Abstract
Electronic contact lenses are used for noninvasively monitoring vital human signs and medical parameters. However, maintaining a secure communications connection and a self‐sustainable power source are still looming challenges. Herein, a proof‐of‐concept electronic contact lens is demonstrated that includes a spiral antenna with its wireless circuit unit for data telemetry, a rectifier circuit for power conditioning, and a micro‐light‐emitting diode (μLED) as a load. The spiral antenna with its rectifying circuit is designed considering operation in the industrial, scientific, and medical (ISM) band of 2.4 GHz. The spiral coil with an inner diameter of 10 mm, an outer diameter of 12 mm, and a wire width of 0.2 mm is fabricated on a donut‐shaped flexible polyimide substrate. For biocompatibility purposes, polyimide is used as the contact lens substrate and polydimethylsiloxane (PDMS) is used for encapsulation. A 3D‐printed eye model is developed for accurately shaping the curvature of the PDMS‐encapsulated contact lens. The reflection coefficient (S11) of the fabricated antenna is tested in different conditions and on an eye model to mimic the liquid condition of the human eye. In a wide range of conditions, a minimum of −20 dB reflection coefficient (S11) is obtained.
Highlights
Electronic contact lenses are used for noninvasively monitoring vital human signs been considered for protecting eyes and medical parameters
An Agilent E8362B Vector Network Analyzer (VNA) was used to measure the antenna performance, which has a frequency range from 10 MHz to 20 GHz
A comparison among these results indicates that the measurement with hand was the closest to simulation, as shown in Figure 5a. indicating that the contact lens antenna resonates at 2.4 GHz with more than À12 dB return loss
Summary
For a circular spiral antenna, the inductance of the antenna is a vital parameter which mainly relies on the geometry design. The resonant frequency has a positive correlation with the copper wire width, and the antenna can achieve a lower frequency, because the start point is closer to the centre point, which would block the wearer’s vision This impedance-matching process is nonlinear, as the single variable method is not applicable to this spiral configuration. As for lighting a μLED at the load side, a half-wave circuit was fabricated for testing the influence of the electronic components on the antenna performance, where the input signal was a 5 V sinusoidal wave with a Schottky diode, a 1 pF capacitator, and a μLED
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