Techtextil Focus | November 2019
Electromagnetic protective textile fabric
Conductive polymers such as polyacetylene, polypyrrole and polyaniline are applied to textile materials and hence prepared composites have given satisfactory results for protecting electromagnetic rays, reveal Jeyaraman Anandha Kumar and Dr M Senthil Kumar.
Various electromagnetic radiations exist in our modern life. Many researchers have proved that the electromagnetic radiation can produce adverse reaction, and even does harm to people’s health. The electromagnetic radiation has been listed as pollution and must be controlled by Human Environment Conference of United Nations, and many national governments have warned people against electromagnetic radiation. Therefore, related theoretical research and application about electromagnetic shielding fabric have gradually become hot, and it has great significance to prevent people from electromagnetic radiation damage.
In order to shield electromagnetic waves, electromagnetic shielding fabric is obtained by adding metals and other methods. With the advancement of wireless technology, people are becoming adaptable to more and more electronic devices which become indispensable parts of our daily lives. These devices raise different radiations in different frequency bands. As per the definition given in Oxford dictionary, radiation is the emission of bulk of high velocity energy as electromagnetic waves or as moving sub-atomic particles, especially high energy particles which cause ionisation. This ionisation causes chemical reactions in body tissues which leads to serious health problems like cancer, nausea, genetic damage, etc. So, protection against these radiations is gaining importance nowadays.
Besides the protection against harmful effects to the human body, shielding against electromagnetic interference is a serious concern. Conventionally, metals, due to their high conductivity, are considered the best material to shield electromagnetic waves. But their use is very limited due to certain limitations like a heavyweight, poor dexterity, corrosion etc. The incorporation of conductivity in textiles has overcome these limitations. Different ways to incorporate shielding properties in textiles and different test methods to check shielding effectiveness will be discussed later in this article.
Sources of radiation
Radiations can arise from many man-made sources such as microwave ovens, industrial electric furnaces, and wireless networks like Wi-Fi and Bluetooth or from main sources such as the magnetic field of the Earth and sunlight that contains visible, infrared and UV rays and many more harmful frequencies. Patients are exposed to nuclear radiations in diagnosis and cancer therapy, etc. Depending on occupation, risks can be greater than average. People working in nuclear power plants, underground miners, radiologists, medical technologists are under different levels of radiation exposure.
Electromagnetic shielding textiles protect the passage by blocking the penetrations of radiations to the levels at which the effect can be minimised. The easiest way to impart EM shielding ability is by making the textiles conductive. In the recent past, various techniques are developed for achieving this level of conductivity, either it by metalising the textiles, by using ferromagnetic substances or by use of ICPs like polyaniline and polypyrole, etc.
Electromagnetic shielding is the process of limiting the penetration of electromagnetic fields into a space, by blocking them with a barrier made of conductive material. Typically it is applied to enclosures, separating electrical devices from the outside world, and to cables, separating wires from the environment the cable runs through. Shielding is a very popular method of protecting electronic and electrical equipment and human beings against radiated electromagnetic energy. The materials or protector which protects a body, environment or a circuit from harmful electro-magnetic radiation is called shield.
Shields are used either to isolate a space (a room, an apparatus, a circuit etc) from outside sources of electromagnetic radiation, or to prevent the unwanted emission of electromagnetic energy radiated by internal sources. Traditionally, such shields are based on the use of stiff metallic materials with well-known electromagnetic properties. Plastics with a metallic coat or with metal fibres injected during the molding stage are used also. But they are still not flexible. Recently attention has been paid to light weight and flexible materials, such as textiles covered with conductive layer. These materials, owing to their flexibility, durability, ease of manufacturing and application, are considered promising for shield of electro-magnetic radiation.
