Hey peoples. I'm building a robot based around arduino and it needs to detect 25kHz and 30kHz tones (seperately). Where on earth (preferably australia) can I get a microphone that will cover those frequencies? Ultrasonic transducers seem to drop off in the mid 30kHz region (or are rangefinders) and regular mics only go up to 15kHz or so.
Any advice? Should I be cannibalizing a range finder or something?
Could be tricky - rangefinder transducers are designed to resonate strongly, and don't operate well away from their designed frequencies (for good reason).
You could try and see if Murata do transducers in these ranges.
What are you building? An automatic bat hunter? 
Hmm it makes sense that rangefinders won't help much.
From what I can see the ones on murara only go down to 40kHz, so that is probably not going to help much.
I'm building a robot for a uni group project - it drops marbles in target areas and uses infrared morse code an ultrasound signals to know which marbles to drop. Fortunately, it only has to detect if ultrasound is present in the chosen frequencies or not.
I might try asking around at uni and see what I can find out.
Have you try a google?
It returns a bunch on " ultrasound microphone", 110 kHz is o'k?
http://www.avisoft.com/usg/microphones.htm
If they cost a lot, I'd look at speakers/tweeters , just design low input impedance amplifier
If you can find what they are using to TRANSMIT 25kHz and 30kHz ultrasound tones, then you can use that. An ultrasound transmitter element works just fine as a receiver too.
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The Gadget Shield: accelerometer, RGB LED, IR transmit/receive, speaker, microphone, light sensor, potentiometer, pushbuttons
Magician I don't think 110kHz will help as it's way outside the range I'm looking at, and yes I have tried google.
RuggetCircuits, you make an excellent point. I'll go in and ask them tomorrow. Thanks guys.
Relative flatness of the frequency response poor poor poor good poor
Frequency range [kHz] 10-120 10-110 10-150 10-250 10-150
Relative sensitivity at 50 kHz medium high medium high high
If you spend couple second on a page-link above, you 'd see three parameters in specification:
flatness, freq. range and sensitivity. Range itself tell you practically nothing, w/o others two.
It just show, that in order to have high sensitivity on 50 kHz, range must goes up to 110 for this type of microphones.
Righto, thanks Magician. I'll check it out.
I also got sent a link from my lecturer with a place that does sell stuff in the relevant range: http://au.element14.com/jsp/search/browse.jsp?N=203546
They are also going to have an alternative option to use regular sound if we want, since several groups have had trouble with this.
Thanks everyone for your help. Case closed 