Design

The use of exclusion zones to keep wireless transmission devices (WTDs) (e.g., radio walkie-talkies, cellular phones, etc) from being too close to instrumentation and control (I&C) equipment and system cabinets containing this equipment remains a primary concern in existing and advanced (future) nuclear power plants. In Part 1 of this article, a background and history of how exclusion zones were developed and implemented in these plants was presented along with their advantages and limitations. In Part 2, presented here, the elements of the exclusion zone strategy are discussed followed by the demonstration of a concept often used in studying the electromagnetic compatibility (EMC) immunity of modern electronic systems. This concept—called layered immunity—is key to understanding the parts of a system where EMC system immunity must be applied. The initial thought that readers must accept before proceeding to read and understand this concept described in this article is that system immunity involves other parts of the system besides just the immunity of the individual piece of equipment requiring protection.

An experimental validation of an electromagnetic band-gap (EBG) based common mode filter is given in this article. The proposed layout technique is based on planar EBG structures altered by removing the connecting bridges between adjacent patches. The patches are properly dimensioned for ensuring the presence of frequency notches at the frequencies that should be filtered in the common-mode transfer function. The notch frequency is associated with the first resonant mode of the patch.

In our ideal world, safety, quality and performance are paramount.  However, the cost of the final component (which includes the ferrite) has in many cases, become the deciding factor. This article is written as an aide for the design engineer looking for alternative ferrite materials as a means to reduce cost.

Overview of EMI Shielding Compounds

Electromagnetic radiation that adversely affects device performance is generally termed EMI (ElectroMagnetic Interference). Interference takes many forms such as distortion on a television, disrupted/lost data on a computer, or “crackling” on a radio broadcast. Many electronic devices not only emit electromagnetic fields which might cause interference in other systems, but they are also susceptible to stray external fields which could affect its performance. As a result, they must be shielded to ensure proper performance.

Utilities operating nuclear power plants have been dealing with electromagnetic interference (EMI) problems for over two decades. Many early problems that affected the operation of instrumentation and control (I&C) equipment in plants stemmed from the use of wireless transmission devices (WTDs) (e.g., radio walkie-talkies, cellular phones, etc) inside the plant in the vicinity of system cabinets and cable trays carrying bundles of cables. A simple and partially effective method of reducing EMI events caused by WTDs has been to mark off exclusion zones around system cabinets and areas where I&C equipment is installed. The use of these zones has presented some problems for existing plants. For example, some plants have had to expand the area of some zones that became ineffective upon the use of new WTDs that evidently presented an increased risk to the operation and EMI protection of I&C equipment. The sizes of some expanded zones are larger than 2,000 square feet. In addition, some zones encroach upon human traffic areas used by plant personnel to move from area to area within a plant.

There may be a better use for PCB planes than to just distribute power, namely to provide shielding.

Antenna characteristics, such as input impedance are considerably deviated from those in free space when another antenna is located in the vicinity of the antenna. This often causes system degradation problems. In this article, effects of a parasitic wire located beneath the slotted ground plane are investigated on the coupling between monopole antennas above the ground plane. The method of moments is applied to the problem and a combined matrix formulation that includes mutual coupling effects between the elements located in both regions is newly introduced.  It is shown that a wire beneath the ground plane considerably affects coupling characteristics between two monopoles above the ground plane when the slot resonates.

A case study describing the influence of TFT LCD graphics on automotive radiated emissions testing and its impact to the FM band receiver. The underlying root-cause of the EMI issue is determined using a novel technique that decodes the display’s graphics into the transmitted RGB data and predicts the data’s impact to radiated emissions. The countermeasure implemented to resolve the issue is equally novel and does not involve any hardware optimizations. The use of test images to be used in component level EMC testing is also discussed.