k-Wave

1. K_J_Francis
   

   Member
   Joined: Oct '19
   Posts: 1

   Hi

   What is the best way to model the directivity of a linear transducer array using k-Wave? We are trying to simulate a 128 element, 7MHz transducer. The goal is to mimic directivity as close as possible to the measured one. As per k-Wave examples, there are two ways (i) using spatial averaging and (ii) by modifying sensor.directivity_angle.

   We are performing 2D simulations and to be more realistic, we considered the second option of assigning directivity angle to each sensor point. How should we assign the sensor.directivity_angle matrix? We thought of the following implementations and we would like to know how to make it more realistic?

   (i) Assume that there are 5 sensor points in a transducer element. Should we assign [-θ2 -θ1 0 θ1 θ2], corresponding to 5 sensor points of an element and repeat it for all 128 elements to obtain sensor.directivity_angle? θi are equispaced angles within the opening angle of the single element.

   (ii) Consider the whole transducer array and assigning equispaced angles as in the k-Wave example.
   dir_angles = (-1:1/15:1).' * pi/2;
   sensor.directivity_angle = zeros(Nx, Ny);
   sensor.directivity_angle(sensor.mask == 1) = dir_angles;
   In this case, how to change it to the directivity of the transducer, considering each element has an opening angle and transducer has the combined effect?

   (iii) Simply make all sensor element forward-looking (sensor.directivity_angle(sensor.mask == 1) = 0) and spatial averaging of sensor points within an element. Is this an option?

   Is there a better way to implement the same?

   Thank you,
   Francis

   Posted 4 years ago #

2. bencox
   

   Developer
   Joined: Mar '10
   Posts: 285

   Hi Francis,

   If you have a single point detector (a single 1 in a binary mask) then it will be equally sensitive to waves arriving at it (passing over it) from all directions. You can endow it with a directional sensitivity by defining the direction in which it will be most sensitive to (by giving a single value to sensor.directivity_angle. The directional pattern (the sensitivity at the other angles) can be either set to sensor.directivity_pattern = 'gradient', which gives a cosine dependence or sensor.directivity_pattern = 'pressure' which gives the kind of dependence you would get from spatial averaging (hence this also requires sensor.directivity_size to be set, as that is the averaging area that would give the same directional response). Of course, you could just do the spatial averaging by hand yourself but I wouldn't do that by setting the angle to 0 but by not setting any directivity at all, ie. average the measurements from a set of omnidirectional point detectors.

   You might also want to look at the Transducer class. See the 'Defining An Ultrasound Transducer' Example.

   Hope that helps!

   Best wishes,
   Ben

   Posted 4 years ago #

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