José Luis San Emeterio

Diffraction impulse response of rectangular transducers

A closed‐form expression for the impulse velocity potential of rectangular pistonlike transducers, without any far field or paraxial approximation, is presented. The classical time‐domain impulse response approach is used considering free‐field, rigid baffle, and pressure release boundary conditions. Previous approaches to the rigid baffled rectangular piston require the use of superposition methods in order to find a general solution numerically. These must add or subtract, according to the field point location, the analytical expressions that were derived only for specific field points or geometrical regions. In this paper the complexity introduced by the geometrical discontinuities of rectangular apertures is analyzed. A new compacting methodology is proposed and applied to obtain a general solution for the impulse response. This new solution provides the value of the impulse response directly in the time domain, without requiring superposition methods. In addition, a closed‐form solution for the press...

Models for Piezoelectric Transducers Used in Broadband Ultrasonic Applications

Piezoelectric transducers are key elements of many broadband ultrasonic systems, either pulse-echo or through-transmission, used for imaging and detection purposes. In ultrasonic broadband applications such as medical imaging, or non-destructive testing, piezoelectric transducers should generate/receive ultrasonic signals with good efficiency over a large frequency range. This implies the use of piezoelectric transducers with high sensitivity, broad bandwidth and short-duration impulse responses. High sensitivity provides large signal amplitudes which determine a good dynamic range for the system and the short duration of the received ultrasonic signal provides a good axial resolution.

Noise reduction using wavelet cycle spinning: analysis of useful periodicities in the z-transform domain

Cycle spinning (CS) and a’trous algorithms are different implementations of the undecimated wavelet transform (UWT). Both algorithms can be used for UWT and even though the resulting wavelet coefficients are different, they keep a correspondence. This paper describes an analysis of the CS algorithm performed in the z-transform domain, showing the similarities and differences with the a’trous implementation. CS generates more wavelet coefficients than a’trous, but the number of significative and different coefficients is the same in both cases because of the occurrence of a periodic repetition in CS coefficients. Mathematical expressions for the relationship between CS and a’trous coefficients and for CS coefficient periodicities are provided in the z-transform domain. In some wavelet denoising applications, periodicities (present in the coefficients of the CS procedure) can also be found in the performance measure of the processed signals. In particular, in ultrasonic CS denoising applications, periodicities have been appreciated in the signal-to-noise ratio (SNR) of the ultrasonic denoised signals. These periodicities can be used to optimize the number of CS coefficients for an efficient implementation. Two examples showing the periodicities in the SNR are included. A selection of several reduced sets of CS wavelet coefficients has been utilized in the examples, and the SNRs resulting after denoising are analyzed.

Flaw location from perpendicular NDE ultrasonic transducers using the wavelet packet transform

Ultrasonic inspection of materials from different planes is a technique that produces complementary information of the same piece using different echographic traces. The combination of these traces in order to obtain an improved representation of the inspected area is a problem that can be solved by means of digital signal processing techniques. A new method for the combination of the traces coming from perpendicular transducers is presented in this paper. The method is based on the undecimated wavelet packet transform and it is applied to the localization of isolated flaws in a plastic piece.

Ultrasonic Systems for Non-Destructive Testing Using Piezoelectric Transducers:.Electrical Responses and Main Schemes

In very distinct areas of industry the quality control of the fabrication products, as well as of the equipment used to fabricate them, is performed by means of Non-Destructive Testing (NDT) techniques. This control procedure acquires still more relevance when aspects of public security are present such as in the nuclear and aeronautics sectors. In many NDT applications, high frequency ultrasonic waves are employed. In most cases they are produced and detected by piezoelectric transducers operated in a pulsed mode. The ultrasonic radiation of these transducers is used as a tool to visualize internal parts. The propagation of these pulsed elastic waves can provide information about the internal structure of the medium by means of the analysis of reflections, scattering and attenuation in the mechanical discontinuities encountered along the ultrasonic path. Figure 16.1 shows a very general block diagram of NDT systems based on ultrasonic waves. It includes one or more ultrasonic transceivers depending on the number of piezoelectric channels involved.

Ultrasonic system for remote non-destructive testing using mobile telephony

In distributed non-destructive testing (NDT), the acquisition of ultrasonic measurements occasionally has to be performed at different locations distant from the central station, where the ultrasonic data must be analysed and displayed. In this paper, the design details of an ultrasonic system with such objective are described. The system aims to perform remote acquisitions and transmit them to a central station using mobile telephony. Ultrasonic and telecommunication sub-systems involved in this system are described. The practical implementation here depicted combines own-designed modules with some low-cost commercial devices. Some design consideration and the block schemes of each subsystem are detailed. Finally, a laboratory prototype, developed for design viability purposes, is presented. This development includes stages for: transducer driving by means of a high-voltage pulse generator, broad-band amplification, acquisition, multiplexing and A/D conversion of signals, ultrasonic data transmission by mobile telephony, and the control of telemetering aspects by remote and local software.

Ultrasonic pulse propagation in a bonded three‐layered structure

Bonded layers are used in the assembly of many critical functional parts of industrial equipment. In this work, ultrasonic pulse propagation in a steel‐rubber‐rubber bonded composite structure is investigated by means of computer simulation and pulse echo experimental evaluation. Ultrasonic pulse propagation is modelled using a 2D time domain finite‐difference software. For the experimental measurements, two test samples were fabricated by bonding a thin layer of steel and two thin layers of rubber, including debonded areas at marked regions of each interface. Several ultrasonic traces were acquired by contact pulse‐echo testing, using a 5 MHz wideband transducer, from the external steel surface. The large acoustic impedance mismatch existing between steel and rubber layers makes that only a very small part of the ultrasonic energy is transmitted through the first (steel‐rubber)interface. The high attenuation in rubber materials and the possible overlapping of multiple echoes are additional characteristics of the complex ultrasonic pulse propagation in this flat structure. Some differences in time and frequency domains, between the received signals from normal bonded areas and completely debonded areas are discussed, looking for defect detection at the first (steel‐rubber) and second (rubber‐rubber) interfaces.

Wavelet cycle-spinning denoising of ultrasonic traces acquired from austenitic steel

Ultrasonic non-destructive evaluation of austenitic steel components or welded unions usually presents difficulty for small flaw detection, due to complex structure and wave scattering at grain boundaries. Ultrasonic signals from small flaws are masked by grain or structural noise whose frequency band partially overlaps the frequency response of the ultrasonic transducer. The main objective of this work is the application and performance analysis of a cycle-spinning undecimated wavelet transform processor for denoising ultrasonic traces acquired from a test block made of austenitic steel.

Ultrasonic Systems for Non-Destructive Testing Using Piezoelectric Transducers

In very distinct areas of industry, the quality control of the fabrication products, as well as of the equipment used to fabricate them, is performed by means of Non-Destructive Testing (NDT) techniques. This control procedure acquires still more relevance when aspects of public security are present such as in the nuclear and aeronautics sectors.

Interface Electronic Systems for Broadband Ultrasonic Applications

There is a wide variety of applications where broadband piezoelectric systems are used, mainly in order to obtain ultrasonic information for detection or visualization of the internal parts of diverse structures. These applications require external inspections with ultrasonic waves and the use of an echo-graphic procedure. The main application areas are in industry and medicine.