Recent Improvement of Medical Optical Fibre Pressure and Temperature Sensors

Abstract

This investigation describes a detailed analysis of the fabrication and testing of optical fibre pressure and temperature sensors (OFPTS). The optical sensor of this research is based on an extrinsic Fabry–Perot interferometer (EFPI) with integrated fibre Bragg grating (FBG) for simultaneous pressure and temperature measurements. The sensor is fabricated exclusively in glass and with a small diameter of 0.2 mm, making it suitable for volume-restricted bio-medical applications. Diaphragm shrinking techniques based on polishing, hydrofluoric (HF) acid and femtosecond (FS) laser micro-machining are described and analysed. The presented sensors were examined carefully and demonstrated a pressure sensitivity in the range of \(s_p\) = 2–10 \(\frac{\text{nm}}{\text{kPa}}\) and a resolution of better than \(\Delta P\) = 10 Pa protect (0.1 cm H\(_2\)O). A static pressure test in 38 cmH\(_2\)O shows no drift of the sensor in a six-day period. Additionally, a dynamic pressure analysis demonstrated that the OFPTS never exceeded a drift of more than 130 Pa (1.3 cm H\(_2\)O) in a 12-h measurement, carried out in a cardiovascular simulator. The temperature sensitivity is given by \(k=10.7\) \(\frac{\text{pm}}{\text{K}}\), which results in a temperature resolution of better than \(\Delta T\) = 0.1 K. Since the temperature sensing element is placed close to the pressure sensing element, the pressure sensor is insensitive to temperature changes.

Keywords

• optical fibre sensors
• Fabry–Perot interferometer
• pressure sensors