Flexible Electrodes based Smart Mattress for Non-Contact Cardiac Signals Measurement.

For more convenient use in sleep monitoring than conventional electrocardiogram (ECG) measurement systems, a mattress that could measure ECG signal and ballistocardiogram (BCG) signal through clothes was designed. Three electrodes made of silver fiber conductive fabric were embedded in this mattress, which make it very comfortable and it does not disturb user's sleep. In addition to the mattress, the proposed system contains a signal acquisition module, and a data transmission module and a user interface. To reduce the effect of surrounding electromagnetic radiation to the two signal sensing electrodes, two equipotential shielding layers are placed under them respectively. The proposed system was verified by an experiment of ECG signal and BCG signal measurement, where reference ECG signal was measured by Ag/AgCl electrodes synchronously. The result shows that both ECG signal and BCG signal were measured by the proposed system through clothes successfully. Compared with the reference signal, both R-R intervals and J-J intervals extracted have high correlation coefficients, which are 0.988 and 0.963 respectively, and also have small errors (the root mean square errors are 3.64ms and 6.39ms respectively). Furthermore, the proposed system may be used to measure blood pressure indirectly based on ECG signal and BCG signal measured directly.