Re: Ultrasonic sensor interactions

In lugnet.robotics, steve <[email protected]> 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.

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. 

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.

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.

JB