k-Wave

1. acosse
   

   Member
   Joined: May '12
   Posts: 1

   Hi there,

   I would like to use the beam steering option when defining the transducer and I have questions concerning transmission and reception delays.

   I first had problems when using negative delays for received signals. When steering the beam at 45°, a 0-delay was set to the central element. Left and right elements got positive and negative delays -(pitch x n x sin(theta))/speed and (pitch x n x sin(theta))/speed respectively. But the function "kWaveTransducer" didn't seem to like negative delays so I slightly changed it. It seems to work now.

   To check the transmitted signals delays, I set the steering angle at 45° and took the sensor_data as it was, without adding zeros to the sensor_data signals. In order to do this, I commented out the inside of the "scan_line" function in file kWaveTransducer.m, line 633). And here arose my problem: When I ploted the signals from each one of my transducer's elements using the "stackedPlot" function, it seemed that my transmitted signals hadn't been delayed... the input tone burst was at the same position in every recorded signals from every transducer element

   I used the transducer as source and sensor. My question is thus the following: Are the transmitted tone bursts delayed when using a steered beam in k-wave ?

   Thanks in advance,

   Posted 12 years ago #

2. Bradley Treeby
   

   Developer
   Joined: Mar '10
   Posts: 1,643

   Hi acosse,

   Thanks for your post and for pointing out the problem with using a transducer as a sensor with a non-zero steering angle. The fix (which you may have already implemented) is to replace the offset code (around line 641) with:

   % offset the received sensor_data by the beamforming delays and
   % apply receive apodization
   for element_index = 1:obj.number_active_elements
      if delays(element_index) > 0
         sensor_data(element_index, :) = apodization(element_index).*[sensor_data(element_index, 1 + delays(element_index):end), zeros(1, delays(element_index))];
      elseif delays(element_index) < 0
         sensor_data(element_index, :) = apodization(element_index).*[zeros(1, -delays(element_index)), sensor_data(element_index, 1:end + delays(element_index))];
      end
   end

   I'm not sure I follow your second problem. If you try the Simulating Ultrasound Beam Patterns Example and change the steering angle, does it do what you expect?

   When using a the kWaveTransducer class, only a single tone burst is used to save memory, but it is delayed automatically within kspaceFirstOrder3D based on the steering angle and focus distance settings.

   Brad.

   Posted 12 years ago #

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