Spring 2013 Team 5

Dry, Noninvasive, Wireless EEG System

Nicholas Hawkins, Thang La, David Tran, and Henry Truong

Department of Electrical and Computer Engineering University of Houston, Houston, TX 77204-4005

Project Sponsored by The University of Houston Engineer: Dr. Jose Luis Contreras-Vidal

Faculty Advisor: Dr. Jose Luis Contreras-Vidal

Abstract

Electroencephalography (EEG) is the measurement of electrical activity of the brain along the

scalp. Traditionally, EEG systems are implemented using wet, gel based, active electrodes in a

wired system. The need to apply a wet gel and be physically constrained due to wires make these

systems inconvenient for patients, researchers, and medical personnel.

The goal of this project is to develop a dry, noninvasive, wireless EEG system that will be

interfaced with a smartphone to allow for mobile recording of brain activities. The dry,

noninvasive, electrodes were implemented with silver-coated bristles, a concept developed by

Fraunhofer Institute FIRST (Figure 1). The bristle electrodes were tested by recording EEG

signals in the occipital lobe simultaneously with a wet, passive electrode to detect the opening

and closing of the eyes. The power spectral density plot of the EEG signals in the occipital lobe

illustrates that the signal acquired by the bristle electrodes are comparable to that of a wet,

passive electrode (Figure 2). From the power spectral density plots, the Pearson product-moment

correlation coefficient for the two signals was calculated to be 0.7162, meaning there is a high

positive correlation between the two signals. A headgear was also designed to ensure the bristle

electrodes were properly mounted to the scalp with enough pressure to increase the conductivity

of the electrodes (Figure 3). An MSP430 microcontroller is used to sample the EEG signals from

the bristle electrodes at 500 Hz. The acquired signals are sent to a smartphone, via Bluetooth,

which displays both the raw data signals as well as the power spectral density of the signal

(Figure 4).

Spring 2013 Team 5

Figure 1: Dry bristle electrode design. The bristle electrodes are designed from toothbrush bristles to provide a soft and flexible contact with the scalp. The bristles are coated with conductive silver ink to acquire electrical signals.

Figure 2: Power spectral density plot of the signals acquired by the dry bristle electrode and wet, passive electrode. The two electrodes were tested simultaneously by placing the electrodes about 5cm away from each other in the occipital lobe to detect eyes closing and opening. Both electrodes shared the same ground and reference electrodes, which were implemented with wet, passive electrodes. The PSD for the dry bristle electrodes is in red (bottom), and the PSD for the wet, passive electrode is in blue (top). The Pearson correlation coefficient was calculated to be 0.7162, indicating that there is a high positive correlation between the two signal.

Figure 3: Head gear design to secure the dry bristle electrodes to the scalp. The bristle electrodes are housed inside the pre-amplifier module, shown by the red box. Velcro straps are used to accommodate varying size heads.

Figure 4: EEG Android application. The application displays the raw signal acquired by the electrodes as well as the power spectral density (PSD) for that electrode. The application above displays the raw signal for a 5µV Pk-Pk, 10Hz sine wave in the bottom plot, with its corresponding PSD in the top plot.