If you find that fascinating already... did you know that all cellphones use mechanical filters in the GHz range? They combine very good performance with very low energy consumption.

https://en.wikipedia.org/wiki/Surface_acoustic_wave

https://de.wikipedia.org/wiki/Akustische-Oberfl%C3%A4chenwel... (pictures)

Very little uses crystal oscillators, they’re gigantic compared with electronics today and have very wonky performance over temperature and shock.