What is an EMF Shield?

Mary McMahon
Mary McMahon

An EMF field is a component of the structure of a device or object which is designed to provide some shielding from electromagnetic fields. Such fields can interfere or severely disrupt the normal operation of a device, making shielding very important, especially with delicate equipment like sensitive scientific instruments. Most electronic devices are required by law to include EMF shielding, and citizens of some nations may note that such devices are often stamped with information indicating that they comply with laws requiring EMF shielding of electronics.

Faraday cage with bolt of electricity.
Faraday cage with bolt of electricity.

Typically, an EMF shield is designed both to prevent electromagnetic fields from interrupting a device, and to limit the electromagnetic field generated by a device so that it cannot interfere with other devices. While such shielding cannot be perfect, it can be very high quality, making it difficult for EMF disruptions to occur.

Electromagnetic shielding is most often employed to protect something or someone against radio waves.
Electromagnetic shielding is most often employed to protect something or someone against radio waves.

A simple example of an EMF shield is a component in an electrical cord which covers the conductive area of the cord and lies underneath the insulation, designed to prevent the field generated by the passage of electricity through the cord from spreading. EMF shields are also used in the casing and housing of electrical devices in the same way. These fields can protect from electromagnetic radiation, but they will not necessarily block radio waves.

Even a good EMF shield, such fields can still cause disruptions. For example, leaving a cell phone next to a computer monitor can distort the display, even though both devices are theoretically shielded. Concerns about electromagnetic fields have also led to requirements to turn off devices such as cell phones and computers in certain environments. In a hospital, for example, cell phones are not allowed in some areas because they could interrupt medical equipment, and on aircraft, the use of electronic devices is restricted due to concerns that they could interfere with the operation of the aircraft.

A more sophisticated variation on the basic EMF shield known as a Faraday shield or Faraday cage provides additional protection, and may be used around sensitive equipment or when very high volumes of electricity are being used. Whatever the type, an EMF field must be regularly evaluated and tested to confirm that it is working properly, as degradation of the shield can cause it to malfunction. Consumers may also have noticed that older devices can have imperfect shielding, caused by different manufacturing standards or natural wear and tear which damaged the EMF shield.

Cables use the concept of electromagnetic shielding to separate the wires from outside environments.
Cables use the concept of electromagnetic shielding to separate the wires from outside environments.
Mary McMahon
Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a wiseGEEK researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

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Discussion Comments


Do these waves pose any danger like EMFs? I read that EMFs may be potentially harmful to small children. I would love to learn if there are any potential negative effects.


Can an EMI wave interfere with implanted medical devices such as pacemakers? If so, why do the manufacturers of such devices create a shielding box around such devices?

I know that persons with pacemakers can not have MRI's. Can a Faraday box eliminate EMI waves from the sun's EMI waves?


What about protecting your car?


@strawCake - Well, maybe that guy had never flown before. On the other hand, it's not that hard to follow the directions. They do announce it over the speaker system if I remember correctly.

I actually got in trouble awhile ago in a hospital. I had no idea you weren't supposed to use your cell phone in certain areas. I was visiting someone and merrily chatting away on my phone while I was waiting for the doctor to get done with them. Imagine my surprise when a nurse politely asked me to finish my phone call elsewhere!

The nurse was nice, but I was still a little embarrassed. Next time I go visit someone in the hospital I'm going to turn my phone off and leave it in my purse!


I'm not that familiar with EMF shielding, but I do know that you're not supposed to have your cell phone on when a plane is taking off. Until recently, I thought everyone knew that.

However, on the last flight I was on, the guy behind me would not turn off his phone! They announced it over the speaker system several times and finally the flight attendant had to make him do it. I don't know if he was experiencing some jitters about flying or something, but I thought it was a little ridiculous!

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