Smart Textile Based Optical Sensing for Health Care

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Smart Textile Based Optical Sensing for Health Care


• Photoplethysmograph (PPG) technology is used extensively in applied optics sensors that are most commonly found in medical devices. The PPG technique can be implemented in transmission and reflection modes, and provides information about blood volume changes, the heart rate (HR) by using one wavelength and can also be used to monitor the oxygen saturation (SpO2) levels by using two wavelengths.

• Capillary refill time (CRT) is Recording the time that taken for the skin to regain its colour back after blanching.

Working Principle

• Red and IR wavelength lights are needed in order to operate the SpO2 devices because the level of absorption for both lights varies for oxyhaemoglobin (HbO2) and deoxyhaemoglobin (Hb) blood. The red and IR PPG signals of pulse oximeter devices are used to calculate the absorbance ratio (R) that can be calculated by Equation 1.1.

                                              Equation 1.1: R=  ((Red_AC)/(Red_DC ))⁄((IR_AC)/(IR_DC ))

The ratio calibration between red and IR can be measured by Equation 1.2 in order to calculate the SpO2.

                                                          Equation 1.2: % SpO2 = 110 – 25 R 

• Measuring the CRT (colour change) by detecting the reflected light from the skin also while measuring the contact pressure using Fibre Bragg Grating (FBG).

Project aim

• Develop a multi-channel textile-based optical fibre measurement system for detecting of the PPG,

• Monitoring the SpO2 using two different wavelengths (660nm and 850nm),

• Measure the CRT and the contact pressure.