Ultrasonic Planar Scanned Tomography

Lee, Hua; Schueler, Carl F.; Flesher, Gail T.; Wade, G.

doi:10.1007/978-1-4684-1137-9_20

Cited by 19 publications

(5 citation statements)

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“…W e can conclude that the term w t h the amplitude Znf,A(z,) is generally dominant. Equation (4) can be approximately written as …”

Section: Signal Deteci'ion In Siammentioning

confidence: 99%

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Data Acquisition in Tomographic Acoustic Microscopy

Lin¹,

Lee²,

Wade³

et al. 1983

1983 Ultrasonics Symposium

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The principles of tomography can be used to enhance the capability of acoustic microscopy. An approach for employing these principles, called scanning tomographc acoustic microscopy (STAM), applies t e c b q u e s of tomographic reconstruction in order t o process data acquired by usmg a modified scanmng laser acoustic microscope (SLAM). Thls paper contains a study of signal detection performed in a conventional SLAM system. The paper describes mecharucal and electronic modlfications of SLAM in order to facihtate proper data acquisition for STAM. The question of rotatmg either the transducer or the specimen to provide tomographic projections is addressed. I t is shown that in principle both rotations will work but rotatlng the specimen is mechanically the more feasible of the two. INTRODUCI'IONAcoustic microscopy is an important branch of nondestructive evaluation whch provides hgh-resolution micrographs of specimens to be evaluated. Acoustic energy can often give a view of a cross section not available with X-rays or other types of ra&ation. The principles of tomography can be used to enhance the capability of acoustic microscopy. A techmque for applying these principles, called scanning tomographc acoustic microscopy (STAM), utilizes digital signal processing of information obtained by employing a mo&fied scanning laser acoustic microscope (SLAM). The t e c h q u e is holographc in character [I] and is reminiscent of conventional X-ray focal-plane tomography. It is most

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“…W e can conclude that the term w t h the amplitude Znf,A(z,) is generally dominant. Equation (4) can be approximately written as …”

Section: Signal Deteci'ion In Siammentioning

confidence: 99%

“…In general, many holograms, corresponding to different directions of illumination of the object, are needed to reconstruct the three dimensional structure. Back-and-forth propagation is a holographic approach for tomographc image reconstruction [4].…”

Section: Data Acquisition For Si'mmentioning

confidence: 99%

Data Acquisition in Tomographic Acoustic Microscopy

Lin¹,

Lee²,

Wade³

et al. 1983

1983 Ultrasonics Symposium

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“…The quadrature receiver is operated at 32.4 MHz after first down-converting the frequency from 100 MHz. The holographic image reconstruction is performed by the backward propagation algorithm [2]. Figure 3 shows the holographic images of the two layers.…”

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confidence: 99%

Tomographic reconstruction of multiple‐layer specimens with the scanning tomographic acoustic microscope

Lee

Chiao

1990

Int J Imaging Syst Tech

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In this article we report the recent results of tomographic image reconstructions of multiple-layer specimens at 100 MHz with the Scanning Tomographic Acoustic Microscope (STAM) system. The experiment utilizes 12 uniformly spaced projections and the results show significant improvement over the holographic images.Acoustic microscopy has been a very important approach to high-resolution nondestructive evaluation of microscopic structures. The Scanning Laser Acoustic Microscope (SLAM) is one of the most widely used systems among the acoustic microscopes currently available. Based on the operating format, SLAM is a transmission-mode system with plane-wave illumination, The data acquisition is performed by a scanned laser beam that picks up the dynamic surface profile of the resultant acoustic waveform. The SLAM system has several fundamental advantages. It does not require focusing of the illumination beam. There is no mechanical movement of the specimen. The laser read-out approach provides a high-speed data acquisition capability. However, the SLAM remains limited to an orthographic imaging device because of the lack of subsurface imaging capability. This seriously limits the applications of the SLAM systems for specimens with certain thickness. Figure 1 illustrates the structure of the two-layer test specimen. Figure 2 is the orthographic image produced by a conventional SLAM system.With the addition of a quadrature receiver, the SLAM system is then capable of holographic subsurface imaging because of the detection of both the amplitude and phase of the dynamic wavefield [1]. For this experiment, the illumination acoustic wave is operated at 100MHz. The quadrature receiver is operated at 32.4 MHz after first down-converting the frequency from 100 MHz. The holographic image reconstruction is performed by the backward propagation algorithm [2]. Figure 3 shows the holographic images of the two layers. The holographic images demonstrate some improvement over the conventional SLAM image in terms of better separation of layers. However, leakage between layers still exists.The objective to upgrade the capability of the SLAM system to the tomographic level is to improve the depth resolution over the holographic reconstruction. Tomographic microscopy can be achieved by extending the spatial-frequen- cy content of the image information with a wider coverage of the observation angle. The experiment included in this article utilized 12 projections. These projections are evenly spaced with the spacing of 30 degrees to form a complete perspective coverage. The tomographic reconstruction is the superposition of the holographic images reconstructed from the 12 projections by backward propagation. The tomographic superposition process also requires an extensive sequence of preprocessing procedures, including data-acquisition-phase error removal, resampling for uniform data sample spacing, estimation of the initial phase of projections, and displacement estimation for accurate array alignment [3,4]. Figure 4 shows the tomograph...

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“…At an operating frequency of about 100 MHz, the SLAM can achieve high resolution in the azimuthal direction; however, the depth (range) resolution of the SLAM is poor due to diffraction and overlapping of depthplanes. Lee et al [2] first proposed the Scanning Tomographic Acoustic Microscope (STAM), which uses tomographic processing to overcome the image degradation experienced by the SLAM. The resolution improvement of the STAM is obtained by detecting the phase as well as the amplitude of the acoustic wavefield and by using using multiple projections for image reconstruction.…”

Section: Introductionmentioning

confidence: 99%

“…This paper presents recent experimental results for the STAM, and discusses some of the problems encountered during its implementation. The implementation problems can be grouped into two categories: (1) phase errors in the tomographic projections, and (2) misalignment of the projections during tomographic processing. Two types of phase errors which can result in significant degradation of the tomographic reconstruction are identified: the quadrature phase error and the initial phase error.…”

Section: Introductionmentioning

confidence: 99%

Multiple-frequency and multiple-angle tomography with the scanning tomographic acoustic microscope

Chiao

Lee

IEEE Symposium on Ultrasonics

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In this paper we present recent developments in multiple-frequency and multiple-angle tomography for the Scanning Tomographic Acoustic Microscope (STAM). The STAM extends the capabilities of the Scanning Laser Acoustic Microscope (SLAM) by using tomographic processing to recover the depth information. Recently, high quality tomographic reconstructions were obtained by addressing the problems of projection phase errors and projection misalignment. In addition to discussing these implementation problems for the STAM, we present reconstructions using experimental data for both multiple-frequency and multiple-angle tomography. These results demonstrate the feasibility and reconstruction improvement of the STAM.

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Ultrasonic Planar Scanned Tomography

Cited by 19 publications

References 1 publication

Data Acquisition in Tomographic Acoustic Microscopy

Data Acquisition in Tomographic Acoustic Microscopy

Tomographic reconstruction of multiple‐layer specimens with the scanning tomographic acoustic microscope

Multiple-frequency and multiple-angle tomography with the scanning tomographic acoustic microscope

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