Flexible Pressure Sensor Realized by a Chirped Fiber Bragg Grating Pair for Vital Signs Monitoring

A chirped Fabry-Perot interferometric (CFPI) pressure sensor based on two cascaded chirped 50-micron fiber Bragg gratings is proposed in this paper. Two packaging architectures of linear and circular structures using polydimethylsiloxane (PDMS) are demonstrated, while the latter one significantly improves pressure sensitivity owing to the annular light path in the FP cavity. Compared to the linear packaging configuration, the circular structure exhibits 3.438 times higher sensitivity in terms of wavelength drift with pressure, and a 21.307-fold increase in electrical signal sensitivity to pressure changes. Furthermore, the sensor was employed to measure pulse waveform on the wrist, and blood predictions were made using a convolutional neural network and long short-term memory (CNN-LSTM) model. As a result, the measurement errors for systolic blood pressure (SBP) and diastolic blood pressure (DBP) were -0.122±2.781 mmHg and 0.051±1.711 mmHg, respectively, which meet the standards set by the American Association for the Advancement of Medical Devices (AAMI). The proposed sensor employs a narrowband laser as light source and a photodiode for demodulation, showing the potential of miniaturization and cost reduction in sensing devices while maintaining high sensitivity. Additionally, the flexible sensor structure showcases the feasibility of a simple and highly accurate real-time medical wearable device, offering a promising solution for daily health monitoring.