Swiss startup puts MEMS sensor, ASIC, RF link in a tiny package that gathers and sends real-time data.

Renee Robbins

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Taking wearable technology and real-time data acquisition to new extremes, a Swiss company working with STMicroelectronics has developed a micromachined sensor and radio frequency (RF) link packaged in a contact lens.

Sensimed AG, a startup whose principal focus is the design, development and commercialization of integrated microsystems for medical devices, says its first product is a non-invasive solution for continuous monitoring of intra-ocular pressure to aid the diagnosis and treatment of glaucoma. The device is a wireless MEMS sensor that acts as a transducer, antenna and mechanical support for additional read-out electronics.
Wireless instruments frequently deliver a wealth of new data. In this example of a wireless optical sensor, a smart contact lens with a tiny embedded strain gauge continuously monitors the curvature of the patient's eye over a period of 24 hours—providing data not currently obtainable any other way.

The lens also contains an antenna, a tiny dedicated processing circuit, and a passive RF transmitter to communicate the measurements to a receiver that is hung around the patient's neck. The embedded components are positioned in the lens in such a way that they do not interfere with the patient's vision. The microprocessor is a small full custom ASIC about 2mm square and 50 microns thick.

"We have a strong focus on developing and manufacturing wireless sensor networks for diagnostics and other applications in medicine," said Benedetto Vigna, general manager of STMicroelectronics' MEMS, sensors and high performance analogue division. "This wireless, self-powered, on-body sensor will be used in a product that promises to greatly help the millions of people at risk and suffering from glaucoma."

The product combines leading edge technologies in three different fields: microtechnology(the MEMS sensor), microelectronics (the telemetric microprocessor) and micropackaging (embedding it all in a soft contact lens). The first challenge was to design a sensor sensitive enough to measure the tiny changecorneal curvature. A MEMS sensor based on a tiny circular strain gage was developed at the microtechnology department of the Swiss Fedral Institute of Technology of Lausanne. The sensor will pick up intraocular pulsation, a tiny modulation of eye pressure due to blood pressure.

"Designing a telemetric system respecting norms and regulatory constraints such as electromagnetic spectrum or heat generation was not trivial," says Jean-Marc Wismer, CEO of Sensimed. "Norms strictly limit the maximum heat to which the eye can be exposed, as well as the maximum amount of harmonic frequencies emitted by the system."

Bringing the prototype to an industrial, comfortable product was one of the main challenges.

"Production of our MEMS sensor is on the edge of technology for most MEMS manufacturers," says Wismer. "Furthermore, the design of a comfortable shape of the lens, while encapsulating the MEMS, the microantenna and the microprocessor required combined efforts of a number of experts in the field of molding and contactology."

Large growth

Wismer expects manufacturing to start in Q3 2010, with various parts of the solution manufactured by different subcontractors around the world. The company expects to ship about 20,000 sensors by 2010, and about 100,000 by 2011, says Wismer.

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www.sensimed.ch

- Edited by Renee Robbins, senior editor Control Engineering News Deskwww.controleng.com