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Unformatted text preview: the range of an ultrasonic sensor. Physical law With the propagation of sound in air, the sound pressure amplitude decreases
exponentially with the distance
∧ ∧ p = p0 ⋅ e −αd
∧ p= Peak value of the sinusoidal sound pressure wave on the output of the
emitter (d = 0) ∧ p 0 = Peak value of sound pressure wave at distance d from emitter (assuming that the sound ray does not diverge)
Attenuation coefficient (Unit m-1) α= Correspondingly, the following applies in respect of accoustic power:
P = P0 ⋅ e −2αd = P0 ⋅ e − α'd This formulation is often used with 2α = α' representing the attenuation coefficient. Logarithmic
attenuation ratio Instead of the (linear) attenuation coefficient α or α', a logarithmic attenuation ratio
αL is also used, which on examination of the sound pressure amplitude is defined by
∧ ∧ p = p 0 ⋅ 10 − αL d
20 or on examination of the accoustic power by the relation P = P0 ⋅ 10 − α'L d
10 with α’L = 2α αL or α'L are indicated in dB/m (1 dB = 1 decibel). 182 © Festo Didactic Gm...
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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