TY - GEN A1 - Ono, K. A1 - Erhard, Anton T1 - Nondestructive testing, 3. Ultrasonics N2 - The field of acoustics deals with sound Propagation in solids, liquids, and gases, whereby the frequencies may lie above or below the Audio band, that is, infrasound (<16 Hz) and ultrasound (>16 kHz), respectively. The speed of sound depends on mechanical properties of the material like elastic constants and compressibility. Interaction of imperfections such as grains, cracks, pores, and inclusions with sound waves results in reflection, refraction, scattering, and attenuation due to discontinuities in elastic moduli and density. By sending a pulse and receiving its reflection, the presence and Location of defects can be determined (pulse-echo technique). Ultrasound was applied in nondestructive testing (NDT) earlier than in medicine, but visualization of the data in a unicolor-scale image was first used in medical ultrasound diagnostics. The principle of ultrasonic testing, for example, the wave types that are suitable for different applications, the frequency ränge employed, reflectivity behavior, mode conversions, probe types, and so on are described in various publications, and a newer ultrasonic method, namely, the phased array technique, is treated in. KW - Ultrasonic waves KW - Piezocomposite materials for ultrasound generation KW - Phased array technique PY - 2011 SN - 978-3-52730-673-2 U6 - https://doi.org/10.1002/14356007.o17_o02 SP - 1 EP - 17 PB - Wiley-VCH AN - OPUS4-24090 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -