Our active magnetic shielding systems are used primarily for reduction of powerline fields. They are effective for both overhead and underground lines. Within a defined area, the magnetic field can often be reduced to a very low level. While passive shielding using metal plates is commonly used for single rooms, active shielding is usually the only practical approach to power line field mitigation at the whole-building level. Similar technology is commonly used for room-level field reduction for scanning electron microscopes (SEMs) and other electron beam devices, but our work is limited to wide area, building level applications. We currently have systems installed and operating throughout the U.S., Canada, Israel, and Sweden, in commercial, school, and residential environments.
Significant misunderstanding exists about the true nature of active magnetic shielding (active cancellation) and its use as a field reduction technique. This is because magnetic field remediation
is poorly understood by many people, and until recent years, active shielding has seen limited use outside the laboratory environment. The
problem is exacerbated by the availability of outrageous products which claim to reduce magnetic fields through various unexplained means,
but which in reality do nothing at all.
A magnetic field can be thought of as a force that has both strength and direction. If it is met with an equal force of exactly opposite direction, the forces will cancel and the net force will be zero. This is the basic principle of active cancellation. Fundamental principles of physics are applied in the real world to solve a problem. The term "cancellation" is sometimes taken to mean complete elimination, but this is never achieved. Rather, EMF cancellation efficiencies of 65% to 90% are typical. From this perspective, the term "active magnetic shielding" is perhaps more appropriate, although both terms can be used interchangeably.
The systems that we install consist of three basic elements: (1) a sensor to monitor the power line
field, (2) a control and power unit, and (3) a network of driven coils. The system tracks the power line field and instantaneously adjusts
to compensate for changes that normally occur due to load variation on the line. In large commercial or school applications, our systems
can supply virtually unlimited power, with adjustable phase correction for increased cancellation percentage and improved stability. In many
cases, the external driven coils can be placed underground where they are obscured from view. In other cases, especially those involving elliptical polarization, above-ground components are required. We strive to harmonize the system with the architectural style and topographic conditions prevailing at the site. Total costs for a residential system are typically in the $10,000 to $25,000 range. Systems for schools or commercial buildings can run from $10,000 to $100,000 or more, depending on size and field complexity. This technology can represent a viable solution for powerline magnetic field reduction in cases where no other possibilities exist.
The primary limitations to deployment of such a system are inadequate free space surrounding the area where field reduction is desired, and in some cases the requirement for an overhead conductor span (which may not be aesthetically acceptable). For any active cancellation/active shielding system, the challenge to producing good performance is design of the driven coil network that surrounds the treated area and produces the counter field. This is completely unique to each job. The specialized cancellation equipment is an essential element, but it is secondary to coil design. EMF Services has performed pioneering work to address issues of elliptical polarization, strong field gradients, inductive delay, and spatial phase variance, which have in the past precluded effective deployment of active EMF cancellation on a large scale.
A preliminary determination of the applicability of active magnetic shielding for your location can sometimes be made from a review of measurement data, photos, and a sketch showing building and lot dimensions. However, this is not a packaged system that can be purchased and installed by the customer or by local personnel. Each application is unique because field intensity, field angles, and available space vary widely. Therefore, each system is custom designed to match the field conditions at the site, and installed by local contractors under our direct supervision. Commercial, school, and residential client references are available.
Active Shielding / EMF Cancellation Photo Gallery
