I am not sure if you are replying to my post, but I guess so.
Anyway here goes.
dknguyen said:
Are you sure that they aren't just measuring the beamwidth from different points/distances away from the arpature?
Given that beamwidth is usually quoted in degrees (in my experience) it seems reasonable to do the measurements by rotating the transducer.
There was a thread here some months ago where hydrophone resopnses were produced by moving a metal object in a cartesian coordinate manner wrt the transducer.
Whatever works for you I guess.
dknguyen said:
Because I'm pretty sure the beam width is something mostly dictated by frequency, and the only things that really affect it are the width of the transducer which causes diffraction which makes the signal messier and wider.
My experience of ultrasonic transducers is minimal, but "gut feel" tells me that the physical construction of the transducer will affect the beam pattern.
dknguyen said:
The beamwidth is also not a perfect triangle and is messy with lobes and stuff so depending where you measure it you may get different readings.
I am not sure what you are getting at here, nobody has said that the beam pattern would be a perfect triangle. It is usual for beamwidth to be specified at the "half power points" (-3dB) wrt the peak response of the beam.
If you want to specify the beamwidth at some other response value, it needs to be stated.
dknguyen said:
Have you ever seen a polar coordinate graph of beamwidth measurement?
Yes, frequently. It is normal to present the response of a radio antenna as a polar plot. Always for azimuth and sometimes for elevation.
See the attachment.
I did a plot of an 40khz ultrasonic transducer under less than ideal conditions (transmitter and receiver were attached to a hard bench using Blu-Tac).
Although the measurements were done by rotating the transducer, I have graphed the data in a cartesian manner, mainly because I was not able to batter the Excel Chart Wizard into submission! I did not want to produce a polat plot using may data. (I have never used it to produce a polar plot before).
My results show a 3dB beamwidth of about 40 degrees.
JimB