Shielding AC Magnetic Fields

Historically, shielding AC magnetic fields has been difficult and therefore expensive. At the ELF or AC frequency, the electric and magnetic fields operate independently of each other. While most common building materials block the electric portion of the fields, the magnetic portion will pass undiminished through earth, concrete, most conventional building materials including wood, drywall and even a thick layer of lead!

Historically, shielding of AC magnetic field sources has relied exclusively on the use of a ferrous material, such as "Mu-metal" or thick steel plates to accomplish a shielding technique known as "Flux Shunting". This techniques works by displacing magnetic fields which can unfortunately, create new problems in areas peripheral to the shielding, a phenomena known as "blooming". It is also disadvantaged by thickness and weight of the steel shielding plates, making it difficult for shielding installation in existing buildings. Moreover, Flux Shunting is unlikely without considerable effort and cost, to achieve field reductions below 10 mG (the upper threshold level for interference on most monitors).

Alternately, FMS uses an advanced and superior technique called Eddy Current Cancellation. Special conductive shielding material is utilized to achieve a very high degree of shielding efficiency by the induction of eddy-currents that occur within conductive materials when placed in an ELF magnetic field. AC electrical currents are induced within the conductive material in closed circular paths which are perpendicular to the inducing external magnetic field. Such induced eddy-currents oppose changes in the inducing external magnetic field and as a result, AC magnetic fields produced by the circulating eddy-currents cancel the larger external AC magnetic fields near the conductive material surface.

Implemented correctly, this technique results in a very high degree of shielding efficiency without excessive weight, blooming and other problems associated with Flux Shunting. This technique is the product of many years of research and allows and allows cost efficient shielding schemes capable of reducing AC magnetic fields to much lower levels than by traditional shielding methods.