Recent demand and interest in wireless, mobile-based healthcare has driven significant interest towards developing alternative biopotential electrodes for patient physiological monitoring. The conventional wet adhesive Ag/AgCl electrodes used almost universally in clinical applications today provide an excellent signal but are cumbersome and irritating for mobile use. While electrodes that operate without gels, adhesives and even skin contact have been known for many decades, they have yet to achieve any acceptance for medical use. In addition, detailed knowledge and comparisons between different electrodes are not well known in the literature. In this paper, we explore the use of dry/noncontact electrodes for clinical use by first explaining the electrical models for dry, insulated and noncontact electrodes and show the performance limits, along with measured data. The theory and data show that the common practice of minimizing electrode resistance may not always be necessary and actually lead to increased noise depending on coupling capacitance. Theoretical analysis is followed by an extensive review of the latest dry electrode developments in the literature. The paper concludes with highlighting some of the novel systems that dry electrode technology has enabled for cardiac and neural monitoring followed by a discussion of the current challenges and a roadmap going forward.

/pdf/dry-contact-and-noncontact-biopotential-electrodes-43xov09vpd.pdf

Dry-Contact and Noncontact Biopotential Electrodes: Methodological Review

Alternatives to conventional wet electrode types are keenly sought for biomedical use and physiological research, especially when prolonged recording of biosignals is demanded. This paper describes a quantitative comparison of three types of bioelectrode (wet, dry and insulating) based on tests involving electrode impedance, static interference and motion artefact induced by various means. Data were collected simultaneously, and in the same physical environment for all electrode types. Results indicate that in many situations the performance of dry and insulating electrodes compares favourably with wet electrodes. The influence of non-stationary electric fields on shielded dry and insulating electrode types was compared to wet types. It was observed that interference experienced by dry and insulating electrode types was 40 dB and 34 dB less than that experienced by wet electrode types. Similarly, the effect of motion artefact on dry and insulating electrodes was compared to wet types. Artefact levels for dry and insulating electrodes were significantly higher than those for wet types at the beginning of trials conducted. By the end of the trial periods artefact levels for dry and insulating types were lower than wet electrodes by an average of 8.2 dB and 6.8 dB respectively. The reservations expressed in other studies regarding the viability of dry and insulating electrodes for reliable sensing of biosignals are not supported by the work described here.

https://iopscience.iop.org/article/10.1088/0967-3334/21/2/307/pdf

A direct comparison of wet, dry and insulating bioelectric recording electrodes.

Braincomputer interfaces (BCIs) allow their users to communicate or control external devices using brain signals rather than the brain's normal output pathways of peripheral nerves and muscles. Motivated by the hope of restoring independence to severely disabled individuals and by interest in further extending human control of external systems, researchers from many fields are engaged in this challenging new work. BCI research and development has grown explosively over the past two decades. Efforts have begun recently to provide laboratory-validated BCI systems to severely disabled individuals for real-world applications. In this paper, we discuss the current status and future prospects of BCI technology and its clinical applications. We will define BCI, review the BCI-relevant signals from the human brain, and describe the functional components of BCIs. We will also review current clinical applications of BCI technology and identify potential users and potential applications. Lastly, we will discuss current limitations of BCI technology, impediments to its widespread clinical use, and expectations for the future.

/pdf/clinical-applications-of-brain-computer-interfaces-current-54hq0xzy9o.pdf

Clinical Applications of Brain-Computer Interfaces: Current State and Future Prospects

https://sccn.ucsd.edu/~scott/pdf/IJP08_share.pdf

Linking brain, mind and behavior

Dry and noncontact electroencephalographic (EEG) electrodes, which do not require gel or even direct scalp coupling, have been considered as an enabler of practical, real-world, brain-computer interface (BCI) platforms. This study compares wet electrodes to dry and through hair, noncontact electrodes within a steady state visual evoked potential (SSVEP) BCI paradigm. The construction of a dry contact electrode, featuring fingered contact posts and active buffering circuitry is presented. Additionally, the development of a new, noncontact, capacitive electrode that utilizes a custom integrated, high-impedance analog front-end is introduced. Offline tests on 10 subjects characterize the signal quality from the different electrodes and demonstrate that acquisition of small amplitude, SSVEP signals is possible, even through hair using the new integrated noncontact sensor. Online BCI experiments demonstrate that the information transfer rate (ITR) with the dry electrodes is comparable to that of wet electrodes, completely without the need for gel or other conductive media. In addition, data from the noncontact electrode, operating on the top of hair, show a maximum ITR in excess of 19 bits/min at 100% accuracy (versus 29.2 bits/min for wet electrodes and 34.4 bits/min for dry electrodes), a level that has never been demonstrated before. The results of these experiments show that both dry and noncontact electrodes, with further development, may become a viable tool for both future mobile BCI and general EEG applications.

Dry and Noncontact EEG Sensors for Mobile Brain–Computer Interfaces

We describe the microfabrication, packaging, and testing of an active, dry, scalp electroencephalogram (EEG) electrode. The electrode consists of a silicon sensor substrate and a custom circuit substrate (2 μm CMOS technology). A via-hole technology has been developed using reactive ion etching with SF 6 O 2 gas mixture to make electrical contacts between the sensor and circuit substrates. These substrates and batteries (power source) are then assembled in a custom package for testing on bench and human subjects.

An active, microfabricated, scalp electrode array for EEG recording

We describe the microfabrication, packaging, and testing of an active, dry, scalp electroencephalogram (EEG) electrode. The electrode consists of a silicon sensor substrate and a custom circuit substrate (2-/spl mu/m CMOS technology). A via hole technology was developed using reactive ion etching with SF/sub 6//O/sub 2/ gas mixture to make electrical contacts between the sensor and circuit substrates. These substrates and batteries (power source) were then assembled in a custom package for testing on bench and human subjects.

Babak Alizadeh-Taheri

Papers

An active, microfabricated, scalp electrode array for EEG recording

An Active, Microfabricated, Scalp Electrode-array For EEG Recording