model for hillock growth in thin films such as those of lead and tin is developed. It is proposed that hillock growth is a form of stress relaxation in which atomic species diffuse along the film‐substrate interface to the base of the hillock. The latter extrudes out along the grain boundaries connecting it to the rest of the film. The stability and kinetics of this process are considered. Taking into account Nabarro‐Herring diffusion creep as a parallel stress relaxation mechanism observations such as an incubation period for hillock growth and the effects of film thickness on hillock density are accounted for. In addition, observations on lateral growth of hillocks and unusually tall hillocks (whiskers) are interpreted within the framework of the present model.

ISSN:0021-8979    

DOI:10.1063/1.1663054

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

In a slightly dispersivey‐cut sample of LiNbO3the complex coupling coefficient between fundamental and second harmonic acoustic surface waves has been measured through the intensities of the light reflected from the corrugated surface into second diffraction orders. The values have been separately obtained for both +zand −zpropagation directions.

ISSN:0021-8979    

DOI:10.1063/1.1663055

出版商:AIP    

年代:1974

数据来源: AIP

摘要:

The use of acoustic detection for the measurement of infrared absorption in gases has been shown to be of value in measuring atmospheric pollutant gases. Further improvements in detection sensitivity may be achieved by the use of an acoustically resonant system and multipass optics wherein the incident laser radiation is reflected many times through the absorption sample. We have demonstrated acousticQ's exceeding 750 and sensitivity increases of at least 10 using multipass optics. A microphone amplifier pair is described whose noise limitation approaches the thermal noise on the microphone diaphragm.

ISSN:0021-8979    

DOI:10.1063/1.1663056

出版商:AIP    

年代:1974

数据来源: AIP