About ultrasonic's amplitude

Hello.

I have a question that is really simple thing.. I'm using ultrasonic transducer and testing energy harvesting. At my project, I will adjust FDA limitation. So I limit the power of ultrasonic. So The power is square of amplitude.

I'm just wondering how could I control amplitude. Does it controlled by voltage?

What ultrasonic transducer? What is FDA limitation?

Surely there are two transducers if one is harvesting energy - another must be generating it?

Now I am finding ultratransducer And fda limiation is the guideline of ultrasonic about effect of human health. So when I over that limitation , then it will harmful at body. It said 720mW/cm^,2 I use one transducer and the other is piezo material.

Is this through air? or a liquid?

You need to provide as much detail as possible, otherwise you'll be getting questions in reply until we understand what you are actually trying to do.

Ultrasonic energy harvesting is being explored by researchers as a means to non-invasively power medical devices implanted in the body (and the FDA limit appears to be applicable).

dongjee33: Now I am finding ultratransducer And fda limiation is the guideline of ultrasonic about effect of human health. So when I over that limitation , then it will harmful at body. It said 720mW/cm^,2 I use one transducer and the other is piezo material.

Are not both devices piezo material?

Paul

transducers have a inertial component to their pressure wave generation function which can interfere with its ability to transmit at the rated frequency with less/more power than designed for.

dongjee33: Now I am finding ultratransducer And fda limiation is the guideline of ultrasonic about effect of human health. So when I over that limitation , then it will harmful at body. It said 720mW/cm^,2 I use one transducer and the other is piezo material.

I see that limit is for diagnostic equipment, not what you are doing. And the "amplitude" they refer to seems to be rep rate of the sound pulses.

Paul

Paul_KD7HB: I see that limit is for diagnostic equipment, not what you are doing.

And what would be the significance of that?

To your question, yes you can vary the amplitude of the square (or sine) wave to the Piezo transmitter.

You could use an LM317 controlled to a specified voltage. You could use the PWM output of the Arduino (with RC filtering) to control the LM317.

What I’m not sure of is the specification 720mW/cm2. Is it at the input of the Piezo (likely not) or the energy coupled to the transmitting medium? If so how is it evaluated?

If you are trying to pass energy through some (non air) medium be aware that any changes in the Speed of Sound (SOS) in the mediums with reflect energy back to the transducer.

For instance: If you are going through human tissue. You have to go through fat and muscle. I’m going to assume the SOS in fat is not = to the SOS in muscle. So when the piezo induced wave travels through the Fat - muscle interface, some of the energy will be reflected back to the transmitting piezo. The amount reflected back is proportional to the change in SOS between the two mediums.

Paul__B: And what would be the significance of that?

That is at the surface of the skin, plus some kind of jell. The op may be doing the ultrasound transmission inside a body.

Paul

Or more likely simulating it. Not sure about the right measuring equipment for something like this, I suspect an ultrasonic measurement hydrophone is a very expensive and specialist piece of kit...

Done a bit of reading and only very low efficiency seems possible, 3 orders of magnitude below input power.