Bismillahirrahmanirrahim.
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from last post. There are a few designs of surface electrodes. There are
Silver–Silver Chloride Electrodes, Gold Electrodes, Conductive Polymer
Electrodes, Metal or Carbon Electrodes and Needle Electrodes.
Silver-Silver Chloride
The
common surface electrode design used is the Silver-Silver Chloride design of
electrode. This is the classic design that high-quality electrode design
consists of highly conductive metal, silver, interfaced to its salt, silver
chloride, and connected via an electrolytic gel to the human body. This design
is known to produce the lowest and most stable junction potentials.
Additionally, an electrolytic gel typically based on sodium or potassium
chloride is applied to the electrode.
Reusable
silver–silver chloride electrodes (a) are made of silver disks coated
electrolytically by silver chloride, or, alternatively, particles of silver and
silver chloride are sintered together to form the metallic structure of the
electrode. The gel is typically soaked into a foam pad or is applied directly
in a pocket produced by the electrode housing. The electrode is secured to the
skin by means of nonallergenic adhesive tape.
Disposable
electrodes (b) are made similarly, although the use of silver may be minimized
because of the snap-on button itself may be silver coated and chlorided. To
allow for a secure attachment, a large foam pad attaches the electrode body
with adhesive coating on one side. Such electrodes are particularly suited for
ambulatory or long term use.
Gold-plated electrodes
Gold-plated
electrodes have the advantages of high conductivity and inertness desirable in
reusable electrodes, are commonly used in EEG recordings. Small reusable
electrodes are designed so that they can be securely attached to the scalp. The
electrode body is also shaped to make a recessed space for electrolytic gel,
which can be applied through a hole in the electrode body. The electrodes are
attached in hair-free areas by use of a strong adhesive such as colloidon or
securely attached with elastic bandages or wire mesh. Disadvantages of using
gold electrodes over silver–silver chloride electrodes include greater expense,
higher junction potentials, and greater susceptibility to motion artifacts. On
the other hand, gold electrodes maintain low impedance, are inert and reusable,
and are good for short-term recordings as long as a highly conductive gel is
applied and they are attached securely.
Conductive Polymer
Electrodes
This
electrode does not need additional adhesive or electrolytic gel and hence can
be immediately and conveniently used. The conductive polymeric electrode
performs adequately as long as its relatively higher resistivity over metallic
electrodes and greater likelihood of generating artifacts are acceptable. The
higher resistivity of the polymer makes these electrodes unsuitable for low-noise
measurement. The polymer does not attach as effectively to the skin as does the
conventional adhesive on disposable ECG electrodes built with a foam base and,
furthermore, the potentials generated at the electrode–skin interface are more
readily disturbed by motion.
Metal
or Carbon Electrodes
These
electrodes have a much higher resistivity and are noisier and more susceptible
to artifacts, but they are inexpensive, flexible, and reusable and are thus
chosen for applications such as electric stimulation or impedance
plethysmography. For these applications, gel is usually not applied and the
electrodes are used in “dry” form for easy attachment and removal. These
electrodes have the potential for producing very high levels of artifact and
are bulky and awkward to use, but do offer the advantage of being reusable and
tend to be inexpensive. Carbon or carbon-impregnated polymer electrodes are
also used occasionally although they are mainly used as electrical stimulation
electrodes.
Needle electrodes
Needle
electrodes (e) comprise a small class of invasive electrodes, used when it is
absolutely essential to record from the organ itself. The most common
application is in recording from muscles or muscle fibers. A metallic,
typically steel, wire is delivered via a needle inserted at the site of the
muscle fiber. The wire is hooked and hence fastens to the muscle fiber, even as
the needle is removed. Small signals such as motor unit potentials can be
recorded in this manner. For research applications, similar needle or wire
electrodes are sometimes connected directly to the heart muscle. Since such
electrodes are noninvasive, their use is limited to only highly specialized and
supervised clinical or research applications.
For
my project, I use Silver-Silver Chloride disposable electrode even though the
reusable one is maybe better in most aspect.
Barakallah.
