Wristband for Bio-signal Monitoring

Highly flexible wristband based on utilization of structural electronics processing technologies and applied for bio-signal monitoring is introduced in this paper. Wristband designed to measure heart rate (HR) and oxygen saturation (SpO2) based on reflective photoplethysmography (PPG) method. Wristband consisted of stretchable thermoplastic polyurethane (TPU) substrate equipped with conductive printed tracks. Three rigid FR4 PCBs contacted on TPU substrate using isotropic conductive adhesive (ICA) and supported mechanically using non-conductive adhesive (NCA). Distances of two sensor PCBs from main PCB were 20 mm and 50 mm to allow measurement of bio-signals from two different locations on wrist or forearm having distance of 115mm in between. Sensor modules were equipped with photonic transceiver component providing capability for PPG sensing. RGB LEDs placed on the main PCB and covered with decorative crystal designed to inform operational status of wristband to the user. Specific aluminum mold tool designed and tooled by mechanical milling for elastomer embedding. Tool equipped with thin pins, which lifted the TPU assembly up from the tool cavity surface to enable embedding of the TPU substrate fully within elastomer. Tool design enabled photonic transceivers optical window surfaces to be open for bio-signals sensing after elastomer embedding. Silicone and polyurethane elastomers applied for TPU assembly embedding. Functionality of processed wristband samples tested by performing HR and SpO2 measurements with volunteer test persons under physical stress. Achieved results verified that both silicone and polyurethane wristbands were functional and capable to monitor HR and SpO2 levels of test persons.