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Metal Microelectrodes Basics |
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Written by Lisa J Fulghum
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Types of Metal Electrodes
WPI offers a large variety of metal electrodes and they come in four basic styles (profiles). The selection guide that follows references the four electrode profiles. In addition, concentric bipolar electrodes are also discussed, as well as some of the options offered for the metal electrodes.
NOTE: The electrode diagrams below are not shown to scale.
Profile A
Profile B
Profile C
Profile D
Concentric Bipolar Electrodes
These electrodes are excellent for shielded macro recording, as well as evoked potentials. They are especially well suited for bipolar stimulation. The tungsten electrode is sharpened to a point and is 75μm in
diameter. The outer stainless steel conductor is insulated with Polyimide tubing
to within 0.2mm of the end of the stainless steel tube. This electrode is also available without
the outer Polyimide insulation.
This figure shows an insulated metal conductor with an exposed concentric surface.
♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦
Metal Electrode Options
Exposed Tip Dimensions (nominal)
WPI electrodes
made from a variety of metals and tip diameters to offer the nominal
impedance ratings you require. Use the table below to determine which
type of electrode will meet your criteria.
Nominal
Impedance |
Tungsten
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Elgiloy
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Platinum
Iridium
|
Pure
Iridium |
| 0.1 MegΩ |
100µ |
120µ |
60µ |
45µ |
| 0.5MegΩ |
55µ |
66µ
|
18µ |
14µ |
| 1.0MegΩ |
30µ |
36µ |
10µ |
10µ |
| 2.0MegΩ |
12µ |
15µ |
6µ |
5µ |
| 5.0MegΩ |
5µ
|
6µ |
3µ |
2.5µ |
Kapton (KT) Tubing
Kapton* tubing, indicated by “KT” in the part number, extends from the
connector to within 5mm of the tip, providing stiffness and additional
insulation to the electrode shaft. Kapton-clad electrodes are recommended when
the electrode is to be inserted through a cannula for extra deep
penetration.
Heat Treated Tip
The Heat Treated Tip (see image below) is ideal for penetrating tough membranes. (It is not
recommended for chronic implantation.) This process is performed using a
microforge in which the heating element is positioned in close proximity to the
tip in order to melt the Parylene-C distal to the exposed metal. It provides a
smooth transition and produces better adherence of the Parylene-C to the
metal.
Both the KT and non-KT electrodes are heat-treatable. The heat
treatment is applied only to the parylene coating. The heat melts the parylene
so it feathers down close to the shank near where the tip is exposed.
This removes the abrupt edge where the parylene has been removed to
create the tip exposure. The purpose is to prevent the parylene from
delaminating from the electrode during implantation into tissue which could
catch on the edge. Heat treatment does not work well in chronic
applications, because the feather edge is susceptible to fluid intrusion over
time, which will alter the impedance characteristics of the electrode
unfavorably.
To have your electrodes heat treated, just add the suffix “H” to any of the
“KT” numbers on the facing page. This treatment incurs an additional cost. Please call for pricing.
* Parylene is a trade mark of Union Carbide. Kapton is a trade mark of
DuPont. Elgiloy is a trade mark of Elgiloy Ltd.
Gold Plated Pins
Gold-plated pins (WPI #5482) and sockets (WPI #5483) may be attached to 24-, 26- or
28-gauge wire.
Additional Accessories
300102
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Micromanipulator holder, 4 in., 2mm to 0.031 socket
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| 5468 |
2 mm receptacle to 0.031-inch jack (for Omega-TipZ
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| 5469 |
Adapts mini banana plug (DAM80) to 0.031-inch receptacle (metal
microelectrode) |
| 5470 |
0.031-inch jack, 28 ga. wire, 12 inch (pkg of 4) |
| 5482 |
Pins, 0.031-inch, gold-plated (pkg of 50) |
| 5483 |
Sockets, 0.031-inch gold-plated (pkg of 50) |
If you
have any questions regarding metal microelectrodes or other WPI products, give us a call toll-free
at 866.606.1974 or email us at
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.
Visit our online store to purchase WPI products.
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Last Updated ( Friday, 05 March 2010 )
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