tx pulse drive ideas

[bklein]

I was going to put this in the previous thread but it may be too distracting from the central subject of damping so I'll put it here...
I suggested momentarily shorting the coil after the pulse in a previous thread and got no reply so I thought I was a *******. Well, maybe I still am - but what about another idea:
What if we were to do a coil phase reversal (H bridge configuration) instead of just a short? I would think this would be the ultimate "kick the target" mode. You'd have design challenges and a lot of interesting tweaking to do but might be worth it?

Two related questions:
1) do you get the same "kick the target" effect at the beginning of the TX pulse? So if you had a "RX" coil it too would get the TX pulse but you could then sense the target response while the TX is held on? Design difficulties for sure but just curious.
2) what if you split the coil into two sections. Drive both as parallel TX coils, then release and reconfigure as series RX coils. As inductance is halved, capacitance halved, decay time quickened... right? (Maybe you can't do this quickly enough to be worthwhile...)

[mikebg]

Barry,
The realisation of your idea is described in this forum:
http://www.geotech1.com/forums/showp...65&postcount=2
http://www.geotech1.com/forums/showp...63&postcount=6

[Carl-NC]

Two related questions:
1) do you get the same "kick the target" effect at the beginning of the TX pulse? So if you had a "RX" coil it too would get the TX pulse but you could then sense the target response while the TX is held on? Design difficulties for sure but just curious.
2) what if you split the coil into two sections. Drive both as parallel TX coils, then release and reconfigure as series RX coils. As inductance is halved, capacitance halved, decay time quickened... right? (Maybe you can't do this quickly enough to be worthwhile...)

1) If the turn-on has the same di/dt as the turn-off, then yes. Most PI designs have a lazy turn-on, so the target kick is much smaller. An H-bridge design doesn't fix the the turn-on speed problem, it only allows you to do bipolar pulsing (which has other advantages).

2) I think this was in a patent, either by Carl V Nelson or Allen Westerstein. Personally, I would just use a separate RX coil.