摘要:

A method is presented for generating a beam with a beam shape that is independent of distance and frequency over large axial and frequency ranges. The half‐width of the beam can be less than a wavelength at the low end of the frequency range and can hold this narrow waist for hundreds of wavelengths, giving a large depth of field. The phase fronts of this beam are planar and perpendicular to the beam axis over the depth of field. By virtue of the flat phase fronts and the frequency independence of the beam, a pulsed beam with flat pulse fronts and an unchanging time response can be created. This beam is shown to share some of the properties of an axicon. A numerical simulation is done to demonstrate the feasibility of generating such a beam with an annular array.

ISSN:0001-4966    

DOI:10.1121/1.400087

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Measurements of the electrical driving‐point impedance loop of a small sonar transducer mounted at an air–water surface were made in the presence of a single concentric ring. A soft (styrofoam) and then a hard (brass) ring was placed around the transducer with the top surface of the ring coincident with the air–water surface. A significant unloading of the transducer was seen for the styrofoam ring. The effect for the brass ring was to increase the loading on the transducer. This experiment might be used in an instructional acoustics laboratory.

ISSN:0001-4966    

DOI:10.1121/1.400088

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

In this investigation, the dispersive, transient wave propagation field of a complete violin excited by a mechanically induced impulse at the top of the bridge is presented. By means of double pulsed holographic interferometry with a ruby laser as light source the propagating wave field is recorded. From presented interferograms, it is seen that initially the top plate acts mainly as a nonsymmetric dipole with centers at the two bridge feet. The back plate is strongly coupled to the motion of the top plate by the sound post and acts more like a monopole. Thus the position of the sound post is crucial to the performance of the instrument. The free edges at thef‐holes are very early reached by the dispersive bending waves of high amplitude probably giving a significant contribution to the sound of the violin family instruments.

ISSN:0001-4966    

DOI:10.1121/1.400089

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Regression equations for the transfer functions displayed in Fig. 15 of ANSI Standard S3.5‐1969 are reported. Predicted values are within 2.15 percentage points of the expected values for most inputs.

ISSN:0001-4966    

DOI:10.1121/1.400090

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Differences between ‘‘exact rays’’ and ‘‘rigorous rays’’ are noted.

ISSN:0001-4966    

DOI:10.1121/1.400091

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

摘要:

Fluid‐filled, focusing spheres are often used as passive acoustic targets because of their relatively high target strength and aspect‐independent characteristics. A fluid mixture consisting of equal parts by weight of trichlorotrifluoroethane and carbon tetrachloride provides a near‐optimum index of refraction. The incentive to investigate alternate filling fluids arises because of the potentially hazardous nature of carbon tetrachloride. Target strength measurements were made on stainless steel spherical floats filled with pure inert fluorochemicals as well as other fluid mixtures. Results indicate that passive acoustic targets can be successfully designed using focusing fluids less hazardous than carbon tetrachloride.

ISSN:0001-4966    

DOI:10.1121/1.400092

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.400366

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.400093

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.400041

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP

ISSN:0001-4966    

DOI:10.1121/1.400047

出版商:Acoustical Society of America    

年代:1990

数据来源: AIP