Check out this article describing a double helix antenna for implantable devices. The double helix structure is unique as it is printed “flat” but captures magnetic flux after wrapping. This allows much more flexibility for surgical deployment or other form factors compared to traditional wound wire inductors.
The paper mainly focuses on modeling the antenna, but we also demonstrated a proof-of-concept using RFID to monitor blood flow. This could be used, for example, as a post-surgery monitoring system.
A Flexible Double Helix Inductive Antenna for RFID Vascular Flow Sensing
IEEE Sensors Journal
Authors: Yaneev Hacohen and Steve J.A. Majerus