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Comment by mikewarot | Hacker News Reader

Surface Acoustic Wave filters are used in RF signal processing. They work by converting an electrical signal to a sound wave on the surface of a piezoelectric material, then using mechanical resonance effects to filter the signal to a very narrow band before converting it back to an electrical signal.

In this setup, they have figured out how to amplify the sound waves without having to convert them back to electrical signals first. The first prototype got hot, so they could only run it in pulses... the second device worked continuously, and delivered about a modest amount of power.

Eventually this technology will work its way down into all of our communications gear, making it even smaller, and more efficient.

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Their device is tiny. I don't understand how it works with low frequency / large wavelength sound wave. Do you?

It doesn't work with low frequencies, it works with very high frequencies but in the acoustic domain. You're looking at wavelengths on the order of micrometers.

From what they said, an incoming RF signal is converted to acoustic signal. That acoustic signal is probably not in the human audible range. It’s that signal which is filtered and then amplified with this new device, IIUC.

I hope won't produce some nasty coil whine.

It is thousands of times higher than the highest frequency that you can hear. That doesn't rule out interference with another frequency leading to a difference that is in the audible range but all things considered this should not happen. Also, there are no coils involved, it's piezo-electric.

I should have clarified "acoustic" just means a vibration, like sound, but in this case 274 megahertz, about 14,000 times higher pitch than human hearing... twice FM radio transmissions.

It eventually should result in devices that work past WiFi frequencies.

Your instinct is spot on - it does not, and just does high frequencies in the RF range using acoustic resonance to amplify instead of using electrical amplification. https://en.wikipedia.org/wiki/Acoustic_resonance

One big aspect of this is that is from what can tell, has lower noise and with that a pre-amp/amp that has less noise in the RF domain is epic, it will allow lower power to be used for transmit and also offer longer range at the same power used today. But an amplification that has less noise than existing electrical only options has so many uses that for discovery - I'd rank this up there with graphite.

It's because the speed of sound (in any material) is much slower than the speed of light (even in high dk materials). To make a selective and low loss filter you want to use resonators which have dimensions which are a large fraction of a wavelength (i.e. a quarter wave). When the wave speed is slower, a wavelength is compressed into less space ( cycles per second / meters per second ) which is what enables the miniaturization.

I believe the acoustic loss in many of these materials is also lower than the dielectric loss in most materials, which also improves filter q and achievable selectivity.

That's helpful and makes sense for filtering. But do you have a sense for how their setup amplifies?

"The gain mechanism, which is analogous to an electromagnetic traveling-wave tube amplifer32, depends on the average interaction of the charge carriers with the piezoelectric electric field. This interaction controls the energy transfer from or to the acoustic wave, resulting in acoustic wave attenuation or amplification, respectively."

Source: https://www.nature.com/articles/s41467-021-22935-1

I was pleasantly surprised that it wasn't paywalled.

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