Electromagnetic compatibility is a system-level property, not a property that can be added after an enclosure has been mechanically finalized. A product must operate in its intended electromagnetic environment without causing intolerable disturbance to other equipment, and it must also tolerate the disturbances present around it. When unintended electromagnetic energy couples into a circuit, cable, or enclosure, the result is electromagnetic interference. The practical problem is that interference does not respect the boundaries drawn on a schematic: it can leave a circuit through a seam in the enclosure, enter through a cable, or couple from one part of a product to another. This article explains the origin of EMC problems, the two main coupling paths by which EMI leaves or enters a circuit, and the shielding methods used to control those paths. It also examines the relationship between enclosure materials and gasket selection, because a shield is only as effective as its joints, seams, and cable penetrations.
Highlights:
- EMI coupling occurs through radiation and conduction. Enclosure seams, slots, openings, and line penetrations are the practical leakage paths that determine whether a shield works.
- Effective shielding combines source suppression, isolation of noisy circuits, immunity of sensitive circuits, and continuous electrical bonding across enclosure joints.
- Enclosure material choice and gasket selection are linked. Metal enclosures and conductively coated plastic enclosures both require a gasket strategy that preserves electrical continuity across mating surfaces.
EMC and EMI in Electronic Systems
Electromagnetic compatibility, or EMC, is defined as the ability of a device, equipment, or system to function satisfactorily in its electromagnetic environment without introducing intolerable electromagnetic disturbance to anything in that environment. This definition is not limited to a single product. It describes a relationship between the equipment and the environment in which it operates. A product that works correctly on a bench but disturbs a nearby receiver is not electromagnetically compatible. A product that is disturbed by an external field is also not compatible, even if its own emissions are low.
For wireless transceivers, the use of non-continuous spectrum can partially achieve EMC performance. The radio is designed to operate within allocated bands, and the receiver can be made selective. However, many practical examples show that EMC is not always achieved by frequency planning alone. High-frequency interference can occur between a laptop and test equipment, between a printer and a desktop computer, and between a cellular phone and a medical instrument. In each case, the interference is unintended, and the affected equipment may be operating exactly as designed. This unintended electromagnetic interference is what is normally called EMI.
The distinction between EMC and EMI is useful during design reviews. EMC is the desired condition: the product and its environment coexist. EMI is the failure mechanism that prevents that condition. Shielding is one tool for controlling EMI, but it is not the only tool, and it is rarely sufficient on its own. A shield that is added without understanding the coupling path may reduce one emission while leaving another path untouched. For this reason, shielding design begins with an understanding of where the interference is generated, how it propagates, and which circuits are sensitive.
Sources of EMC Problems
All electrical and electronic equipment produces voltage and current changes during operation. These changes may be intermittent or continuous. In some circuits, the rate of change is relatively slow. In others, the voltage and current can change at a very fast rate. Fast changes are significant because they generate electromagnetic energy over a range of frequencies or across a frequency band. The associated circuit does not need to be an intentional transmitter. Any conductor that carries changing current can emit energy into the surrounding environment.
This is why EMC problems often appear in products that contain both digital and analog functions, or in systems where power conversion, data transfer, and sensitive measurement coexist. The source of the disturbance may be a switching event, a clock edge, a repeated current pulse, or a transient caused by load change. The energy generated by these events can couple to nearby conductors, cables, or enclosure surfaces. Once coupled, it can be conducted to another part of the system or radiated into space.
The first design question is therefore not "Which shield material should be used?" but "Where is the energy coming from, and how does it reach the victim?" A product may have more than one source and more than one victim. The same circuit can be a source at one frequency and a victim at another. In a laptop, for example, high-speed digital activity may disturb a test instrument; in a printer, motor drive or power switching may disturb a desktop computer; in a medical instrument, a cellular phone may introduce an external field that the instrument was not designed to reject. The physical arrangement of the equipment, the length of cables, and the quality of enclosure joints all influence whether the interference becomes a real problem.
Radiated and Conducted Interference Paths
EMI has two principal paths by which it leaves or enters a circuit: radiation and conduction. Radiation occurs when electromagnetic energy propagates through space. In an enclosure, radiation can leak through seams, slots, openings, or other gaps. These features are often introduced for mechanical assembly, ventilation, connector access, or display visibility. From an electrical point of view, however, they are discontinuities in the conductive surface. A seam that appears mechanically tight can still provide a path for high-frequency energy if the mating surfaces do not maintain continuous electrical contact.
Conduction occurs when interference couples onto power, signal, or control lines. The line then acts as a path out of the enclosure. Once the cable leaves the enclosure, it can radiate freely in open space and cause interference at another location. This mechanism is important because it means that an enclosure can be well shielded at its panels and still fail because of an untreated cable penetration. The cable becomes an antenna, and the enclosure opening around the cable becomes part of the coupling path.
Radiated and conducted paths are not independent. Energy that is conducted out of an enclosure can be radiated by the cable. Energy that is radiated onto a cable can be conducted back into the enclosure. A design that treats only the enclosure panels and ignores cables, connectors, and line filters may therefore leave a complete path intact. In practice, shielding design must consider the enclosure, the seams, the apertures, and every conductor that crosses the enclosure boundary. The purpose is to control the path, not merely to add a metal surface.
