Acoustical Physics 

About: Acoustical Physics is an academic journal published by Springer Science+Business Media. The journal publishes majorly in the area(s): Acoustic wave & Waveguide (acoustics). It has an ISSN identifier of 1063-7710. Over the lifetime, 2556 publications have been published receiving 14593 citations.

Physical mechanisms of the therapeutic effect of ultrasound (a review)

Abstract: Therapeutic ultrasound is an emerging field with many medical applications. High intensity focused ultrasound (HIFU) provides the ability to localize the deposition of acoustic energy within the body, which can cause tissue necrosis and hemostasis. Similarly, shock waves from a lithotripter penetrate the body to comminute kidney stones, and transcutaneous ultrasound enhances the transport of chemotherapy agents. New medical applications have required advances in transducer design and advances in numerical and experimental studies of the interaction of sound with biological tissues and fluids. The primary physical mechanism in HIFU is the conversion of acoustic energy into heat, which is often enhanced by nonlinear acoustic propagation and nonlinear scattering from bubbles. Other mechanical effects from ultrasound appear to stimulate an immune response, and bubble dynamics play an important role in lithotripsy and ultrasound-enhanced drug delivery. A dramatic shift to understand and exploit these nonlinear and mechanical mechanisms has occurred over the last few years. Specific challenges remain, such as treatment protocol planning and real-time treatment monitoring. An improved understanding of the physical mechanisms is essential to meet these challenges and to further advance therapeutic ultrasound.

Effect of acoustic nonlinearity on heating of biological tissue by high-intensity focused ultrasound

Abstract: Effect of strong acoustic nonlinearity on the efficiency of heating of a biological tissue by high-intensity focused ultrasound in the modes of operation used in real clinical setups is studied. The spatial distributions of thermal sources and the corresponding temperature increments caused by ultrasonic absorption are analyzed. Numerical algorithms are developed for simulating the nonlinear focusing of ultrasound in the calculations of both the heat sources on the basis of the Khokhlov-Zabolotskaya-Kuznetsov-type equations and the temperature field in a tissue on the basis of an inhomogeneous thermal conduction equation with a relaxation term. It is demonstrated that in the mode of operation typical of acoustic surgery, the nonlinearity improves the locality of heating and leads to an increase in the power of thermal sources in the focus by approximately an order of magnitude. The diffusion phenomena in the tissue lead to a smoothing of the spatial temperature distributions, as compared to the distributions of thermal sources. In the case of one-second exposure in the nonlinear mode of focusing, the maximal temperature in the focus exceeds the values obtained in the approximation of linear wave propagation by a factor of three.

Some applications of the reciprocity principle in experimental vibroacoustics

Abstract: The principles of acoustic and vibroacoustic reciprocity are explained. Examples are then given of applications of acoustic reciprocity to the experimental analysis of sound radiation by various systems of interest to noise control engineers. The final part of the paper is devoted to a presentation of examples of the practical application of Lyamshev reciprocity to problems of identifying and quantifying sources of noise that operate in a variety of engineering systems.

Noise as an indicator of cavitation in a centrifugal pump

Abstract: One of the sources of instability in a centrifugal pump is cavitation within the pump. Cavitation of a centrifugal pump is the result of insufficient net positive suction head (NPSH) and can occur within the entire range of operating conditions. Cavitation may cause three different and undesirable effects: (1) a drop in head-capacity and efficiency curves, (2) damage to the impeller by pitting and erosion, and (3) structure vibration and resulting noise. Therefore, the cavitation process must be prevented by all means. To prevent the onset of cavitation we have to detect the beginning of the cavitation process in the pump. To detect the beginning of the cavitation process, the emitted noise can be used, among other possibilities. Specifically, a noise spectra structure can be used to detect the beginning of cavitation and its development. Experiments have shown that there is a discrete frequency tone, at 147 Hz, which is strongly dependent on the cavitation process and its development. Therefore, noise spectra can also be used to determine the NPSH required or the critical value, representing the upper limit of the permissible pump operation without cavitation.

Simulation of three-dimensional nonlinear fields of ultrasound therapeutic arrays

Abstract: A novel numerical model was developed to simulate three-dimensional nonlinear fields generated by high intensity focused ultrasound (HIFU) arrays. The model is based on the solution to the Westervelt equation; the developed algorithm makes it possible to model nonlinear pressure fields of periodic waves in the presence of shock fronts localized near the focus. The role of nonlinear effects in a focused beam of a two-dimensional array was investigated in a numerical experiment in water. The array consisting of 256 elements and intensity range on the array elements of up to 10 W/cm2 was considered. The results of simulations have shown that for characteristic intensity outputs of modern HIFU arrays, nonlinear effects play an important role and shock fronts develop in the pressure waveforms at the focus.