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Bubbles oscillating at resonance frequency dramatically enhance nonlinearity of a bubbly liquid. A second-order nonlinear wave equation taking account of bubble pulsation is solved. Numerical calculations based on the equation are compared favorably with experimental results. Possible biological significance of the highly nonlinear medium is also discussed.

The temperature elevation in a homogeneous tissue-mimicking material with tissue-like thermal and acoustic properties, generated by unfocused and focused ultrasonic transducers operating at 1.0 and 3.5 MHz frequencies, was measured. It was found that in the vicinity of a transducer front face, both transducer surface heating and ultrasound absorption are important sources for tissue heating. As for heating due to ultrasound absorption, the experimental results are compared with theoretical predictions for nonperfused tissues resulting from different beam models. The experimental data are in reasonable agreement with the results calculated from a model developed by Nyborg and Steele, a Gaussian beam model and from the model used by the National Council on Radiation Protection and Measurements (NCRP).

The effective nonlinearity parameter B/A of water containing a three-dimensional ensemble of randomly distributed uniform-sized trapped cylindrical bubbles was measured. The experimental results indicate that the dramatic enhancement of the effective nonlinear parameter B/A is due to the nonlinear resonance oscillation of the trapped bubbles. The measured effective B/A for the system is of the magnitude of 10(4) to 10(5).

Based on the analytic expressions given by T. Hasegawa, et al.. (J.Acoust. Soc. Am. 79(4) 927-931 1986) an integral for calculation of the radiation force on a plane absorbing target in spherically focused field is derived. For focused fields a general relation between acoustic power P and normal radiation force Fn, P=GFn is obtained from the integral. Numerical computation of the integral is carried out for the practical HIFU source and absorbing circular target, through which the value of calibration constant G can be obtained The experiments are conducted for the same source and target used in the calculation. For the given source and targets, the calculations and experiments show that there is a range of target's position where the radiation force is independent of target's position.

Over the past decade, community structure, a statistical property of networked systems such as social network and World Wide Web, has attracted considerable attention in data mining field because it enables description and prediction of complex networks. Many highly sensitive graph clustering algorithms were developed for identification of communities having dense connections internally and loose connections with others. In this context, Newman and Girvan proposed modularity Q score for quantifying the strength of community structure and measuring the fitness of a division. The Q function has become an important standard recently. In this paper, combining the strengths of the Q score and multilevel paradigm first developed for graph partitioning, we introduced a scalable algorithm MOME (i.e. modularity-based multilevel graph clustering) to efficiently discover communities from a network. The experimental results indicated that MOME ran extremely faster and finally achieved a division with a slightly higher Q score against the latest modularity-based method and its variants, particularly when the network was of a large-scale.

Two kinds of approaches have been used in literature to study the linear acoustics in a liquid-bubble mixture: The effective medium theory approach and the multiple scattering theory approach. Theoretical comparisons of mathematical formulations and intrinsic relations between these two approaches are given in this paper and show their consistency in dealing with the linear acoustics in bubbly liquids. Possible applications of these two methods are also generally discussed.

The dispersive characteristics of higher order mode Lamb waves (HOMLW) excited by interdigital transducers (IDT) are measured and analyzed, which are necessary for designing micro-sensor in ultrahigh frequency (UHF). A measurement system is set up, in which dispersive characteristics of HOMLW are obtained by the method of transform between frequency and time domains. The characteristics of amplitude-frequency and phase-frequency of Lamb wave are auto-measured by the system. By IFFT, the pulse response of the IDT device was obtained. Different modes were separated in time domain and dispersive curve of each mode is calculated by FFT. The best mode is chosen to design the micro-sensor in UHF. The phase velocity of HOMLW is greater than the surface wave (SAW) velocity and an oscillator in higher frequency can be made, so the absolute sensitivity of micro-sensor can be increased. In this paper, the dispersive characteristics of HOMLW excited by an IDT in a 127.86 degrees rotated Y-cut, X propagating lithium niobate plate is analyzed. An oscillator using a(13) mode is made, the phase velocity of which is measured about 19,652 m/s when h/lambda=0.94 (h=plate thickness, lambda=wavelength).

