k-Wave

1. Farnaz
   

   Member
   Joined: Oct '18
   Posts: 20

   Hi,

   In the Steering linear angle example the delay is applied through the toneBurst function as offset but my problem is slightly different and I am wondering whether there are other functions to apply delays. (I have 2D simulation so I can't use transducer class)
   I am using source.u with a ricker wavelet. I have a 2D linear transducer with 4 grid points for each element and 4 grid point for kerf. How do I apply delays for different angles in this scenario?

   % =========================================================================
   % Define Source
   % =========================================================================
   kerf = 4;
   groupspacing = 4;
   element_num = 128;
   source_shape = reshape((1:kerf)' + (0:element_num-1)*(kerf+groupspacing), 1, []);

   % % define source mask for a linear transducer with an odd number of elements
   num_elements = element_num*groupspacing ;
   x_offset = 1; % [grid points]
   source.u_mask = zeros(Nx, Ny);
   source.u_mask(x_offset , source_shape ) = 1 ;

   %activate middle elements
   active_elements = element_num/2 ;
   sensor_offset_mask = groupspacing*element_num/4+kerf*(element_num/4)-1 ;
   source.u_mask(x_offset , 1:sensor_offset_mask) = 0 ;
   source.u_mask(x_offset , Ny-sensor_offset_mask:Ny)=0 ;

   % define the properties of the tone burst used to drive the transducer
   sampling_freq = 1/kgrid.dt; % [Hz]
   steering_angle = 0; % [deg]
   element_spacing = dx; % [m]
   tone_burst_freq = 5e6; % [Hz]

   source.ux = ricker(tone_burst_freq,120, kgrid.dt) ;

   Thanks in advance,

   Posted 5 years ago #

2. Bradley Treeby
   

   Developer
   Joined: Mar '10
   Posts: 1,643

   Hi Farnaz,

   I'm not familiar with the ricker function, but essentially, you need to add the appropriate time offset to the signal for each element (group of four grid points).

   One simple way would be to create the time signal with a lot of trailing zeros, then replicate this to match the total number of grid points in your source with repmat. Finally, for each time signal, use circshift to add the appropriate amount of zeros to the beginning to give the desired time offset (in discrete steps of kgrid.dt).

   If using discrete time delays is a problem, you could also use the equation of the ricker wavelet and sample it with the appropriate offsets.

   Brad.

   Posted 5 years ago #

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