Y. Gómez-Ullate

P3R-3 Design and Characterization of Air Coupled Ultrasonic Transducers Based on MUMPs

This paper deals with the design and characterization of several capacitive micromachined ultrasonic transducer (cMUT) cells for the future design of an air-coupled transducer for non destructive testing (NDT). Each design was manufactured using the multi-user MEMS process (MUMPs). Special boundary conditions were used to obtain high efficiency: two opposite sides of the 150 mum square shaped membranes are free while the other sides are anchored to a fixed layer of the process. Using these designs a large displacement of the membrane and a higher surface contact is obtained in spite of their mechanical losses

7D-4 Non Destructive Evaluation of Carbon Fiber Reinforced Plates Using Lamb Waves: A Comparison Between Pitch-Catch Air Coupled Techniques and Sector Images Obtained with Embedded Piezoelectric Linear Arrays

In this work, a carbon fiber composite plate with uniform thickness has been implemented with a flexible piezoelectric linear array bonded on it. A four cycles tone burst of 48 kHz has been used to excite an antisymmetric Lamb mode. Then, a 2D sector image of the plate with a delamination has been obtained using a synthetic aperture algorithm. Next, the same process has been repeated for a carbon fiber reinforced plate (CFRP) with attached stiffeners and varying thickness, with no evidence of delamination. Therefore, a conventional ultrasonic inspection, with two air coupled transducers in a pitch-catch configuration, has been performed in the same plate and compared with the sector array image. The same Lamb mode has been excited. An optical vibrometer has been used to measure the out-of-plane displacement of the propagating Lamb wave modes to calculate the propagation velocity and to help understanding the artifacts produced by the stiffeners. An optical interferometric image of the propagating wave-front showing the artifacts and signal shadows produced by a longitudinal stiffener is shown.

Ultrasonic air-coupled metrology of material surfaces

This paper describes a new design of air-coupled transducers based on a 1-3 piezocomposite that can be shaped with different focal geometries. Flat and focused transducers up to 4 MHz have been developed and characterized. Surface information of soft and hard materials has been obtained showing the big potential of air-coupled ultrasound to perform profilometry of material surfaces where traditional optical and contact methods are inadequate.

Experimental validation of ultrasonic guided modes in electrical cables by optical interferometry

In this work, the dispersion curves of elastic waves propagating in electrical cables and in bare copper wires are obtained theoretically and validated experimentally. The theoretical model, based on Gazis equations formulated according to the global matrix methodology, is resolved numerically. Viscoelasticity and attenuation are modeled theoretically using the Kelvin-Voigt model. Experimental tests are carried out using interferometry. There is good agreement between the simulations and the experiments despite the peculiarities of electrical cables.