Signal and Power Transfer Through Metal Shielding

An innovative development described recently in Interference Technology magazine (click to see article) provides a way to couple data and power through metal shielding. This has been tested by the developers through steel up to 15mm thick, and could be very useful in a multitude of monitoring-type and other applications which could benefit from the simplicity and cost saving possibly afforded by being able to pass signals and power through the walls of vessels, pipes, other enclosures and large barriers.

Of course it always has been possible to pass electromagnetic signals and possibly a little useful power through most forms of metal shielding, provided, with an appropriate system, that the often considerable power loss involved could be tolerated and/or a low frequency could be used.

Shielding does not form a perfect barrier to electromagnetic disturbances; it merely attenuates very strongly, ideally to a point of insignificance for the relevant frequencies in the context of the intended shielding purpose. And the attenuation encountered is dependent on frequency; in simple terms, increasing with higher frequency and (importantly) tending to zero at very low frequency.

The technology described apparently mitgates the attenuation encountered through steel (a very common containment material) by modifying its properties, namely by magnetically saturating an area of the wall. This reduces the effective magnetic permeability of the steel in that area, thus increasing the skin depth for any given frequency and thereby reducing the attenuation. Thus it is possible to significantly improve the practical frequency range available for coupling through a thickness of steel, and so for many walls more commonly encountered.

What if you suspect that you may be suffering from sporadic Electromagnetic Interference (EMI)? It could be ESD

Interference suffered by equipment does not only occur as a result of power-supply borne disturbances or from electromagnetic disturbances generated by, and conveyed from or radiated by, other electrical/electronic equipment, nor from internal problems in other parts of the equipment.

It can also arise as a result of purely mechanical phenomena, quite independent of and unrelated to any electrical or electronic system, through the creation and building up of static electric charges leading to a subsequent abrupt discharge via a spark.

Such an electrostatic discharge (ESD) does not need to be visible or audible for an electromagnetic disturbance to be produced.

While the energy of the discharge often may be small, its short duration results in high instantaneous power levels and short intense electromagnetic bursts, with potentially significant local effects.

Amongst sensitive equipments that may be affected, are some test, measurement and detection systems.

To determine the solution, it is first necessary to find the causes, and suitably-configured logging equipment will capture detailed information on large numbers of individual interference events to enable this to be done. Such equipment with an appropriately-designed Antenna and RF Amplifier can also provide information in 3 axes on the incident electromagnetic fields, to provide additional geometric and diversity data.

For more information please see our page on EMI Investigation.