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1. yguo
   

   Member
   Joined: Jul '13
   Posts: 3

   Hello,

   Thank you for making this toolbox; it's been a lot of fun exploring the features. I'm only about halfway through the tutorial now, but I figured it couldn't hurt to ask for help on my project.

   I'm attempting to model two single element 3MHz transducers in the shape of flattened domes (think of a circular cutout on the surface of a sphere). They'll be angled towards each other about 30 degrees; I want to see their beam field patterns interact. I'm confident that I can create two sources in that shape and then place them in a 3D grid with a medium simulating soft tissue.

   However, I'm unclear about other aspects. The sources I've tried making so far all emitting omnidirectional. Is there a way I can limit sources to one direction, say using a vector, and have a limited degree of beam divergence? Also, is there a way for me to change the frequency of one source? I've only been able to program 3MHz from every source.

   Any insight into these questions would be very appreciated.

   Thank you kindly.

   Posted 11 years ago #

2. bencox
   

   Developer
   Joined: Mar '10
   Posts: 292

   Hi yguo,

   You can define vector velocity sources, as well as pressure sources, so you can make the transmission directional. You can also apply a different time series to each source point in the grid. This is from the documentation:

   "An initial pressure distribution can be specified by assigning a matrix (the same size as the computational grid) of arbitrary numeric values to source.p0. A time varying pressure source can similarly be specified by assigning a binary matrix (i.e., a matrix of 1's and 0's with the same dimensions as the computational grid) to source.p_mask where the 1's represent the grid points that form part of the source. The time varying input signals are then assigned to source.p. This must be the same length as kgrid.t_array and can be a single time series (in which case it is applied to all source elements), or a matrix of time series following the source elements using MATLAB's standard column-wise linear matrix index ordering. A time varying velocity source can be specified in an analogous fashion, where the source location is specified by source.u_mask, and the time varying input velocity is assigned to source.ux, source.uy, and source.uz."

   You change the frequency of the source by changing the time series allocated to source.p, source.ux, etc. See for example this example. In fact, you're not even restricted to a single frequency, you can use any arbitrary time series you like.

   Good luck with your simulations!

   Ben

   Posted 11 years ago #

3. yguo
   

   Member
   Joined: Jul '13
   Posts: 3

   Hi Ben,

   Thanks for your response! I will give vector velocity sources a try. I'm still a bit confused about the method for time series. In the example you post, all source points in the source mask are set to a time varying input of 250kHz.

   I've defined a binary source mask that places two parallel lines on the grid. If I'm understanding correctly, in order to have one line's source input be a different frequency from the other line, I need to:
   - figure out the indexing of my two lines in source.p, based on MATLAB's column-wise indexing
   - create a matrix of time series for source.p that corresponds to the source point indexing

   Is this the right idea?

   Posted 11 years ago #

4. yguo
   

   Member
   Joined: Jul '13
   Posts: 3

   Wait, I think I did it! Just took some playing around. Thanks again!

   Posted 11 years ago #

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