I have a very strange error. My ultrasonic sensor, when both speakers are sticking out of my case, doesn't work at all. It's a black case. It gives very "near" readings. But it does work when outside. Why could this be an issue?
Electronic – arduino – Ultrasonic sensor doesn’t work inside case
arduinorange-detectorsensorultrasound
Related Solutions
I have found an omni-drectional transmitter/receiver.
http://www.metrolog.net/transdutores/piezofilm/ultra40k.php?lang=en
More info and approximate pricing can be found on page 22 of this pdf: http://physics.ucsd.edu/neurophysics/Manuals/Measurement%20Specialities,%20Inc/Piezo%20Film%20Sensors%20Product%20Guide%20and%20Price%20List.pdf
There may be other/better sensors too, so I will wait a while to mark this as the answer.
The sensitivity of ultrasonic transducers does vary over frequency. The following example is from a Kobitone 255-400PT16-ROX datasheet. It would also be fair to assume it would fall further outside the normal operating frequencies that are shown below.
However in my opinion using it do determine distance isn't likely to be a good solution. When operating outside normal ranges you may find differences in performance between parts but for experimental / hobbyist purposes I see no harm in trying it as a simple solution.
Another way you could go about it is to change the amplitude of the signal at the ultrasonic emitter end and encode it with a digital signal that indicates the transmission level used. That does get quite a bit more complex though. If you wanted to take a look at going that way perhaps the VirtualWire project would be worth a look at for encoding and decoding the digital signal.
Best Answer
It is likely that the transducer and receiver are being coupled together by the enclosure, so that the signal being received first is the vibration through the enclosure rather than an external object. I would recommend enlarging the holes so they are not in physical contact with the enclosure.
You may also be getting similar problems if the board is secured very rigidly to the base of the enclosure, in that case maybe consider using some o-rings between the mounting hardware and the enclosure. But try step 1 first if the holes are tight fitting.