Wireless non-contact cardiac and neural monitoring

Abstract

Ubiquitous physiological monitoring will be a key driving force in the upcoming wireless health revolution. Cardiac and brain signals in the form of ECG and EEG are two critical health indicators that directly benefit from long-term monitoring. Despite advancements in wireless technology and electronics miniaturization, however, the use of wireless home ECG/EEG monitoring is still limited by the inconvenience and discomfort of wet adhesive electrodes.We have developed a wireless biopotential instrumentation system using non-contact capacitive electrodes that operate without skin contact. The sensors can be embedded within comfortable layers of fabric for unobtrusive use. All of the issues relating to the design of low noise, high performance capacitive sensors are discussed along with full technical details, circuit schematics and construction techniques.The non-contact electrode has been integrated into both a wearable ECG chest harness as well a EEG headband. We have also designed a compact, battery-powered, wireless data acquisition system to interface with multiple electrodes and monitor patient cardiac and neural signals in real time. Experimental data shows that the non-contact capacitive electrode perform comparable to Ag/AgCl electrodes using our special chest harness and head bands to ensure tight, movement-free electrode positioning.

Dry-Contact and Noncontact Biopotential Electrodes: Methodological Review

“…In particular, the critical information relating to input biasing, input capacitance neutralization and circuit reference/ grounding that allow someone to duplicate the sensor and experiments have been scarce. A complete design for a noncontact, wireless ECG/EEG system can be found in [14], which improves and summarizes their previous designs [12], [27], [38], [39]. These noncontact sensor designs are very simple and robust, manufactured completely on a standard PCB with inexpensive and commonly available components (chip resistors, capacitors and the National LMP7723 and LMP2232).…”

“…One interesting result from this experiment is that for "capacitive" noncontact electrodes operating through clothing [14], [15] , the noise performance and electrode coupling is actually dominated by the resistive component of the cotton layer rather than a capacitance. In many cases, dry contact electrodes are much more capacitively dominated than noncontact electrodes through clothing.…”

“…Active shield guards high-impedance input from interference by other sources and implies capacitive coupling between source and amplifier output. (Right) Simple implementation for dry active electrode made from standard PCB [14]. Exposed metal on bottom surface contacts skin.…”

“…6 qualitatively illustrates the effect of walking and running body activity, inducing motion and friction in random directions, on the ECG signal recorded using noncontact electrodes over a cotton shirt, in comparison to wet contact sensors simultaneously mounted on the skin under the shirt. A tight vest around the waist assisted in mechanically containing the relative motion, and a wireless interface provided mobility while avoiding common-mode noise and line noise pick-up [14]. The wet contact sensors showed reduced, but not completely eliminated, signal artifacts during activity relative to the noncontact sensors.…”

“…Several authors have demonstrated performance comparable to clinical adhesive electrodes [13], [14], through a t-shirt, with a moving subject for ECG. The caveat, however, was that this required a tight vest and chest band to secure the noncontact electrodes in place [14]. This highlights the key, unresolved problem with noncontact electrodes-susceptibility to motioninduced artifacts.…”