A focused ultrasound beam in water carries an acoustic power and is fully absorbed by…

PHYSICS · Multi-part · Fermi University Physics · Oscillations, Waves & Acoustics · Fluids & Continuum Physics · Waves, acoustics and compressible flow

Signal Speeds in Fluids, Ch Sound in a moving, absorbing fluid: sources, refraction and loss

Problem

A focused ultrasound beam in water carries an acoustic power

P=3\,\mathrm{W}

and is fully absorbed by a target. Take

c_0=1482\,\mathrm{m\,s^{-1}}

for water. ((a)) Find the radiation force on the target. ((b)) A second beam, at

1\,\mathrm{MHz}

and intensity

I=2\,\mathrm{W\,cm^{-2}}

, passes through water whose absorption coefficient at that frequency is

\alpha=0.025\,\mathrm{Np\,m^{-1}}

. Find the mean force per unit volume that this beam leaves in the water it crosses.

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