Noncontact Electrocardiogram System for Mattresses Using Silver Conductive Fabric

Electrocardiography (ECG) is an essential diagnostic tool in healthcare and widely used for monitoring heart activity. However, conventional wet electrodes, which rely on hydrogels containing nickel particles and acrylic adhesives, often cause discomfort and skin irritation during prolonged use. These drawbacks are particularly concerning for long-term ECG monitoring, which is crucial for detecting variations in heart rhythm that may not be obvious in shorter recordings. To overcome these challenges, this study explores a noncontact ECG measuring approach using silver fabric conductive dry electrodes. These dry electrodes were strategically placed under the shoulder blades, waist, and pelvis to effectively capture ECG signals. Given that raw ECG signals are inherently weak, they were amplified using an AD620 instrumentation amplifier, which offers a high common mode rejection ratio (CMRR) and differential gain, effectively reducing noise. The following amplification, the signals were subjected to filtering and baseline adjustment to ensure compatibility with microcontroller processing. The ECG signals were then processed using a 3rd level Discrete Wavelet Transform (DWT) to detect QRS complexes, which were used to calculate the heart rate and compare it with PPG sensor readings. Results indicated that the system performed best in the supine and right lateral positions, with error rates of 3.15% and 1.47%, respectively. This research demonstrated that silver fabric-conductive dry electrodes offer a more comfortable and less irritating solution for long-term cardiac monitoring.