Electromagnetic Compatibility Measurement Near Field

Near and far-fields, EMC, and the low-frequency power supply

In any radiation source, whether it is an antenna, some sort of circuitry, or a low-frequency power supply, there is a “near” and a “far” field. Considering the case of a low-frequency power supply and electromagnetic compatibility measurement (EMC,) the dominating radiating force close to the power supply is electromagnetic, whereas farther out the dominating force in the wavelength becomes electrostatic (Jackson 1998, Straus 2001). Thus, the names “near field” and “far-field” refer to these phenomena (Williamson Labs 2007). These radiation fields vary depending on specific conditions of the radiated wavelength. Normally, the near field is considered the portion of the field within a defined radius where this radius is “much less” than the wavelength (represented with ℜ«λ) (Capps 2001, Straus 2001).

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Near and far-fields, EMC, and the low-frequency power supply

The near field is commonly known for its creation of what is known as electromagnetic induction and the resultant electrical influence on the electromagnetic field, while for a low-frequency power supply these affect diminish proportionally with increasing distance from the supply. The effects of the near field furthermore relate to the distributional effects of energy with other equipment which may be included in a device.

Considering the case of measurement of ASUS ADM and Dell ADM using magnetic field probes, the GDS-2000 oscilloscope, and a spectrum analyzer, we can consider additional conditions. The energy transfer from inductance affects the output of power as it is transmitted when they do not function dually as a pair. Otherwise, a classical magnetic induction occurs, while the near field transmits energy to a receiving component when the energy is actively drawn (and not otherwise.) Transmitters in equipment can sense the conditions and act according to them, whereas in far fields the energy is constantly drawn regardless of immediate reception.

Thus, the relations between the configuration of the equipment used as a source, the distance between the measurement equipment and the items being measured, and the impendence of the low-frequency waves are all relevant and integrated with this case. The low-frequency wave impedance in this case is described by the ratio of the magnitude of the electromagnetic field (usually defined by the variable E) to the magnitude of the magnetic field (usually defined by the variable H) (Straus 2001). The ratio of E (described in terms of volts per meter) to H (described in Amperes per meter) is defined in ohms, while the actions of reflection and absorption are highly relevant in this inductance as well (Straus 2001).

Electromagnetic emissions and interference: causes and prevention for low-frequency devices

Electromagnetic emissions causing interference (EMI, also referred to as radio frequency interference (RFI)) is the phenomena of disturbance in an electrical field; this can describe either the interference with electromagnetic emissions through the radiation of a device (such as a low-frequency power supply) or the conducting of electromagnetic waves in a circuit. While this may occur from natural bodies such as the sun or the Northern Lights, we will consider the artificial case of circuitry according to the low-frequency electromagnetic emissions in a low-frequency power supply (Oxford 2008).

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EMI may be used intentionally for deliberate jamming of electromagnetic emissions from radio broadcasting (especially in instances where warfare is an issue,) while it may occur unintentionally as it commonly does in AM radio within city limits (Hutchinson 1987). The electromagnetic emissions and receptions of devices such as personal cellular telephones, small radios, home televisions, and other devices are also vulnerable to interference (though they are less vulnerable than the above cases) while the FCC governs the limits which are allowed (Williamson Labs 2007).

Electromagnetic emissions and interference: causes and prevention for low-frequency devices

In the case of a low-frequency power supply, this may be relevant to the other circuitry used in the experiment. Normally the emissions of electromagnetic interference (“radiated EMI” or “emitted EMI”) is typically measured on a frequency range between 30 MHz to 10 GHz; while the power supply itself is the emission source, for this experiment the potential susceptible equipment is the ASUS ADM and Dell ADM circuitry, the oscilloscope, and perhaps the circuitry of other devices.

However, in the case of this low-frequency power supply, the chances for significant interference from the resultant electromagnetic emissions may be considered negligible. Assuming it is not negligible, however, we can consider some possible means towards a solution from the emissions causing interference. Balancing the wiring responsible for the emissions, proper termination, filtering, grounding, shielding, changing the layout of the experiment, and other such methods may be used to block the emissions or otherwise prevent them from interfering with equipment and the experiment (Williamson Labs 2007).

Another perspective we must consider in this case is the conduction of the emissions of electromagnetic interference. Common instances of this include such sources as motors, relays, power rails, and power supplies, while the susceptibility is a result of the A.C. cord inadequately filtered or the power rails being inadequately decoupled; solutions to this may be found through proper bypassing and decoupling methodologies, as well as proper practicing in layouts, shielding, filtering, and ground planes (Williamson Labs 2007).

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As mentioned, the power supply and power distribution are among the most observed causes of emissions and paths of both radiated and conducted electromagnetic interference, while the low-frequency power supply is no exception to this. Meanwhile, linear power supplies do not contribute much or any interference when they are designed or arranged according to best practices. In such practices, the arrangement, decoupling, and bypassing are essential for fluid experimentation, while switching power supplies creates an even higher demand for these precautions.