An approach based on the equivalent medium method is used to describe the propagation of acoustic longitudinal wave in porous viscoelastic medium. Combining the wave equation for the porous medium and the dynamic equation for micropores and using the perturbation method, equations for fundamental and second harmonic are obtained. Treating medium containing micropores as a homogeneous medium, the effective nonlinearity parameter is defined, and a formula for it is achieved. The frequency dependence of effective nonlinear parameter is studied in detail, and its low frequency limit consists with Ostrovsky’s static results.

— The phenomenon of image distortions caused by the multiple scattering (MS) effects of encapsulated microbubbles in ultrasoniqc imaging was experimentally found in previous studies ( Soetanto and Chan 2000a ), but its mechanism has not been fully understood. To study the MS effects of microbubbles in contrast imaging, two approaches are employed in this article—the effective medium approach initialized by Kargl (2002) , which includes all the high-order rescattering of free bubbles, and the classic lowest-order approximation approach of Commander and Prosperetti (1989), which ignores the higher-order rescattering between bubbles. In this work, they are modified to model encapsulated microbubble suspensions, and the discrepancies in attenuation coefficients calculated by these two approaches, i.e., the higher-order rescattering of bubbles are defined as the measure of the MS effects of microbubbles. The intrinsic relations between the MS effects of microbubbles in suspensions and physical properties of the microbubbles, such as the bubble concentrations, sizes, and the shell thicknesses etc., are simulated and discussed. It is found that in suspensions for identical microbubbles >12 μm in size, the MS effects come to be significant when the bubble concentrations exceed 1 × 105 bubbles/mL. The MS effects of microbubbles with broad size spectrums are examined by simulating Soetanto and Chan’s experiments. Also, the MS effects of UCAs in current ultrasonic imaging practice are discussed. The STARs and extinction cross-sections of different-sized individual encapsulated microbubbles are calculated for further investigations on the mechanism of the MS effects of UCAs. (E-mail: zhudu@nju.edu.cn )

This paper investigates the shock formation distance in a bounded sound beam of finite amplitude by solving the Khokhlov-Zabolotskaya-Kuznetsov (KZK) equation using frequency-domain numerical method. Simulation results reveal that, besides the nonlinearity and absorption, the diffraction is another important factor that affects the shock formation of a bounded sound beam. More detailed discussions of the shock formation in a bounded sound beam, such as the waveform of sound pressure and the spatial distribution of shock formation, are also presented and compared for different parameters.

The influence of liquid layers on the propagation of Lamb waves in a plate of finite thickness is studied theoretically. The dispersion equations of Lamb waves in a plate bordered with layers of liquids are derived. Numerical solutions of the equations show that the phase velocity of Lamb waves changes with the thickness of the liquid layers. For the lowest antisymmetrical mode of very thin plates, the numerical results calculated from the dispersion equations are compared with those derived from the bending wave acoustic impedance approach. The limitation of the latter is discussed. Applications of Lamb waves pertinent to biosensing are also presented.

A sensor which measures physical parameters of a liquid with high sensitivity and accuracy is in great demand in medicine, biology, chemistry and environmental science [1]. Recently, resurgent interest in Lamb waves was initiated in their applications of multisensors [2]. The principle of these Lamb-Wave Sensors is that the propagation velocity of Lamb waves changes when a plate is bordered with a liquid. In this paper, we report the results of our recent theoretical investigations of the effects of bordering liquid layers on the propagation of Lamb waves in a solid plate.

Some comparisons of C. E. Bradley’s and W. L. Nyborg’s theories on acoustic streaming are given.

The differences of the sensitivities of liquid- and solid-sensing of Lamb wave sensors are discussed. It is shown that the sensitivity of S/sub 0/ mode in liquid sensing is much smaller than that in solid sensing, and also much smaller than that of the A/sub 0/ mode.

