- Email: [email protected]
Flotation mechanism of pulsating gas bubbles
solution is proposed. Data obtained for a fundamental frequency of 450 kHz and source levels of 109 and 127 dB (re 1 pbar at 1 yd) is presented. Some invariance properties ambiguity function Altes, R. A. 53 (April 1973) 1154-1160
of the wideband
Certain changes in pulse shape do not affect the resolution capability of sonar systems. These changes can be expressed as mathematical transformations that leave invariant important properties of the wideband ambiguity function. Such transformations provide a large number of signal and filter functions, all of which satisfy a given rangeDoppler resolution requirement. The sonar designer can then choose the signal and filter that best satisfy other system constraints (eg, ease of signal generation and filter synthesis, clutter suppression capability, and peak power). Error analysis of velocity and direction measurements of plane waves using thick large-aperture arrays Clay, C. S., Hinich, M. J., Sharman, P. The statistical properties of estimators for plane-wave parameters are discussed. A thick large-aperture array is assumed to be detecting a signal from an unknown continuous wave source. The signal is assumed to be a plane wave embedded in a spatially incoherent Gaussian noise field. Maximumlikelihood estimators of velocities and directions are derived and their root-meansquare errors are obtained for single and multiple arrivals for linear arrays and square arrays with a large number of sensors. The rms errors of the propagation parameter estimators are proportional to K“ for a square-lattice array of K sensors and to K -3’2 for a linear array of K sensors. The rms error of the waveform_: gmator, however, is proportional to K s m each case.
MATERIALS
EVALUATION
Ultrasonic inspection procedures mercial shipbuilding Stern, I. L. 31 (May 1973) 85-89
SONICS
AND
in com-
ULTRASONICS
The design of surface acoustic wave bandpass filters which utilize interdigital electrode transducers is reviewed. The impulse-response description of interdigital transducers is extended to allow calculation of transducer input admittance and filter frequency response with much less effort than required by earlier equivalent-circuit model approaches. The application of the impulse model to the design of vhf and higher frequency bandpass filters is discussed and several examples of high-performance surface wave bandpass filters are given.
SEPTEMBER
The development of a low-pass broadband linear fm dispersive filter having a timebandwidth product of 1 000 is discussed. Two systems applications’of highly dispersive linear fm filters - pulse compression radar and a microscan receiver - are discussed with emphasis on filter performance requirements. The principal factors which influence the design of surface wave filters are reviewed and theoretical design procedures are outlined. The IMCON pulse compression its applications Martin, T. A. SU-20 (April 1973) 104-112
filter and
The IMCON is a reflection mode dispersive delay line capable of high performance in large time-bandwidth product pulse compression systems. The unique characteristics of the IMCON are obtained bv reflection from a double grating array that is applied to the surface of a strip. Current models of the device have centre frequencies in the 4-30 MHz range with bandwidths up to 15 MHz, dispersion to 320 ps, time sidelobes in the order -40 dB (with equalization) and other spurious signals at least 70 dB below the compressed output. The use of surface elastic wave reflection gratings in large time-bandwidth pulse compression filters Williamson, R. C., Smith, H. I. SU-20 (April 1973) 113-123 A new type of surface device has been developed which uses the reflection of surface elastic waves to achieve a desired transfer function. A series of experiments on the reflection of surface waves at normal and oblique incidence from periodic arrays of grooves and overlayer strips provided guidelines for the choice of the type of reflector, the reflection angle and the depth of grooves. A prototype pulse compression filter with a time-bandwidth product of 1 500 (T = 30 ps, Af= 50 MHz) has been developed. Theory and design of the surface acoustic wave multistrip coupler Marshall, F. G., Newton, C. O., Paige, E. G. S. SU-20 (April 1973) 124-133
Impulse design of acoustic surface wave filters Hartmann, C. S., Bell, D. T., Rosenfeld, R. C. SU-20 (April 1973) 80-93
ULTRASONICS.
The design and applications of highly dispersive acoustic surface-wave filters Gerard, H. M., Smith, W. R., Jones, W. R., Harrington, J. B. SU-20 (April 1973) 94-104
1973
The multistrip coupler performs the function of a directional coupler for freely propagating acoustic waves on a piezoelectrically active substrate. Its operation is analysed in terms of a transmission line based on an equivalent circuit: Expressions are obtained for the directionality in terms of the number of coupler strips and the acoustic frequency. Surface acoustic wave multistrip components and their applications Marshall, F. G., Newton, C. O., Paige, E. G. S. SU-20 (April 1973) 134-143 The multistrip coupler is a directional coupler which operates on freely propagating surface acoustic waves with broad bandwidth and low loss. The applications of simple multistrip couplers with straight
strips are discussed together with descriptions and properties of a family of multistrip components that can perform particular operations. Acoustic surface waveguides - analysis and assessment Lagasse, P. E., Mason, I. M., Ash, E. A. SU-20 (April 1973) 143-154 The properties of acoustic surface waveguides are reviewed with particular reference to topographic structures in which guiding is achieved by drastic deformation of the substrate surface. A numerical technique, capable of computing efficiently and with high accuracy the mode spectrum of an anisotropic piezoelectric heterogene ous waveguide of arbitrary cross section is described.
