Tex­tiles for shield­ing elec­tro­mag­netic fields (realy shield­ing?)

In marked there are lot of tex­tile promis­ing to pro­tect from Elec­tro­mag­netic fields (EMF). There are bunch of sites sell­ing them. All of tex­tiles are char­ac­ter­ized like: shield­ing in dB, con­duc­tive sur­face Ohm/​square, pro­tec­tion 99.5%, pro­tects from EMF, etc. But there are only few prod­ucts that are really tested and only frac­tion of them are tested using valid/​standardized methods.

In our lab­o­ra­tory, we have tested hun­dreds of sam­ples for clients all round the world. Some of clients are shocked after the tests, when we pro­vide test report where it is writ­ten that tex­tile have no impact on elec­tro­mag­netic field– respec­tively it is use­less to pro­tect from EMF Fig. 3.

My aim here is not to point out the dirty play­ers in EMF tex­tile shield­ing mar­ket, but to give some use­ful and easy under­stand­able infor­ma­tion with­out com­plex math, on how tex­tiles are tested.

There are sev­eral test­ing meth­ods defined in inter­na­tional stan­dards, but one of most rec­og­nized is to use shielded cham­ber with hole in the wall Fig.1. Shielded cham­ber is room made out of few mm thick steel, so inside the cham­ber there is no EMF, if the hole in the wall is cow­ered by steel plate. Dur­ing the tests, metal­lic plate is replaced by tex­tile sam­ple and on each side of sam­ple anten­nas are installed. Trans­mit­ting antenna inside cham­ber and receiv­ing antenna out­side the chamber.

Fig.1 Shield­ing effec­tive­ness measurements

Trans­mit­ting antenna trans­mits RF sig­nal and receiv­ing antenna receives sig­nal, that have trav­eled through the sam­ple. If sam­ple is ideal pro­tec­tor for EMF there are no sig­nal received out­side the cham­ber, but don’t be fooled by EMF tex­tile sales man­agers, there are not ideal tex­tiles.
Shield­ing Effec­tive­ness (SE) is the ratio of the RF energy on one side of the shield to the RF energy on the other side of the shield expressed in deci­bels (dB) Fig.2.

Fig.2 Shield­ing effec­tive­ness definition

Mate­r­ial shield­ing effec­tive­ness is not con­stant in fre­quency range. Tex­tile are thin mate­ri­als, where usu­ally con­duc­tive mate­ri­als are inte­grated (usu­ally met­als, rarely car­bon). So, usu­ally it is not very good shield­ing below few MHz. Usu­ally tex­tiles are usable in fre­quency range ~100MHz– ~10GHz. On other fre­quency ranges they are use­less, espe­cially at mains fre­quen­cies 50/​60Hz. Your EMF tex­tile shorts and T-​shirt will not pro­tect you from the fields com­ing from power lines above your head and fields com­ing from the cables at your house. Will EMF tex­tile shorts and T-​shirt pro­tect you from cell­phone, wire­less router, radio and TV sta­tion cre­ated fields, depends on many, many para­me­ters and one of them is tex­tile shield­ing effec­tive­ness.
Some of tex­tile mea­sure­ment pho­tos in lab­o­ra­tory with anten­nas.

Fig.3 Shield­ing effec­tive­ness measurements

Elec­tro­mag­netic field are invis­i­ble, so for some of you it is hard to under­stand, what is shield­ing effec­tive­ness and how tex­tile mate­r­ial affects elec­tro­mag­netic waves. For these rea­son 3D elec­tro­mag­netic mod­el­ing can be used to visu­al­ize the shield­ing of waves. Basi­cally, model con­sists of wall (width 1m, height 1m) with aper­ture (0.5x0.5m) in it Fig. 4. On left side, elec­tro­mag­netic wave is gen­er­ated and it trav­els through the aper­ture to the right side. If aper­ture in wall is cov­ered with tex­tile, it has impact on elec­tro­mag­netic field, elec­tro­mag­netic waves should be damped.

Fig.4 Shielded wall with aperture

Fig.5 1GHz wave pen­e­trat­ing through open aper­ture in wall (dimen­sional view)

Fig.6 1GHz wave pen­e­trat­ing through open aper­ture in wall (side view)

As you can see in Fig.5 and Fig.6 field freely pen­e­trates through aper­ture in wall. If aper­ture is cov­ered by shield­ing tex­tile elec­tro­mag­netic waves are atten­u­ated, atten­u­a­tion depends on tex­tile para­me­ters. In this arti­cle three type sam­ples are mod­eled sam­ple with 200 Ohm/​square, sam­ple with 5 Ohm/​square and sam­ple with 0.1 Ohm/​square.

If aper­ture in wall is cov­ered by tex­tile with 200 Ohm/​square field is atten­u­ated and can not freely pen­e­trate through aper­ture Fig. 7, Fig. 8.

Fig.7 1GHz wave pen­e­trat­ing through sam­ple tex­tile with 200 Ohm/​square (dimen­sional view)

Fig.8 1GHz wave pen­e­trat­ing through sam­ple tex­tile with 200 Ohm/​square (side view)

If tex­tile resis­tance is decreased down to 50 Ohm/​square, field is atten­u­ated and only frac­tion of it is trans­mit­ted to the other side of the wall.

Fig.9 1GHz wave pen­e­trat­ing through sam­ple tex­tile with 50 Ohm/​square (dimen­sional view)

Fig.10 1GHz wave pen­e­trat­ing through sam­ple tex­tile with 50 Ohm/​square (side view)

If tex­tile resis­tance is decreased down to 0.1 Ohm/​square, field is not trans­mit­ted to the other side of the wall Fig. 11, Fig. 12. So, it can be assumed that the tex­tile mate­r­ial is ideal EMF pro­tec­tor at 1GHz fre­quency. I have not seen such mate­ri­als in our lab.

Fig.11 1GHz wave pen­e­trat­ing through sam­ple tex­tile with 0.1 Ohm/​square (dimen­sional view)

Fig.12 1GHz wave pen­e­trat­ing through sam­ple tex­tile with 0.1 Ohm/​square (side view)

As you can see in fig­ures the higher the resis­tance, the less effec­tive tex­tile mate­r­ial shields elec­tro­mag­netic waves. 200 Ohm/​square mate­r­ial have prop­er­ties to pro­tect you from EMF but it is not as far as good as 0.1 Ohm/​square which looks like blocks all EMF (in real life I guess there is not tex­tile with 0.1 Ohm/​square, it is used only for visu­al­iza­tion purposes).

Some visu­al­i­sa­tions

1GHz wave pen­e­trat­ing through aper­ture in shielded wall

1GHz wave pen­e­trat­ing through sam­ple tex­tile with 200Ohm/​square

1GHz wave pen­e­trat­ing through sam­ple tex­tile with 50Ohm/​square

1GHz wave pen­e­trat­ing through sam­ple tex­tile with 0.1Ohm/​square