摘要:

Starting from the fundamental acoustic and electromagnetic field equations an approximate expression is obtained for the perturbation in propagation wavenumber of a surface acoustic wave in a piezoelectric crystal. The source of perturbation is taken to be a surface spaced an air‐gap distancehabove the piezoelectric and is described in terms of an electrical impedance. The resulting perturbation is found in terms of the perturbing electrical impedance, an effective dielectric constant for the piezoelectric, the air‐gap spacingh, and a perturbation coupling constant defined in terms of the unperturbed electric potential at the piezoelectric surface and the average acoustic power flow per unit frequency. The theory is applied to the case of a short‐circuit perturbing surface and found to be in excellent agreement with certain numerical results forY‐cutZ‐propagating LiNbO3and several cuts of Bi12GeO20. In the general case of a complex perturbing impedance, such as that exhibited by a semiconductor, the theory indicates that attenuation or gain and dispersion may be introduced by the perturbation, in close agreement with experimental observations.

ISSN:0021-8979    

DOI:10.1063/1.1660184

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The parametric interaction between two oppositely traveling sound waves and a nonspatially varying (k= 0) rf electric field in lithium niobate is illustrated in this paper. A pump frequency near 3 GHz is used to parametrically amplify the sound wave at one‐half the pump frequency. In addition with a pump field that is sufficiently strong parametric oscillations occur within the crystal and this process forms a method of generating sound waves throughout the crystal volume. Finally, we have found that this type of parametric mixing of two sound waves can be used to obtain convolution signals in real time by monitoring the electric polarization generated within the crystal at twice the signal frequency.

ISSN:0021-8979    

DOI:10.1063/1.1660185

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Propagation of shear horizontal waves in classC6vpiezoelectric 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.

ISSN:0021-8979    

DOI:10.1063/1.1660186

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The observation of acoustoelectric current saturation and domain propagation inn‐type InP single crystals is reported. The electromechanical coupling constantKand the dominant acoustic frequencyfare obtained from the variation of the incubation time for current decay with applied drift field.K2= 1.0×10−3andf= 17 GHz. The enhancement of acoustic gain in a transverse magnetic field is examined and compared to the predictions of the microscopic theory. Semiquantitative agreement can be obtained by assuming a slight scan of the dominant accoustic frequency with magnetic field.

ISSN:0021-8979    

DOI:10.1063/1.1660187

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

This paper analyzes equivalence properties of linear distributed‐parameter systems characterized by Sturm‐Liouville‐type differential equations. The approach taken here may be regarded as an application of the method of independent‐variable transformation to those fundamental equations. In accord with the meaning of equivalence used for lumped‐parameter systems, distributed‐parameter systems are considered here as equivalent when they possess the same terminal behavior. The principal result is an equivalence theorem which establishes a general method of equivalent transformation of Sturm‐Liouville systems. The fact that we can generate any number of equivalent parameter distributions from a given one is not only of theoretical interest but also of practical importance, because it offers a flexibility in the design of distributed‐parameter structures. The derivation of the transformation function which plays a central role in the equivalent transformation is briefly described. Discussion is also given to the quantities which are invariant under the equivalent transformation. In the later part of the paper applications of the general theory to several problems of practical interest are considered, which include guiding systems for electromagnetic and space‐charge waves such as nonuniform transmission lines, lens‐like media, and nonuniform drift regions. The physical meanings of the transformation function, the parameters introduced, and various transformation invariants are discussed in detail. A simple example of equivalent systems is also illustrated in the case of nonuniform transmission lines.

ISSN:0021-8979    

DOI:10.1063/1.1660188

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

Patterns of fluid flow are investigated by a technique utilizing NMR spin echoes. Spin‐echo amplitudes are sensitive to the phase distribution of the resonating nuclei in the fluid, and the phase distribution is dependent upon the flow. A mathematical transformation of the spin‐echo amplitudes observed provides a velocity distribution function which indicates the relative number of molecules flowing in any given velocity range when plotted. Experimental data are obtained from ordinary laminar flow, and blood flow in human fingers.

