Problems with Generating a Complex Exponential Wave

[imperial-aero]

Hi,

I'm trying to generate waves of the form, p = a*cos(theta)*exp(i*w*t), where t is the time, w is the frequency and theta is just an angle. In my VI (attached),

I used exp(i*w*t) = cos(w*t)+i*sin(w*t) and formed this using the Re/Im to Complex Function. And I used four different values of theta.

However, when I output the values on a graph I only see a straight line, rather than  time-varying sinusoidal waveforms. When I output just the exponential part (without multiplying by different values of theta) I do get a sinusoidally varying waveform. Also, I only get a single line on the graph, even though I'm expecting to obtain four different waveforms corresponding to the four different theta values I used.  I suspect that it's something to do with building arrays, but can't quite figure out why.

Thanks for the help.

Ruf.

[MikeS81]

Hi imperial-aero,

the problem in your code is the way how you multiply the two arrays (400 Elements and 4 Elements). To get what you want, you have to use a For Loop. See the attached picture. With your multiplikation you get only four values in your result array.

Hope it helps.

Mike

[imperial-aero]

Hey Mike. Thanks for the worked sample. I tried using your method, but i still keep getting a single line, however i do get a sinusoidal wave 🙂

I've tried something different now (please see the attached pic). I basically generated a sine and a cosine wave from the Waveform Generator VI and then followed a similar method to obtain exp(i*w*t). Does the sine waves created by the Waveform Generator have the equation x = a*sin*(w*t)? If it is, then I think I'll get exp(i*w*t).

After multiplying by the four cosine values I'm able to obtain four different waves. However, in the picture as you can see the inputs to the waveform graph has a small red dot on it, which I suppose indicates a mismatch between the data types. Is there a way to fix that? I know in your previous program you converted the number type to double precision.

[MikeS81]

Hi imperial-aero,

try this vi.

Mike

Message Edited by MikeS81 on 02-17-2008 06:43 AM