摘要:

The relative importance of the receiving sensitivity, impedance, efficiency, and equivalent noise pressure of a hydrophone in determining signal‐to noise ratio is discussed. It is concluded that even when the threshold is determined by the self‐noise of the preamplifier, it is the equivalent noise pressure, or rather the efficiency, that ultimately determines the signal‐to‐noise ratio, provided the hydrophone impedance is taken into account.

ISSN:0001-4966    

DOI:10.1121/1.1908533

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.1908535

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

It is well known that a large plane reflector directly above and normal to the axis of a cylindrical transducer can have a rather drastic effect on the beam patterns of such a transducer. The degree of such an effect is, of course, dependent on size and material of the reflector, distance above the active face of the transducer, and the size of the active face of the transducer in wavelengths. Experimental data will be presented indicating some of the precautions one must take to guard against such effects or to use these effects to one's advantage if desired. Information will be presented, for both plane and conical reflectors, as to the beam depression, beam width, effective hydrophone sensitivity, and minor‐lobe structure as a function of reflector dimensions and for various distances of the reflectors above the active face. (This work is supported by the Bureau of Ships.)

ISSN:0001-4966    

DOI:10.1121/1.1936587

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

It is often desirable for an acoustic target to have a large target strength independent of target aspect. A sphere is considered to have a low target strength that is independent of target aspect, whereas a cylinder is considered to have a high target strength for a particular target aspect but low target strength for other aspects. The measured target strength in water of a finite 90‐deg biconical surface as a function of target aspect is compared to similar data for a finite cylinder and sphere with the same relative dimensions. The biconical surface targets are two metal cones, having a common axis, and joined at their vertices with the vertex angles equal to 90 deg. The finite 90‐deg biconical surface is shown to have a lower maximum target strength than the cylinder but has a target strength that is less dependent upon target aspect than that of the cylinder. Target strength data for four right‐circular conical surfaces measured in water at two frequencies in the plane normal to the conical axis are compared to the empirical formulaT = 10 logR3/3λ, whereRis the radius of the base of the finite 90‐deg biconical surface and λ is the wavelength of the incident acoustic wave. (This work is supported by the Bureau of Ships.)

ISSN:0001-4966    

DOI:10.1121/1.1936594

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

The Panoramic Tone system is a new means for enhancing electrically produced or reproduced sound. Organ music has traditionally been heard in environments with long reverberation times. Therefore, it is desirable from a musical standpoint for this effect to be present in the sound produced by electronic organs played in homes and small churches. The heart of the new system is a long wire equipped with an electromechanical transmitter and receiver at its ends. Multiple reflections and termination losses control the properties of the tonal enhancement. The wire is coiled into a helical shape only for convenience in packaging. The sound transmitted along the wire has been translated to the ultrasonic frequency range. This greatly attenuates any disturbance from noises and shock at audible frequencies. It also gives a more uniform trend for the response‐frequency characteristic and the reverberation time‐frequency characteristic than other methods have provided.

ISSN:0001-4966    

DOI:10.1121/1.1936600

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

The depletion layer transducer is a new ultrasonic transducer made from piezoelectric semiconductors, such as gallium arsenide, and is best suited for use at microwave frequencies. The electromechanically active region is a thin, flat, high‐resistance depletion layer such as ap‐njunction or the surface barrier at a metal semiconductor contact. Since the transducer is a thin piezoelectric layer, its behavior is more like that of a flat piezoelectric transducer plate used at low frequencies than other microwave transducers. Advantages expected when the thickness is comparable to a half wavelength of sound are large electromechanical coupling and large bandwidth. The major difficulty is the low impedance due to the extreme thinness. It is also possible to change the thickness, hence the resonant frequency, by a dc bias. The first models utilized metal semiconductor contacts to form the depletion layers. Frequencies above 1000 Mc were generated and detected, and bandwidths of 5% were observed. The insertion loss was much higher than theoretically predicted. Current efforts are directed toward transducers formed byp‐njunctions. It is anticipated that improvements in fabrication techniques and circuitry will extend the frequency range and lower the insertion loss.

