摘要:

We describe the principle of folded‐path single‐crystal delay lines for pure shear modes, utilizing the fact that in most crystal classes there exist special planes with the following properties: (1) A pure shear wave with polarization normal to such a plane can propagate along any direction in it. (2) Upon reflection of this wave on a boundary normal to the plane, no mode conversion occurs. Hence, in a crystal with two or more boundary surfaces normal to such a special plane, a pure shear wave can be reflected back and fourth between these boundaries without reflection loss. Moreover, with an entire plane of propagation directions available, the design can be optimized by selecting the path giving either the largest delay, or, if the attenuation for all propagation directions is known, giving the lowest loss per unit delay. Examples for the propagation and reflection of pure shear modes in cubic and rhombohedral crystals are presented.

ISSN:0021-8979    

DOI:10.1063/1.1660519

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

All of the elastic and photoelastic constants of crystalline lead molybdate (PbMoO4) and various optical and thermal properties of the material have been measured. This information has been used to evaluate the material for a number of practical acousto‐optic device applications. The high figure of merit found in earlier preliminary studies is only 10% smaller than the maximum figure of merit of the material. Thus the material is well suited for acousto‐optic modulator and deflector applications. However, the material is not particularly useful for tunable acousto‐optic filters because the relevant elasto‐optic coefficient is small. Acoustic and optical losses, and changes in sound velocity and index of refraction with temperature, can cause operating limitations in practical devices, and these are discussed.

ISSN:0021-8979    

DOI:10.1063/1.1660520

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

An underwater acoustic imaging system is described which has been developed especially for close‐range, high‐resolution (on the order of millimeters) viewing in very turbid water. The system operates at nominal 2.5‐MHz frequency and has a range up to 10 m in water of suspended ocean sediment concentration as high as several thousand parts per million. Larger range capability is possible with lower sediment concentration. Real‐time kinescope displays are presented by the system of the acoustic field of view, which is that insonified by a high‐intensity sound transmitter of total beamwidth variable up to 30° in 10° increments. The sensitive (better than 10−10W/cm2) piezoelectric image converter is augmented by a mechanical scanning system to provide in effect a 10 000‐element pickup matrix. A Plexiglas lens moved by remote‐control drive is employed for focusing. System parameters and performance are discussed, and some typical hydroacoustic images are displayed.

ISSN:0021-8979    

DOI:10.1063/1.1660521

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The temperature dependence of the susceptibilities of amorphous magnetic oxides with various iron/yttrium and iron/gadolinium stoichiometries have been studied between 4.2° and 320°K. The reciprocal susceptibilities of the iron/yttrium oxides exhibited an unusual downward curvature at low temperatures. These measurements are interpreted by means of a simple effective field model for amorphous antiferromagnetic materials recently proposed by one of the authors. Good agreement between the experimental results and the theory is obtained. The analysis enables certain broad conclusions to be drawn about the number and distribution of interacting pairs of magnetic atoms.

ISSN:0021-8979    

DOI:10.1063/1.1660522

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The temperature gradient induced migration of gas bubbles has been studied in KCl. This material was selected because of its high vapor pressure and transparency. The experimental variables of temperature, temperature gradient, and diffusion coefficient of the vapor species were investigated and the observed velocities were shown to agree with those expected from the theoretically derived model. The ratio of the temperature difference across a bubble of low thermal conductivity to that across an equal length of the surrounding solid was determined from analogue experiments.

ISSN:0021-8979    

DOI:10.1063/1.1660523

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Gas bubbles migrating under the influence of a temperature gradient in KCl gradually evolve stable shapes which have a low length (in the direction of migration) to width ratio and are bounded by cube planes (100). The shape is determined by evaporation‐condensation kinetics and not by the equilibrium surface energies. A significant part of the bubble volume is left behind in a trail of very fine bubbles resulting in as much as a fivefold increase in bubble surface area. Most of the observed phenomena can be correlated with the detailed temperature distribution around a migrating bubble.

ISSN:0021-8979    

DOI:10.1063/1.1660524

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The dislocation substructure of ⟨111⟩ Cu single crystals has been controlled by varying crystal growth rates from 1.57 to 109 cm/h. Etch‐pitting and x‐ray studies reveal that the substructure consists of a random dislocation network, with density 1×106/cm1independent of growth rate, and dislocation cells whose size and intercell misorientation angle increase with decreasing growth rate. Longitudinal resonance bar and ultrasonic pulse‐echo damping measurements at frequencies from 25 kHz to 100 MHz show that the larger the cell size, the higher the damping over the entire frequency range. There is strong evidence that damping from cell‐wall dislocations overshadows that due to the random network. The results are interpreted in terms of a modification of the Granato‐Lu¨cke damping theory, which treats cell walls as pseudomembranes vibrating under the action of the applied stress.

ISSN:0021-8979    

DOI:10.1063/1.1660525

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A modification of the etchant used by Levinstein and Robinson is shown to be a reliable solution in producing etch pits at dislocations on the (111) surface of silver crystals and is used to investigate the dislocation structures in as‐grown, annealed, and deformed silver crystals. Single crystals of silver with dislocation densities on the order of 104cm−2with a few subboundaries were prepared by high‐temperature annealing. Two distinct sizes of dislocation etch pits are found in both as‐grown and deformed crystals. The two sizes of etch pits are concluded to be associated with positive and negative edge dislocations through detailed observations of etch‐pit rosettes produced by indentation. The modified Levinstein‐Robinson etchant for silver thus corresponds to the Livingston etchant for copper. Additional observations are made on polygonization, dislocation interactions, and etch‐pit morphology. Large etch pits not associated with individual dislocations are also described.

ISSN:0021-8979    

DOI:10.1063/1.1660526

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The 1000‐Hz 300°K dielectric constants of the alkaline earth fluorides were measured to an accuracy of 0.01% by the method of substitution. Reproducibly different values for various crystals of the same type were obtained which varied beyond the experimental error. The ranges of results for various crystals of each type measured along with further separation by manufacturer are: CaF2, Harshaw, 6.7984–6.7988, Optovac, 6.8074–6.8432; SrF2, Harshaw, 6.4647–6.4664, Optovac, 6.4700–6.4703; and BaF2, Harshaw, 7.3590–7.3595, Optovac, 7.3606–7.3630. The spread for each type of crystal is thought to be attributable to random trace impurities.

ISSN:0021-8979    

DOI:10.1063/1.1660527

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The elastic, piezoelectric, and dielectric constants, and their temperature dependence within the range 0°–110°C, have been determined for single crystals of lithium tantalate and lithium niobate. For each material, the constants were extracted from a combination of many ultrasonic phase‐velocity measurements, the measured resonant and antiresonant frequencies of a single length‐extensional bar resonator, and the measured low‐frequency capacitances of two thin flat‐plate specimens. For lithium tantalate, the normalized first temperature derivatives of the elastic constants range from −0.4 to −6.7×10−4/°C, while the derivatives for the piezoelectric stress constants range from −1.3 to +1.5×10−4/°C. In the case of lithium niobate, the elastic constant temperature derivatives are all on the order of −2×10−4/°C, while the piezoelectric temperature derivatives are all positive in the range 0.8–8.9×10−4/°C. The dielectric or permittivity temperature derivatives are positive for both materials.

ISSN:0021-8979    

DOI:10.1063/1.1660528

出版商:AIP    

年代:1971

数据来源: AIP