k-Wave

1. zak10000
   

   Member
   Joined: Jan '20
   Posts: 4

   Hi

   I have a question about implementing the FFT reconstruction with a focused detector.

   To obtain better results in the using the FFT reconstruction , the cosine transform is performed by symetrizing the recorded signals around t=0. However in the instance of the focussed detector where the focus acts as a virtual point and there is acoustics sources in the near and far field how would one go about the reconstruction ?

   would the correct method be to split the far field and near field and then apply symmetry around zero seperately, apply the reconstruction and sum the results in the end?

   Thanks
   Zak

   Posted 4 years ago #

2. bencox
   

   Developer
   Joined: Mar '10
   Posts: 292

   Hi Zak,

   The FFT reconstruction algorithm explicitly assume you have a planar array (or a linear array in 2D). The enforced symmetry in time (the cosine transform) is linked to an assumed symmetry in space about the detector plane. This allows the reconstruction to be put into the form of a Fourier transform.

   I'm not sure I follow what you're trying to do with it with a focussed array, but to be able to apply an FFT for the reconstruction you need to work out how to extract the amplitudes and phases of the plane wave components incident on the array. For the planar case that turns out to be straightforward. Could you perhaps project your data onto a plane (using a Rayleigh integral for example) and then use the FFT algorithm?

   Best wishes,
   Ben

   Posted 4 years ago #

3. zak10000
   

   Member
   Joined: Jan '20
   Posts: 4

   Hi Ben

   Thanks for the answer, i was able to find a solution to reconstruct in the far field of the detector by introducing the virtual point time delay in the frequency domain by multiplication with exp(-iwtd)

   Thanks

   Posted 4 years ago #

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