Ultrasonic Transmitter's type of applied voltage

[HighTechPower]

Hi. I'm using an ultrasonic transmitter. Please attached here find it's datasheet. I'm confused if it will operate from DC 5 V or from square wave 40 KHz, 5 V pulses? Also can I operate it at 25 KHz by just giving 25 KHz, 5 V pulses?

 

[betwixt]

It has no electronic parts inside so it will work on a lower voltage with less output. Think of it as a tiny loudspeaker but mounted inside a resonant chamber. It you drive it at any frequency other than 40KHz it will work but at very much reduced efficiency.


Brian.

 

[FvM]

These transducers are built with a resonant piezo disc with high Q and small bandwidth. They produce no useable sound level outside the resonance frequency.

--- Updated Feb 11, 2021 ---

Transcucers from major manufacturers, e.g. Murata come with detailed datasheets that include a sensitivity curve.

 

[Audioguru]

The 40khz piezo transducer must be driven by a 40kHz power oscillator, not from DC. Since it resonates at 40kHz then it cannot be used at 25kHz.
For 25khz you should use a 25kHz piezo transducer.

 

[BradtheRad]

A thought experiment about the effect of pulsed DC versus true AC...

I imagine that bipolar AC provides definite force to both halves of the cycle, both forward and return strokes. Thus greater power.

Pulsed DC gives no force during 1/2 of the cycle. Instead the return stroke depends on springiness inherent in the device. Less power.

 

[betwixt]

That is correct Brad but as with any diaphragm transducer there is some overshoot as the voltage is removed and it relaxes so it wouldn't be exactly half power. The very high 'Q' would also tend to cause ringing on the waveform so even unipolar pulses would produce a near sine pressure wave out. How effective the 'Q' would make that happen is difficult to estimate and depends to some extent on the damping factor of the driving circuit.

They DO work at other frequencies but as I said, very inefficiently. More than a few hundred Hz from resonance will typically drop output to 10% or less and it gets lower the further away from resonance you drive it. If you hook one up to an audio source you will still hear something but not exactly 'rave party' loudness (although maybe rave party quality!)

Brian.

 

[Audioguru]

Many 40kHz piezo transducers have a bandwidth spec of -6dB at 1500Hz away from the peak frequency. Of course, -6dB is half the voltage swing.
Then 25kHz might be at -60dB which is one/thousandth of the voltage at the 40kHz peak frequency. The bandwidth is a curve without straight sides so the output at 25kHz might be "only" -30dB.