Subject:
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Re: Ultrasonic sensor interactions
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Newsgroups:
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lugnet.robotics
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Date:
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Sun, 21 May 2006 14:40:15 GMT
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Original-From:
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steve <sjbaker1@airmail.=nospam=net>
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Viewed:
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2578 times
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John Barnes wrote:
> In lugnet.robotics, steve <sjbaker1@airmail.net> wrote:
>
> > Ultrasound travels at about 350 meters per second. If it's
> > detectable range is (say) 3.5 meters then we only need (theoretically)
> > 1/50th of a second to emit a ping and get the echo back at
> > maximum range. The actual duration of the ultrasound ping should
> > be very short - the sound frequency should be up in the 100kHz to
> > MHz range so a very brief pulse is enough.
>
>
> The device operates at 40kHz, the transmit and receive piezo devices are only
> resonant at that frequency.
Wow! That's a lot lower than I'd have expected - at that frequency
there is a good risk of harmonics from normal sound interfering with it.
> Even though the measurement period is short (time from transmit to time to
> receive) it is necessary to wait quite a while for the sound pulse to finish
> bouncing around the environment before starting a new measurement cycle.
Right - 350 meters per second is pretty slow by computer standards.
> The actual quality of the received signal is such that it is difficult to do
> more than measure the time to the earliest received pulse. After the arrival of
> this pulse, which has taken the most direct route to the nearest surface within
> its "beam" width, further echos will continue to arrive for quite a while, often
> with intensities higher than the first pulse because they are coming back from
> more highly ultrasound reflective surfaces.
(Not to mention things like concave right-angled corners - which make
excellent ultrasound reflectors - but which 'smear out' the signal.)
> It would thus be hard to emit an "id" string of pulses and do any kind of pulse
> compression (by correlation techniques as radar does) to avoid interference or
> even to detect it.
We're doomed.
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Message is in Reply To:
 | | Re: Ultrasonic sensor interactions
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| (...) The device operates at 40kHz, the transmit and receive piezo devices are only resonant at that frequency. Even though the measurement period is short (time from transmit to time to receive) it is necessary to wait quite a while for the sound (...) (18 years ago, 21-May-06, to lugnet.robotics)
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