The instant invention related to electromagnetic shielding fabrics, and more particularly fabric formed entirely of metal coated synthetic yarns. It is well known that exposure to long term or acute electromagnetic radiation can have harmful effects on human tissue, and furthermore, it is also known that electromagnetic radiation can interfere with certain bio-electronic devices, such as pacemakers, which are essential to the daily lives of affected people. The recent proliferation of electronic devices, such as cell phones, and computer equipment, that emit low levels of electromagnetic radiation, or interference, has significantly increased the problem and created a need of everyday shielding garments. In this regard, a variety of electromagnetic shielding fabrics, and garments formed produced in order to prevent electromagnetic radiations.
Types of Ionising radiation
Alpha particles have little power of penetration and can be easily stopped by a sheet of paper or the outer layer of the skin. However, alpha emitting materials are harmful to health if they enter the body by inhalation or along with food or water. Beta particles are high speed electrons and are more penetrating than alpha particles. A sheet of aluminium a few millimetre thick can stop beta particles.
X-rays and gamma rays are both very penetrating and can pass right through human body. Dense materials such as lead or concrete are more effective in absorbing these rays. Neutrons do not carry any electric and are constituents of atomic nuclei. Hydrogen-rich materials, such as water or paraffin can shield against these highly penetrating particles.
Criteria for selection of materials and fabrication technologies for shielding
materials used in the technique of electromagnetic field shielding must meet following conditions:
- Non-ionising radiation – e.g, visible light, signals from mobile phones, and radio waves; and
- Ionising radiation – e.g, radiation emissions from uranium ore, and high frequency waves in the electromagnetic spectrum such as x-rays.
The growth of the electronic industry and the widespread use of electronic equipment in communications, computations, automations, biomedicine, space, and other purposes have led to many electromagnetic interference (EMI) problems as systems operate in close proximity. Table 1 shows the radiation level of different electronic devices. Increased awareness of EMI has led to the formulation of new regulations around the globe for the manufacturers of electrical and electronic equipment to comply with the electromagnetic compatibility requirements.
NaturaShield: Some useful commercial products for application of electromagnetic radiation shielding fabric are described here . NaturaShield is a high performance shielding fabric with the crisp look and soft feel. Advance technology has created a fibre which has the conductive components on the inside, with pure natural cotton on the outside. The result is a fabric which is gentle to the skin, has a great feel, and still provides 20-35 dB from 100 MHz to 2.2 GHz, and residual performance is up to 10 GHz. Surface resistivity is 109 Ohm/sq.
This fabric is perfect for bedding, clothing, drapes and most other applications where shielding is required without the harshness of metalised fabrics. It is washable by machine and dryable (cool) without losing shielding performance. It is tailorable and sews like ordinary cotton. Other specifications are 125 g/m², 60 inch wide, white in colour as snow with a fine grey grid.
FlecTron®: FlecTron® is a high quality copper plated nylon ripstop fabric with an amazingly low surface resistivity of less than 0.1 Ohms/sq. It is light in weight and flexible. It is highly tear resistant and can be cut and sewn like ordinary fabric. It has Attractive satiny copper colour finish. It can be used to make highly effective shielded enclosures or clothing. Thickness is 0.06 inch and weight is 2.1 oz/yd².
Ex-static™: Ex-static™ is a conductive fabric light weight, durable conductive fabric containing 87 per cent polyester, 13 per cent gray BASF (carbon) fibres woven right into the fabric in an attractive diamond pattern providing surface resistivity of 105 ohms per square. It is very comfortable and only 3 oz per square yard in weight. It can be tailorable and washable like polyester fabric. Conductivity will hold up to 50 or more low heat washings. Can be used to make E-field shielding bedding, appliance covers, clothing, drapes, room dividers, and anything else you can sew. The Ex-Static Fabric is excellent at reducing electric fields.
See-Through Conductive Fabric: See-Through Conductive Fabric is stretchable silver coated sheer nylon weave. It can shield low intensity radio frequency and microwaves (with a shielding effectiveness up to 67 dB at 1 MHz and 33 dB at 1 GHz), and is an excellent E-field shield when grounded. Resistivity <5 Ohms/sq. it can be used as sandwich in between bed sheets, line a vest, as cover of microwave oven, computer monitor or keyboard, stereo, light cords, circuit box, vacuum cleaner. It is very delicate fabric, rubbing and heavy handling can cause grayish silver to wear off.
