Acoustic microscopy—1979

Study of beamforming techniques for ultrasound imaging in nondestructive testing

“…Ultrasound waves are elastic waves which can be transmitted through both fluids and solids. One of the required criteria of ultrasound is that the medium be continuous for the energy to propagate freely [34]. Any obstruction such as internal voids, delaminations, inclusions or cracks will interfere with the transmission/reflection of ultrasound signals.…”

Applications of Ultrasonic Microscopy to the Evaluation of Ceramic Materials

“…The former systems are now conveniently referred to [5] as "SLAM's" (Scanning Laser Acoustic Microscopes), and the latter as "SAM's" (Scanning Acoustic Microscopes). The frequency of operation of a SLAM is typically 100 to 500 MHz, and of the SAM, 100 to 3000 MHz, although both systems have been operated at frequencies outside these ranges.…”

“…The frequency of operation of a SLAM is typically 100 to 500 MHz, and of the SAM, 100 to 3000 MHz, although both systems have been operated at frequencies outside these ranges. SAM's have also been built to operate in a reflection (pulseecho) mode, using a single transducer; for both transmission and reflection versions, scannable thicknesses are very restricted, due both to the lens design requirements and to the high attenuation of most materials (including the necessary couplants) at these high frequencies; reflection SAM's are categorized as surface inspection devices [5]. A SLAM is somewhat less restricted, since it does not use the short focal-length and -depth lenses of the SAM, and because it is possible to eliminate all or most of the couplant, but images of multi-layered objects can be complicated since they represent the entire thickness of the sample.…”

“…In 1979, Kessler and Yuhas (6] wrote that "acoustic microscopes use frequencies ranging from 100-3000 MHz". The upper limit has now been passed, using liquid helium as a couplant to reduce attenuation, allowing frequencies up to 8 GHz, and it is now recognized that the lower limit was arbitrary and unrealistic.…”

Measurement of ultrasonic velocity in several biological tissues

“…The scanning laser acoustic microscope has been shown to be a valuable tool for imaging both biological and non-biological materials (Eggleton and Kessler, 1975;Kessler and Yuhas, 1979). Information on the elastic properties of specimens at 100MHz and higher frequencies is provided through two types of acoustic modes.…”