摘要:

Results are given of measurements made on a 175‐section network representing the basilar membrane, which was modified to include the effects of dissipation in the cochlear partition. The results show that the dynamical theory of the cochlea, when dissipation is considered, is in good agreement with experimental evidence.

ISSN:0001-4966    

DOI:10.1121/1.1906737

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

This is a report of results obtained in preliminary tests of perception of signals applied directly to the skin in the form of electrical potentials. The lowest signal level that could be felt and the highest level that could be applied without extreme discomfort to the observers were determined for sine wave potentials ranging from 100 to 10,000 cps. The difference between the lowest and highest levels was about 25 db over this frequency range.Difference limen measurements for intensity and frequency showed that intensity discrimination is not greatly different from what it is for hearing, but the ear is vastly superior in the matter of frequency discrimination.

ISSN:0001-4966    

DOI:10.1121/1.1906738

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

This paper discusses the general physical problems underlying the portrayal of ventricular geometry by ultrasonic techniques. This offers another means somewhat analogous to x‐ray ventriculography for the detection of brain tumors. Progress is reported on studies of ultra‐sound propagation properties in the tissues involved. Preliminary conclusions on safety thresholds of pain and damage are discussed. The most promising method to date is straight‐through transcranial transmission (not echo ranging) utilizing changes in attenuation owing to differing amounts of ventricle along the transmission path. The optimum compromise frequency appears to be about 2.5 megacycles for which frequency results are reported on studies of receiver sensitivity and dynamic range, resolution, shielding, transducers, and presentation problems.

ISSN:0001-4966    

DOI:10.1121/1.1906739

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

The mean‐square pressure distributions in the ultrasonic fields generated in water by quartz transducers of various shapes were presented on an oscilloscope screen and photographed. The beams, pulsed at an audiofrequency, were swept back and forth across a small pressure‐sensitive microphone placed at various distances from the source. The pulse envelopes were square‐law detected and amplified before presentation. All the transducers were of X‐cut quartz, excited near their resonance frequency of about 1 mc. Square pieces with circular and ring‐shaped electrodes, as well as circular and ring‐shaped pieces, were used; all were about 2 cm in diameter. Comparisons with theory were made for radial and axial mean‐square pressure distributions. From study of the axial distributions it was concluded that simple piston theory adequately describes these transducers, provided the baffles and electrodes satisfy certain geometrical conditions. It appears that 18.5° X‐cut crystals tend to vibrate over the whole exposed surfaces, even outside the electrode regions.

ISSN:0001-4966    

DOI:10.1121/1.1906740

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

When a small microphone is used in an ultrasonic beam, the direct acoustic signal is mixed with electric pick‐up and reflected signals. The use of pulses may not entirely remove these interferences. The mixing process is analyzed here for a particular situation and experimental evidence is adduced to support these conclusions: (1) that the main response pattern of the microphone shows space variations of both half the acoustic wavelength and the full wavelength; (2) that the former variation dies out at sufficiently great distances from the source at a rate showing that a single echo path (source‐microphone‐source‐microphone) is responsible along with a constant electric signal; and (3) that the three signals can be resolved analytically.

ISSN:0001-4966    

DOI:10.1121/1.1906741

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

An ultrasonic interferometer with high sensitivity is used to measure acoustic velocities at 0°C in gases, as the wavelength approaches the mean free path of the molecules. Measurements are made of velocity as a function of pressure down to about 2 mm of Hg, the frequency being kept constant at approximately 970 kc. The following increases in velocity (at the lowest pressures) over that at standard conditions were observed: argon 27 percent, nitrogen 16 percent, oxygen 20 percent, and dryCO2‐free air 7 percent.

