Forums

Ultrasound beamforming

Started by Unknown February 16, 2019
dbd  <d.dalrymple@sbcglobal.net> wrote:

>On Tuesday, March 5, 2019 at 7:51:47 AM UTC-8, mako...@yahoo.com wrote: > >> I agree with your statement, but >> >> I think the beam created by this "time domain method" will still vary >as a function of frequency? >> >> Because delay lines create a phase shift that varies with frequency. >> >> Because it is phase shift (not time delay) that controls the beam >> >> Am I wrong? > >Yes. > >> >> m > >In the broadband time delay beamformer, the delays set the beam pointing >angles, which are constant in frequency. The beam widths will vary with >frequency as the effective size of the array, in wavelengths, changes >with frequency.
I am thinking that a yagi antenna is a narrowband beamformer whereas a log periodic antenna is broadband, and their must be equivalents in DSP. Steve
On Tuesday, March 5, 2019 at 9:51:48 PM UTC-5, Steve Pope wrote:
> dbd <d.dalrymple@sbcglobal.net> wrote: > > >On Tuesday, March 5, 2019 at 7:51:47 AM UTC-8, mako...@yahoo.com wrote: > > > >> I agree with your statement, but > >> > >> I think the beam created by this "time domain method" will still vary > >as a function of frequency? > >> > >> Because delay lines create a phase shift that varies with frequency. > >> > >> Because it is phase shift (not time delay) that controls the beam > >> > >> Am I wrong? > > > >Yes. > > > >> > >> m > > > >In the broadband time delay beamformer, the delays set the beam pointing > >angles, which are constant in frequency. The beam widths will vary with > >frequency as the effective size of the array, in wavelengths, changes > >with frequency. > > I am thinking that a yagi antenna is a narrowband beamformer whereas > a log periodic antenna is broadband, and their must be equivalents > in DSP. > > Steve
OK I get it now. The geometry of the array creates signals that are offset in TIME, not offset in PHASE as I was thinking. Therefore to get the signals to add constructively over a wide range of frequencies, "all you need to do" is use time delays to time align the multiple signals and they will remain time aligned over a range of frequencies. I was so accustomed to thinking in terms of phase that I was incorrectly thinking that the array created signals that are shifted by a given amount of phase. This is false. They are shifted by a given amount of time, so all it takes is time delays to get the signals back in alignment. Thank you all for the discussion. Mark