Biomedical subjects

Shi-Chang Wooh

Publications and source records attributed to Shi-Chang Wooh.

3 recordsLinked to original sources

PubMed2004

Design of ultrasonic wedge transducer.

Cones and wedges inserted between an ultrasonic transducer and the specimen provide the transducer (circular or rectangular shape) with enhanced capability for point or line contact with the specimen. Such an arrangement is useful in that the transducer can be used for transmitting to and receiving from a point (or line) source, and that it can eliminate the undesirable aperture effect that makes the transducer blind to waves traveling in certain directions and those of certain frequencies. In this paper, a comprehensive numerical analysis based on a wave propagation model is carried out for the study of characteristics and parameters of cones and wedges influencing their performance. We study the effect of the dimensions, shape and aperture on the frequency response and the angle of incidence of the wave. For computational accuracy and efficiency, the boundary element method is used in the analysis.

Journal Article↗

PubMed2003

Laser-ultrasonic generation of Lamb waves in the reaction force range.

The Laser-ultrasonic generation of Lamb waves in an elastic plate is investigated theoretically and experimentally for a laser source whose intensity is high enough to create reaction forces (normal tractions) on the illuminated surface of the specimen. The analytical solutions for transient waves are derived using the integral transform method first by considering an arbitrary source shape and time excitation function, and then specifically for circular and line source shapes. The simulation study allows us not only to predict the behavior of individual wave modes but also to construct the overall responses; thus it helps us better understand the wave excitation mechanisms. The dispersive and multi-modal nature of laser-generated Lamb waves is presented by showing the spatiotemporal Fourier transform of displacements obtained by the simulation study. The transform, displayed in the frequency-wave number domain, enunciates the characteristics of the propagating individual Lamb wave modes. The simulation results are then compared with the 2-D Fourier transform of a set of experimental data obtained by scanning an aluminum plate specimen.

Aluminum↗

PubMed2002

Phased array element shapes for suppressing grating lobes.

Most techniques for suppressing grating lobes in phased arrays while relaxing the interelement spacing requirement involve redistributing array elements in sparse aperiodic patterns, or varying the transmit-receive beam patterns. An alternative is presented which uses oversized array elements to eliminate grating lobes as a direct consequence of the element shape. It is shown that by using carefully shaped, overlapping elements, maximum scan angle can be exchanged for a reduced interelement spacing requirement.

Models, Theoretical↗