Chapter 6 Conclusions and Future Works
6.2 Future Works
In future work, our system could combine with the utility of other physiological parameters, such as EKG and EMG, to improve both the sensitivity and positive predictive value. Besides, a non-linear algorithm as fuzzy neural network could be used to make the prediction more precise and increase the accuracy of drowsiness detection. On the other hand, the portable bio-signal acquisition system and DSP module could be integrated as one device to minimize the size of whole system and reduce the signal distortion result from using wireless transmission. Furthermore, there is a novel dry foam bio-signal electrode developed, fabricated and experimentally validated in our lab. The dry electrode was shown in Fig. 6-1:
Fig. 6-1: (a) top view, (b) exploded view of the proposed dry foam EEG electrode.
The foam electrode was covered by the conductive fabric on all surfaces and then paste on an Au layer.
The major merits of this dry foam electrode include follows: (1) It is applied with zero preparation of scalp, compared to the conventional wet electrodes, (2) the soft substrate of dry foam electrode is able to adapt to irregular scalp surface and the hairy site, and (3) Its fabrication process is low-cost. Therefore, compared to the standard wet electrodes, the proposed dry foam electrode provided a potential for routine and
repetitive measurement, and also provided convenience, and comfort for clinical and research applications. The performance and signal quality of dry electrodes are introduced below:
A. Impedance Measurements
In order to test the impedance between the skin and electrode interface, two dry electrodes were placed on the forehead (4 cm apart), and then current was applied to the electrode pair to measure the impedance [49]. Nineteen tests were performed on five different participants. Two different electrodes were used: One is standard wet electrode and the other is dry foam electrode. Fig. 6-2(a) showed the impedance measurement under different conditions. Here, the black line denotes the impedance of dry foam electrode pair without skin preparation and conducting gel. Blue and red lines denote the impedances of conventional wet electrodes without and with skin preparation respectively. All of the conventional wet electrodes were applied with conduction gels. The results showed that the impedance between the skin and dry foam electrode without skin preparation and conducting gel is similar to that of the conventional wet electrode with skin preparation and conducting gel. Therefore, the conduction performance of dry foam electrode outperformed the conventional wet electrode [48, 49].
(a)
(b)
Fig. 6-2: Frequency characteristic of the proposed dry foam electrodes on (a) forehead and (b) hairy site.
Figure 6-2(b) showed the impedance measurement on the hairy site. It showed that, for dry foam electrode, the impedance on the hairy site nearly equals that on the hairless skin, but that on hairless skin is even lower. Evidently, the foam of dry foam electrode is soft enough to contact the skin properly, and the fabric layer is very stable.
These properties make the standard skin preparation unnecessary. Certainly, dry
electrodes will hardly surpass the properties of the conventional electrodes with conduction gel. Fig.6-3 showed the impedance variation for different electrodes under long-term EEG measurement. For long-term EEG measurement, the impedance variation of the conventional wet electrode with conduction gel is more obvious than that of dry foam electrode. The impedance variation of dry foam electrode was observed in the range from 4 k to 26 k, and is in the acceptable range for normal EEG measurement [48, 54]. Furthermore, compared to the conventional wet electrode under long-term EEG measurement (5 hours), dry foam electrode can significantly provide better stability of the skin–electrode impedance. This result can be explained by that dry foam electrode does not need conduction gel, which is apt to drying.
Fig. 6-3: Impedance variation of dry foam electrode and conventional wet electrode under long-term EEG measurement.
B. Comparison of the Signals between Dry/Wet Electrodes
Fig. 6-4(a) and Fig. 6-4(b) showed the placements and the results of EEG measurement by using dry/ wet electrode pairs in the locations of forehead (F10) and hairy site (POz) respectively. Fig. 6-4(c) showed the placements and the results of
EOG measurement by using different types of electrodes. The correlation between signals obtained by dry foam electrode and conventional wet electrode are typically in excess of 96.32 %, 92.18 % in the locations of forehead and hairy sites respectively.
For EOG measurement, the correlation between EOG signals obtained by dry/wet electrodes is also very significant (in excess of 97.28 %). Therefore, the performance of bio-potential measurement by using dry foam electrode is almost identical to that of the conventional wet electrodes.
Fig. 6-4: Placements and results of (a) EEG measurement on forehead (F10), (b) EEG measurement on hairy site (POz), and (c) EOG measurement by using different types of electrodes.
In the future, we will integrate the dry foam electrode with our portable bio-signal acquisition system to become a more complete and convenient system.
Using this system could simplify the procedure of bio-signal acquired preparation and also maintain the stability and make user feel comfortable. Come to a conclusion, our system is feasible for further extension, and within above future works could make our system more complete and better.
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