October R&D Round Up

E-mail Melanie Martella

This month we have diamond electrodes for long-lasting implants, image sensors that can handle high temperatures, and a sensor-laden web for aircraft that could turn its outer skin into a sensory organ.

An Implanted Electrode is Forever
We're a long ways from turning into the Borg, but there are definitely situations where we'd like to be able to implant electrodes into the body long-term—to sense nerve activity for prosthetics and monitor neurotransmitters, for instance. Case Western Reserve University's Heidi Martin and Christian Zorman are working on diamond-studded electrodes that could be implanted in the body and remain there for a lifetime. Martin, a professor of chemical engineering professor, and Zorman, a professor of electrical engineering and computer science, have paired the diamond with a flexible polymer to create the electrodes.

Diamond, it turns out, in addition to having wonderful thermal conductivity properties, is also very good when it comes to chemical sensing. The diamond in the electrode thus enables monitoring of both chemical and electrical activity while also allowing the electrode to stimulate nerves. To create an implant that won't be encapsulated by the body, the diamond is limited to the interface between the electrode and the nerve or tissue it's in contact with. To achieve this, tiny squares of pure diamond (doped with boron to let the diamond conduct electricity) are grown on silicon dioxide. A thin, flexible polymer is then added to fill the gaps between the diamond squares, followed by a metal layer to connect to the back of the diamonds and provide a conductive path. After adding a thick layer of flexible polymer, the silicon dioxide is etched away, leaving the diamond squares encased in polymer. (Make sure to read the article linked above for more details.)

Extreme-Temperature Image Sensors
Image sensors have not only made serious inroads into the consumer electronics market, they're also finding new uses in cars, particularly as electronic parking aids. But as anyone knows who has had to get into a car that's been sitting in full sun on a hot summer day, sensors used in automotive applications need to survive some surprisingly extreme conditions. Werner Brockherde and fellow researchers at the Fraunhofer Institute for Microelectronic Circuits and Systems IMS in Duisburg, Germany, have developed a 2.5 cm by 2.5 cm CMOS image sensor with an operating temperature range of –40°C to 115°C. The secret lies in the fact that the sensor's pixels exhibit a very low dark current at high temperatures, reducing image noise. Its sensitivity enables the sensor to react even in low-light conditions, expanding its possible applications to include night vision equipment and metal rolling mills.

A Gossamer Sensor Web for Aircraft
Inspired by spider webs, Stanford University researchers have developed a fine mesh of plastic polymer on which sit tiny gold sensors to measure strain and temperature. The material can expand to more than 265 times its original size and the idea is to stretch the sensor-seeded mesh over the skin of an aircraft and thus provide feedback as to the conditions being experienced as the aircraft flies or undergoes various maneuvers. Work is also underway to add piezoelectric devices that could generate ultrasonic waves, enabling the mesh to sense the formation of any tiny cracks. (I'd be interested to know more about how the data is retrieved from the mesh.) More details are available in the Discovery News article, "Sensor-Equipped Spider Webs to Coat Aircraft." Not surprisingly, this could come in awfully handy in many other applications.

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