A Flexible Double Helix Inductive Antenna for RFID Vascular Flow Sensing

This work demonstrates a batteryless, implan- table blood-flow sensor with radio frequency identification (RFID) readout. This flexible sensor system was developed specifically for surgical implantation around a blood vessel, without contacting blood to reduce platelet deposition, clotting, and other complications with blood-contacting sensors. A flexible sensor and circuit architecture was adopted to enable a cuff-like form factor for surgical implantation around an artery, vein, or graft without piercing or cutting the vessel. This required the development of a flexible RFID data/power antenna using a split-double helix antenna (DHA), which could be opened and closed, unlike a solenoidal or flat spiral antenna. DHAs with diameter of 3–10 mm were fabricated and characterized on the bench, showing a typical coupling coefficient of 0.007 when placed 5 cm from a reader. Prototype implantable DHA systems were developed to wrap around vessels of 3–8 mm. A flexible pulsation sensor (FPS) was developed from a piezoresistive carbon black-polydimethylsiloxane (PDMS) nanocomposite, which enabled the measurement of vascular distension caused by blood flow. A commercial RFID chip enabled sensor readout to an external transceiver in real time with a sample rate of 12 Hz when immersed in saline test media. Validation experiments on a vascular phantom with simulated stenosis demonstrated a blood-flow rate monitoring from 200 to 400 mL/min with the capacity to distinguish flow changes as low as 10 mL/min.