Tension Structure And Pedestal Design; Features - Geodesic Sensor Net Technical Manual

3: GSN 200

Tension Structure and Pedestal Design

The sensors that make up the GSN 200 are sewn into a geodesic structure using
durable polyurethane elastomer threads that form the tension lines of multiple
icosahedra.
As the GSN 200 is stretched over a subject's head, the sensors make electrical contact
with the scalp and are held firmly in place, normal to the head surface, by the
geodesic tension network. Pressure is evenly distributed across all sensors, providing
a comfortable array that can be worn for several hours.
The foot or scalp end of the sensor pedestal is flared, causing
the pedestal to lift and rake the hair as it is moved against the
head. This produces a self-seating action, so that the pedestal
Flared
sponge, with its load of electrolyte, is inserted beneath the
foot
hair, directly against the scalp.
All sensors for recording (except eye channels on infant GSN 200s), plus reference and
isolated common, are contained in the Net's structure, making application a rapid,
one-step process. Typical application times are less than 10 minutes—even for 256-
channel GSN 200s—with impedances in the 10–50 kΩ range for the GSN 200.
The GSN 200 is designed for use with HydroCel Saline, which is EGI's classic
potassium chloride saline and surfactant solution. No special scalp preparation is
required, and no electrolyte gel residue is left in the hair following the recording
session.

Features

Sensors and Electrodes
Each GSN 200 contains an array of 64, 128, or 256 EEG sensors, plus a reference sensor
and an isolated common sensor. Each sensor corresponds to an amplifier channel.
Sensor maps are shown in Appendix B, "Net Sizing and Sensor Layouts." Inside each
sensor is a sintered silver/silver chloride or silver chloride–plated carbon pellet
connected by a 1-meter-long insulated lead wire to a Hypertronics-compatible, gold-
plated pin.
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Geodesic Sensor Net Technical Manual
S-MAN-200-GSNR-001 • January 31, 2007