h a l f b a k e r yThe leaning tower of Piezo
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A recently bought a bat detector, which makes the chirrups of bats
audible by modulating them against another high frequency.
It is, of course, effective at detecting bats. But it also opens up a
whole new ultrasonic world. A quartz watch whistles, a mechanical
watch becomes a rhythm-and-bell
orchestra, and a walk in the woods
becomes a cacophony of crushed leaves and previously unheard
animalogenic noises.
Most mobile telephones and many other gadgets have microphones
which will pick up ultrasonics quite well. I suggest an app for such
devices, to translate ultrasonics into the audio range, opening up a an
entirely new (if largely useless) world to, ah, the world.
Bat Detector Kits
http://www.google.c...urce=og&sa=N&tab=wi
Many available. [csea, Aug 19 2010]
http://en.wikipedia...ki/Beat_(acoustics)
[hippo, Aug 19 2010]
Frequency of Bat Sonar
http://hypertextboo...98/JuanCancel.shtml
[Wrongfellow, Aug 19 2010]
[link]
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It would take a bit more than just software. Maybe the microphone can reproduce ultrasonic frequencies, but the A-to-D converter it's attached to probably cuts off somewhere around 16kHz at best. |
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That said, a hearing aid which could do this would be a very interesting device. I'd certainly enjoy having a play with one. |
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I'm sure there's ultrasonic A/D's which you could use in digitally dropping stuff down a few octaves... might be ultrasonic microphones available. |
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I'm not sure how you're going to "modulate it against another HF sound" though. |
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Certainly there are - but I bet they aren't fitted as standard in mobile phones. |
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The fastest A-to-D converter I ever got to play with sampled at 40MHz. That's more than enough to reproduce a bat's sonar. It wouldn't have run for long from a phone battery though. |
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As for the modulation bit, that's easily done in software. It could be as simple as inverting the sign of every second block of N samples, followed by a simple low-pass filter. Something like a Nexus One has plenty of CPU grunt to do this kind of DSP in real time. |
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not useless in any way! Pair with a speaker and
another mic for ultrasonic sonar to see in the dark! |
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//Most mobile telephones and many other gadgets have microphones which will pick up ultrasonics quite well.// |
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I strongly doubt this. Please provide reference. Most mobile phones use electret elements with FET impedance converters, and response drops off rapidly over 16-20 kHz. |
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I have also used an ultrasonic hetrodyne "bat detector," based on a cheap piezo transducer and a CMOS 20xx quad inverter biased for use as oscillator/ mixer / amplifier. |
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//but I've not heard anything that indicates they can//
Maybe the frequency was too high for you. |
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[Useless segway] What gets me is that I can hear bats. Click click as they fly around. I've told people and generally I get funny looks, but I can hear (at least part of) the sonar used by several bat species from where I live. [/UW] |
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...Anyhoo, can the ultrasonic transducers used for thickness testing and the like be used? How about the ultrasonic transducers used for stockpile height or feedbin/hopper level? Or maybe depth sounder/fish finder transducers? I suppose I just want this to work, sounds fun... |
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//Useless segway// - (sp. "segue", unless you're suggesting that Dean Kamen's transportation device is useless, which would be right)
I'm wondering if you'd be able to hear ultrasonic sound by playing a similar frequency sound and listening for the 'beats' between the two frequencies (see link) - e.g. if there's an ultrasonic sound at 25kHz, could I play a 20kHz tone and hear 'beats' at 5kHz? I think probably not, as the beat frequency is that of the modulated volume and you still wouldn't be able to hear the underlying frequencies, but I'm not sure. |
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You need some kind of non-linearity for heterodyning to work. Normal air is too linear, at least at normal amplitudes. |
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It's quite possible that [Custardguts] can hear bats, if he's got decent hearing. The low end of their frequency range overlaps with the high end of ours (link). |
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//Bone until you can cite a reliable source for your
technology claims.// |
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Point taken, alas. I hereby bone myself. However, I
should point out that bats, at least, are bloody loud at 15-
30kHz, so a cellphone mike would probably pick up
enough. |
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//Click click as they fly around. I've told people and
generally I get funny looks//
A lot depends on the species of bat and what it's doing.
Most people pre-middle-age can hear at least some of the
noise made by many bat species. But what you can hear is
only a teeny fraction of what they're saying. |
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//long-term stability and ultra-flat response needed for a
measurement microphone// |
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Yes, but those in phones are typically only flat up to about
20kHz at the top end. The guy who posted this idea is an
idiot. |
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