Advantages and disadvantages of the low-frequency power supply and the near field

Using a low-frequency power supply to measure ASUS ADM and Dell ADM using magnetic field probes (large loop EMC-C,) an oscilloscope, and spectrum analyzers has advantages and disadvantages.

Considering the power supply itself, it is low-frequency while the near field will not have the advantages as the far field, as these include the dominant force being electricity and the applications extending to those which benefit from these wavelengths and energies. However, the required protection from interference also increased proportionally with higher frequencies. For example, frequencies higher than ~500 MHz wave shaping and series resistors are commonly used as a substitute to the aforementioned methods, while these methods are more complex and thus less ideal. Furthermore, they may not be substantial enough and require combined methods for adequate protection against emitted electromagnetic interference. Here extra measures must be taken, such as shielding with metal or conductive plastic (Atmel 2009). Meanwhile, the main advantage to low-frequency power supplies is their reduced emissions and resultant interference.

The equipment which may be used in the experiment is not as susceptible to interference, however other power supplies may have further applications. For the measurements of circuitry, as described using the oscilloscope, magnetic field probes, and spectrum analyzer, the low-frequency power supply is ideal over other common power supplies. It, however, would not be ideal in cases of emission on a larger scale, such as radio applications (DeMaw 1987).

Applications of EMC for near field devices using low-frequency power supplies

There are numerous applications and patents relevant to the near field electromagnetic compatibility with low-frequency power supplies. As the field of electromagnetic compatibility, in general, is concerned with blocking emissions and eliminating interference, the applications are subcategories of design to block interference, similar to the solutions mentioned above. While the far-field is relevant to radio applications, the applications of the near field include all types of lab measurements and electronic circuitry which does not involve lengthy transmission.

Considering the case of conduction, however, in multiple electronic devices involved in the receiving of far-field transmission, near-field effects and applications may still be relevant. Recent patents in this area include the antenna near field coupling system, the trapped electromagnetic radiation communication system, noise reduction with dual-mode antennas, and a variety of probe instruments and devices for determining near field antenna patterns (Coffin et al 1972, Grossi et al 1969, Laydorf 1966, Hansen et al. 1975, U.S. Patent 2009).

Considering broader subject areas, applications may include coupling mechanisms (such as conductive coupling and modes, inductive coupling through magnetism and capacitance, and radioactive coupling,) grounding, shielding, emission suppression, and susceptibility insulation, grounding, arrangement strategy, engineering timer clocks to function with spread spectrums, line drivers containing rise and fall times, and more (Williamson Labs 2007).

Meanwhile, as a source of interference may be from inadequately terminated or faulty transmission lines, another application in this area is known as “time-domain reflectometry measurements.” While standing waves from this situation may result in the shielding devices radiating the emissions, similar to an antenna, which they are supposed to block, this situation is highly relevant. To counter this, a rapid pulse can be applied to a transmission line as the reflection in one line can be analyzed as the observers consider the behavior or discontinuity and the distance of possible faults (here knowing the velocity factor or the dielectric material used in transmission is required.)

There are essentially infinite applications to near-field EMC in this case of a low-frequency power supply as there are so many circuit applications and designs. Any measurement and all circuit functionality that is concerned with near fields, which includes the majority of modern electronics and circuitry, is thus relevant. While the interference from emissions can be related to the wiring of a building, the combination of variables included for short-range (near field) applications is quite expansive. Nearly all electronics-based functioning and measurement have relevance, while the applications mentioned above are the most common concerning interference and emissions.

Continuing and future work

Continuing the current work in the area of EMC in the future is mostly (if not entirely) dependent on the changing technology of instruments for which it is used. Modern digital circuitry is becoming increasingly popular, while the increase of switching speeds results in increased emissions, and thus an increased need. Meanwhile, the voltages in the circuitry are becoming increasingly low as well, and while this increases susceptibility, the need for EMC becomes higher still. Current speculation highly implies the need for not only continual progress in EMC, but increasingly expanding continual progress in EMC will be required for the technology to be as adequately compatible as it is according to the standards of the present and recent past.

More countries are also becoming aware of the issue, meaning the need for enhancement of interference reduction is combined with a larger demand per capita. Regulatory agencies are also implementing measures which these increased methods for reducing susceptibility and removing the increasing level of emissions will be required to follow as they develop.

While many current and future applications in the modern world involve far fields, as mobile communications and wireless internet are developing at a rapid pace, the relevant requirements for adequate inference protection will increase (Taylor 2008). This may relate to the conduction of near field devices, and perhaps to the extent that it will interfere with the functionality of devices powered by low-frequency supplies even in near field applications. Currently, the continuing development of low-voltage digital circuits has become more vulnerable to emissions as they have become smaller in size (CMOS transistors are a great example of this) and thus new regulations have developed for the changes. The future will continue this trend in this way and the aforementioned ways, with the possibility of effects from related far-field devices.

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