user39307: Can we potentially use an ultrasonic sensor to differentiate between objects based on the reflective capacity of the object?
For example to differentiate between metals and biodegradable wastes.

user4143: No. No, you can't. All they sense is the "time of flight".
The closest you would come would be to have a sensor which can detect physical properties of the target.  That could be colour, sound absorption, etc.  You'd need something that sends out a "broad spectrum" signal (white light, white noise, etc) and detects the reflected spectrum (colour sensor, wide-band microphone) and do spectral analysis of it.  The signal would also have to be fairly tightly focussed to exclude signals from the environment.
All-in-all not something for a little Arduino to consider without lots of extra expensive hardware.

39307: <p>Can we potentially use an ultrasonic sensor to differentiate between objects based on the reflective capacity of the object?
For example to differentiate between metals and biodegradable wastes.</p>
 4143: <p>No. No, you can't. All they sense is the "time of flight".</p>

<p>The closest you would come would be to have a sensor which can detect physical properties of the target.  That could be colour, sound absorption, etc.  You'd need something that sends out a "broad spectrum" signal (white light, white noise, etc) and detects the <em>reflected spectrum</em> (colour sensor, wide-band microphone) and do spectral analysis of it.  The signal would also have to be fairly tightly focussed to exclude signals from the environment.</p>

<p>All-in-all not something for a little Arduino to consider without lots of extra expensive hardware.</p>
