Capacitors

knitted capacitors (knitted radio)
woven capacitors

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How does capacitive sensing work
https://www.youtube.com/watch?v=bhspPkxOMxs

A deeper explanation of what capacitance is
https://www.youtube.com/watch?v=QItuf6lNvmI

Swept Frequency Capacitive Sensing
https://www.youtube.com/watch?v=E4tYpXVTjxA