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 in 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 $\mu$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 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 indicates two different differences in the propagation  patterns. At low energy, first central  displacements are negative directed outside the medium  and we distinguish three half cycles. At high energy, first displacements are positive directed inside the medium  and only two half cycles are distinguished, with a larger wavelength. can be distinguished.