Capacitive Measurement of ECG for Ubiquitous Healthcare

Abstract

The technology for measuring ECG using capacitive electrodes and its applications are reviewed. Capacitive electrodes are built with a high-input-impedance preamplifier and a shield on their rear side. Guarding and driving ground are used to reduce noise. An analysis of the intrinsic noise shows that the thermal noise caused by the resistance in the preamplifier is the dominant factor of the intrinsic noise. A fully non-contact capacitive measurement has been developed using capacitive grounding and applied to a non-intrusive ECG measurement in daily life. Many ongoing studies are examining how to enhance the quality and ease of applying electrodes, thus extending their applications in ubiquitous healthcare from attached-on-object measurements to wearable or EEG measurements.

Data Quality Assessment of Capacitively-coupled ECG Signals

“…Long-term electrocardiography (ECG) recordings from real-life environments have been an important focus of recent research [1][2][3][4]. Capacitively-coupled ECG (ccECG) has been demonstrated as a technology that has the potential to achieve recordings from real-life environments and enable unobtrusive health monitoring [1,2], thereby improving the quality of life of people and lowering healthcare costs (e.g. by early diagnosis and timely treatment).…”

“…Despite the advantages of ccECG, it is highly susceptible to motion artefacts (MAs) [1][2][3], which are particularly problematic in recordings from real-life environments (e.g. while driving, while sleeping).…”

Evaluation of a Multichannel Non-Contact ECG System and Signal Quality Algorithms for Sleep Apnea Detection and Monitoring

“…Unobtrusive monitoring of physiological signals is a field of research that has seen an increased interest during the last decades, due to its potential to enable a patient-centered healthcare with lower costs, higher population screening and an increased patient/user comfort. Non-contact, capacitively-coupled electrocardiography (ccECG) [ 1 , 2 , 3 ] is one of the technologies suited for long-term physiological monitoring without affecting people’s daily life; potential applications range from heart rate (HR) and heart rate variability (HRV) monitoring, to the diagnosis and follow-up of conditions involving the cardiorespiratory system. Despite this, the challenge of its use in real-life scenarios remains, due to its high sensitivity to motion artefacts, which leads to a high variation in the quality of the acquired signals.…”

Noise-Resistant CECG Using Novel Capacitive Electrodes

“…The one in Figure 3 b has a high input impedance, and is most commonly employed in CECG measurements [ 9 ]. The one in Figure 3 c is enclosed by a guard ring to reduce noise interference [ 10 ]. For convenience of comparison, the electrodes in Figure 3 a–c are hereafter referred to as electrodes 1–3, respectively.…”

“…In light of this, non-contact electrodes have been used over recent years to address the disadvantage of using electrodes in ECG [9]. In contrast, in capacitive ECG (CECG) the signals are capacitively coupled to non-contact electrodes through the clothing worn by a subject as a dielectric layer [10]. A major advantage of CEGG over ECG is that the wet conductive gel required in ECG dries as time elapses, resulting in unwanted noise due to poor contact between electrodes and the skin of a subject.…”