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Unformatted text preview: thin 1/4 to 1/6 of the sound wavelength, the
waves are reflected diffusely, whereas smooth surfaces have a maximum angle of
approx. ±5° to the sound cone, roughly structured substances, e.g. bulk goods, can
be detected up to an angle of approx. ±45°.
The wavelength λ equals:
ν λ = Wavelength
ν = Frequency
v = Speed of sound Example At a frequency of 200 kHz and a speed of sound in air of approx. 340 m/s, the
following value is obtained in respect of the wavelength
= 1.7 ⋅ 10 −3 m = 1.7 mm
ν 200 ⋅ 10 3 Hz 178 © Festo Didactic GmbH & Co. KG • FP 1110 11. Physical fundamentals 11.3.1 Generation of ultrasound
There are three different methods of generating ultrasound: mechanical, magnetic
and electrical. In this context, mechanical generation of ultrasound is only of minor
importance. Magnetic generation With the help of magnetorestriction, it is possible to generate ultrasound of up to
approx. 50 kHz. Ferromagnetic substances change their length in a magnetic field.
The relative change in length is within a maximum range of 4 · 10-5. -6 x 10 40
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This note was uploaded on 11/01/2012 for the course CHEMICAL 102 taught by Professor Jamesrodriguez during the Spring '12 term at Universidad Politécnica de Cartagena.
- Spring '12