It has been known for some years that the presence of bubbles enhance the nonlinearity of a liquid dramatically. Wu and Zhu [J. Acoust. Soc. Am. 89, 2634–2639 (1991)] measured the nonlinearity parameter B/A of water containing a three‐dimensional ensemble of randomly distributed uniform‐sized trapped cylindrical bubbles. The measured effective B/A for the system is of the order of 104 to 105, when the bubbles were driven at their resonance frequency. A physical model of a second‐order nonlinear wave equation taking account of dissipation as well as the variation of air volume fraction due to bubbles’ pulsation at resonance is developed. The results calculated using this model are in good agreement with the experimental values.

It was reported that acoustic streaming generated by a Lamb‐wave sensor (LWS) can be used to pump fluids and transport solids in a small‐scale system [Appl. Phys. Lett. 59 (1991)]. The speed, observed by attracting small polystyrene spheres suspended in water, is proportional to the square of the wave amplitude and is about 100 μm/s for 6.5‐nm surface displacement of the plate. In this paper, a fairly practical model, i.e., a thin isotropic plate in contact with a viscous liquid layer on its side, is presented. Based on the rigorous propagation theory of Lamb waves and Nyborg’s [Phys. Acoust. B 2, 265–295] and Bradley’s [J. Acoust. Soc. Am. 100, 1399–1408 (1996)] theories of acoustic streaming, the first‐order ultrasonic field in the viscous liquid layer and the second‐order mass‐transport velocity distribution of the liquid are calculated. Comparison between our theoretical values of the Ao‐mode Lamb wave and Moroney et al.’s experimental result is given. It shows good agreement. [Work supported by NSF of China.]

Strong nonlinearity of bubbly liquids is a most interesting property not only for its theoretical importance in nonlinear acoustics but also for its potential application in, for example, ultrasound imaging technology. A physical model which describes the nonlinear property of liquids containing uniform size bubbles is presented [Ultrasound Med. Biol. 21, 545–552 (1995)]. The theory is successful to some extent but still has some limitations since the sizes of the bubbles are usually not exactly the same. In this paper, a model dealing with more practical situations, i.e., liquids containing many bubbles whose sizes are randomly distributed is extended. The effective nonlinearity parameter B/A (as high as about 104) and attenuation coefficient for these bubbly liquids are given. Calculations and comparisons show that the improved model explains the existent experiments more satisfactorily. [Work supported by the National Science Foundation of China.]

There are basically two approaches in studies of sensing using Lamb wave sensors [J. Acoust. Soc. Am. 91, 861–867 (1992)]: the dispersion equation method and the acoustic impedance method. The first approach is exact but complicated; the latter is simple but approximate. In many Lamb wave sensing applications, changes of the boundary conditions to be detected can be considered to be small perturbations to the propagation of free Lamb wave in a thin plate. General dispersion equations for Lamb waves in a plate with proper perturbed boundary conditions are derived. The equations are then applied to various sensing applications including viscous mass loading. [Work of JWU supported by NSF and Vermont EPSCoR.]

The influence of liquid layers on the propagation of Lamb waves in a plate of finite thickness is studied theoretically. The dispersion equations of Lamb waves in a plate bordered with layers of liquids are derived and solved numerically. For the zeroth‐order antisymmetrical mode (A0 mode) of very thin plates, the numerical results calculated from the dispersion equations are compared with those derived from the bending wave acoustic impedance approach. The limitation of the latter is discussed. [Work supported by BFGoodrich Simmonds Precision Aircraft System.]

The principles of the detection of thin layers of frost and ice formation on an aircraft will be discussed. The theoretical and experimental results of the influence of liquid layers on the propagation of Lamb waves in a plate of finite thickness will be presented. The dispersion equations of Lamb waves in a plate bordered with layers of liquids were derived. Numerical solutions of the equations show the phase velocity of Lamb waves changes with the thickness of the liquid layers. In the vicinity where the thickness of the liquid is equal to a quarter of a wavelength, there is no real solution of the equations. The experiment qualitatively agrees with the theory. [Work supported by Hercules Aerospace Co., Simmons Precision Aircraft System Div.]