SOVIET
PHYSICS-ACOUSTICS
Flotation mechanism of pulsating gas bubbles Il’in, A. V., Kuznetsov, V. P., Novitskii, B. G., Fridman, V. M. 18 (April-June 1973) 448-453 A theoretical foundation is given for the flotation of suspended solid particles by a pulsating cavitation bubble in a liquid. It is shown that the force acting on one particle in the vicinity of the bubble, whose walls obey a certain law of motion, depends on the ratio of two parameters: the characteristic scale a of the particles and the distance r of the particle from the bubble centre. The particle equation of motion is integrated by the Kapitsa-Van der Pol method. It is shown that the motion of the particle in the vicinity of the pulsating bubble is equivalent to motion in a certain field with Veff = (,4/X4) - (B/X6), A, B > 0. Holographic vizualization of traveiling sound waves Kakichashvili, V. I., Kakichashvili, Sh. D. 18 (April-June 1973) 454-455 The formation of an optical image of an acoustical object is investigated in the case of light diffraction by a travelling sound wave in a thin layer of the medium. The Doppler shifts of the reconstructed virtual and real images have opposite signs. Waves propagating along edges of plates Kouzov, D. P., Luk’yanov, V. D. 18 (April-June 1973) 456-459 A wave travelling along the edge of a plate immersed in an acoustic medium is analysed. A situation is described in which propagation is not accompanied by radiation into the external medium. The dispersion relation for the wave number of the investigated wave is derived on the basis of the boundarycontact conditions at the edge of the plate. A special effect in a waveguide having a negative sound velocity gradient Krupin, V. D. 18 (April-June 1973) 460-465 A waveguide in which the velocity of sound decreases in the direction of an absorbing impedance boundary is analysed. It is shown that the normal-mode attenuation factors in this case form a non-monotonic sequence, the smallest attenuation factor being associated with a normal mode other
239
of the wideband
Certain changes in pulse shape do not affect the resolution capability of sonar systems. These changes can be expressed as mathematical transformations that leave invariant important properties of the wideband ambiguity function. Such transformations provide a large number of signal and filter functions, all of which satisfy a given rangeDoppler resolution requirement. The sonar designer can then choose the signal and filter that best satisfy other system constraints (eg, ease of signal generation and filter synthesis, clutter suppression capability, and peak power). Error analysis of velocity and direction measurements of plane waves using thick large-aperture arrays Clay, C. S., Hinich, M. J., Sharman, P. The statistical properties of estimators for plane-wave parameters are discussed. A thick large-aperture array is assumed to be detecting a signal from an unknown continuous wave source. The signal is assumed to be a plane wave embedded in a spatially incoherent Gaussian noise field. Maximumlikelihood estimators of velocities and directions are derived and their root-meansquare errors are obtained for single and multiple arrivals for linear arrays and square arrays with a large number of sensors. The rms errors of the propagation parameter estimators are proportional to K“ for a square-lattice array of K sensors and to K -3’2 for a linear array of K sensors. The rms error of the waveform_: gmator, however, is proportional to K s m each case.
MATERIALS
EVALUATION
Ultrasonic inspection procedures mercial shipbuilding Stern, I. L. 31 (May 1973) 85-89
SONICS
AND
in com-
ULTRASONICS
The design of surface acoustic wave bandpass filters which utilize interdigital electrode transducers is reviewed. The impulse-response description of interdigital transducers is extended to allow calculation of transducer input admittance and filter frequency response with much less effort than required by earlier equivalent-circuit model approaches. The application of the impulse model to the design of vhf and higher frequency bandpass filters is discussed and several examples of high-performance surface wave bandpass filters are given.