Phantom fabric: Phantom fabric has excellent shielding effectiveness (~45 dB) and nearly transparent, this conductive fabric is tough and durable too. It is composed of copper over Nickel coated polyester mesh and has 90 threads per inch. It allows plenty of light penetration and air circulation. It makes a great lining for shielded clothing, hats, bedding or drapes. Cover windows, monitor screens and LED’s to shield electric field. It can be used over computers, TV’s microwave ovens, clock/radios and most appliances.
Shieldit® Super shield fabric: Shieldit® Super is Based with a rugged plain weave nylon (for superior strength and handling), plated with tin and copper (for excellent shielding, low corrosion, and low toxicity), then coated on one side with conductive acrylic (less than 0.1 Ohm/sq) plus a hot melt (203°-338°F) adhesive with polyethylene barrier on the other side. It can be ironed on to cotton, wood, glass or paper, or rolled into a tube and then heat seal the seam. It can also be cut and sewn like ordinary fabric. This fabric offers an amazing shielding performance: 80 dB (99.99 per cent) at 100 MHz; 100 dB.
EMF protection fabrics: Emf Blocker Made of Super Thin Polyester and Conductive Thread. a High Tech Emf Shield to Block All Kind of Electromagnetic Fields and Rfid Signals .
Ripstop silver fabric: The Ripstop Silver Fabric works really well for shielding Wi-Fi routers and other microwave transmitters. At nearly 60 dB, this fabric will block approximately 99.9 per cent of the microwave radiation. It also reduces electric fields.
Shield Naturell fabric: For excellent reduction of microwave radiation, the Swiss Shield Naturell Fabric is ideal. This fabric shields to 40 dB (approximately 99.99 per cent reduction in RF). The Naturell fabric is primarily made of organic cotton that is interwoven with silver coated copper wires.
GIRON magnetic field shielding: Magnetic fields are very important to fix as they are likely the most harmful to human health. GIRON is strips of GOES in opposite directions. If the magnetic fields are coming from outside your home (from high-tension power lines for example), it can be quite cost prohibitive to shield and may only be able to reduce the fields by 50 per cent unless you completely surround the area with multiple layer of shielding material.
Copper wire mesh: Copper wire mesh can be useful for electrical field reduction and RF shielding.
Aluminium mesh: This will reduce the RF by 40 dB (10,000 times reduction) if installed in a way where there are no leaks. If grounded, this product will also reduce AC electric fields the home.
AL60 Wall Shield: AL60 Wall Shield is a very effective material for reducing RF and electric fields. It is also very cost effective for its shielding capability (60 dB at 2.0 GHz).
Various approaches have been observed to prepare textile materials as electromagnetic shield. Conventionally, metallic fibres were used in yarn and fabrics and afterwards metal coating was applied to textile materials. Then conductive particles such as copper, silver or even carbon particles were also applied to textile material by suitable techniques to prepare electro-conductive textiles for electromagnetic shield.
In recent years, conductive polymers such as polyacetylene, polypyrrole, polyaniline, etc are applied to textile materials and hence prepared composites are proven satisfactory results for protecting electromagnetic rays. This article highlighted some protective measures as well as commercial fabrics available to reduce the harmful effects of the electromagnetic fields and radiation.
- high coefficient of the shielding effectiveness,
- be resistant to mechanical impact and easy to handle,
- be resistant to harmful influence of external environment (oxidation, corrosion), durable, homogenous, easy to form the shield,
- and low costs of production.
Jeyaraman Anandha Kumar is a Lecturer with the Department of Textile Processing, G.R.G.Polytechnic College, Kuppepalayam, Sarkar Samakulam, Coimbatore, India.
Dr.M.Senthil Kumar is an Associate Professor with the Department of Textile Technology, PSG College of Technology, Peelamedu, Coimbatore. Corresponding Author: email@example.com
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