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The paper presents the results of evaluating the thickness profile of a skull phantom using a two-dimensional ultrasound array consisting of piezoelectric elements with a center frequency of 2.1 MHz. Two pulse-echo ultrasound methods were used in the experiment: the A-mode elementwise measurements and scanning with a focused probing beam created by the entire array using delay-and-sum (DAS) beamforming. The obtained thickness profiles are compared with the reference thickness profile obtained using X-ray computed tomography. It was shown that ultrasound DAS beamforming with a focused probing beam makes it technically possible to estimate the thickness profile of the skull phantom. [ABSTRACT FROM AUTHOR]

The acoustic holography method was used to characterize a therapeutic focused fully populated 256-element ultrasonic transducer array. Elements of the array with the shape of equal area polygons are densely arranged in an irregular pattern on a spherically concave surface with a radius of curvature of 150 mm and a diameter of 200 mm. The array has a central frequency of 1.2 MHz and is designed to operate in water. The performance of individual array elements was studied based on the holographically reconstructed normal velocity distribution over the array surface. It was shown that with the same electrical signals applied to the elements, their acoustic responses had a phase deviation relative to the nominal values, which can be caused either by the asphericity of the array surface, or by the introduction of additional phase delays by the electrical matching network. To compensate for the detected parasitic phase shifts of the elements and restore the effective sphericity of the radiating surface, the Verasonics V-1 control system was used. The hologram measured after making the correction, as well as the shape of the focal region and acoustic pressure magnitude at the focus, separately measured by a hydrophone, showed that the proposed method reconstructed the nominal operating parameters of the array with high accuracy. [ABSTRACT FROM AUTHOR]

The article describes an experimental facility for studying and testing sound-absorbing linings made of acoustic metamaterials designed to reduce the noise generated by a source in a finite waveguide. The main focus is on the features of acoustic field formation in a waveguide and its emission from the open ends. The article centers on the results of a study of how different facility parameters influence the efficiency of linings. The large influence of the parameter "type of source" on the lining efficiency has been revealed and investigated for the first time. It is rigorously defined, and the physical mechanism of its influence on the efficiency is described. Conditions are formulated under which the efficiency of a sound-absorbing lining measured on the experimental facility will be equal to or close to its efficiency measured on a real object. It is shown that one of the most important conditions is the coincidence of types of acoustic sources used in the facility with a real one. The results obtained are useful in designing efficient sound-absorbing linings, as well as in creating experimental facilities for their development and testing. [ABSTRACT FROM AUTHOR]