Shielding as an EMI Suppression Strategy
Many EMI suppression implementations use a combination of enclosure shielding and seam shielding. The enclosure provides a conductive barrier around the noisy or sensitive circuitry. The seam shielding maintains electrical continuity across joints where separate mechanical parts meet. Neither element works well without the other. A conductive enclosure with poor seam bonding behaves like a resonant cavity with deliberate openings. A seam gasket without a continuous conductive surface behind it cannot compensate for a poorly prepared enclosure.
Several simple principles help guide EMI shielding design. The first is to reduce interference at the source. This is the most direct approach because it lowers the amount of energy that must be contained or filtered. The second is to isolate interference-producing circuits by shielding, filtering, or grounding. The third is to increase the immunity of sensitive circuits. These measures are complementary. Source suppression reduces the disturbance, isolation blocks the coupling path, and immunity improvement makes the victim less responsive to whatever disturbance remains.
EMI suppression, isolation, and low susceptibility should be design goals for all circuit designers, not only for EMC specialists. These goals should be addressed early in the design phase, when the board partition, cable routing, enclosure concept, and grounding architecture are still flexible. If shielding is considered only after the mechanical design is complete, the available remedies are usually more expensive and less effective. A gasket can be added to a seam, but it is much harder to redesign a cable entry or relocate a noisy circuit once the enclosure has been tooled.
For design engineers, shielding materials provide an effective way to reduce EMI. The choice of material should follow the coupling path and the mechanical requirements. A metal can may be appropriate for a localized shield on a board. A thin metal sheet or foil tape may be used where a conformable conductive surface is needed. Conductive fabric or tape, spray coatings, and platings can cover larger or more complex surfaces. Conductive paint and zinc wire spraying are examples of coatings applied to plastic enclosures. Each option has a different mechanical behavior, but all depend on continuous electrical contact and proper termination.
Shielding Effectiveness Targets and Interpretation
Shielding performance is commonly expressed as shielding effectiveness, or SE, in decibels. The number describes how much an enclosure reduces an electromagnetic field relative to an unshielded condition. A target of 20 dB (i.e., SE equals 20 dB) represents a modest level of attenuation, while a target of 100 dB (i.e., SE must equal 100 dB) represents a much more demanding enclosure. The difference is not merely numerical. A high-SE design has less margin for seams, apertures, cable penetrations, and gasket contact resistance, so the mechanical details become more critical as the target rises.
A simplified relation associated with 10 dB should be used with care: this relation applies only in a near magnetic field environment and when absorption loss is less than the value for which the relation was established. Extending such a relation outside its stated conditions can produce an overly optimistic estimate. The same caution applies to any single-number SE claim. Shielding effectiveness varies with frequency, direction, and location. A material sample measured in a fixture is not the same as a finished enclosure with seams, ventilation openings, connectors, and a cable harness inside.
This is why shielding design should be verified at the enclosure level. The relevant question is not only how well the base material conducts, but how well the assembled product maintains continuity across every joint and penetration. Gaskets, fasteners, conductive coatings, and contact surfaces all contribute to the result. If one seam is left untreated, the overall shielding effectiveness can be limited by that seam rather than by the material itself.
Enclosure Materials and Gasket Selection
A wide range of enclosure shielding materials is now in common use. These include metal cans, thin metal sheets, foil tapes, and spray coatings or platings applied to conductive fabric or rolls. Conductive paint and zinc wire spraying are representative coating processes. The materials differ in form, but the design requirement is the same: the enclosure must provide a continuous conductive surface around the protected volume, and every intentional opening must be treated as part of the shielding system.
Metal enclosures have the advantage of intrinsic conductivity, but they still require attention at seams, joints, and removable panels. A metal box that is fastened at intervals may have good contact at the fasteners and poor contact between them. The resulting gaps can behave as slots. Thin metal sheets and foil tapes can be effective where they are properly bonded and supported, but they are less tolerant of mechanical distortion. Conductive coatings on plastic allow the mechanical benefits of plastic while providing a conductive surface, but the coating must be continuous and must remain compatible with the gasket and with the mating conductive surfaces.
Once the designer has determined whether the enclosure will be metal or plastic with a conductive layer, the next step is to select the gasket. The gasket is not an accessory added after the enclosure design is complete; it is part of the seam design. Its function is to bridge mating surfaces and maintain electrical contact across the joint. The gasket must be compatible with the enclosure material, the coating, and the mechanical load applied by the fasteners. It must also be selected with the operating environment in mind, because compression set, corrosion, and contamination can change contact resistance over time.
A common mistake is to treat the gasket as a cure for a poorly designed seam. In practice, the gasket works only when the mating surfaces are prepared for it. The contact surfaces should be conductive, clean, and mechanically stable. The gasket should be placed so that it is compressed uniformly and so that no gap remains between fasteners. If the enclosure uses a conductive coating, the coating must extend under the gasket contact area and should not be damaged during assembly. If the enclosure is metal, the mating surfaces should be free of insulating finishes, anodizing, or contamination that would interrupt contact.
