Modeling of dynamic stability of flexible ultrasonic waveguides

The article considers mathematical model intended for study of dynamic stability and parametric resonance of flexible ultrasonic waveguides for applications in technology and medicine. Considered problem is reduced to the well-known Mathieu equation applied in the theory of dynamic stability of elastic systems. Parameters of the Mathieu equation defining stability of the waveguide are determined by means of finite elements method using ANSYS software and APDL programming languag

EXPERIMENTAL MODAL ANALYSIS OF ULTRASONIC SURGICAL WAVEGUIDES USING EFFECT OF INVERSE MAGNETOSTRICTION

Experimental modal analysis (EMA) of ultrasonic waveguides is important for many applications including design of ultrasonic surgical tools. However, most of the known sensors and instruments for measuring parameters of ultrasonic vibrations are limited to the measurements on the face surface of the ultrasonic waveguide and therefore unable to determine the spatial distribution of the parameters along its length, which in turn makes it difficult to identify natural modes and shapes. The article describes EMA of ultrasonic surgical waveguides based on the effect of inverse magnetostriction. During vibration of an ultrasonic waveguide the inverse magnetostriction generates alternating magnetic field which can be detected by means of an induction coil. Spatial resolution of the measurements can be achieved by application of the sensors with flat (spiral) induction coils. The sensors used in the study have simple design and low cost making them affordable for wide circle of scientists and engineers. The results of experimental studies implemented on exemplary waveguide for ultrasonic angioplasty made of AISI 321 steel are presented and discussed. The article also discusses the methods for theoretical and experimental determination of the sensitivity of the sensors used in the study. Experimental data are validated by comparing them to the results of computer-aided modal analysis using the finite element method (FEM) and found to be in good agreement with the results of FEM modeling (relative deviation of the vibratory displacements amplitude is about 4.7 %). As it follows from the experimental data and their comparison to the results of FEM modeling, the effect of inverse magnetostriction can be efficiently used for EMA of ultrasonic waveguides

Propagation of weak waves in the inhomogeneous elastoviscoplastic medium with a cell structure

Non-stationary acceleration waves in the fluid-saturated inhomogeneous elastoviscoplastic porous medium are studied using the mathematical theory of discontinuities. The equations for determining the intensity and the geometry of wave fronts of the fluidsaturated elastoviscoplastic medium were first derived. It is shown that in the medium under consideration there are two types of irrotational waves and one equivoluminal wave, that are equal to the velocities in the homogeneous elastic porous media at every point

Nonlinear effects related to vibrations of long elastic waveguides: formulation of nonlinear equations

A number of effects arising during vibrations of long elastic waveguides can not be explained in the context of the linear theory. One of these effects is redistribution of energy between the longitudinal and transverse vibration modes. Nonlinear equations describing such effects have been studied in momentless approximation with application to vibrations of strings and they account for tension of the string axis as a result of transverse vibrations. The authors have studied a possibility of generalization of these equations for the case of elastic waveguides taking into account internal moments and lateral forces arising during bending of the waveguid

Increase of productivity in brittle material processing by the application of intermediate elastic elements in tool structure

Productivity in ultrasonic treatment of materials is defined by a number of acoustic and technological factors. As the acoustic ones frequency, amplitude and type of oscillations and as technological – materials of the blank and the tool, the speed of relative motion, static pressure force of the tool to the treated part, type and dimensions of abrasive grains, concentration of the grains in suspension, treatment depth and conditions for abrasive flow can be mentioned. Typically these factors are interrelated. Nevertheless the influence of structural features of the applied acoustic systems is not yet studied sufficiently deeply. A new kind of ultrasonic tools with elastic elements in their structure are developed and researched what introduced the possibility to select the oscillation mode the most efficient for ultrasonic treatment together with the possibility of amplitude increase what in turn allows increasing performance characteristics of the tool if compared with the traditional rod shaped tool. Simulation of the elastic tool performance was carried out using simulation software package “ANSYS”. The impact of the forced vibration frequency on modal response of the elastic elements is shown in the paper

Boundary Element Modeling of Acoustic Fields Generated During Ultrasonic Angioplasty

