Ultragarsas / Ultrasound

Ultrasonic methods and their implementation for evaluating porous materials

A. Petrauskas — 2011-12-15

In this article application of direct and indirect ultrasonic methods for evaluating and measuring porous materials are reviewed. Ultrasonic waves, due to their physical properties and wide frequency range can successfully be applied when evaluating the porosity of materials. Ultrasonic methods have many advantages when comparing them with other, non-acoustic measurement methods, which are also briefly reviewed in this article. We examine application of the proposed acoustic echolocation method when evaluating porous materials directly and indirectly. The possibilities to apply Lamb waves for evaluation of porous structures are also examined. The application of ultrasonic echolocation measurement method to evaluate porous structures indirectly is presented in depth, along with the process description and various possible implementations. The basic principle along with advantages and shortcomings of such methods are explained. Physical-mechanical properties of porous materials are also described, along with mathematical equations, which are necessary for their theoretical analysis. The ability to determine porosity of various materials is necessary to insure the quality of the final product. We also present a working real-world system, which implements an indirect ultrasonic porosity evaluation method. For indirect porosity determination, we use a very accurate ultrasonic echolocation-based distance meter. Block diagram for such unit is presented. The most important component in the acoustic porosity evaluation system is the electro-acoustic transducer. We describe the most suitable transducers for use in this case, along with acoustic antennas constructed using such transducers. Antennas, designed for measurements in air, consist of transducers vibrating in a flexural mode, which give the best possibility to match acoustic impedances between air and the transducer. Specific type of transducers for acoustic antennas is described, along with their schematic diagrams. The necessary expressions for calculating radiations patterns are also supplied. Schematic diagrams of actual antennas, along with their directivity patterns are presented. A method for eliminating peripheral radiation of these antennas is also described.

http://dx.doi.org/10.5755/j01.u.66.4.1021

Viscosity and density measurement methods for polymer melts

R. Kažys — 2011-12-15

In this article review of density and viscosity measurement methods is presented, including ultrasonic pulse echo methods, which are capable to measure these properties of polymer melts. The methods are presented according to measurement principles, methodology, accuracy and possibility to measure density and viscosity of polymer melts on-line during extrusion process. Such measurements are very important for process automation, process monitoring and control. The ultrasonic pulse echo methods are separated from other methods, because very often they are superior to other techniques. The advantage of this technique is that at the same time sound velocity and attenuation in a plastic melt may be measured, what gives more information. For this purpose polarized shear waves as well as longitudinal, torsional and other types of waves in a wide frequency range may be employed.

http://dx.doi.org/10.5755/j01.u.66.4.1022

Application of ultrasonic measurement method for investigation of green ceramic tiles

M. Kulokas — 2011-12-15

High quality requirements are established for ceramic tiles manufacturing, because they must be weather-resistant, durable, in general, hard, wear and corrosion resistant and also can withstand high stresses at elevated temperatures. One of the possible control methods of the manufactured tiles quality is ultrasonic method based on measurement of ultrasonic wave propagation speed. However, measurements of ultrasonic wave velocity in green ceramic tiles with an uneven surface are difficult. Therefore attention must be directed to the individual measurement problems of this method, which are the following: uneven surface of the inspected tile; necessity of a dry acoustic contact, non-uniform elastic properties of the tested tile.

http://dx.doi.org/10.5755/j01.u.66.4.1023

Investigation of different operating modes of ultrasonic annular array used in ophthalmology

M. Urnavičius — 2011-12-15

The early-stage diagnosis of malignant tumours in eye is very important in ophthalmology in order metastasis of cancer could be prevented and the human life could be saved. Ultrasonography of eye is used already for some time and as it possesses no risk to a patient health it can be repeatedly performed for following of the disease progression.

In order to get as much as possible valuable information about the tumours and their structure it is necessary to create new methods and instruments for extraction of qualitative and valuable information from the received ultrasonic signals. In order to overcome limitations of the existing equipment the new knowledge concerning interaction of ultrasonic waves with intraocular tissue and back-scattering from the tissue affected by the tumour are necessary to be collected. For example, for optimization of the design and operation performance of ultrasonic annular arrays, numerical simulation can be performed.