SEPTEMBER
The development of a low-pass broadband linear fm dispersive filter having a timebandwidth product of 1 000 is discussed. Two systems applications’of highly dispersive linear fm filters - pulse compression radar and a microscan receiver - are discussed with emphasis on filter performance requirements. The principal factors which influence the design of surface wave filters are reviewed and theoretical design procedures are outlined. The IMCON pulse compression its applications Martin, T. A. SU-20 (April 1973) 104-112
filter and
The IMCON is a reflection mode dispersive delay line capable of high performance in large time-bandwidth product pulse compression systems. The unique characteristics of the IMCON are obtained bv reflection from a double grating array that is applied to the surface of a strip. Current models of the device have centre frequencies in the 4-30 MHz range with bandwidths up to 15 MHz, dispersion to 320 ps, time sidelobes in the order -40 dB (with equalization) and other spurious signals at least 70 dB below the compressed output. The use of surface elastic wave reflection gratings in large time-bandwidth pulse compression filters Williamson, R. C., Smith, H. I. SU-20 (April 1973) 113-123 A new type of surface device has been developed which uses the reflection of surface elastic waves to achieve a desired transfer function. A series of experiments on the reflection of surface waves at normal and oblique incidence from periodic arrays of grooves and overlayer strips provided guidelines for the choice of the type of reflector, the reflection angle and the depth of grooves. A prototype pulse compression filter with a time-bandwidth product of 1 500 (T = 30 ps, Af= 50 MHz) has been developed. Theory and design of the surface acoustic wave multistrip coupler Marshall, F. G., Newton, C. O., Paige, E. G. S. SU-20 (April 1973) 124-133
Impulse design of acoustic surface wave filters Hartmann, C. S., Bell, D. T., Rosenfeld, R. C. SU-20 (April 1973) 80-93
ULTRASONICS.
The design and applications of highly dispersive acoustic surface-wave filters Gerard, H. M., Smith, W. R., Jones, W. R., Harrington, J. B. SU-20 (April 1973) 94-104
1973
The multistrip coupler performs the function of a directional coupler for freely propagating acoustic waves on a piezoelectrically active substrate. Its operation is analysed in terms of a transmission line based on an equivalent circuit: Expressions are obtained for the directionality in terms of the number of coupler strips and the acoustic frequency. Surface acoustic wave multistrip components and their applications Marshall, F. G., Newton, C. O., Paige, E. G. S. SU-20 (April 1973) 134-143 The multistrip coupler is a directional coupler which operates on freely propagating surface acoustic waves with broad bandwidth and low loss. The applications of simple multistrip couplers with straight
strips are discussed together with descriptions and properties of a family of multistrip components that can perform particular operations. Acoustic surface waveguides - analysis and assessment Lagasse, P. E., Mason, I. M., Ash, E. A. SU-20 (April 1973) 143-154 The properties of acoustic surface waveguides are reviewed with particular reference to topographic structures in which guiding is achieved by drastic deformation of the substrate surface. A numerical technique, capable of computing efficiently and with high accuracy the mode spectrum of an anisotropic piezoelectric heterogene ous waveguide of arbitrary cross section is described.
SOVIET
PHYSICS-ACOUSTICS
Flotation mechanism of pulsating gas bubbles Il’in, A. V., Kuznetsov, V. P., Novitskii, B. G., Fridman, V. M. 18 (April-June 1973) 448-453 A theoretical foundation is given for the flotation of suspended solid particles by a pulsating cavitation bubble in a liquid. It is shown that the force acting on one particle in the vicinity of the bubble, whose walls obey a certain law of motion, depends on the ratio of two parameters: the characteristic scale a of the particles and the distance r of the particle from the bubble centre. The particle equation of motion is integrated by the Kapitsa-Van der Pol method. It is shown that the motion of the particle in the vicinity of the pulsating bubble is equivalent to motion in a certain field with Veff = (,4/X4) - (B/X6), A, B > 0. Holographic vizualization of traveiling sound waves Kakichashvili, V. I., Kakichashvili, Sh. D. 18 (April-June 1973) 454-455 The formation of an optical image of an acoustical object is investigated in the case of light diffraction by a travelling sound wave in a thin layer of the medium. The Doppler shifts of the reconstructed virtual and real images have opposite signs. Waves propagating along edges of plates Kouzov, D. P., Luk’yanov, V. D. 18 (April-June 1973) 456-459 A wave travelling along the edge of a plate immersed in an acoustic medium is analysed. A situation is described in which propagation is not accompanied by radiation into the external medium. The dispersion relation for the wave number of the investigated wave is derived on the basis of the boundarycontact conditions at the edge of the plate. A special effect in a waveguide having a negative sound velocity gradient Krupin, V. D. 18 (April-June 1973) 460-465 A waveguide in which the velocity of sound decreases in the direction of an absorbing impedance boundary is analysed. It is shown that the normal-mode attenuation factors in this case form a non-monotonic sequence, the smallest attenuation factor being associated with a normal mode other
239