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In-fibre Bragg grating taps spinal pressure

12 Aug 2008

Canadian researchers have unveiled a tiny fibre Bragg grating that could replace conventional spinal disc pressure sensors with a less invasive alternative.

Researchers from the University of Victoria and the University of British Columbia have engineered the smallest disc pressure sensor to date. Based on a fibre Bragg grating (FBG), the compact sensor measures just 0.4 mm in diameter and could be used in regions of the human spine that current sensors cannot reach (Measurement Science and Technology 19 085201).

"This is one of the first applications of FBGs for biomedical pressure measurements," Christopher Dennison, a researcher from the University of Victoria, told optics.org. "Our sensor can resolve low magnitudes of disc pressure accurately and repeatedly, while maintaining the key attributes of FBGs such as biocompatibility and small size."

Existing medical pressure sensors are usually electronic, and have been proven to be extremely fragile and unstable over time. FBGs offer a non-electrical alternative. However, until now researchers have not been able to develop FBG-based pressure sensors that are sensitive enough to measure low magnitude pressure, while maintaining the small size required for biomedical use.

Dennison and colleagues have developed a "bare-FBG", which is simply a FBG that is contained in an optical fibre and is bare of any external coverings. The FBG is housed within a steel tube held in place with a compliant silicone seal. In the design, just the FBG tip is exposed to hydrostatic pressure and the rest of the FBG is shielded in the tube.

"By constructing the sensor in this manner, it is possible to maintain small sensor size and also increase pressure sensitivity by a factor of seven compared with a conventional bare FBG," explained Dennison.

When pressure is applied to the sensor, strains are induced within the region of the Bragg grating, which corresponds to a change in the wavelength of light that is reflected by the grating. The wavelength shifts correspond to changes in hydrostatic pressure, which can be used to calibrate the sensor. By shielding the Bragg grating within a tube, the strains induced by pressure are primarily compressive, along the axis of the Bragg grating, which increases the sensitivity of the device.

In a bid to commercialize the instrument, the group has tested the sensor in the spines of live pigs and is currently in discussions to conduct human trials. "We are also developing other FBG based medical pressure sensors that are even smaller and more sensitive than this device," concluded Dennison. "Our latest prototype is 20 times more sensitive than a bare-FBG and has a major diameter of only 200 microns."

Scitec Instruments LtdKentek CorpPhoton Engineering, LLCEaling UGNanoscribe GmbHBRD Optical Co., LtdSpectrum Scientific Inc. -  SSI Optics
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