Theoretical and experimental responses for a large-aperture broadband spherical transducer probing a liquid–solid boundary

Abstract

A theoretical analysis of a spherical focusing transducer for broadband acoustic microscopy is proposed. The originality of the present contribution is the particular attention we have paid to describe, as rigorously as possible, the diffraction phenomena. Our analysis starts in the harmonic domain with the well-known angular spectrum method, and then gets into the time domain. A new formulation of the angular spectrum in the focal plane has been obtained and compared to other expressions previously reported. This article is deliberately limited to isotropic semi-infinite plane reflectors in order to carry out the inverse Fourier transform in an analytical way. The analytical approach is helpful for the physical interpretation of particular interesting phenomena observed in the transient analysis. A new kind of contribution to the echographic response has been identified and named “geometrical edge waves.” The weight and the arrival time of each discontinuity of the impulse response is analytically evaluated and the physical meaning of each of them is clearly established with the help of a ray model. In the last part of this article, a broadband polyvinylidene fluoride transducer excited by short pulses is used for the experimental validation of the model. The excellent quantitative agreement observed on the time waveforms confirms the efficiency of our approach both in the time domain and in the harmonic one. The comparison between theory and experiment is limited here to some typical examples, but similar results have been obtained on a wide range of defocus and for a large variety of materials. Applications for the characterization of materials will be discussed in future publications.

<title>NDT of wafer direct bonding by non-confocal transmission phase sensitive acoustic microscopy</title>

“…It has been shown in ref. [10] that the GEW contributions are noticeably larger than those of the direct wave. The same observations were made for the case of non-confocal transmission microscopy in [7].…”

“…This amplitude peak was identified in [7] to be due to "edge-to-focus" waves. They were termed Geometrical Edge Waves (GEW) by Zhang et al in [10] and Fig. 3 Travel paths for "straight edge-to-edge" (dashed line), "diagonal edge-to-edge" (dot-dashed line), "edge-to focus" (dotted line), and "direct" waves (solid line), obeying ray acoustics rules.…”

High-Frequency Time-Resolved Scanning Acoustic Microscopy for Biomedical Applications

“…(14). However, computational methods allow for the numerical modeling of the propagating short acoustic pulses in TRSAM [59,60]. Schubert et al reported the numerical simulation of the acoustic pulse propagation and reflection of the focusing incident waves for different types of scatterers using the elasto-dynamic finite integration technique (EFIT) [61].…”

Polymer acoustic matching layer for broadband ultrasonic applications

“…1,2 The recent trend toward micro-and nano-technologies demands higher resolution and also cross-sectional images with higher signal-tonoise ratio in advanced samples, e.g., microelectronic packages. [3][4][5] Pushing the operating frequency of acoustic devices up to the gigahertz range, and also the realization of broadband ultrasound, 6 have been shown to be effective in improving spatial resolution, and sometimes the resolution that can be achieved is superior to that of an optical microscope. 7,8 However, the penetration depth of the highfrequency components of ultrasound is shallow, and the area that can be evaluated is limited to only the surface or the subsurface.…”