cr0sh - I didn't post it because there is nothing to it, 7 ultrasonic transducers in parallel with a 1mH inductor in series. The size of the inductor depends on the capacitance of the particular transducers you ar using. Yee I could spend another precious day writing a better article but no one would look at it. It's easier to answer subsidiary questions when the occur. It would, of course have been a lot easier to post nothing...
jremington - thanks, that's interesting, that unit wasn't available when I was looking (over a year ago). My experience with those kind of devices is that taking a readings is quite slow (they have to modulate the laser beam at several different frequencies and take readings at each) so scanning it around could also be slow.