Airborne ultrasonic vortex generation using flexible ferroelectrets

Cellular ferroelectrets exhibit interesting electromechanical- acoustical characteristics. Their recent appearance and remarkable properties open up new possibilities for the design and development of ultrasonic transducers. In particular, the feasibility of fabricating ultrasonic vortex generators using ferroelectret films is demonstrated in this work. To this end, a transducer prototype was built by gluing the material onto a tangential-helical surface (outer diameter: 40 mm, pitch: 3.45 mm). Experimental results agree well with the theoretical estimation of the pressure and phase of the acoustic field in the near field and far field, which corroborates the potential of ferroelectrets to customize special acoustic fields. Furthermore, the proposed fabrication procedure is inexpensive and represents a new alternative for exploring and analyzing the special characteristics of acoustical helical wavefront

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

Diseño, construcción y calibración de un fotogoniómetro para la empresa colombiana de luminarias Roy Alpha S.A.

En este trabajo se describe el diseño, construcción y calibración mecánica de un fotogoniómetro para el laboratorio de fotometrías de la empresa colombiana de luminarias Roy Alpha S.A. Este desarrollo fue realizado en el marco de un proyecto universidad-empresa entre Roy Alpha S.A. y la Universidad del Valle. Se presenta primero un breve resumen de los diferentes tipos posibles de fotogoniómetros, su modo de funcionamiento y su importancia para el diseño de luminarias. Igualmente, se hace una descripción resumida del diseño concebido y construido. Finalmente, se expone la metodología de calibración implementada, la cual permitió establecer, antes de realizar medidas fotométricas, que la calidad del diseño mecánico del fotogoniómetro era la adecuada para la realización de medidas fotométricas en laboratorio. La comparación entre las fotometrías obtenidas con el fotogoniómetro construido y calibrado y las que se realizaron en un laboratorio de mayor infraestructura tecnológica, mostró diferencias no mayores al 3%. La inversión realizada por Roy Alpha S.A. fue de aproximadamente el 25 % del costo que implicaría adquirir un sistema de fotogoniómetro importado

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