Biomedical subjects

Robert E Green

Publications and source records attributed to Robert E Green.

4 recordsLinked to original sources

PubMed2007

Generation of narrowband antisymmetric lamb waves using a formed laser source in the ablative regime.

A formed laser source, using a four-element lenticular array, is used in the ablative regime to generate select, narrowband, acoustic plate waves. The arrangement of the array produces acoustical signals that have frequencies compatible with the response of the broadband capacitive air-coupled transducer used in this study. A simplified concept is presented to explain the effect of a line array source on the frequency content of acoustic waves. The analytical model for a point pulse surface displacement is derived from the point load solution to Lamb's problem. The point pulse displacement elements of a line array source are summed mathematically, taking into account all applicable propagation modes and dispersion of plate waves. The model considers only the out-of-plane displacement of the antisymmetric plate modes to represent the detection capability of the broadband receiver. The distribution function of the laser beam energy profile is modified to depict the actual energy distribution that illuminates the surface of the plate. Filtering functions are made compatible with the sensitivity of the broadband receiver so as to retain only the detected frequencies in the model. The theoretical model showed good agreement with experimental results.

Computer Simulation↗

PubMed2004

Non-contact ultrasonic techniques.

Non-contact generation and detection of acoustic and ultrasound waveforms is of practical importance, since it permits making acoustic and ultrasonic measurements at elevated temperatures, in corrosive and other hostile environments, in geometrically difficult to reach locations, in outer space and doing this at relatively large distances from the test structure. Non-contact acoustical and ultrasonic techniques currently available are laser generation, optical interferometric detection, electromagnetic acoustic transducers (EMATs), air(gas)-coupled systems and hybrid combinations of the above. The present paper will describe how several such systems have been used in unique materials characterization applications.

Journal Article↗

PubMed2003

Sensitivity of point- and line-source laser-generated acoustic wave to surface flaws.

Laser generation and air-coupled detection were combined as a hybrid ultrasonic technique for the inspection of surface flaws in rail. Narrowband acoustic signals were generated using a formed laser source by focusing the laser light to a point and to a line on the surface of the rail. The pulse energy, and therefore the intensity of the laser source, varied such that the generated signal transitioned from the weak thermoelastic to the strong ablative regime. The detection of flaws using laser-generated surface acoustic wave, to the presence of surface flaws, was compared between both point and line laser sources operating under different pulse energy levels. The line source was found to be more sensitive to the presence of surface flaws than a point source. The sensitivity of the laser-generated acoustic signal appeared to be independent of the severity of the flaw and, within the ablative regime, independent of the laser-pulse energy. Theoretical analysis is provided to explain the underlying cause that influences the interaction of a formed laser-generated surface acoustic wave to surface flaws and how this sensitivity may vary between the thermoelastic and ablative regimes.

Journal Article↗

PubMed2003

Narrow band laser-generated surface acoustic waves using a formed source in the ablative regime.

A narrow band laser-generated acoustic signal was created using a 4-element lenticular array. This arrangement of the array produces an acoustical signal with frequency content that is compatible with the response of a noncontact and remote broadband receiver, such as a capacitive air-coupled transducer. To support the experimental observations, a simplified concept is presented to explain the effect of a line array source on the frequency content of a surface acoustic wave. The analytical model solution for the wave front shape is derived from the point load solution of Lamb's problem that represents the displacement of a surface acoustic wave generated by an ablative line array. The distribution function, which was used for the model to represent the laser light energy, was tailored to depict the actual energy distribution that illuminates the lenticular array. Filtering functions are applied to the resultant surface displacement function to retain frequencies similar to those detected by the broadband 50 kHz-2.25 MHz receiver. The theoretical model showed good agreement with experimental results.

Journal Article↗