Split-ring resonator-based sensors on flexible substrates for glaucoma monitoring

Glaucoma is an eye disease that may cause blindness by damaging the optic nerve due to elevation of the intraocular pressure. Patients with glaucoma require monitoring of intraocular pressure. This paper presents split-ring resonator-based strain sensors designed and characterized for glaucoma detection application. The geometry of the sensor is optimized such that it can be embedded in a conventional contact lens. Silver conductive paint is used to form the sensors realized on flexible substrates made of cellulose acetate and latex rubber. The devices are excited and interrogated using a pair of monopole antennas. Scattering parameters are measured between the ports of the antennas, and the characteristics of devices with different curvature profiles are obtained. Finite-element based models are developed to analyse the operation of the devices and to optimize the sensor structure. The sensitivity of the device, i.e. the change in resonant frequency for a unit change in radius of curvature, on acetate film is experimentally characterized as -4.73 MHz/mm and the sensitivity of the device on latex is 33.2 MHz/mm. The experimental results supported by finite-element based models indicate that the demonstrated device is suitable for glaucoma diagnosis and monitoring. (C) 2017 Elsevier B.V. All rights reserved.