Biomedical Engineering Reference
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Figure 1.7: Geometrical variables used for the calculations of the pressure
distributions P ( r ,θ, t ) for a planar circular transducer of radius a .
Again, ρ is the density of the medium and c is the speed of sound. The impulse
function ζ ( t ) is generally approximated [15] by a Gaussian (Fig. 1.9(a)), which
envelopes the intensity distribution, and is given by:
ζ ( t ) = I ( r ,θ, t ) exp
( t δ ) 2
2 σ
(1.4)
2
where σ is the pulse standard deviation. We consider that the beam is colli-
mated by θ = θ a . In our model only the corresponding interval d θ 0 . 1 is used
that corresponds to the transducer lateral resolution zone (Fig. 1.9(b)). Hence
Figure 1.8:
Transducer pressure distribution.
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