Power Amplifier for Ultrasonic Transducers

Question

I have come across similar questions, but my problem has some specific requirements so I had to ask a new one.

I'm working on an ultrasonic speaker array for my PhD thesis. My work is focused on the DSP side of things, but I have to have a working ultrasonic speaker system to be able to test and reproduce the stuff I am going to work on. I have almost no background on electronics and have been working on driving the ultrasonic speakers properly (with almost no progress) for the past month. So I am in desperate need of guidance.

I designed a modulation software to pre-process my audio signal for ultrasonic reproduction. It uses a 40kHz sine wave as the carrier and modulates it with the target audio signal. So I have a complex sinusoidal signal between 20kHz-40kHz that I have to drive the ultrasonic speakers with.

I have a USB Audio Interface as my primary signal source, and its maximum output values are 3Vpeak and 16mA. I have to amplify this signal to 10Vpeak and 320mA to be able to drive the speakers. I have 20 speakers and they have 2400pF capacitance each. What approach would you suggest I take?

Note: I have looked around the internet for DIY ultrasonic loudspeaker solutions, and every design I came across used PWM with a 555 timer in order to modulate the signal. The thing is, my work is focused on optimizing the modulation techniques, so my unamplified signal is already pre-modulated. So I essentially want to amplify a 20kHz-40kHz sinusoidal "audio" signal wihout extra modulation that would introduce new harmonic content. I am desperate enough to work with some distortion, but hard clipping would be too harsh to measure anything useful. Thanks for all your help in advance.

Answer 1

You don't say if you must build up an amplifier yourself or if you could use a commercially available part. Ideally you would need a linear amplifier with low distortion. This wouldn't necessarily be an audio amplifier as those frequencies are non-audible (at least for human ears).

Here is an example of a module that uses a high power amplifier chip (20W). You could purchase the module complete from here. Also note that the amplifiers datasheet includes the internal schematic so you could build up something similar if that were needed. The datasheet for the actual chip used in the module is here.

Also note that for this amplifier module you may need to tone down (reduce) the input from your system as the datasheet lists a maximum input level of 650 mVrms.

This is just the first part that I found. You should be able to find many other commercially available linear amplifiers from suppliers such as Digikey, Mouser, Amazon, etc. Just be sure to check that the specifications satisfy you frequency range and power requirements.