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Preparatory Notes for ASNT NDT Level III Examination - Ultrasonic Testing, UT

Preparatory Notes for ASNT NDT Level III Examination - Ultrasonic Testing

Preparatory Notes for ASNT NDT Level III Examination - Ultrasonic Testing

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At Interface: Reflection & Transmittance<br />

At first glance a sound pressure exceeding<br />

100 % seems paradoxical and one suspects<br />

a contradiction of the energy law. However,<br />

according to Eq. (1.4) the intensity, i.e. the<br />

energy per unit time and unit area, is not<br />

calculated from the sound pressure<br />

(squared) only but also from the acoustic<br />

impedance of the material in which the wave<br />

travels. However, since this impedance in<br />

steel is very much greater than in water, the<br />

calculation shows that the intensity of the<br />

transmitted wave is very much smaller there<br />

than in water in spite of the higher sound<br />

pressure.

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