# Dispersion relation with Matlab

1. Apr 24, 2006

### Beer-monster

I'm studying the phenemenon of band gaps in a experiment, however the stop bands are proving hard to define using just a transmission spectrum dervived from the fft alogrithm.

I've heard that it may be possible to define the band region by plotting the dispersion relation of sound waves the sound waves and looking for regions of anomalous dispersion. Unfortunately I have no idea how to go about this, does anyone have any info on this sort of analysis that could get me started?

Could someone tell me which FT alogorithm I would need to get phase data as I think the fft only give amplitude and requency info?

Oh and one last thing, does anyone know how I can convert a matrix in matlab into one long vector (so that each successive column is kind of added to the end of one large column) I've been trying this for a while but not getting very far.

Thanks

2. May 21, 2006

### abercrombiems02

solved it in 5 mins, enjoy the function!!!!!!! here ya go!

function out = mat2col(A)
[row col] = size(A)

for n = 1:col
out([1+(n-1)*row:n*row],1) = A(:,n);
end

3. May 23, 2006

### dimensionless

Are you treating electrons within a solid as an incident beam of electrons?

If you have a plot of the transmission spectrum, I would think that you could estimate the stop band from that.

I think frequencies below the stop band in a diatomic lattice are acoustical, while frquencies above the stop band are optical.

What are you trying to find the tranmission spectrum of? What are you trying to find the dispersion ralation of? Of what are you trying to find the phase?