# Beam width!

Discussion in 'Electronic Design' started by Adam, Oct 17, 2006.

Hello,
I have few 40kHz T and R ultrasonic transduces, and don't have any
can anyone let me know how to measure their beam width please?

2. ### Jim ThompsonGuest

If they're like the bunch I have in my junk box... pretty wide. I
used them as motion detectors for an alarm system design, and they
covered a 4' hallway within a few feet away from the transducer.

"Measure"? I don't know :-(

...Jim Thompson

3. ### Rene TschaggelarGuest

Measure ... lets see, if you position both of them in
free space, meaning without refections from anything,
and have them rotateable around 3 axis,
then operating them should give you an idea. Beam
width means where the signal drops off by 3dB.

Rene

4. ### JoergGuest

Basically by CW transmission and then rotating the receiving tranducer
on a circular arch around the transmitter. Ideally you'd want a
professional sound pressure sensor as a receiver but a crystal should do
for a rough overview. Lots of web resources, such as this one:

http://www.ndt.net/article/v05n09/felix/felix.htm

5. ### qrkGuest

You can get a rough idea about the beamwidth of simple circular
transducers with the following equation:

bw = 2*asin(lambda/(2*D))

where lambda = wavelength = c/f
D = diameter of the active face of the transducer

In air at room temp, lambda is appx (345 m/s)/(40kHz) = 0.00863 m =
8.63 mm.

Be sure wavelength and diameter use the same units (e.g. meters,
inches, rods, ...).

If you want a slightly more accurate answer, the "2" in the equation
is closer to 1.9436.

6. ### Rich GriseGuest

Set up a test bench in a soundproofed room - maybe hang blankets on
the walls or something, and ping the TX and move the RX around and
see what you get.

Good Luck!
Rich