deletions | additions       diff --git a/Material_methods.tex b/Material_methods.tex  index 14ee196..f09950a 100644  --- a/Material_methods.tex  +++ b/Material_methods.tex 
...
The magnetic field was induced by a 5x5x5 cm$^3$ N48 NdFeB magnet (model BY0Y0Y0, K\&J Magnetics, Pipersville, PA, USA). The magnet was placed 1 cm away from the medium, without any contact, and fixed to a second independent support. In the medium location, the magnetic field intensity ranged from 50 to 150 mT, as measured by a gaussmeter (Model GM2, AlphaLab, Salt Lake City, UT, USA).   Main tested sample was a 4x8x8 cm$^3$ water-based tissue-mimicking phantom made with 5\% polyvinyl alcohol (PVA), 0.1 \% graphite powder and 5\% salt, giving an electrical conductivity of 7 7.5  S.m$^{-1}$. Three freezing/thawing cycles were applied to stiffen the material \cite{fromageau2007estimation}. The graphite powder (\#282863 product, Sigma-Aldrich, Saint-Louis, MO, USA) was made of submillimeter particles, which presented a speckle pattern on ultrasound images. The sample was placed in a rigid plastic box of 2 mm thick layers with an opening on a side to introduce the ultrasound probe. The rigid box simulated a solid interface such as a skull and ensure also that any observed movement was not due to surrounding displacement of air. Alternatively, we used a similar phantom made of 5\% PVA, 0.1 \% graphite powder and 0.9\% 2\%  salt, giving an electrical conductivity of 1.8 3.5  S.m$^{-1}$. A biological tissue sample was also tested. This tissue was a chicken breast sample bought in local grocery of approximately 3x5x5 cm$^3$. It was degassed in a 20$^o$C saline water (0.9 \% NaCl) during two hours prior to the experiment. Each sample was observed with a 5 MHz ultrasonic probe made of 128 elements (ATL L7-4, Philips, Amsterdam, Netherlands) coupled to a Verasonics scanner (Verasonics V-1, Redmond, WA, USA). The probe was in contact with the sample with an ultrasound coupling gel but was fixed on a third independent support. It was used in ultrafast mode \cite{bercoff2004supersonic}, to acquire 1000 frames per second using plane waves and Stolt's fk migration algorithm \cite{garcia2013stolt}. The Z component of the displacement in the sample was observed by performing cross-correlations between radiofrequency images with a speckle-tracking technique \cite{montagnon2012real}. Noise was partly reduced using a low-pass frequency filter. Time $t$ = 0 ms was defined as the electrical burst emission.