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Abstract
This Ph.D. dissertation addresses ultrasound transducer modeling for medical
ultrasound imaging and combines the modeling with the ultrasound simulation
program Field II. The project firstly presents two new models for spatial
impulse responses (SIR)s to a rectangular elevation focused transducer
(REFT) and to a convex rectangular elevation focused transducer (CREFT).
These models are solvable on an analog time scale and give exact smooth solutions
to the Rayleigh integral. The REFT model exhibits a root mean square
(RMS) error relative to Field II predictions of 0.41 % at 3400 MHz, and 1.37 %
at 100MHz. The CREFT model exhibits a RMS deviation of 0.01 % relative to
the exact numerical solution on a CREFT transducer. A convex nonelevation
focused, a REFT, and a linear flat transducer are shown to be covered with
the CREFT model as well. Pressure pulses calculated with a onedimensional
transducer model in combination with Field II are calculated on a circular
piezoceramic transducer and a convex 128 element commercial transducer.
The pulses are shown to be predictable within ±2 dB of the amplitude which
is excellent for this modeling. Intensity profiles are shown to be predicted
with a RMS deviation of 5.5 % to 11.0 %. Finite element modeling of piezoceramics
in combination with Field II is addressed and reveals the influence
of restricting the modeling of transducers to the onedimensional case. An
investigation on modeling capacitive micromachined ultrasonic transducers
(CMUT)s with Field II is addressed. It is shown how a single circular CMUT
cell can be well approximated with a simple square transducer encapsulating
the cell, and how this influence the modeling of full array elements. An
optimal cell discretization with Field II’s mathematical elements is addressed
as well. The error in modeling CMUT cells as squares or flat circular plates
instead of curved circular cells is also addressed.
Original language  English 

Place of Publication  Kgs. Lyngby 

Publisher  Technical University of Denmark 
Number of pages  166 
Publication status  Published  2010 
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Projects
 1 Finished

Calibrated modelling of ultrasonic fields using Field II
Bæk, D., Jensen, J. A., Sams, T., Persson, H. W., Stepinski, T. & Willatzen, M.
01/08/2007 → 24/11/2010
Project: PhD