Scanning Acoustic Microscopy (SAM)

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Scanning Acoustic Microscopy (SAM) or Ultrasonic microscopy

General information

Ultrasonic microscopy is an ultrasonic inspection method for visualising surfaces in the 10 µm range. High frequencies and focussing ultrasonic sensors are used to generate small wavelengths and a focus that can still detect the fine differences in surface topography.

An ultrasonic microscope is used to examine surfaces of materials or components. Due to the higher contrast or the light sensitivity of the components, sound waves with a high frequency are used to examine surface structures (see: surface testing technology). Ultrasonic sensors with frequencies in the range from 5 MHz to 500 MHz [1] or even higher are used for their examination (Fig. 1).

Fig. 1:

Classification of the sound ranges in relation to the frequency [1]

Schematic structure of an ultrasonic microscope

The design of an ultrasonic microscope is basically the same as that of any ultrasonic measuring device, with the only difference being that acoustic lenses, which are in direct contact with the transducer, are used to reduce the focus and thus further improve the resolution (Fig. 2). Ultrasonic microscopes have been sold commercially since 1985 and their design has been described in detail by Boseck [2].

Fig. 2:

Schematic structure of an ultrasonic microscope

For good sound transmission (see: ultrasonic transmitter (S)-receiver (E) sensors) to the surface of the test material requires an isotropic coupling agent. In practice, distilled water is therefore often used, but gels are also used [3].

Because the high frequencies guarantee a high resolution, but the sound waves also experience a high attenuation of their amplitudes (see: absorption sound waves), ultrasonic microscopes are mainly used to characterise surfaces and areas close to the surface.

These microscopes basically work using the pulse-echo method. Here, the transmitter is the same as the receiver. The sound waves are reflected at the interfaces of different media and materials because they have different acoustic properties (Table 1).

Table 1: Acoustic values of selected materials

material	sound velocity (long.) cL (m s-1)	Specific attenuation V (dB mm-1)
steel	5900	0.25
aluminium	6400	0.13
brass	4300	0.15
synthetic rubber	1460	4.12
PMMA	2540	0.31
PS	2350	2.07
PVC	2300	1.85
PA6	2570	2.38
PP	2550	2.26
PE	1800	2.26

Applications

Ultrasonic microscopy is primarily used to examine complex surfaces, but can also be used to characterise flat and sufficiently thin assemblies, such as those commonly used in the material characterisation of metals, plastics and fibre composites (see also: composite materials testing) and in microelectronics (see also: testing of microcomponents). Measurement frequencies of up to 2 GHz are used [4], [5].

There is also research work in medicine for analysing bone tissue [6], but also in biology [7].

See also

• Ultrasonic runtime measurement
• Non-destructive polymer testing
• Ultrasonic testing
• Testing microcomponents
• Composite materials testing

References

[1]	Die Chemie-Schule. Anorganische Chemie. Organische Chemie. Lexikon: Akustische Mikroskopie (https://www.chemie-schule.de/KnowHow/Akustische_Mikroskopie) (last accessed on 12/10/2025)
[2]	Boseck, S.: Akustische Mikroskopie. In: Angewandte Optik. Phys. Bl. 49,6 (1993) Nr. 6, 497–502
[3]	Hipp, R., Gommlich, A., Großmann, C., Schubert, F. (2014). Hochaufgelöste Ultraschallprüfung an Widerstandspunktschweißverbindungen. DGZfP-Jahrestagung 2013, Dresden, Germany, May 6–8, 2013. Online als PDF (last accessed on 12/10/2025)
[4]	Neumann, L. u. a.: Ultraschallmikroskopie an laserpolierten Aluminium-Druckgussproben. Tagungsband DGZfP-Jahrestagung 7. – 9. May 2018
[5]	Bauch, J.; Rosenkranz, R.: SAM – Ultraschallmikroskopie. In: Physikalische Werkstoffdiagnostik. Springer Vieweg, Berlin und Heidelberg (2017)
[6]	Winkler-Budenhofer, U. C.: Scanning Acoustic Microscopy zur Beurteilung von neu gebildetem Knochen. Dissertation Universität München (2007)
[7]	Prüfer, H.-P.: Strukturmechanische Untersuchungen zur Carapax-Verstärkung von Daphnia cucullata. In: Bröckel, K. Stelzer, R.; Feldhusen, J.; Rieg, F.; Grote, K.-H.: 9. Gemeinsames Kolloquium Konstruktionstechnik 2011 – Integrierte Produktentwicklung für einen globalen Markt. Rostock, 6. + 7. Oktober 2011. Shaker Verlag (2011) (ISBN: 978-3-8440-0381-9)