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Fiber sensor tackles blood pressure

07 Jun 2005

A Slovenian team thinks its polymer diaphragm could enable miniature pressure sensors for medical use.

Scientists in Slovenia have developed a miniature, polymer capped fiber sensor for measuring the pressure of blood in arteries and veins. According to the team from the University of Maribor, the fast-acting, 125 µm diameter device could replace fluid-filled catheters and pressure lines, which are vulnerable to mechanical disturbances. (APPLIED OPTICS 44 2736)

Typically, optical pressure sensors use a silicon diaphragm placed at the end of an optical fiber interferometer. Variations in pressure cause the diaphragm to flex, altering the interferometer's cavity length and changing the intensity of light falling on a detector.

However, because the sensitivity of this style of pressure sensor is highly dependent on diaphragm radius, the task of miniaturizing a stiff, silicon-based sensor below several hundred microns is a challenge.

The team from the University of Maribor has managed to shrink its device by switching from silicon to a flexible a polymer membrane. Still relying on the concept of an interferometer, the researchers have demonstrated two versions of their polymer-based pressure sensor. The first device uses a diaphragm made of polyurethane to detect pressures over the range 0-40 kPa with a resolution of 10 Pa. A second, high pressure version (0-1200 kPa) features a more rigid polystyrene membrane.

"To our knowledge, this is by far the highest sensitivity ever reported for this size of [pressure] sensor," Denis Donlagic of the faculty of Electrical Engineering and Computer Science told Optics.org. "Potentially, the sensor could also be simpler and more cost-effective to fabricate than silicon-based devices."

Tests showed the sensors to be biocompatible and immune to electromagnetic interference, which makes them ideal candidates for biomedical applications. Furthermore, Donlagic believes that the optical-based sensors can be made even smaller to tackle pressure measurements in tiny blood vessels.

The group has applied for a patent and is currently looking for potential partners to commercialise its design.

James Tyrrell is reporter on Optics.org and Opto & Laser Europe magazine.

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