Our cells communicate with each other by transporting ions through the cell membrane. It is required to send signals throughout the body and to the brain, making it possible for us to move, think and feel. This movement of ions can be measured electrically. These signals are very small – a thousandth of a volt.
An electrode is a conductor (so something that can transfer electricity) that makes electrical contact with a non-metallic part of the circuit. Electrodes either sense tiny electrical signals from, for example, the heart, or they stimulate tissues in the human body, like suppressing pain in pregnant women.
Electrode pads come in many different shapes, materials, and sizes; the most well-known version is the disposable adhesive hydrogel electrode, to which a cable can be connected through a snap button.
Electrodes as sensors
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ECG electrodes
The first example of an electrode as a sensor can be seen in electrocardiography, also known as ECG, where the electrical activity of the heart is charted over time. A medical ECG uses ten electrodes and gives a doctor a three-dimensional view of the electrical activity in the heart. This data can then be used for diagnosing misfunction of each part of the heart. Often cheap disposable adhesive hydrogel electrodes are used in this application.
Another example is the EMG or electromyography, which is often used to analyse muscle activation. In medical applications, it is used to diagnose neural and muscular problems, while in research and sports, the application is to study muscular activation. Often the same disposable adhesive electrodes as in ECG are used.
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EEG electrodes
The third example is electroencephalography or EEG, which measures the electrical activity of the brain. Typical medical applications are the diagnosing of epilepsy or sleep disorders.
Researchers used EEG to study brain function and for example to control a computer by thoughts in a brain-computer interface (BCI). During EEG research, typically tens of small metal disc-electrodes are placed in a cap over the scalp.
Electrodes for stimulation
Besides sensing electrical signals, electrodes can also give electrical signals to the human body. For example, electrical stimulation of muscles can move. But it can also reduce pain and can even stimulate the regrowth of neural fibres after a neural injury.
A well-known example is Electro Muscle Stimulation (EMS), in which muscles are excited (tensed) by a large stimulation current. A cool product example where Ems Muscle Stimulator Machine is used is the full body training suits to intensify your workout routine. The additional electrical current applied to the muscles makes them work harder, resulting in an intensified workout.
Another example of electrodes as actuators is Transcutaneous Electrical Neurostimulation (TENS), which sends a small electrical current through the skin, usually smaller than EMS. The current through the nerve fibres blocks or at least reduces the pain signals travelling to the brain. TENS units are often used by pregnant women on the lower back.
The tens pads are often inexpensive large reusable hydrogel electrode pads. Alternatively, there are wet textile electrodes made from conductive textiles that are non-adhesive and reusable.
The challenge with stimulation electrodes is that the large current induces pain as it activates the underlying pain-sensing neural fibres. By using a large surface area and wet electrodes, we can reduce hot spots in current density and avoid activating the pain nerves.
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