Focalization of Acoustic Vortices Using Phased Array Systems

AbstractAcoustic vortices (AV) are helical wavefronts that exhibit a screw-type dislocation and a phase singularity along its principal axis of propagation, at which the pressure of the field is zero. AV can be generated using various methods among which stands out the use of phased array systems because they allow us to electronically control the acoustic beam by means of the application of a given delay law to the array elements. Little research has been reported regarding the focalization of AV to obtain a higher pressure distribution. In view of this, this work presents the study of different delay laws for generating and focusing AV. The analysis of the resultant geometry and pressure distribution of the focused beams is included. We demonstrate that it is possible to increase the pressure amplitude up to 3 times with respect to a non-focalized, at the focal distance. Experimental tests were carried out using a hexagonal multitransducer of 30 elements at 40kHz. A good agreement between simulations and experimental results was obtained

A Non-expensive Massive Transducer Array to Generate Helical Wavefronts in Air

AbstractIn this work we present experimental characterization results of a non- expensive massive ultrasonic transducer array to generate helical wavefronts in air. The multitransducer is composed by 390 elements operating at a nominal frequency of 40kHz, precisely located on a helical surface substrate. The same excitation signal is applied to all elements. Due to the “spatial” delay applied to each element, the device is able to generate a helical wavefront of topological charge m =+1. A maximum sound pressure level of 137dB was measured, on a transverse plane located 1.8 m far from the device, when a 15 Vpp excitation voltage was applied. This work also includes a detailed description of the excitation electronics, the electroacoustic characterization of the array elements (phase, directivity and frequency response) and the inter-element cross-talk quantification. Furthermore, a discussion of the potential of use of this multitransducer device is presented

Ultrasonic Determination of the Elastic Constants of Epoxy-natural Fiber Composites

AbstractThis paper shows the applications ultrasonic through–transmission technique to determine the elastic constants of two polymer-natural fiber composite materials with potential industrial application and economic and environmental advantages. The transversely isotropic coconut-epoxy and fique-epoxy samples were analyzed using an experimental setup which allows the sample to be rotated with respect to transducers faces and measures the time-of-flight at different angles of incidence. Then, the elastic properties of the material were obtained by fitting the experimental data to the Christoffel equation. Results show a good agreement between the measured elastic constants and the values predicted by an analytical model. The velocities as a function of the incidence angle are reported and the effect of the natural fiber on the stiffness of the composite is discussed