Beam width!

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

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

Hello Adam,

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:

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 =

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.

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