Measurement of Cardiorespiratory Activity Using Planar Coils and a High-Resolution Inductance-to-Digital Converter

This article presents a noncontact device for monitoring cardiorespiratory activity based on an inductive method using a high-resolution 24-bit inductance-to-digital converter (LDC3114). We describe experimental setup, encompassing the LDC configuration procedure, energy consumption analysis and its optimization, and the electromagnetic (EM) biocompatibility of the device. The device’s functionality was evaluated through various measurements, including tests with distilled water to investigate the influence of capacitive coupling. Measurements from the chest area yielded information on cardiorespiratory activity, which was compared with established electrocardiography and respiratory activity sensing methods. The proposed device utilizes the LDC for excitation and signal acquisition, offering improved noise immunity and signal quality. We highlight the advantages of this method, such as noncontact operation, noninvasiveness, high resolution, and minimized hardware complexity. In addition, the device incorporates wireless data transfer, facilitating convenient data acquisition. The measurements demonstrate that the device’s resolution is sufficient for reliable cardiorespiratory monitoring. An important aspect of this research is the implementation of capacitive coupling shielding to enhance measurement accuracy. We propose a shielding scheme that preserves the device’s ability to detect volume changes inductively. Preliminary results indicate distinct signal characteristics when using shielding, potentially mitigating the impact of some side sensing effects in the region of interest—the arterial tree. The proposed capacitive coupling shielding scheme shows potential for improving measurement accuracy. Future studies should explore this direction further to advance the understanding of the distinctive characteristics of shielded and unshielded measurements.