Volume 118, Issue 6, December 2005
Index of content:
- ACOUSTIC SIGNAL PROCESSING 
118(2005); http://dx.doi.org/10.1121/1.2126935View Description Hide Description
Advancements in integrated circuit (IC) package technology are increasingly leading to size shrinkage of modern microelectronic packages. This size reduction presents a challenge for the detection and location of the internal features/defects in the packages, which have approached the resolution limit of conventional acoustic microimaging, an important nondestructive inspection technique in the semiconductor industry. In this paper, to meet the challenge the learning overcomplete representation technique is pursued to decompose an ultrasonic A-scan signal into overcomplete representations over a learned overcomplete dictionary.Ultrasonicecho separation and reflectivity function estimation are then performed by exploiting the sparse representability of ultrasonic pulses. An improved acoustic microimaging technique is proposed by integrating these operations into the conventional acoustic microimaging technique. Its performance is quantitatively evaluated by elaborated experiments on ultrasonic A-scan signals using acoustic microimaging (AMI) error criteria. Results obtained both from simulated and measured A-scans are presented to demonstrate the superior axial resolution and robustness of the proposed technique.
118(2005); http://dx.doi.org/10.1121/1.2047267View Description Hide Description
Spatial discrete Fourier transform-based near-field acoustical holography is known to suffer from windowing effects since the measurement aperture is necessarily finite. The latter effect can be mitigated by using patch holography, in which the measured field is extended beyond the measurement aperture based on successive smoothing operations. In this article, the application of a patch holography algorithm to cylindrical geometries is described. In planar geometry, initial zero-padding can be applied to the hologram pressure to an arbitrary degree in both in-plane directions since the pressure magnitude is expected to limit ultimately towards zero in both directions. In a cylindrical geometry, zero-padding can be implemented axially in the same way, but the number of zeros added in the circumferential direction is necessarily determined by the angular sample spacing owing to the periodic nature of the field in this direction. By using both numerical simulation and experimental results, it is shown that the patch extrapolation procedure works well in the cylindrical case, and a discussion of rigid reflecting boundaries is also included. Finally, reconstruction results obtained by the combined use of pressures measured in the finite aperture and two different regularization parameter selection techniques are compared, and the effect of projection distance is discussed.
118(2005); http://dx.doi.org/10.1121/1.2130965View Description Hide Description
An experimental and numerical study is reported on focused, phase-conjugated sound beams of finite amplitude produced in water by a solid-state parametric amplifier, referred to as the conjugator. The sound beams incident on the conjugator were radiated by a focused circular source. Field distributions were measured along the beam axis and in the focal plane of the source. Both linear and nonlinear propagation were investigated. Apertures of different diameters were placed in front of the conjugator to demonstrate diffractioneffects associated with size of the active surface of the conjugator. Peak-to-peak acoustic pressures of and strongly distorted, asymmetric waveforms were measured at the focus of conjugate beams having a fundamental frequency of . Numerical simulations of harmonic generation in the conjugate beams are in agreement with the measurements. The study reveals that the conjugate beams accurately reproduce the focal region of the incident beams when a sufficiently large aperture is used, even when substantial waveform distortion due to nonlinear propagation effects are observed in the conjugate beams.