BIOPOTENTIAL AMPLIFIERS - Design and Development of Medical Electronic Instrumentation - page 11

Figure 1.9 er arrays are used to detect muscle signals from 256

points for a high-resolution large-array surface electromyography system. Arrays of gold-plated pins
soldered directly to array inputs are used as the electrodes.

Eight high-input-impedance bu ff

using a long fl flat cable. Power could be supplied either locally, using a single 9-V battery and

two 10-k resistors, to create a virtual ground, or directly from a remotely placed symmet-

rical isolated power supply.
Low-impedance op-amp outputs are compatible with the inputs of most biopotential
ampli

Ω

ers. Wires from J2 can be connected to the inputs of instrumentation just as normal
electrodes would. The isolated common post of the biopotential ampli

fi

ers should be con-
nected to the ground electrode on the subject or preparation as well as to the ground point
of the bu

fi

ff er array.

PASTELESS BIOPOTENTIAL ELECTRODES

Op-amp voltage followers are often used to bu er signals detected from biopotential

sources with intrinsically high input impedance. One such application is detecting biopo-
tential signals through capacitive bioelectrodes. One area in which these electrodes are par-
ticularly useful is in the measurement and analysis of biopotentials in humans subjected to
conditions similar to those existing during

ff

fl flight. Knowledge regarding physiological reac-

tions to flight maneuvers has resulted in the development of devices capable of predicting,

detecting, and preventing certain conditions that might endanger the lives of crew members.
For example, the detection of gravitationally induced loss of consciousness (loss of con-
sciousness caused by extreme g -forces during sharp high-speed

fl

flight maneuvers in war
planes) may save many pilots and their aircraft by allowing an onboard computer to take
over the controls while the aviator regains consciousness [Whinnery et al., 1987]. G z -
induced loss of consciousness (GLOC) detection is achieved through the analysis of vari-
ous biosignals, the most important of which is the electroencephalogram (EEG).
Another new application is the use of the electrocardiography (ECG) signal to syn-
chronize the in

fl

ation of pressure suits adaptively to gain an increase in the
level of gravitational accelerations that an airman is capable of tolerating. Additional appli-
cations, such as the use of the processed electromyography (EMG) signal as a measure of
muscle fatigue and pain as well as an analysis of eye blinks and eyeball movement through
the detection of biopotentials around the eye as a measure of pilot alertness, constitute the
promise of added safety in air operations.
One problem in making these techniques practical is that most electrodes used for the
detection of bioelectric signals require skin preparation to decrease the electrical impedance

fl ation and de fl