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Published on Tuesday, 02 March 2010 14:22

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Scanning Acoustic Microscopy Laboratory

• Development of acoustic microscopes, imaging techniques (C-scan, B-scan, amplitude and phase imaging) and measuring procedures in low frequency (35MHz-200MHz) range
• Visualization of surface and interior of solids and biological materials using waves of the frequency up to 1GHz
• 3 dimensional microscopic imaging
• Bones sonography

Low Frequency Scanning Acoustic Microscope

Fig.1.Scanning Acoustic Microscope built in the Division of Acoustic Microscopy. Operating frequency 35MHz - 200MHz.

Scanning Acoustic Microscope (SAM) operates at the frequencies of 35MHz, 100MHz and 200MHz and The corresponding lateral resolution of 40μm, 15μm and 7μm for the surface imaging can be achieved. The image is created by amplitude or phase of the reflected signal. The microscope enables surface, subsurface and surface layer imaging.

Amplitude imaging

Operating in amplitude mode the microscope can be used for non-destructive micro-defectoscopy of materials as well as for imaging of soft biological samples or hard materials (bone samples). Acoustic images of the soft unstained tissues enable differentiation of various tissue types that differ in acoustic impedance values less than 1%. We have a good experience with subsurface imaging in metals up to several millimeters beneath the surface. The amplitude inspection of the surface layer is very sensitive to impedance changes and it can provide information about the quality of adhesion of diffusion bonds, welds and laminates because any lack of coupling between materials changes dramatically the reflection coefficient.

Fig.2.Scanning Acoustic Microscope (SAM) C-scan images of biological samples obtained at 100MHz frequency. Successively from the left: eye section, artery section and eyeball cross-section (retina).

Fig.3.SAM C-scan image of the one-cent coin surface (left) and SAM B-scan image of flaws beneath the surface of a turbine blade (right).

Phase imaging

Phase imaging is very powerful and sensitive method for topography imaging. At 100MHz the distance changes less than 0.1μm can be detected. Our experience with phase imaging of the thin gold layers deposited on quartz samples show that this technique is sensitive to any cracks, voids and other defects of the layer. At lower frequencies the topography of the big objects (spherical transducer for example) can be examined.

Fig.5.SAM phase-images. Left – topography of a coin surface, right – gold layer, 0.07mm thick, deposited on the part of quartz surface.

Imaging with surface waves

The microscope can generate surface waves that may be used for imaging and measurements. The contrast of the surface waves-images depends on the velocity of these waves. Thus, the quality or homogeneity of material can be determined from the images that reflect the velocity distributions. The surface waves-imaging technique may be also applied for investigations of the grained materials like metals or alloys. Also, some stress introduced in samples can be investigated due to elasto-acoustic effect (ultrasonic wave velocity changes due to stress variation). So, in very homogeneous samples the stress distribution can be visualized and determined.

Fig.6.SAM amplitude images obtained with surface waves.Left – grains of ALNICO alloy, right – trabeculae of cancellous bone.

High Frequency Scanning Acoustic Microscope

Acoustic Microscopy Laboratory is equipped with commercial acoustic microscope (KSI) that operates in GHz range with the resolution up to 1 micron.

Fig.7.KSI Scanning Acoustic Microscope.

Fig.8.SAM images of integrated circuit structures obtained at 400MHz (left) and at 1GHz frequency (right).

Fig.9.XTH-2 living cell image

Acoustic microscope enables investigations of living cells. Above, XTH-2 living cell image (1GHz) is presented with characteristic fringe-structure that results from interference of waves reflected from the bottom and upper surface of the cell. Additionally, the amplitude of the received signal along the marked line is shown.

3 Dimensional Scanning Acoustic Microscope

A new Acoustic Microscope operating at the frequency up to 200MHz intended for internal structures visualization was developed in the Division of Acoustic Microscopy. The system was built basing on the commercially available components (transmitter, receiver, scanner and 1GHz sampling board) and the self-constructed acoustic lenses. The dedicated software was developed to control the process of 3D RF-data acquisition, processing and presenting the data in 2D cross-sections or 3D surface rendering mode.

Inside ceramic package

Bones sonography

Development of instrumentations and techniques for the complex characterization of the cancellous (trabecular) bone, including acoustic microscopy of a single trabeculae and investigations of the trabecular bone structure by sound transmission and scattering.

Acoustic microscopy of trabecular bone

Fig.12.Cancellous bone structure imaged with the microscope at 100MHz. Resolution = 7μm. Image size = 3mm x 3mm.

The SAM image can be converted into parametric images that reflect the distribution of acoustic impedance (product of density and velocity) or attenuation coefficient within the bone sample.

Fig.13.Successively from the left: Single trabeculae and cortical bone image, parametric-impedance image and parametric-attenuation coefficient image. Bone investigation at low frequency

BUA = 0 dB/MHz BUA = 160 dB/MHz

Parametric image (obtained in vivo) of a heel bone. Image brightness is coded with values of Broadband Ultrasonic Attenuation (BUA) coefficient.