The objective of this research was to investigate using CIVA software different possibilities of beam focusing in eye using on ultrasonic annular array and to find the optimal solution, which can be used in practice. The ultrasonic fields focused at different distances from the transducer are presented. The propagation of the ultrasonic wave in the eye with tumour and without has been simulated. The simulated and experimental B-scans of the healthy eye and the eye affected by tumour are presented as well. The presented results demonstrate that it is possible to locate malignant tumours in the eye using the optimised ultrasonic annular array.

http://dx.doi.org/10.5755/j01.u.66.4.1027

Synchronization of B-scan diagnostic imaging with transducer position tracking for three-dimensional ultrasonic scanning

A. Sakalauskas — 2011-12-15

Diagnostic value of ultrasonic B-mode imaging is dependent on interpretation and competence of physician, because only information about single section of tissues volume is used for evaluation. 3D sonography systems for abdominal diagnostics are available, but such systems are not yet available in transcranial sonography and etc. One of possibilities to improve current diagnostic systems could be supplementing the 3D function, by combining a conventional B-mode system with a probe position tracking system. The aim of this study was to synchronize two sub-systems: the position tracker and the B-mode ultrasound apparatus for freehand three-dimensional ultrasonic scanning and to evaluate supplementary 3D system estimating volume of the reconstructed 3D surface image of a tissue mimicking phantom of known dimensions.

The 3D scanning method was implemented by synchronous sampling of B-scan diagnostic images, linear position scanning with position tracking sensors. To evaluate experimentally our method we have used four units: ultrasound diagnostic B-scan system, three axis positioning system, electromagnetic position tracker and frame grabber. The 3D phantom of defined dimensions was laboratory-made from dental duplicating silicon. B-mode transducer positioning was deterministic, but time intervals between position changes where random simulating free-hand positioning. Synchronization of video sequence record with a position tracing was assured using the second channel of the position tracing system.

3D surface was reconstructed relating B-mode images to the position data. The volume of phantom calculated according to physical measurements of the caliper was assumed as a true value V_true = 47.054 ml. The estimated volume of a 3D model of a phantom was V_model = 46.87 ml. The estimated relative error of the volume was 0.4 %. We concluded that a common B-mode sonography diagnostic system could be extended for 3D functionality with the use of a two channel position tracing system without invasive reengineering, but more experiments should be done for approval.

http://dx.doi.org/10.5755/j01.u.66.4.1028

Investigation of an internal friction in piezoceramic elements of electro-acoustic transducers

V. Sharapov — 2011-12-15

The results of investigation of an internal friction in the piezoelectric elements used in electro-acoustic transducers are presented in this paper.

http://dx.doi.org/10.5755/j01.u.66.4.1025

Measurement of the group velocity of Lamb waves in aluminium plate using spectrum decomposition technique

L. Draudvilienė — 2011-12-15

In the previous our article the technique for measurement of the group velocity using spectrum decomposition was proposed and demonstrated on the signals obtained from the finite element modelling. The objective of this work is to check this technique using experimental signals. The experiments were carried out on the 2mm thickness aluminium plate with dimensions 1100mm x 620mm. The guided waves were generated using a wide band contact type transducer. The excitation signal was 300 kHz, 3 periods burst with the Gaussian envelop. The signals were processed using the proposed spectrum decomposition algorithm and corresponding segments of the group velocity dispersion curves of the A₀ and the S₀ modes of Lamb waves were obtained. The analysis demonstrated that scattering and errors of the results essentially depends on the bandwidth of the filter used for decomposition. So, it is necessary to select parameters of the filters separately for each mode under investigation. The obtain results were compared with the theoretical dispersions curve and good correspondence was obtained.

http://dx.doi.org/10.5755/j01.u.66.4.1026