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Wearable Health Monitoring System - Fabric Electrodes

by Reshma Anand on  August 23, 2015 at 11:54 AM Health In Focus   - G J E 4
Fabric electrodes are just textile materials that can conduct electricity. In today's world, the importance of flexible and portable electronic devices are on the rise.
 Wearable Health Monitoring System - Fabric Electrodes
Wearable Health Monitoring System - Fabric Electrodes
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These electrodes are gaining popularity in the medical field, as it can be used widely for biological signal acquisition. This is nothing but recording biological signals from humans directly. It is also widely used in metal plating, conductive polymer coating, magnetron sputtering, and gas phase deposition and impregnation.

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As cardiovascular diseases are on the rise, the importance of health monitoring systems has also increased. ECG is used to monitor patients who are at high-risk for cardiovascular diseases. Previously metal electrodes, polymer electrodes that used conductive gel were used to monitor a patient's biological signals. But nowadays, fabric electrodes are preferred as health monitoring systems due to its several advantages.

Advantages

Fabric electrode, which is a wearable ECG monitoring system is comfortable, breathable and have non-irritating properties. They can be easily folded, and are skin-friendly. Compared to conductive gels, long-term use of fabric electrodes does not cause skin irritation. They are intelligent and accurate in detecting biological signals.

Principle

The human body is made of semi-permeable membranes that transfer signals in and out of the skin. The device that is wearable can touch the skin, and it has sensors that can easily receive ECG and EMG signals from the body. The electrical signals received are then amplified using a signal amplifier where it is filtered to remove noise. Thus the electric signals of patients can be acquired accurately using fabric electrodes.

The device acts as electrical sensor to collect and pass the biological signals obtained through a series of signal conditioning and micro-processing systems and finally display these processed signals on the human-machine interface (such as personal digital assistant).

Design Criteria

Design of fabric electrodes is generally based on the following factors:

Size: The size of fabric electrode is a key factor because it directly affects the accuracy of biological signals. The derivation surface of the fabric electrode is 10mm in diameter. Greater diameter could cause some disturbances between the skin and the device and can reduce its accuracy.

Shape: The shape of fabric electrode is the main factor affecting the potential distribution on the electrode surface. Generally rectangular electrode is preferred to a circular electrode, as its uniformity of current distribution is higher as compared to the circular electrode by 30%.

Selection of textile materials: The main role of the filler material used in making the fabric electrode is to ensure close and complete contact with the skin, as well as reduce SNR (signal to noise ratio) and motion artifacts. Deformation or the interface slip between the fabric electrode and skin will produce complex interfering noise, which is called as motion artifact.

Adhesion between fabric electrodes and skin: Generally conductive cloth should be filled with sponge-like materials in order to maintain the three-dimensional shape of the fabric electrode. This also ensures a close contact with the skin. In this way, artifact reduces, and SNR increases for accurate measurement.

Preparation

Choice of conductive materials: Conductive materials of fabric electrode are mainly conductive metal, conductive polymer and conductive ink.

Conductive thread: Inert metal is selected as conductive wire metal due to its stability and anti-allergic properties.

Conductive rubber: Rubber is used since it is soft and does not cause any stimulation on the skin.

Conductive ink: It constitutes of silver powder and petroleum jelly. This does not cause any damage to the patient's skin due to friction.

Applications

ECG Monitoring

In the modern world, the rise in chronic heart diseases like stroke, cardiac arrest has increased the importance of wearable health monitoring systems. Fabric electrodes are made up of cloth and therefore they can be easily used to monitor ECG in heart patients. It does not cause any allergies on the skin like conductive gel, and it also helps in recording the biological signals accurately. It can be easily attached to the wrists or biceps of a heart patient to measure ECG.

Myoelectric Prosthesis

The myoelectric prosthesis is an alternative to conventional hook prostheses for patients with traumatic or congenital absence of hands. The myoelectric prostheses are controlled by the user using the contraction of specific muscles triggering prosthesis movement through electromyographic (EMG) signals. The fabric electrodes are fixed by an elastic belt on the hands of the patient to record the EMG signals during the contraction and relaxation movement of muscles.

Supercapacitors

Supercapacitors are nothing but double-layered capacitors that can store energy.

Generally metal coated electrodes are only used in these capacitors. But recent research has focused on developing stretchable supercapacitors, where it has shown that poly-pyrrole coated fabric can be used as supercapacitors. Taiwan Institute of textile industry has recently developed a light-weight, foldable fabric supercapacitor.

Reference

http://www.scirp.org/journal/PaperInformation.aspx?PaperID=56684
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