EMI material reflects the radiations, conducting materials like metals can also be used but they are bulky , so any material which shows some conductivity and is flexible can be used as a material for EMI shielding like flexible graphite etc. For more details the following paper may be referred:

http://wings.buffalo.edu/academic/department/eng/mae/cmrl/Materials%20for%20electromagnetic%20interference%20shielding.pdf

EMI material reflects the radiations, conducting materials like metals can also be used but they are bulky , so any material which shows some conductivity and is flexible can be used as a material for EMI shielding like flexible graphite etc. For more details the following paper may be referred:

http://wings.buffalo.edu/academic/department/eng/mae/cmrl/Materials%20for%20electromagnetic%20interference%20shielding.pdf

I agree with Naresh regarding the usage of conducting materials to shield somethign against EMI. Nevertheless, the proper shielding depend on the EMI type. There are some tehcniques applicable to shield against electric fields (high conductive materials are advisable) and other should be employed for shielding magnetic fields (usually high permeabilty materials are employed). Shields can be composed by several layers depending on the EMI, frequency band and intensity. Another fundamental issue regarding shielding is the shape of the shield. For further information, I would suggest Clayton Paul's "Introduction to Electromagnetic Compatibility" as a very good first reference.

Regards.

Thank you so much for your helpful comments.

There are many forms of shielding. Shielding materials that work well for electric fields will not necessarily be very good for low-frequency magnetic fields. Materials that make good shielded enclosures are not necessarily the best materials to use for electric or magnetic field shielding. Usually the design of the shield is just as important as the material used. You can find more information at http://www.learnemc.com/tutorials/Shielding02/Practical_Shielding.html as well as Clayton Paul's book.

When a question like this comes up, the best response is "It depends" commonly stated by Professor Todd Hubing who has already responded. In the question you asked for comments but did not provide details on what is to be accomplished. When working on a real product answers will vary. Being a medical device is weight an issue, or cost? Depending on the answer, there are various composites that provide shielding effectiveness which does not include conductive paints or metalized foil shields. What field intensity is the device to be protected against? Shields work based on both reflection and absorption. If using a really thin shield then how many skin depths are required for optimal performance? Are you trying to shield against magnetic or electric fields and what frequencies are the components susceptible to? Do you want to protect a particular component or section of the printed circuit board, or the entire assembly? If weight is not an issue then almost any metal or composite shield barrier will work. How is the shield bonded to 0V for fields absorbed which are generally transformed into heat within the material? Is the shield to be used exclusively for susceptibility concerns or to create a shield partition to keep undesired internally generated EMI from propagating into the environment of use? Is there a potential shock hazard from leakage current is the shield is connected to AC ground?

These are just some of the concerns related to the answer "It depends". I am sure many others that may post will have similar responses which are highly encouraged. If you can provide specifics about the application and environment of use, enhanced comments can be provided.

Farshad,

I have a question to you in return: Do you want reflection or absorption ? Cavity effects have to brought down by damping rather than using thicker or more conductive materials. Oppositely, the distance between the source (or victim) and its shield determine its effectiveness assuming you're not interested in far shield shielding effectiveness. Proper use of thin copper layers at close distance help to reduce the effective area orders better than at an few mm or cm away. Last but not least, H-field shielding below 10 kHz will be a battle unless active compensation can be used.

actually in our present work we would like to have absorption as dominant shielding mechanism.

In life supporting medical devices electric field intensity shouldn't 10 v/m and also we want to develop a new composite material that can be used in frequency range of 900 MHz to 12 GHz.

In our work shielding against both magnetic and electric fields are important and also we want to do shielding effectiveness measurement in far field.Furthermore material size and weight are more important than the expenses for us.

Farshad,

you've put us in the wrong direction with your initial question. Now it is clear that you want to achieve absorption above 900 MHz. Then comes the question: how much ?

W.r.t density, size and weight, RAM foam sounds suited

Hallo,

I think the best shielding material is a Zn thick layer.

All the best

A PMC with Cu or graphite as reinforcements!

Goodluck

hybrid polymer composite fabricated by thin films followed by compression molding.

use GRAPHANE as fillers and carbon fiber as reinforcement i polymer matrix

Polymer composite materials would be useful

Dear Farshad, please check this link

https://www.modusadvanced.com/resources/blog/what-is-emi-shielding-and-why-is-it-important-for-your-design

the catch about EM shielding are often poor contacts...and don't forget about the "box in a box "concept..For Rf and microwave this way more than 300 dB shielding have been obtained AND measured(not to easy to measure reliably) However proper shielding at low frequencies is more tricky and may require magnetic shielding (e.g. low transfer impedance coaxial cables).In addition microwave absorbers (foam) and /or ferrite (stealth)are in use.