摘要:

A concave reflector can be used to concentrate a beam of plane ultrasonic waves in the focal region, where the intensityIfis much larger than the intensityIiin the plane wave. When the sound wave‐length is small compared to the dimensions of the beam and reflector, one can use the well‐known Fraunhofer diffraction formulas to calculate the intensity gain, i.e.,If/Ii. Expressions are derived for the maximum and average intensity gain in the zero‐order image when the ultrasonic beam is circular or rectangular, together with formulas giving the total intensity falling upon circular or rectangular areas of arbitrary dimensions in the focal region.

ISSN:0001-4966    

DOI:10.1121/1.1906519

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

This paper discusses a method of producing high intensity sound waves in liquids. A beam of ultrasonic waves (4.25 mc, 15 × 12 mm cross section, acoustic power≃2 watts) was focused with an ordinary watch glass (6.8 cm radius of curvature). The intensity in the focal region is large enough to raise an ultrasonic fountain 10 cm high accompanied by a spray of fog droplets. The distribution of intensity in the focal region was determined by measuring the screening effect of properly placed obstacles. The sound intensity in the focal region and in the plane wave was measured by the radiation pressure on beads of convenient size. The absolute intensity in the plane wave was also calculated from the driving potential and the measured mechanicalQof the crystal, and reasonable agreement was found with the direct measurement. A gain in intensity by a factor of about 70 was measured where simple diffraction theory predicts 74. For the highest voltages used the extrapolated negative peak pressure was 41 atmospheres. No cavitation was observed.

ISSN:0001-4966    

DOI:10.1121/1.1906520

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

Piezoelectric ultrasonic radiators made in the form of a thin spherical shell radiate spherical sound waves which come to a focus at the center of curvature of the shell, thus enabling the production of much greater ultrasonic intensity in a small locality removed from the radiator than it is possible to obtain directly at the surface of a radiator. It is here shown by ultrasonic light diffraction pictures of the radiated sound field that the sharpness of focus is limited by wave diffraction in the manner well known in astronomical telescopes and may be calculated by optical diffraction formulas. By the same means the radiation efficiency of different areas of the curved surface is explored and the results compared with theory. The variation of efficiency is, of course, due to the variation of the effective elastic and piezoelectric constants of the differently oriented areas. Calculations are made of the radiation efficiency of a quartz radiator, and it is shown that a greatly improved focusing spherical radiator may be obtained by varying the thickness of the radiator to compensate for the varying frequency constant. Further, superior focusing cylindrical radiators may be obtained by special orientation or by thickness shaping or both.

ISSN:0001-4966    

DOI:10.1121/1.1906521

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

The properties‐of certain plastic substances have been examined with the idea of using them to construct solid lenses for focussing ultrasonic radiation. Some experiments are described which illustrate the advantages offered by such lenses. The use of a plano‐cylindrical or a plano‐spherical lens permits a reduction to 1/10 or 1/100 respectively of the energy which must be emitted by a quartz crystal to produce a given intensity of ultrasonic radiation over a given region.

ISSN:0001-4966    

DOI:10.1121/1.1906522

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

The description of a lamination design for the magnetostrictive motors of a directional transducer array. The design makes possible the efficient operation of the transducer with a “Q” of 6 under a full water load. Array patterns are presented to show that the laminated motors radiate as plane pistons into the medium.

ISSN:0001-4966    

DOI:10.1121/1.1906523

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

Equipment has been built for measuring vibratory displacements of very small mechanical elements such as phonograph styli and piezoelectric crystals. It employs a probe of small dimensions so that virtually point measurements may be made. The probe does not contact the point under measurement and therefore imposes no mechanical load. The variation in capacitance between probe and vibrating surface is used to measure the displacement. Through the use of a built‐in calibrator, the sensitivity may be adjusted electrically for direct meter reading of vibratory displacement without resorting to precise adjustment of condenser plate spacing. Displacement amplitudes of less than 10−6cm may be measured. The output signal corresponds accurately to the displacement both in magnitude and in phase over a wide frequency range so that complex vibrations are portrayed accurately on a cathode‐ray oscilloscope. The equipment has been calibrated by four independent methods, including a reciprocity method, with close agreement.

