The foil electret microphone

Pivoting back toward science by way of technology.... Some very large fraction of the microphones out there in electronic gadgets are based on electrets.  An electret is an insulating material with a locked-in electrical polarization - for example, take a molten or solvated polymer, embed highly polar molecules in there, and solidify in the presence of a large polarizing electric field.  The electrical polarization means that there is an effective surface charge density.  You can make that electret into a free-standing foil or a film coating a backing to make a diaphragm.  When that film vibrates, it will generate an oscillating voltage on a nearby electrode (which could, say, be the gate electrode of a field-effect transistor).  Voila - a microphone that is simple, readily manufacturable, and doesn't need an external power supply.  

While electret microphones are losing some marketshare to microelectromechanical ones in things like airpods, they've played a huge part in now ubiquitous phone and acoustic technologies in the late 20th and early 21st centuries.  When I was a postdoc I was fortunate one day to meet their coinventor, James West, who was still at Bell Labs, when (if I recall correctly) his summer student gave a presentation on some lead-free ultra-adhesive solder they were working on.  He was still patenting inventions within the last two years, in his late 80s - impressive!