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first post here so feel free to point out my shortcomings.

I am interested in building an Ultrasonic device utilizing two Ultrasonic piezoelectric transducers to create a standing wave between them in order to 'float' droplets of water and other small objects. I am attempting to better understand the nature of focused compression waves in regards to electronic propulsion.

I've purchased these: LYWS High Conversion Efficiency... https://www.amazon.com/dp/B01LXMWLGE?ref=ppx_pop_mob_ap_share

I am attempting to use my laptop as an arbitrary waveform generator using the output of my audio jack. It is a Windows based machine, using MATLAB or similar software outlined in this post "https://www.allaboutcircuits.com/technical-articles/how-to-use-your-computer-as-an-arbitrary-waveform-generator/".

My question is this, what type of amplifier should I use to get the amplitude up to the 50W required to power the transducer? I am thinking of using an audio amp but am unsure if the line voltage will be off or if I'll even be able to reach the 50W. I'm looking to achieve minimal distortion without having to create a special amplifier that only works on specific signals, since I am trying to create something that is adjustable in order to experiment with different materials caught in the compression wave. I'm assuming that there is a range of voltage in the Ultrasonic frequency that this device can use but I'm unsure as this is my first attempt to create something with these devices. Should I just purchase an arbitrary waveform generator? Will that still need some sort of amp?

This whole project is a bit advanced for me and I'll admit that I dropped out of electrical engineering school, but we never really covered analog waveform generation anyway.

Any feedback is much appreciated 😁👍👨‍🔬

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  • \$\begingroup\$ You still need an amp with a function generator. Look up a power booster opamp. \$\endgroup\$ – DKNguyen Jul 20 '19 at 18:57
  • \$\begingroup\$ Your link to the transducer from Amazon also has a 60 watt, 40 kHz driver board for about $37.00. \$\endgroup\$ – Barry Jul 20 '19 at 20:03
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(Replying based on memory, please verify), you'll need a high-voltage amp that can handle a large, capacitive load. Piezo actuators will look like big, slightly-lossy capacitors to the amplifier (the piezo material is, among other things, a high-k dielectric material.) Not all amplifiers can handle the peak voltage needed to drive (assumed, bare) piezo elements at high power (with any hope of linearity) when presented with a capacitive load that will draw peak current at almost no voltage -- leaving a linear output stage to dissipate a high voltage * a high current. If you can, buy an amp designed to drive a piezo with (as close as you can get to) same impedance, resonant frequency, and power level.

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  • \$\begingroup\$ Yes impedance is the key. This thing claims "50W", but the amp will only drive that power if it's seeing the correct load on its output since P=V^2/R. \$\endgroup\$ – Mr. Snrub Jul 20 '19 at 21:43
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    \$\begingroup\$ It may interest some reading here that some ceramic capacitors, when driven with a healthy AC signal in the audio range, act as inefficient audio drivers. \$\endgroup\$ – Catalyst Jul 21 '19 at 12:46
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No idea how the 50w number is specified. What is relevant is usually a maximum voltage you can use.

One efficient way to achieve this voltage for max output across a capacitive device is to use an h- bridge driver fed from simple square wave.

The h-bridge inversion will double the applied voltage. AND you can get cheap pre-built modules. All you need is the square wave driving signal.

Also since these devices have a high-Q response, it is useful to be able to adjust the frequency +/- 5% around 40khz to get the sweet spot.

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Piezo transducers act like capacitors. Audio amplifiers are designed for loudspeakers, which are mostly inductive loads. Don't use an audio amp, it could oscillate, run out of slew rate and bandwidth, or simply blow the output transistors due to Safe operating Area violation.

An H-bridge is a much safer option, however it will output a square wave, and driving a capacitor with a square wave voltage requires large peak currents when the voltage switches, which may blow your MOSFETs. Thus you can add an inductor in series with the transducer to smooth out these current peaks. With this inductor, you can also create a LC resonant circuit and boost the output power and efficiency. You'll need to design the inductor value according to the capacitance of the transducer though, to make sure the resonant peak is at the frequency you want to use.

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  • \$\begingroup\$ "Thus you can add an inductor in series with the transducer to smooth out these current peaks.". Do you mean in line after the transducer to protect the amplifier? If I put an inductor in front of the transducer it is probably going to create some distortion to the signal right? Or will it not be enough to cause any issues with the frequency? \$\endgroup\$ – Kenneth Mikolaichik Jul 21 '19 at 19:23

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