We investigated possibilities of application of boundary element method (BEM) to modelling of acoustic fields generated during ultrasonic angioplasty. It was shown that modelling by means of BEM can be more efficient comparing with traditionally used modelling by means of finite element method (FEM). We also considered test problem of calculation of acoustic field created by ultrasonic waveguide in semi-infinite fluid media and the problem was solved by means of BEM and FEM with comparative analysis of obtained results. Modelling by means of BEM additionally involves application of mirror source method for avoidance of treatment of infinite fluid boundary. On the basis of analysis of the test problem we shown that BEM can be used as efficient tool for modelling of acoustic fields generated during ultrasonic surgical procedures, particularly, during ultrasonic angioplasty. BEM has several advantages in comparison with FEM and can be used as alternative to traditionally used modelling by means of FEM or as supplementary method

Combined effect of low-frequency high-intensity ultrasound and streptokinase on the efficiency of thrombi destruction

Results of numerous experimental studies indicate that low-intensity ultrasound (US) intensifies the drug induced fibrinolysis. However, exits opinion, what high-intensity ultrasound could be not recommending for use in combination with thrombolytic agents due to the transience of exposure of thrombus to ultrasound and relatively low speed of the enzymatic process. We also hypothesise that high-intensity low-frequency US can accelerate the drug induced fibrinolysis. During in vitro studies, we showed that the administration of streptokinase (SK) prevents the formation of particle conglomerates resulting due to destruction of fibrin clots by using low-frequency high-intensity US. In addition, it was established that in conditions of the combined effect of streptokinase and high-intensity US, the process of acoustic-mechanical destruction of thrombus is prevailing, and the fibrinolytic effect of streptokinase is generally witnessed after the termination of US and manifests itself in enzymatic lysis of both resultant particles and residual clot mass. In this study we verified the effect of low-frequency high-intensity ultrasound on the dynamics and efficiency of fibrinolysis induced by streptokinase on various structure thrombi model, characteristic features of the fibrin clot network structure occurring during the combined effect of ultrasound and streptokinase

MEASUREMENT OF VIBRATION PARAMETERS OF THE WAVEGUIDE FOR MEDICAL TREATMENT

Methods allowing investigation of vibrations of the stainless steel waveguide by combining noncontact techniques with the state-of-the-art multiphysics software are developed. The vibrations of the waveguide, used in nowadays surgery are examined by the aids of the holographic interferometry technique, vibrometer based on Doppler shift of backscattered laser light and the virtual model of the waveguide is created by the Comsol Multiphysics software

Study of the process of interaction between low-frequency ultrasound and biological tissue phantoms

This paper presents the results of a series of experimental studies on the impact of low-frequency ultrasound on biological tissue phantoms, acoustic pressure on the motion of particles in an acoustic field generated by annular waveguide. Experiments have demonstrated that when vibrations with a frequency corresponding to its natural frequency of bending vibrations are induced in the annular waveguide, micropowder particles form arranged bulk structures on the substrate. Analysis of results on the behavior of micropowder particles in the ring insonation area revealed that frequency variations of ultrasonic vibrations lead to variations in spatial distribution of acoustic pressure inside the ring. The thermal effect of low-frequency ultrasound from annular waveguide on biological tissue phantoms has been studied. It was established that the annular waveguide enables heating of fluid when it has no direct contact with the media, thereby demonstrating its applicability for non-contact treatment of tumors

Opto-Acoustic Method of Tissue Oxygenation and its Biomedical Application

Novel opto-acoustic method of tissue oxygenation and restoring normal cell metabolism is proposed. The results of in vivo investigation the phenomenon of laser-induced photodissociation of blood oxyhemoglobin and its biomedical applications are presented. Photodissociation of oxyhemoglobin, the main biological function of which is oxygen transportation gives a unique possibility of additional oxygen extraction for restoring normal cell metabolism. Optical method of determination the therapeutic “dose” based on the response of changes in tissue oxygen concentration in dependence on wavelength and intensity of laser radiation has been developed. It is shown that in order to make the methods of phototherapy as well as laser therapy really efficient one has to control the oxygen concentration in tissue keeping it at the necessary level