These were found by looking up the patent number shown in a photo of Radioear 892 hearing aid.
Magnetic microphone patent:
https://worldwide.espacenet.com/publicationDetails/originalDocument?CC=US&NR=2552800A&KC=A&FT=D&ND=3&date=19510515&DB=EPODOC&locale=en_EP
(Tele coil?) Inductive pickup patent:
https://worldwide.espacenet.com/publicationDetails/originalDocument?CC=US&NR=2656421A&KC=A&FT=D&ND=3&date=19531020&DB=EPODOC&locale=en_EP
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