[dll]

I wonder how the licensing issue referenced in the Wikipedia article is handled in the UK. I imagine Ofcom will have had to approve and license these installations, or will they have made these exempt (I can't find any evidence of this)?

[gnfargbl]

I can't see these devices specifically mentioned in https://www.ofcom.org.uk/__data/assets/pdf_file/0028/84970/i..., though the frequency range they operate in (20-140kHz) is allowed to be used by induction loop type applications, at a suitably low power.

[ale42]

... but the cave link uses relatively high power levels (20-30 Watts if I remember correctly)

[detaro]

as far as I know similar general licensing exists for such purposes. Lots of inductive applications need it.