Geophysical prospecting surveys are being increasingly used in non-destructive evaluations of structures, and several methods can be applied in the evaluation of cultural heritage buildings. However, accurate studies of cultural heritage structures usually need the application of combined techniques, historic and structural knowledge also being necessary. The present paper describes the pplication of two nondestructive testing techniques: ground-penetrating radar and seismic tomography, in the analysis of some structural elements' inner geometries and physical properties. This job is part of a more complete project developed to define the Mallorca Cathedral structural behaviour. Both geophysical methods are used in a complementary way. GPR allows the detection of small anomalies (changes of about centimetres), and the results are used to select the most appropriate seismic tomography initial model.
The aim of the study is to define the internal structural configuration as well as the stone quality. Results reveal the internal structure of columns, walls and buttresses, showing different structural elements. Even when the visual inspection points to external damages, the detailed NDT evaluation indicates that the inner structure is in good condition and the ashlars are of good quality.
Perez-Gracia, V.; Di Capua, D.; Gonzalez-Drigo, J.R.; Pujades, L.G. NDT and E international Vol. 42, num. 4, p. 336-344 DOI: 10.1016/j.ndteint.2008.12.007 Data de publicació: 2009-06 Article en revista
High-resolution ground-penetrating radar (GPR) evaluations of structures are usually carried out using antennas with high nominal centre frequencies (between 1 and 2GHz). A comprehensive characterization of such an antenna would make it possible to determine the capabilities of a system and obtain
accurate data interpretations. This paper describes the experimental determination of the radiation pattern of a commercial 1.6 GHz antenna, which forms part of a comprehensive experimental characterization. Radiation patterns are closely related to spatial resolution, so the horizontal and
vertical resolutions are evaluated first. The footprint of the antenna is then measured in air using simple devices at different distances. The final result is the approximate spatial radiation pattern of the emitted energy, measured in air. Finally, these measurements are also taken in sand to obtain the radiation pattern and footprint of the antenna in this medium.
In this paper, an improved pulse generator is proposed to emit a low-voltage square-wave burst. This generator will be used to excite a concave piezoelectric transducer array. Unlike classical single-pulse excitation circuits, this generator is also able to generate a square-wave burst signal. The Lamb waves generated in an aluminium plate with the square-wave burst generator are compared with those obtained using a classical single-pulse generator. Also, the signal conditioning system for all the transducer array elements has been implemented and tested.
Yañez, Y.; Garcia, M.; Salazar, J.; Turo, A.; Chavez-Dominguez, J. A. NDT and E international Vol. 38, num. 6, p. 491-496 DOI: 10.1016/j.ndteint.2005.01.004 Data de publicació: 2005-03 Article en revista
An analytical output noise voltage model of an ultra low noise amplifier for high impedance ultrasonic transducers is presented. Operational amplifier with low input bias current is needed to avoid using compensation resistance that considerably increases the noise at the input of the operational amplifier. The proposed analytical model, including the ultrasonic transducer, provides a useful tool to design, compare and select component values.
Turo, A.; Salazar, J.; Chavez-Dominguez, J. A.; Kichou, H.; Gómez, T.; Montero, F.; Garcia, M. NDT and E international Vol. 36, num. 2, p. 93-100 DOI: 10.1016/S0963-8695(02)00091-9 Data de publicació: 2003-03 Article en revista
Air-coupled ultrasonic inspection has been demonstrated to be a non-contact method of great interest in non-destructive evaluation (NDE) applications. The absence of direct contact or a liquid couplant provides this technique very attractive benefits in front of the well-known and well-developed liquid-coupled ultrasonic inspection systems. A wide range of defects can be detected by means of ultrasound coupled to and harvested from the specimen in absence of contact when using appropriate transducers designed for their operation in air.
This paper presents an easy way to integrate air-coupled piezoelectric transducers in conventional ultrasonic NDE equipment. The design of a specific front-end electronics by using an ultra-low noise amplifier enables existing inspection systems to be used for the dry-coupled ultrasonic test of materials and structures. The amplifier provides the receiver with a signal-to-noise ratio large enough for good quality signal processing and imaging. System dynamic ranges of more than 100 dB are achieved.