ISSN:0001-4966    

DOI:10.1121/1.1936607

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Eight subjects trained in listening were given a variety of taped programs of frequency glissando consisting of items which began at 1500 cps and proceeded at 50 phons either up or down in frequency. S's were required to judge “higher” or “lower.” Periods of glissando from 0.2 to 10 sec and rates of change from 0.5 to 100 cps/sec were used. Sensitivity to this type of frequency modulation is surprisingly good, and inter‐subject variation is not excessive; thus it could well form one sensory input to certain man‐machine systems, either on an absolute or a relative basis. OneS, extremely poor on the more usual pitch test by the constants method, was not much worse than average on glissando. For mostS's, a constant emerges at a total of about 5‐cps change, such that sensitivity to 0.5 cps/sec change over 10 sec is about equally as difficult as 5 cps/sec change over 1 sec, and so on. This constant is in fact of the same order of magnitude as the traditional DL for pitch.

ISSN:0001-4966    

DOI:10.1121/1.1936612

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

The performance characteristics, such as time delay, spurious response levels and bandwidth, of multiple‐reflection‐type delay lines are discussed. State of the art performance is indicated, and efforts to improve these characteristics are described. The time delay is determined by the path length of a given design and size limitations on the fused‐quartz blanks. Multiple symmetry designs are derived from regular polygons by rotating facets to achieve long path lengths. Typical designs are presented, and the delays that can be achieved in readily available blanks of fused quartz are indicated. Spurious responses result from diffraction at the transducer and subsequent reflecting facets, and from reflections at the transducers. “Creation angle” spurious responses characterize multiple symmetry type designs, resulting in the use of simpler designs for many critical applications. Aperturization techniques may be employed to control the size of the reflecting facets, and hence to control certain diffraction effects. The delay‐line bandwidth is a function of the transducer resonant frequency, bonding techniques and delay medium characteristics. The dependence of bandwidth on bonding parameters is discussed in terms of the transducer equivalent circuit. Medium losses increase with frequency, and limit the attainable bandwidth for long delays. The ultimate performance capabilities of multiple reflection type delay lines using materials and techniques currently available are considered. Limitations imposed on the time‐bandwidth product and dynamic range are discussed. Practical upper limits are considered in terms of figures of merit for communications and radar applications.

ISSN:0001-4966    

DOI:10.1121/1.1936621

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

An ultrasonic delay line has been developed which employs water as the delay medium and permits continuous adjustment of delay between the limits of 28 and 58 μsec. Adjustment of delay is effected by movement of a corner reflector relative to two crystal transducers whose positions are fixed. The center frequency is 30 Mc and the bandwidth is in excess of 10 Mc. Uniformity of bandwidth and response over this range is controlled by a combination of measures including selection and design of backing and bonding materials, offsetting the resonant frequency of the transducers from the operating band and use of particular alignment techniques. Delay stability is achieved by operating the unit at the inversion temperature of sound in water. The design features of the unit as well as water. The design features of the unit as well as the electrical characteristics of the system are discussed.

ISSN:0001-4966    

DOI:10.1121/1.1936625

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP

摘要:

Electrical admittances have been measured for rectangular bars of barium titanate, lead zirconate‐titanate, and sodium potassium niobate which were poled in a direction normal to the driving electrodes. Resonant frequencies for the first eight modes of vibration have been determined from these measurements. A comprehensive survey has been made of 50 or more transducers of each material in a width‐to‐thickness (w/t) range from 0.2 to 100. The velocities for longitudinal waves in a thin rod and dilatational waves in an extended body have been determined from the value of frequency‐thickness (fRt) product at the limiting values ofw/t. Graphs show the dependence of electromechanical coupling andfRtonw/tover a range from 0.2 to 6. The results are compared to those for resonant vibrations in circular disks reported by Shaw. Graphical results show the optimum values of width and thickness dimensions for transducer design in the first mode and a technique for determining optimum dimensions for resonance in other modes is outlined. A normalizing parameter is introduced which is determined for a given material from a measurement offRin the first mode for a single transducer. For materials with Poisson's ratio between 0.2 and 0.4, this parameter permits the design of transducers to a frequency within ±3% in the first mode.

ISSN:0001-4966    

DOI:10.1121/1.1936630

出版商:Acoustical Society of America    

年代:1961

数据来源: AIP