Design, fabrication and experimental validation of a novel dry-contact sensor for measuring electroencephalography signals without skin preparation

Abstract

In the present study, novel dry-contact sensors for measuring electro-encephalography (EEG) signals without any skin preparation are designed, fabricated by an injection molding manufacturing process and experimentally validated. Conventional wet electrodes are commonly used to measure EEG signals; they provide excellent EEG signals subject to proper skin preparation and conductive gel application. However, a series of skin preparation procedures for applying the wet electrodes is always required and usually creates trouble for users. To overcome these drawbacks, novel dry-contact EEG sensors were proposed for potential operation in the presence or absence of hair and without any skin preparation or conductive gel usage. The dry EEG sensors were designed to contact the scalp surface with 17 spring contact probes. Each probe was designed to include a probe head, plunger, spring, and barrel. The 17 probes were inserted into a flexible substrate using a one-time forming process via an established injection molding procedure. With these 17 spring contact probes, the flexible substrate allows for high geometric conformity between the sensor and the irregular scalp surface to maintain low skin-sensor interface impedance. Additionally, the flexible substrate also initiates a sensor buffer effect, eliminating pain when force is applied. The proposed dry EEG sensor was reliable in measuring EEG signals without any skin preparation or conductive gel usage, as compared with the conventional wet electrodes.

Keywords: conductive gels; dry electrode; electroencephalography (EEG); skin-sensor interface impedance.

Figure 1.

(A) Several images of the proposed dry EEG sensor are shown. (B) An exploded view of the proposed dry sensor is presented. Each probe includes a probe, plunger, spring, and barrel.

Figure 2.

The fabrication process of novel dry EEG sensors.

Figure 3.

The equivalent circuits of (A) a wet electrode-skin interface and (B) a dry skin-sensor interface.

Figure 4.

(A) The wireless EEG acquisition module and the performance characteristics with (B) a top view of the readout circuit and (C) the design diagram in differential configuration are shown.

Figure 5.

Impedance change data representing the skin-electrode interface on the (A) forehead (F10) and (B) at hairy sites (POz).

Figure 6.

Long-term impedance variation measurements on the forehead site (F10) for wet and dry electrodes.

Figure 7.

Experimental process for signal quality assurance of the dry sensors.

Figure 8.

Prerecorded EEG and corresponding signals recorded by the dry EEG sensor.

Figure 9.

EEG signal comparison, as recorded by wet electrodes and the proposed dry sensors. (A) The EEG measurements on the forehead site (F10) and (B) the hairy site (POz) are presented.

Figure 10.

Signal comparison, as recorded by the wet electrodes and the proposed dry sensors. (A) The EOG measurements on a forehead site and (B) eye-blink signals on a forehead site are shown.