A multi-wavelength, rigid-flex wearable ring oximeter for mitigating motion and skin pigmentation challenges: Hardware development and preliminary characterization

Pulse oximetry faces well-documented accuracy challenges related to skin pigmentation and motion artifacts, contributing to significant health disparities. In response, we present a wearable ring-type pulse oximeter designed to address these limitations through multi-wavelength sensing and stable anatomical coupling. The device features a rigid-flex printed circuit board integrating four LEDs (610–940 nm), dual photodetectors in transmission configuration, and a three-axis accelerometer. A Bluetooth-enabled microcontroller with adaptive acquisition firmware manages the system. The prototype was successfully fabricated and functionally validated. Optoelectronic characterization confirmed wavelength-dependent signal properties, with superior performance at longer wavelengths (740–940 nm). Preliminary testing on four healthy volunteers (Fitzpatrick skin types I–III) demonstrated reliable photoplethysmographic signal acquisition with improved signal-to-noise ratios at longer wavelengths, validating the hardware architecture’s capability to acquire high-quality multi-wavelength PPG signals. This platform establishes technical feasibility for future clinical validation. However, validation against arterial blood gas analysis across all Fitzpatrick types (I–VI), systematic motion artifact assessment, and melanin-compensated SpO₂ algorithm development remain essential before clinical deployment.