ISSN:0021-8979    

DOI:10.1063/1.1660189

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

A new absolute method is developed for measuring electric resistivity in the range of 10−8to 10+8&OHgr; cm of a sample of almost arbitrary shape. This method takes into account the effect of self‐induced conduction and polarization current. Measurements are made with the specimen placed in a constant rotating magnetic field in such an orientation that it experiences maximum torque and has minimum moment of inertia. This can be shown to be the same orientation for which, if the specimen were free to rotate, it would reach the angular velocity of the rotating field in minimum time. This method is applicable to homogeneous and isotropic conducting materials in both solid and liquid states, including ferromagnetic substances. The mathematical formula for the measured torque is developed and the technique for measuring electric resistivity is explained.

ISSN:0021-8979    

DOI:10.1063/1.1660190

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The effect of alloying elements in aluminum on the phenomenon of pit formation has been studied. It is suggested that alloying elements will affect; (1) the vacancy supersaturation, (2) the migration energy of the vacancies; and (3) the nature of the oxide‐metal interface. It was found that there are four main types of effects of solute addition on the formation of pits. (a) Pits are not observed (Al&sngbnd;1.05&percent; Mg alloy). (b) Pits appear with a larger &Dgr;Tthan for pure aluminum, and &Dgr;Tdecreases with increasing holding temperature (Al&sngbnd;1.07&percent; Zn alloy and Al&sngbnd;0.57&percent; Cu alloy). (c) Pits appear with a larger &Dgr;Tthan that for pure aluminum and &Dgr;Tdoes not follow any regular trend (Al&sngbnd;0.0045&percent; Sn alloy). (d) Pits are not observed, but a rippled structure appears on the surface of the specimen (Al&sngbnd;0.96&percent; Sn alloy).

ISSN:0021-8979    

DOI:10.1063/1.1660191

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The stresses of infinite edge dislocation multipoles are investigated with the aid of a B5500 computer, and contour maps are obtained using the line printer. These multipoles consist of infinitely long, parallel edge dislocations of same strength, arranged so as to define a prism whose cross section is a regular polygon and with their Burgers vectors in radial orientation. As will be shown in Part III, multipoles are the prototypes of dislocation cells containing the same Burgers vectors, independent of cell shape, in the same way that the quadrupole, discussed in Part I, is the prototype of all cells composed of dislocations involving two mutually perpendicular Burgers vectors. It is found that the stress fields of &tgr;rr, &tgr;&phgr;&phgr;, and &tgr;r&phgr;all exhibit 2Nsimilar leaves of alternating sign for a multipole ofNth order, except that &tgr;&phgr;&phgr;of the dipole has eight rather than the expected four leaves. The magnitude of the stresses falls as 1/rNat large distances, except that &tgr;&phgr;&phgr;of the dipole falls as 1/r4. Lastly, there exists a ``conservation of zero line'' rule to the effect that a fixed number of contours of vanishing stress passes each dislocation, independent ofN, the order of the multipole, namely, six zero contours of &tgr;&phgr;&phgr;and &tgr;r&phgr;, and two of &tgr;rr, respectively.

ISSN:0021-8979    

DOI:10.1063/1.1660192

出版商:AIP    

年代:1971

数据来源: AIP

摘要:

The electromechanical coupling factors are measured in the frequency range from 100 kHz to 260 MHz for CdS single crystals with various dislocation densities. These measurements show that each of the electromechanical coupling factorskt, k15, andk31begins to decrease in a steep slope as the density of dislocation which terminates atcsurface of the crystal exceeds an amount around 106cm−2. However, these coupling factors come back toward the normal values when the density of dislocation is decreased by means of the annealing of the crystals in a sulfur vapor. No appreciable change of the elastic constants and the dielectric constants is observed. Therefore, the observed variation of the electromechanical coupling factors is attributable to the dependence of the corresponding piezoelectric constants on the dislocation density.

ISSN:0021-8979    

DOI:10.1063/1.1660193

出版商:AIP    

年代:1971

数据来源: AIP