What EMI Shielding is and Why it Matters

Posted by: EMC Technologies
Posted on: 11/09/2017
EMI shielding

It helps to start technical discussions by stating the definitions on which the discussion is based. Here are the two relevant definitions, both supplied by the Tech-Etch website.

Electrostatic interference, EMI is a process by which disruptive electromagnetic energy is transmitted from one electronic device to another via radiated or conducted paths, or both. In electronic components, EMI can adversely affect their performance.

Electronic shielding The practice of surrounding electronics and cables with conductive or magnetic materials to guard against incoming or outgoing emissions of electromagnetic frequencies.

The reasons we need EMI shielding

The use of electrical and electronic equipment has grown exponentially. As an example, mobile phone ownership and usage have exploded and the environments (frequency bands) where they operate are getting crowded. These devices use electronic transmission and the potential for EMI is huge. We are protected by the electromagnetic shielding imposed on manufacturers by international standards.

Stringent regulations largely prevent the potential effects of EMI. I use the word “largely” because uninformed and profit driven people can and will circumvent the regulations and sell uncertified and dangerous products because most countries’ regulations do not apply to exported goods.

The Australian Communications and Media Authority (ACMA) administers regulations that require all electrical and electronic equipment to meet prescribed standards. Manufacturers and distributors must test, certify and label their products as compliant to these standards. Any retailer who imports and sells non-compliant electronic equipment to Australian or New Zealand consumers is liable to severe penalties.

However, Australian travellers and foreign visitors can bring uncertified products which are not detected by Customs. Devices for personal use are generally exempt. Examples include mobile phones and unsafe mobile phone battery chargers.

The definition quoted states that EMI can adversely affect product performance. Illegal electronic devices can cause far worse damage than this. Let’s mention only a few examples. Risks include the effects of EMI and electrical safety, both of which regulated by stringent standards.

    • At the first level there are nuisance factors. For example, an illegal and uncertified mobile phone can emit EMI that interferes with other sound systems. For example, while using the phone in a car, the user may hear his or her conversation relayed over the car radio loudspeakers. This is a simple case of illegal EMI emission.
    • Fake and illegal mobile phone chargers pose serious and life threatening risks to their users. Such devices have been known to explode, cause fires, and electric shock.
    • An illegal device capable of radio transmission can interfere with mission critical electronic systems. A good example is the guided electronic landing systems at airports. Imagine what could happen if it malfunctions because of electromagnetic interference from substandard and illegal handheld devices like computers, tablets, or mobile phones. The potential effect is life-threatening.
  • Sticking with mobile phone, research suggests that electromagnetic emissions from mobiles can cause brain damage when held in close proximity for long periods. The only protection against this is to use certified phones with  electromagnetic shielding as prescribed in appropriate Australian and NZ standards.

What is EMI shielding and how is it enforced

The truth is that many engineers who design electronic equipment are neither qualified, nor do they have the facilities and equipment to test the levels of emission in their prototype equipment. To make matters worse, they do not necessarily have expert knowledge about International and country specific standards, nor a knowledge of the testing procedures and emission levels  allowed in regional or international standards.

This is where a NATA accredited test laboratories come into the picture to advise, conduct tests, and issue test reports. EMC Technologies is the largest and most experience laboratory in Australia with offices in Sydney, Melbourne, and New Zealand. They can give you expert and independent advice.

The applicable shielding techniques

Shielding is applied to device enclosures and cables. The shielding reduces the coupling of radio waves (RF shielding), and blocks electromagnetic and electrostatic fields from interfering with other electronic systems and devices.

Shielding is typically applied to enclosures and to cables. The image shown below illustrates proper coaxial cable shielding.

Enclosure shielding, applied to device enclosures or system sub-components, uses materials like sheet metal, metal screen, or metal foam. Its effectiveness depends on its size, shape, thickness, and aperture orientation.

Other shielding techniques used include:

    • Metallic shields made of metal or ferrite materials.
    • Electromagnetics like solenoids and coils that cancel static or low-frequency fields.
    • Superconducting materials that expel magnetic fields.
    • Metallic foil or braid shield to surround cables or wires to block EMI.
    • Conductive paint that block the emission of electromagnetic frequencies (EMF).
    • Capacitors, ferrules, and grounded wires to minimise EMI noise.
  • Magnetic materials used to draw EMI into the magnetic field.

As you can see, this is very much a field for specialised engineering.

In Australia and New Zealand, EMC Technologies has a team of specially trained engineers ready to consult and offer independent compliance testing and remedial solutions for electromagnetic emissions that exceed the levels prescribed by the applicable standards. Call us now.

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