# An amplifier circuit for a piezoelectric disk for ultrasound generation

#### Isabella__

Joined Apr 26, 2022
15
Hey guys,

I need your help. I am a bit lost. I have to build an amplifier circuit for a piezoelectric disk for ultrasound generation in university.
The technical data (piezoelectric disk):

Resonant frequency = 80 kHz
Electrical capacity = 35 nF
Max. Supply voltage = 400 V

In the university I have a function generator which supplies me with an alternating voltage with the desired frequency (70 kHz). I think it would make most sense to build a driver circuit.

I would be very grateful if you could explain me how to proceed.
How should the amplifier circuit look like, which components and what else I have to consider.

#### MrChips

Joined Oct 2, 2009
30,806
You do not need a special amplifier.
A single BJT or MOSFET will do.

#### Isabella__

Joined Apr 26, 2022
15

#### MrChips

Joined Oct 2, 2009
30,806
Okay is it okay when my Inputsignal is a sinus wave?
Yes. The very high gain of the transistor amplifier turns the sine wave into a square wave.

#### ericgibbs

Joined Jan 29, 2010
18,848
Hi Isabella,
Your Sine amplitude will have to be greater than 0.7V on the positive half cycle in order to drive the transistor into conduction.
What are you setting the Vsupply to the Collector load.?

What is the Power rating of the Disk.?

E

#### Isabella__

Joined Apr 26, 2022
15
Yes. The very high gain of the transistor amplifier turns the sine wave into a square wave.
Okay but my output signal Ua must be a sinus wave because of the piezoelctric disc.

#### Isabella__

Joined Apr 26, 2022
15
Hi Isabella,
Your Sine amplitude will have to be greater than 0.7V on the positive half cycle in order to drive the transistor into conduction.
What are you setting the Vsupply to the Collector load.?

What is the Power rating of the Disk.?

E
My input signal is a sinus wave with 15 V frequency 70 kHz.
Sorry but i can't find the power rating of the disc?

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#### ericgibbs

Joined Jan 29, 2010
18,848
hi Isabella,
So what you are asking is to step a 15V 70kHz Sine wave up to what voltage Sine wave.?

Do you want the output Sine wave to swing positive and negative about zero volts.?

What will be the purpose of driving the disk.?
ie: what will be ultra sound signal be used on.?

E

#### MrChips

Joined Oct 2, 2009
30,806
The piezoelectric disc does not require a sine wave. It really depends on what you plan to do with the disc.
You need to find the datasheet for the disc so that we know its requirements.

If you need better control of the shape of the waveform emitted by the disc the LM675 power amplifier might be suitable.

#### Isabella__

Joined Apr 26, 2022
15
hi Isabella,
So what you are asking is to step a 15V 70kHz Sine wave up to what voltage Sine wave.?

Do you want the output Sine wave to swing positive and negative about zero volts.?

What will be the purpose of driving the disk.?
ie: what will be ultra sound signal be used on.?

E
Yes the outputsignal must be also sinus wave swing to +/- 400 V.
The disc generate an ultrasound with a frequency 70 kHz.
After i generate the ultrsaound i will mess the sound with a mems microphone.

The function generator can give me a sinus wave max +/- 15 V thats the problem.

#### MrChips

Joined Oct 2, 2009
30,806
Yes the outputsignal must be also sinus wave swing to +/- 400 V.
The disc generate an ultrasound with a frequency 70 kHz.
After i generate the ultrsaound i will mess the sound with a mems microphone.

The function generator can give me a sinus wave max +/- 15 V thats the problem.
+/- 15V from the function generator is not the problem.

+/- 400V sine wave is the problem.

We can do this with a 0-400V square wave with a single transistor.
Please tell us what you are attempting to with this.

#### Isabella__

Joined Apr 26, 2022
15
The piezoelectric disc does not require a sine wave. It really depends on what you plan to do with the disc.
You need to find the datasheet for the disc so that we know its requirements.

If you need better control of the shape of the waveform emitted by the disc the LM675 power amplifier might be suitable.
I use a sinus wave because i want generate an ultrasound with the frequency 70 kHz and when i use a sinus wave i don't must add something to get a frequency of 70 kHz. The Screenshot is the only Datasheet what i find.

#### MrChips

Joined Oct 2, 2009
30,806
I use a sinus wave because i want generate an ultrasound with the frequency 70 kHz and when i use a sinus wave i don't must add something to get a frequency of 70 kHz. The Screenshot is the only Datasheet what i find.
We have heard what you are saying but you still do not understand.
We can generate a 70kHz wave from a function generator, sine or square wave.
The disc does not need a sine wave to operate.

Most piezoelectric transducers have a resonant frequency. If your disc resonates at 70kHz it will emit a sine wave when driven from a square wave signal.

#### Isabella__

Joined Apr 26, 2022
15
Okay i'm not sure about that because my teacher wants me to use a sinus wave. Thats why i use a sinus wave. But my question is how can i achieve a voltage gain up to 400 V

#### MrChips

Joined Oct 2, 2009
30,806
Okay i'm not sure about that because my teacher wants me to use a sinus wave. Thats why i use a sinus wave. But my question is how can i achieve a voltage gain up to 400 V
Well then go back to your teacher and ask if a sine wave is absolutely necessary or if a square wave would also work.

#### Isabella__

Joined Apr 26, 2022
15
When i use a square voltage can i use also the frequency 70 kHz and i will generate an ultrasound with 70 kHz

#### MrChips

Joined Oct 2, 2009
30,806
When i use a square voltage can i use also the frequency 70 kHz and i will generate an ultrasound with 70 kHz
Yes. You can use whatever frequency the datasheet tells you to use.

#### Isabella__

Joined Apr 26, 2022
15
Would this make a difference in my amplifier circuitry if i use a sinus wave or square input?

#### Isabella__

Joined Apr 26, 2022
15
Okay i ask him hey says the transducer cannot follow a square signal.

So I MUST use a sinus wave

I'm sorry but i don't what i should do now.

#### MrChips

Joined Oct 2, 2009
30,806
To allow us to assist you better:

1) post a photograph of the ultrasonic disc
2) tell us what is the nature of the project
3) tell us the level of course and schooling, is this secondary or university level?