A prototype implantable eye pressure monitor for glaucoma patients is believed to contain the first complete millimeter-scale computing system. The pressure monitor is designed to be implanted in the eye to conveniently and continuously track the progress of glaucoma, a potentially blinding disease. It is expected to be commercially available in several years.
In a package that is just over 1 cubic millimeter, the system fits an ultra-low-power microprocessor, a pressure sensor, memory, a thin-film battery, a solar cell, and a wireless radio with an antenna that can transmit data to an external reader device that would be held near the eye.
The processor in the eye pressure monitor is the third generation of the Phoenix chip, which uses a unique power gating architecture and an extreme sleep mode to achieve ultra-low power consumption. The newest system wakes every 15 minutes to take measurements and consumes an average of 5.3 nanowatts. To keep the battery charged, it requires exposure to 10 hours of indoor light each day or 1.5 hours of sunlight. It can store up to a week’s worth of information.
Adding a compact radio that needs no tuning to find the right frequency could be a key enabler to organizing millimeter-scale systems into wireless sensor networks. These networks could one day track pollution, monitor structural integrity, perform surveillance, or make virtually any object smart and trackable. Researchers are developing a consolidated radio with an on-chip antenna that does not need the bulky external crystal that engineers rely on today when two isolated devices need to talk to each other. The crystal reference keeps time and selects a radio frequency band. Integrating the antenna and eliminating this crystal significantly shrinks the radio system.
The new antenna will be engineered to keep time on its own and serve as its own reference. By integrating the antenna through an advanced CMOS process, they can precisely control its shape and size and therefore how it oscillates in response to electrical signals. The researchers are now working on lowering the radio’s power consumption so that it is compatible with millimeter-scale batteries.
This technology was done by University of Michigan, Ann Arbor, MI. The university is pursuing patent protection for the intellectual property, and is seeking commercialization partners to help bring the technology to market. For more information, visit http://www.engin.umich.edu.