Acoustic microscopy-a summary

Abstract

Acoustic microscopy enables one to image the interactis:, ef acoustic waves with the elastic properties of a specimen with microscopic reso1u;ion. A lens with good focusing properties on axis can be used for both transmitting and receiving the signal, and an image is formed by scanning the lens mechanically over the specimen. In pressurised superhid helium with nonlinear coupling to harmonics a resolution of 15 nm has been achieved, but for routine use 2 GHz is the highest practical frequency, which offers a resolution of about 0.7 pm. The information is contained in the way that the acoustic wave is retlected from the specimen. For subsurface imaging, especially in polymer based materials such as composites and electronic packaging, the enhanced depth resolution of a confocal imaging system can he exploited to give good contrast from the plane of interest even when the specimen contains many scatters. In higher stilhess specimens, including most metals, semiconductors and ceramics, a dominant role in the contrast can he played by Rayleigh waves in the surface. If the specimen has a surface layer, then the propagation of the Rayleigh waves is sensitive to the perturbing action of the layer. If the specimen is anisotropic, then there will be dependence on the orientation of the surface and the direction of propagation in it. If there are surface cracks or boundaries, then there will he strong contrast when they scatter the Rayleigh waves. Detailed theory is available to relate the elastic properties of the surface to the conmst. and these enable informed interpretation of the acoustic images to be made, and also provide a foundation for more quantitative acoustic microscopy.

Cellular motility in vitro as revealed by scanning acoustic microscopy depends on cell-cell contacts

“…SAM provides a "mechanical picture" of a cell by transducing mechanical parameters like thickness of the object and elasticity or stiffness of the submembrane cortex into optical signals (grey level images). For a detailed description of acoustic microscopy, see Briggs (1992); BereiterHahn (1995). Thus, it allows us to see and compare movements within the membrane and the actomyosin cortex and underneath that cannot be detected by any other method.…”

Low intensity ultrasound

“…The resolution available for imaging is limited by the wavelength of the sound used (1 MHz sound has a wavelength of about 1.5 mm in water) and the significant size of the transducer face. Higher frequency transducers focused to a single measurement point can overcome both of these difficulties and acoustic microscopy can achieve micron resolution (Briggs, 1992;Hafsteinsson & Rivzi, 1984).…”

Picosecond ultrasonic microscopy of semiconductor nanostructures

“…One of the appeals of using sound to image materials is the possibility of detecting subsurface defects in materials that are opaque optically, but relatively transparent (i.e., non-attenuating) acoustically. In addition, an acoustic microscope can image systems where the optical contrast is small but the acoustic contrast, or the difference in mechanical properties, is high [6].…”

“…In pulsed acoustic microscopy, the spatial resolution is fundamentally limited by the attenuation of the high frequency components of the sound pulse [6]. In a linear viscoelastic fluid, the attenuation α of sound is proportional to the square of the frequency f [7], i.e., 2 Af α = .…”