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How can I limit the ringing time and amplitude of an ultrasonic receiver that has just been hit by an incoming wave? [Note - just adding a resistor in parallel does not work well]. Any known techniques?

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  • \$\begingroup\$ You may need to change its mechanical properties to reduce its Q : down in the audio frequency range, a thin coat of rubbery "dope" on a transmitter diaphragm is sometimes used... for a microphone, sometimes damping behind the diaphragm is possible. \$\endgroup\$ – Brian Drummond Jan 30 '14 at 12:03
  • \$\begingroup\$ Are you talking about the bare transducer or a complete electronic module of some sort? In any case, the high Q is an important factor in both the sensitivity and selectivity of the system. Why is this bad in your application? \$\endgroup\$ – Dave Tweed Jan 30 '14 at 12:16
  • \$\begingroup\$ Assuming you're doing some sort of sonar operation, I've had to change the type of transducer to one with a lower 'Q' in order to detect response to an object that is nearby. \$\endgroup\$ – Spehro Pefhany Jan 30 '14 at 12:30
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    \$\begingroup\$ Is a "wave" a large wet ocean resident thing that slaps your sensor about the ears while you are trying to monitor a return from elsewhere OR a signal? Answers will vary radically between the two. If it's a signal then you need to say more about what you are doing overall. \$\endgroup\$ – Russell McMahon Jan 30 '14 at 12:58
  • \$\begingroup\$ Air, 200kHz, bare transducer. I send it n cycles of sine wave, and want to receive n cycles and then kill the ringing as fast as possible after that. Using it off resonance does not work, because as soon as the sound stops driving it it will return to ringing at its resonant frequency. I need something to absorb the mechanical energy. Thinking maybe some kind of LRC in series/parallel \$\endgroup\$ – user32885 Jan 30 '14 at 13:50
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In a project some years ago I had this problem (it was a sonar ranging device intended for close quarters- to detect the approach of an irregular heap of material in an unfriendly environment). As background- the problem is that the transmit pulse of a sonar is enormous compared to the return pulse, and if the receive transducer is still ringing from the transmit pulse, you won't be able to reliably detect the return pulse, so objects close to the transducer might not be detectable.

The coupling of acoustic energy to the output is weak enough that passive damping was simply not possible- even shorting the transducer for a period during the transmit had little effect. I had to pick a transducer that had a lower 'Q' so that the ringing died out more quickly.

Downside to that is that the return signal level is lower, and there is more noise from frequencies that the transducer is not (mechanically) tuned to.

You might be able to modify the transducer by adding mechanical damping in the form of a energy-absorbing material as Brian Drummond suggested.

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The sharpness of the passband of the transducer, its Q, and how long it "rings" are directly related. Any one of these tells you the others without having to know anything about how the transducer actually works.

You therefore need a lower Q receiver. Many receivers are deliberately tuned to a narrow band to reduce noise. Often this is desirable, but it also leads to longer ringing. In your case you want a lower Q receiver. Look around. Talk to the manufacturer of the one you are using as a start. But, be prepared for the additional off-frequency noise such a receiver will pick up, and reduced sensitivity at your frequency. Basically, you are looking more for a microphone that works at ultrasonic frequencies than a ultrasound receiver tuned to your specific frequency.

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This is similar to a radio CTCSS tone squelch ringing issue. what is done in a Radio CTCSS transmit circuit is to do one half cycle of Tone that is 180 degrees out of phase from the initial drive signal. this electronically dampens the ringing. In a radio the CTCSS signal is low frequency but the same principle would apply to a high frequency. you may have to experiment with either just 1/2 wave or more to see what works best.

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