ISSN:0001-4966    

DOI:10.1121/1.1906524

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

One, two, four, and eight simple tones were presented to listeners against a background of thermal noise. The masked thresholds for the single tones and the various combinations were determined, for different spacings of the tones. In the case of two tones, the improvement in threshold with respect to a single tone was slight or negligible unless the tones were within one critical band, when the improvement increased as the spacing decreased. In the case of four or eight tones all separated by more than a critical band, the improvement was slight (less than 3 db) or negligible, apparently depending on the combination of frequencies.

ISSN:0001-4966    

DOI:10.1121/1.1906525

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

A monaural loudness matching technique was used to study differential sensitivity to intensity as a function of tonal duration. The probable error (p.e.) of the loudness matches was used as the measure of differential sensitivity. With one technique, a standard tone of 500 milliseconds duration was followed by a tone of variable duration (10–500 milliseconds) after a silent interval of 50, 100, or 500 milliseconds. In another technique, both standard and comparison tones were of the same duration (10–500 milliseconds) with the same silent intervals between tones as before. (1) When the standard tone was always 500 milliseconds, the p.e. of the loudness matches increased with a decrease in the duration of the comparison tone from approximately 0.60 to 2.30 db, and the length of the silent interval had no effect on the function. (2) When both the standard and comparison tones had the same duration, the p.e. again increased with a decrease in duration; in this case, however, a silent interval of 500 milliseconds caused an increase from approximately 0.60 to 2.50 db while a silent interval of 50 milliseconds caused an increase to only 1.00 db. These differences are explained in terms of two different processes: adissimilarityeffect, and aninterferenceeffect. (3) When a standard tone of constant duration is used to obtain loudness matches, the mean of the matches becomes a measure of the loudness of tones as a function of duration. These measures showed a clear distinction between the six observers used. For three observers, the change in duration caused practically no change in loudness. For the other three, changes in loudness as great as 8.5 db were recorded. This order of loudness change agrees with that reported by Békésy, but is considerably less than that reported by Munson. Possible explanations for the differences are mentioned.

ISSN:0001-4966    

DOI:10.1121/1.1906526

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

I studied principally the mechanics of the middle ear, summarizing the anatomy and the physiology of the ear. I made Diagram I showing the anatomical structure of the ear, and translated it into physical terms of Diagram II, such as mass, spring, and frictional constant. etc. Thereafter I could get equations showing the mechanics of the middle ear through the Lagrangian equation. The complicated treatment for the kinetic, potential, and dissipation energies of the middle ear elements is for the purpose of expressing my opinion about the function of the middle ear which is partly different from the present contradictory medical views. By using the resultant equations of the motion of the ear and Diagram III (showing the electromechanical structure of the middle ear), I studied the mechanism of the middle ear under an assumption that the frequency characteristic curve of the inner ear is flat in a wide range. This assumption may be deduced from Luscher's experiment of the tympanic loading and hearing curves of men with complete defect of the tympanic membrane but with cochlear nerve intact. However, I do not explain it here, and it will be described in detail in further papers. From theoretical results thus obtained I made some experiments and calculation of the natural frequencies of the middle ear elements.My conclusions are as follows: (a) The air vibration system of the ear which consists of the external auditory canal, the tympanic cavity, and the antrum can be shown electromechanically by Diagram III. (b) The middle ear has four main peaks of resonance on the hearing curves. (c) The middle ear and cochlea appear to be regarded as a displacement receiver and a pressure receiver, respectively. (d) The tympanic membrance has two important roles: (1) that of composing the vibration of the external auditory canala, of the antrum, and of the air cells of the mastoid process; and (2) that of propagating these vibrations to the ossicles. (e) The non‐linear vibration of the tympanic membrane, the basilar membrane, and the secondary tympanic membrane, produce combination tones. (f) The air vibration system has an important role in understanding speech sounds. Its magnification of the sound intensity is above 50 db in a range from 700 or 800 cycles to 5000 cycles as in Fig. 5a. (g) This work offers a problem of design of a new audiometer, and is available for diagnosis of otological pathology.

ISSN:0001-4966    

DOI:10.1121/1.1906527

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP

摘要:

The relatively short range of audibility of thunder is explained by use of the observed vertical distributions of temperature and wind velocity in the neighborhood of thunderstorms.

ISSN:0001-4966    

DOI:10.1121/1.1906528

出版商:Acoustical Society of America    

年代:1949

数据来源: AIP