Luis Elvira Segura

Double frequency piezoelectric transducer design for harmonic imaging purposes in NDT

Harmonic imaging (HI) has emerged as a very promising tool for medical imaging, although there has been little published work using this technique in ultrasonic non-destructive testing (NDT). The core of the technique, which uses nonlinear propagation effects arising in the medium due to the microstructure or the existence of defects, is the ability to design transducers capable of emitting at one frequency and receiving at twice this frequency. The transducers that have been used so far are usually double crystal configurations with coaxial geometry, and commonly using a disc surrounded by a ring. Such a geometry permits the design of broadband transducers if each transducer element is adapted to the medium with its corresponding matching layers. Nevertheless, the different geometry of the emission and reception apertures creates difficulties when resolving the images. In this work, a new transducer design with different emission and reception apertures is presented. It makes use of the traditional construction procedures used to make piezocomposite transducers and the well-known theory of the mode coupling in piezoelectric resonators when the lateral dimensions are comparable with the thickness of the piezoceramic. In this work the design, construction, and characterization of a prototype to be used in NDT of metallic materials is presented. The acoustic field is calculated using water as a propagation medium, and these theoretical predictions then are compared with the experimental measurements. The predicted acoustic performances for the case of propagation in stainless steel are shown.

A new ultrasonic signal amplification method for detection of bacteria

A new method is presented that increases the sensitivity of ultrasound-based techniques for detection of bacteria. The technique was developed for the detection of catalase-positive microorganisms. It uses a bubble trapping medium containing hydrogen peroxide that is mixed with the sample for microbiological evaluation. The enzyme catalase is present in catalase-positive bacteria, which induces a rapid hydrolysis of hydrogen peroxide, forming bubbles which remain in the medium. This reaction results in the amplification of the mechanical changes that the microorganisms produce in the medium. The effect can be detected by means of ultrasonic wave amplitude continuous measurement since the bubbles increase the ultrasonic attenuation significantly. It is shown that microorganism concentrations of the order of 10 5 cells ml −1 can be detected using this method. This allows an improvement of three orders of magnitude in the ultrasonic detection threshold of microorganisms in conventional culture media, and is competitive with modern rapid microbiological methods. It can also be used for the characterization of the enzymatic activity.

X-cut quartz crystal impedance meter for liquid characterization

A new procedure to determine the compressional acoustic impedance of liquids within ±0.05% resolution and ±0.25% accuracy is presented. This method is based on the measurement of the bandwidth of a piezoelectric transducer, vibrating in thickness-expansion mode and having a high quality factor (e.g., air-backed X-cut quartz crystal), in direct contact with the sample. In combination with other ultrasonic techniques (pulse-echo or through-transmission), it is possible to simultaneously obtain the main ultrasonic parameters (characteristic acoustic impedance, speed of sound and attenuation coefficient), and deduce important physicochemical properties of liquids, such as density and adiabatic compressibility. Experimental results for selected liquids and solutions are shown.

The Effect of Anisotropic Focusing of Lamb Modes on a Carbon-Epoxy Plain Woven Fabric Composite Plate

10 paginas, 8 figuras, 1 tabla. 6th International Symposium on NDT in Aerospace, 12-14th November 2014, Madrid, Spain

A new ultrasound based method for rapid microorganism detection

A new method for rapid detection of catalase positive microorganisms by using an ultrasonic measuring method is proposed in this work. The developed technique is based on the detection of oxygen bubbles produced by the hydrolysis of hydrogen peroxide induced by the enzyme catalase which is present in many microorganisms. The bubbles are trapped in a media based on agar gel which was especially developed for microbiological evaluation. It is found that microorganism concentrations of the order of 105 c.f.u./ml can be detected by using this method. The results obtained show up that the proposed method is competitive with other modern commercial methods like luminescence by ATP system. The method can also be used for characterization of enzyme activity.

Study of the Nearfield Radiated by Stepped Plate Ultrasonic Transducers in Air

An experimental procedure is used to study the nearfield radiated by a stepped plate transducer. The developed set up allows the acoustic field to be scanned, taking information about the sound pressure level (SPL) distribution. For high power acoustic applications, the nearfield region presents the important practical advantage of the high pressure levels reached in it. Improvements of the acoustic pressure distribution have been tried by using two different configurations of reflectors.