A SU-8-Based Microfabricated Implantable Inductively Coupled Passive RF Wireless Intraocular Pressure Sensor

With the growing demand in noncontact detection of human diseases, this paper presents an implantable passive wireless pressure sensor using an inductively coupled wireless sensing technique, particularly designed to monitor the intraocular pressure (IOP) of glaucoma patients. The microfabricated IOP sensor consists of a planar spiral gold coil inductor, a two-parallel-gold-plate (metal-insulator-metal) capacitor, and a SU-8 pressure-sensitive diaphragm. The IOP sensor is fully encapsulated inside biocompatible SU-8 stacking layers to isolate the IOP sensor from the biological tissue medium environment. By measuring the impedance phase dip frequency shift from the external coil, the IOP signal can be obtained through the implanted IOP sensor. The optimized size of the manually wound external coil was investigated. The readout distance is up to 6 mm from the implanted sensor. Characterization results show that the microfabricated IOP sensor has relatively high sensitivities-7035 ppm/mmHg in air and 3770 ppm/mmHg in saline medium-with pressure resolution lower than 1 mmHg, which is adequate for IOP monitoring application.