Driving an array or Piezo sounders

[sirch]

I have been using the circuit below to drive a 40kHz ultrasonic transducer and it works fine.

However I now want to drive an array of transducers in phase and I was wondering how best to connect them into the circuit. The second diagram below* shows the 4 ways I can think of (there may be others) of connecting them. My hunch is that the series connected ones (A & B) are not necessarily going to be in phase but is it better to have each piezo have its own inductor (D) or just have one for all of them (C)?

The two main requirements are

1. All elements must be in phase
2. Lowest power consumption option is preferable

*the array will actually have 7 transducers but I've only drawn 4 in the example

 

[(*steve*)]

A & B, are essentially equivalent, as are C & D

My gut feeling is that C is probably easier since you can more easily increase your current drive than your voltage drive.

 

[sirch]

I kind of thought they were but wasn't sure if there were any advantages of having an inductor per transducer or just one big inductor, especially wrt keeping them in phase

 

[KrisBlueNZ]

If you want to deliver maximum power to your transducers, make the tuned circuit a series tuned circuit, with the inductor in series with the transducers. This gives the maximum voltage across the transducers. I imagine that multiple transducers would be best connected all in parallel. The inductor probably needs to be fairly close to the value that gives the right resonant frequency for the L-C circuit when calculated with the combined transducer capacitance. For maximum power, drive the series tuned circuit from an H-bridge. Make sure the transducer can withstand the power and the peak voltage!

Edit: Oops, I didn't read your first post properly. I was assuming you were aiming for maximum delivered power. Are you aiming for lowest power consumption, or best efficiency? Because they're not the same thing. I think trial and error is the answer.

 

[sirch]

Thanks, I suppose best efficiency given that a single transducer provides more than enough output. The objective of using an array is to provide beamforming to get a narrow beam rather than more power. Hence having them all in phase is important or the peak signal won't be on the bore-sight of the array.

The intention is to drive this from batteries so efficiency is important.

I may give a series LC circuit a go when I get time...