High amplitude ultrasound pulse generation using time-reversal through a multiple scattering medium

Abstract : In histotripsy, soft tissues can be fragmented using very high pressure ultrasound pulses. Using time-reversal cavity is a way to generate high pressure pulses with a limited number of acoustic sources. The principle was already demonstrated by Montaldo et al. using a solid metal cavity, but low transmission coefficient was obtained due to the strong impedance mismatch at the metal/water interface. We propose here to use a waveguide filled with water containing a 2D multiple-scattering medium made of steel rods (diameter 0.8mm) positioned randomly with controlled density and width. Numerical simulations and experiments performed with a linear probe (1.5MHz) exhibited an amplification of the focal pressure and an enlarged directivity. The optimal density and width of the multiple-scattering medium has been consistently determined both numerically and experimentally. This optimum results from a tradeoff between the gain provided by multiple paths and the losses. The signals recorded by the linear array (total duration of 1.2ms) were time-reversed. After reemission, the beam focused back at the initial location with a gain x12 in amplitude and improved beam steering capabilities. Such a device could become a potential alternative to expensive high power phased arrays.
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Bastien Arnal, Mathieu Pernot, Mathias Fink, Mickaël Tanter. High amplitude ultrasound pulse generation using time-reversal through a multiple scattering medium. Acoustics 2012, Apr 2012, Nantes, France. ⟨hal-00810843⟩

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