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G.H) Sonar

The task I set myself was to develop a simple sonar that could run from the 12V supply that is found on a boat and with a 'decent' range. I already have a fishfinder but like a challenge.

The first element is a transducer. The transducer selected operates at 28 KHz and is rated at 60 W. Two piezo-electric elements drive the transducer body that focuses the sound through the face. It's intended uses include ultrasonic cleaning of jewellry, etc.,

Give it a tap and it it bounces around at (more-or-less) the stated resonant frequency of 28 KHz.

The transducer needs high voltages (c. 140V) in order to get sufficient power through it.



The smart money says to use a trifiliar coil to couple the signal exciting the transducer, the transducer and the receiver. 
This configuration:
  • Electrically separates the functions
  • Allows the impedance of the circuits to be designed for a high Q factor
  • Allows voltages to be stepped-up / down as required.
  • Diodes across the receiver coil short out any voltages greater than 0.7 V.
I couldn't get good results to went back to the drawing board...