ISSN:0001-4966    

DOI:10.1121/1.1906742

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

The Rayleigh surface integral, giving the velocity potential for a plane piston source surrounded by an infinite rigid flange, reduces to a line integral when the coordinates are suitably chosen. As shown by Schoch, for points within the geometrical cylinder whose base is formed by the piston surface, the line integral is expressible as a plane wave term plus a “perturbation” integral. For external points, a different integral results. In the present work, these two complementary expressions are evaluated for a circular piston, as series of half‐integral order Hankel functions inkzand polynomials inx/a;kis the propagation constant,athe piston radius,zthe axial andxthe radial coordinate of a field point. The resulting rigorous equation (valid for points not on the piston surface) converges for any value ofka, providedz>a. For large values ofkz, where asymptotic formulas apply, the expression assumes a particularly simple form. Sample calculations have been made forka= 10,z= 10aandka= 50,z= 50a. Also, an approximate expansion has been derived which may be more useful than the rigorous result in paraxial regions.

ISSN:0001-4966    

DOI:10.1121/1.1906743

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

The velocity potential distribution of a circular emitter vibrating in an infinite wall is calculated by the King method for the points immediately before the wall. It is showed on the close connection between the Rayleigh formula and the expression for the velocity potential which follows from the King method. The equation for the space distribution of the velocity potential expanded in spherical wave functions is transcribed into an abstract form by means of the Dirac bra‐vector, ket‐vector, and linear operator represented by the corresponding matrices. The space distribution of the velocity potential is then computed from the known values in the plane immediately before the emitter by the well‐known method of undetermined coefficients written in its matrix form. Thereafter the space distribution of the velocity potential is determined by another, new method due to H. Stenzel. In both methods explicit expressions are given for the case of a vibrating rigid disk, membrane, and plate.

ISSN:0001-4966    

DOI:10.1121/1.1906744

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

An acoustical radiation field excited by an emitter vibrating freely or in a wall of finite dimensions is considered as superposed by two fields. The first of these is that one where the same emitter is vibrating in an infinite wall and the second is that which (i) causes the resultant field in the free part of the plane going through the wall to vanish, and (ii) has a normal derivative which vanishes on the surface of the emitter and of the wall. While the first field may be considered as known from other papers, the second is computed from an integro‐differential equation that follows from Rayleigh's formula. The equations expressing the velocity potential distribution and those deduced from it are written in an abstract form by means of the Dirac bra‐vectors, ket‐vectors, and linear operators represented by the corresponding matrices. This method of solving the given special diffraction problem of a scalar wave may be used for any mode of vibrations of the emitter and for any shape of the wall, but the computation becomes far easier if the wall is circular. It may be applied also for any wavelength of the radiated sound, but the functions expressing the dependence on the azimuthal angle and containing the Legendre associated functions of the first kind converge faster, the longer the wavelength in comparison with the dimensions of the wall. Numerical calculations are not given. They will be adequate for the difficulty of the problem, i.e., very tedious; but they can be done, especially with the help of modern electronic calculating machines.

ISSN:0001-4966    

DOI:10.1121/1.1906745

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP

摘要:

By using a barium titanate cylinder poled radially a lengthwise motion can be excited in the cylinder whose resonant frequency is controlled by the length of the cylinder. By using a 4 percent lead titanate‐barium titanate combination, stresses up to 1000 pounds per square inch of cross‐sectional dimension and motions up to 50 parts in 106times the length of the cylinder are available for static or slowly varying voltages of 15,000 volts per centimeter along the radial dimension. When such a cylinder is driven at its resonant frequency, the maximum strain appears to be limited to 10−4by heating considerations if no cooling is used. For a cylinder 12 centimeters long, which resonates at 18 kilocycles, this corresponds to a displacement on each end of 3.9 × 10−4cm, a particle velocity of 44 cm/sec and an acceleration of 5 × 10−6cm/sec/sec. All of these quantities can be enhanced by a factor of 10 by soldering a solid brass “horn,” tapered exponential, to the end of the barium titanate cylinder. If the large end of the horn, which is soldered to the cylinder, is 10 times the diameter of the small end, the horn acts as a transformer to increase the particle motion by a factor of 10. Hence, a 1.5‐mil motion is possible with this combination at 18 kilocycles. This structure has been made the basis of several instruments used for testing wear, for measuring magnetic flux, for testing adhesion of films, and for boring odd‐shaped holes. A feedback amplifier system with a diode limiting element is used to keep the amplitude constant.

ISSN:0001-4966    

DOI:10.1121/1.1906746

出版商:Acoustical Society of America    

年代:1951

数据来源: AIP