Design and test of a 915MHz, RFID-based pressure sensor for Glaucoma

A Radio Frequency Identification (RFID)-based pressure sensing system is developed to extend the range of current Intra-Ocular Pressure (IOP) sensing systems. The system described in this work utilizes a unique Electrically Small Antenna (ESA) that measures 7mm × 10mm to receive a 915MHz signal used to power the system. A four-stage Schottky rectifier circuit is used to rectify the received signal and provide dc power via a regulator to a Colpitts oscillator. The Colpitts oscillator senses pressure and provides an output signal that is proportional to the pressure. The system is fabricated using a mature, inexpensive 0.5μm CMOS fabrication process and is capable of operating over a range of 5.4cm.