Pol Grasland-Mongrain edited Exp results.tex  over 8 years ago

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The resulting displacement amplitude maps along Z axis 1.0, 1.5, 2.0, 2.5 and 3.0 ms after laser emission towards the phantom are illustrated in Figure \ref{Figure2}, for two laser beam energies (10 and 200 mJ). Displacements reached an amplitude of 0.02 $\mu$m for the 10 mJ laser beam and 2.5 $\mu$m for the 200 mJ. They propagated at a velocity of 5.5$\pm$0.5 m.s$^{-1}$, which is a typical value for shear wave, and far lower than usual compression wave velocity, about 1500 m.s$^{-1}$ in soft tissues. Supposing the medium density $\rho$ of 1000 kg.m$^{-3}$, it corresponds to a shear modulus of 30$\pm$5 kPa, which is in range of the expected value of the phantom. Shear wave frequency was equal to 500 $\pm$ 50 Hz.  A careful observation reveals differences in the propagation patterns. At low energy, first (central) displacements are directed outside the medium and we distinguish observe  three half cycles. At high energy, first displacements are directed inside the medium and only two half cycles can be distinguished. observed.