Biomedical Engineering Reference
In-Depth Information
30 Hz. Unfortunately, standard anodization breaks down in the presence of saline (e.g.,
from sweat), making the electrodes unreliable for long-term use.
A relatively new anodization process was used by Lisa Sagi-Dolev, the former head of
R&D at the Israeli Airforce Aeromedical Center, and one of us [Prutchi and Sagi-Dolev,
1993] to manufacture pasteless EEG electrodes that could be embedded in
flight helmets.
The hard anodization Super coating process developed by the Sanford Process Corporation
3
is formed on the surface of an aluminum part and penetrates in a uniform manner, making
it very stable and resistant. The main characteristics of this type of coating are hardness
(strength types Rockwell 50c-70c), high resistance to erosion (exceeding military standard
MIL-A-8625), high resistance to corrosion (complete stability after 1200 hours in a saltwa-
ter chamber), stable dielectric properties at high voltages (up to 1500 V with a coating thick-
ness of 50
fl
m), and high uniformity.
Hard anodization Super has been authorized as a coating for aluminum kitchen uten-
sils, and it proves to be very stable even under high temperatures and the presence of cor-
rosive substances used while cooking. The coating does not wear of
µ
m, and up to 4500 V with a coating thickness of 170
µ
with the use of
abrasive scrubbing pads and detergents. These properties indicate that no toxic substances
are released in the presence of heat, alkaline or acid solutions, and organic solvents. This
makes its use safe as a material in direct contact with skin, and resistant to sweat, body
oils, and erosion due to skin friction.
Figure 1.11 is a circuit diagram of a prototype active pasteless bioelectrode. The biopo-
tential source is coupled to bu
ff
ff
er IC1A through resistor R1 and the capacitor formed by
the biological tissues,
aluminum oxide dielectric,
and aluminum electrode plate.
Operational ampli
er and is used to transform
the extremely high impedance of the electrode interface into a low-impedance source that
can carry the biopotential signal to processing equipment with low loss and free of
fi
er IC1A is con
fi
gured as a unity-gain bu
ff
Flat
Cable
Driven
Shield
J1
1
+V
Anodized
Plate
J2
C2
0.01uF
R1
10K
1
-V
C3
0.01uF
IC1A
TL082
3
2
IC1B
R2
100
J3
8
8
5
6
+
+
7
1
1
Output
-
-
C1
5pF
R3
10K
TL082
4
4
Shield
Figure 1.11
Schematic diagram of a capacitive active bioelectrode. Biopotentials are coupled to buffer IC1A through resistor R1 and the
capacitor formed by the biological tissues, aluminum oxide dielectric, and aluminum electrode plate. Operational amplifier IC1A is configured
as a unity-gain buffer. IC1B drives a shield that protects the input from current leakage and noise. Resistors R3 and R2 reduce the gain of the
shield driver to just under unity to improve the stability of the guarding circuit. C1 limits the bandwidth of input signals buffered by IC1.
3
Hard anodization Super is a process licensed by the Sanfor Process Corporation (United States) to Elgat
Aerospace Finishing Services (Israel) and is described in Elgat Technical Publication 100,
Hard Anodizing:
“Super'' Design and Applications
.
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