Research

Acoustic microscopy

Acoustic microscopy is an imaging method and characterization using mechanical waves sufficiently high frequency (several MHz to several GHz) to levels comparable to those of the optical resolution microscopes.

There are many applications in research and industry for detecting defects in multilayer materials, optically opaque, with resolutions ranging from 1 micron to 1 mm.

Advantages of acoustic microscopy are:

  • The ability to image the subsurface structures of opaque materials (without careful preparation area: ex without etching)
  • The non-destructive nature of the technique for most materials (low-intensity ultrasound, qq. MW qq. 100 mW)
  • The acoustic images obtained contain information relating to the mechanical properties and the microstructure of the materials (specific gravity, elasticity, viscosity, porosity, adhesion, topography, ...): method of microstructural characterization
  • Better contrast in optical in specific situations, such as interface glass / transparent Plexiglas ® as one than the other but with a sharp contrast in acousticLes applications sont nombreuses dans la recherche et l’industrie pour détecter des défauts dans des matériaux multicouches, optiquement opaques, avec des résolutions allant de 1 µm à 1 mm.

 

Acoustic micro- ultrasound ( imaging)

 

  • Typically used in reflection
  • Pulsed Operation
  • Opening angle low Translators
  • It works on the amplitude of the received signal . ( simple signal processing )

The scanned images are the property variations of structural origin (mechanical property) or geometric (relief, microcracks , ... ) of the surface of the material studied . The measurement volume is defined by the surface of the size of the focal spot and the subsurface depth (depending on the wavelength in the material ) . The resolution depends on the length of the ultrasound transmission , the natural frequency of the translator, the degree of focusing of the acoustic lens , the coupling liquid .

To achieve the pictures below , we have a scanning acoustic microscope (SAM) SONOSCAN 3100 and developed internally to store the entire time signals for post -treatment ( phase images , time image system theft, etc. . )

Superposition of an optical image and acoustic image information showing the resolution achieved with a low opening focused transducer center frequency and 50 MHz

Images of a specimen of fiber composite materials.
With SONOSCAN 3100 system, each image requires a new scan of the room, the signals are not digitized for storage (encoding the signal amplitude "on the fly" in a given time window)

Comparison between the 3100 SAM SONOSCAN (fast image acquisition 5min approx.) And the NHI system (slow acquisition 2h approx., But with the possibility of subsequent temporal windows for imaging different depths of the specimen)

Illustration of the principle of temporal windows for image rendering subsurface.

Image obtained by time of flight with the NHI system representing the reconstruction of the topography of the immersed part (vertical axis encoded mm from the measurements of time of flight of the pulse in the U.S. water).