5.2-GHz RF Power Harvester in 0.18-/spl mu/m CMOS for Implantable Intraocular Pressure Monitoring

Abstract

A first fully integrated 5.2-GHz CMOS-based RF power harvester with an on-chip antenna is presented in this paper. The design is optimized for sensors implanted inside the eye to wirelessly monitor the intraocular pressure of glaucoma patients. It includes a five-stage RF rectifier with an on-chip antenna, a dc voltage limiter, two voltage sensors, a low dropout voltage regulator, and MOSCAP based on-chip storage. The chip has been designed and fabricated in a standard 0.18-m CMOS technology.To emulate the eye environment in measurements, a custom test setup is developed that comprises Plexiglass cavities filled with saline solution. Measurements in this setup show that the proposed chip can be charged to 1 V wirelessly from a 5-W transmitter 3 cm away from the harvester chip. The energy that is stored on the 5-nF on-chip MOSCAP when charged to 1 V is 2.5 nJ, which is sufficient to drive an arbitrary 100-W load for 9 s at regulated 0.8 V. Simulated efficiency of the rectifier is 42% at 7 dBm of input power.

A microscale optical implant for continuous in vivo monitoring of intraocular pressure

“…Moreover, the area of the core optomechanical cavity is 0.283 mm 2 (600 μm in diameter) occupying only 44% of the entire sensor area and suggesting further miniaturization. This compact size is an order of magnitude smaller than the state-of-the-art research devices 46,62,63 and three orders of magnitude smaller than commercially available sensors 65 . For IOP monitoring, the sensor is implanted into the eye where its deformable SiN membrane is exposed to the IOP and interrogated using the broadband invisible NIR regime (800-1100 nm) of a tungsten light bulb (Figure 1f) (see in vivo testing below for details on the sensor implantation).…”

“…Such measurements can only be obtained for up to 24 h because of side complications that accompany long-term use [41][42][43] . To overcome the aforementioned limitations, implants based on radio-frequency (RF) technologies have been used to monitor endovascular pressure 44 , intracranial pressure (ICP) 45,46 , and IOP [47][48][49][50][51][52][53][54][55][56][57][58] . The typical size of these implants ranges from a millimeter to a few centimetres.…”

“…For ophthalmic implants, sensor miniaturization is important because the space available for an ocular implant is very small, especially in research animals (e.g., mice) with corneal diameters of approximately 3 mm 60,61 . Some of the RF-based IOP sensors were miniaturized down to the millimeter scale, but their practical use has been limited by short readout distances or the need for sophisticated measurement equipment (for example, spectrum, vector-network analyser) for readout 62,63 . As a result, in vivo measurements have thus far been obtained only with large RF implants that measure 0.5 to 1 cm in diameter 51,64,65 .…”

Architecture of Ultra Low Power Micro Energy Harvester Using RF Signal for Health Care Monitoring System: A Review

“…Next, there is a voltage limiter (block 7) which limits the DC-DC boost's output voltage to certain level to prevent the CMOS transistor from breaking down (Ouda et al, 2013). The input voltage of this block is the output voltage of the boost converter.…”

A highly sensitive RF-to-DC power converter with an extended dynamic range

“…Wireless powering is a fundamental requirement for energizing myriad battery-less devices, such as RFIDs [1], implanted biomedical devices [2][3][4] and wireless sensors [5]. Depending on the application, frequencies ranging from low MHz [2,4] up to UHF [1] are used.…”