Event Title

Practical Shear Wave Lens Design for Improved Resolution with Acoustic Microscope

Location

Snowbird, UT, USA

Start Date

1-1-1999 12:00 AM

Description

Ever since the invention of the scanning acoustic microscope (SAM), a key objective has been the enhancement of the resolution in the acoustic images. This challenge has generally been pursued with two directions for approaches: one approach was to raise the acoustic frequency. B. Hadimiooglu and C. F. Quate achieved a resolution of 0.2 micron by operating at about 4.4 GHz with the sample in boiling water in order to minimize the attenuation of the coupling medium [1]. A second approach has been to use low velocity coupling media such as super-fluid liquid helium. J. S. Foster and D. Ruger were able to obtain a resolution of 20 nano-meters using super-fluid liquid helium as coupling medium at a temperature of 0.2° K [2]. These techniques are excellent for increasing resolution on the surface of a specimen but not necessarily in its interior. In the first approach described above, the ultrasonic wave is attenuated in proportion to the square of its frequency. Therefore, when the high frequency ultrasonic wave is used as a probe, the wave may not penetrate the inside of the specimen, so that internal information may not be obtained. In the second technique, also referred to as cryogenic microscopy, the acoustic impedance between the coupler and the specimen are very different, so that most of the ultrasonic waves are reflected at the interface between the coupler and the specimen, and it is unlikely that an image from any significant depth may be obtained. Hence, acoustic microscopy’s most important and unique feature, namely obtaining subsurface information may not be realized by these two approaches.

Book Title

Review of Progress in Quantitative Nondestructive Evaluation

Volume

18A

Chapter

Chapter 4: UT Transducers and Fields, Sensors

Section

UT Transducers and Arrays

Pages

1015-1020

DOI

10.1007/978-1-4615-4791-4_130

Language

en

File Format

application/pdf

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Jan 1st, 12:00 AM

Practical Shear Wave Lens Design for Improved Resolution with Acoustic Microscope

Snowbird, UT, USA

Ever since the invention of the scanning acoustic microscope (SAM), a key objective has been the enhancement of the resolution in the acoustic images. This challenge has generally been pursued with two directions for approaches: one approach was to raise the acoustic frequency. B. Hadimiooglu and C. F. Quate achieved a resolution of 0.2 micron by operating at about 4.4 GHz with the sample in boiling water in order to minimize the attenuation of the coupling medium [1]. A second approach has been to use low velocity coupling media such as super-fluid liquid helium. J. S. Foster and D. Ruger were able to obtain a resolution of 20 nano-meters using super-fluid liquid helium as coupling medium at a temperature of 0.2° K [2]. These techniques are excellent for increasing resolution on the surface of a specimen but not necessarily in its interior. In the first approach described above, the ultrasonic wave is attenuated in proportion to the square of its frequency. Therefore, when the high frequency ultrasonic wave is used as a probe, the wave may not penetrate the inside of the specimen, so that internal information may not be obtained. In the second technique, also referred to as cryogenic microscopy, the acoustic impedance between the coupler and the specimen are very different, so that most of the ultrasonic waves are reflected at the interface between the coupler and the specimen, and it is unlikely that an image from any significant depth may be obtained. Hence, acoustic microscopy’s most important and unique feature, namely obtaining subsurface information may not be realized by these two approaches.