Design Discipline from the Start
Effective PCB EMI shielding is an architectural decision. It requires the designer to identify the noise source, the coupling path, and the sensitive circuit before selecting materials. The enclosure, the PCB partition, the cable routing, and the grounding scheme should be considered together. A shield that is electrically continuous but mechanically impractical will not survive production. A gasket that performs well in a sample but cannot be assembled consistently will not provide reliable contact in the field.
The practical design sequence is straightforward. First, reduce unnecessary energy at the source. Second, isolate noisy circuits through layout, filtering, and grounding. Third, protect sensitive circuits through local shielding or physical separation. Fourth, design the enclosure as a continuous conductive system, with seams, apertures, and cable entries treated as part of the electrical path. Fifth, select gasket materials and coatings that maintain contact over the product life. These steps do not eliminate the need for testing, but they make the tested design more likely to meet its EMC target.
Shielding is therefore not simply the addition of a metal cover. It is the control of electromagnetic energy at the boundaries of a product. The enclosure material establishes the available conductivity, the seams and gaskets determine whether that conductivity is continuous, and the cable penetrations determine whether the enclosure boundary remains intact. When these elements are designed together, shielding becomes a predictable part of the product architecture rather than a late-stage corrective measure.
Metal Shielding Effectiveness
Shielding effectiveness (SE) describes how well a metal shield reduces the electromagnetic field that reaches a protected circuit or region. It is a logarithmic ratio expressed in decibels, which allows a very large reduction in field strength to be stated as a manageable number. The SE of a shield is evaluated through its absorption loss, reflection loss, and a correction factor for multiple reflections inside a thin shield. These terms are not determined by the shield material alone. They also depend on the frequency of the field, the shield thickness, the type of source, and the distance between the source and the shield.
The SE Equation and Loss Terms
The suitability of a shield can be evaluated using shielding effectiveness in decibels. The basic relationship is:
SEdB = A + R + B
Here, A is the absorption loss in dB, R is the reflection loss in dB, and B is a correction factor in dB. The correction factor applies when multiple reflections exist inside a thin shield. Because the terms are expressed in decibels, adding them corresponds to multiplying the attenuation contributions in linear terms. The total shielding effectiveness is therefore a combination of energy absorbed in the shield, energy reflected at the shield surface, and the effect of internal re-reflection within the shield.
A simple shield may reduce the generated electromagnetic field strength to one tenth of its original value, which means that SE equals 20dB. Some applications may require the field strength to be reduced to one hundred-thousandth of its original value, which means that SE must equal 100dB. The decibel scale is logarithmic, so these numbers represent very different levels of attenuation. A reduction to one tenth is 20dB, while a reduction to one hundred-thousandth is 100dB. This is why shielding effectiveness is a convenient way to express both modest and very high attenuation in a single logarithmic quantity.
Absorption Loss
Absorption loss is the amount of energy lost when an electromagnetic wave passes through the shield. As the wave penetrates the metal, energy is dissipated within the shield material. The absorption loss is calculated as:
AdB = 1.314 (f × σ × μ)1/2 × t
In this expression, f is frequency in MHz, μ is the permeability of copper, σ is the conductivity of copper, and t is the shield thickness. The formula shows the main dependencies of absorption loss. For a given material, absorption loss increases with the square root of frequency, conductivity, and permeability, and it increases linearly with shield thickness. A thicker shield provides more material for the wave to penetrate, so the opportunity for energy dissipation increases. Likewise, a material with higher conductivity or permeability produces greater absorption for the same thickness and frequency.
Absorption loss is therefore a material and geometry effect. It is not produced by the shield surface alone. It depends on how far the wave travels through the shield and on the loss mechanisms inside the metal. This is why absorption becomes more important as frequency rises and why thickness is a direct design variable when higher shielding effectiveness is required.
Reflection Loss and Wave Impedance
Reflection loss in the near field depends on the nature of the electromagnetic source and on the distance between the source and the shield. The reflection loss varies with the ratio of the wave impedance to the shield impedance. It is therefore not determined only by the type of wave. It also depends on the distance between the shield and the source. This situation is directly relevant to small shielded equipment, where the source and the shield may be physically close and the field may not behave as a far-field plane wave.
For a rod-like or straight emitting antenna, the wave impedance is higher near the source. As the distance from the source increases, the wave impedance decreases. For a plane wave, however, the wave impedance does not change and remains constant at 377Ω.
Conversely, if the source is a small coil, the field is predominantly magnetic. In this case, the wave impedance is lower near the source. As the distance from the source increases, the wave impedance increases. When the distance exceeds one sixth of the wavelength, the wave impedance no longer changes and remains constant at 377Ω.
These two source conditions produce different near-field behavior. A rod-like or straight antenna creates an electric-field-dominated near field with a high wave impedance close to the source. A small coil creates a magnetic-field-dominated near field with a low wave impedance close to the source. Because reflection loss depends on the mismatch between the wave impedance and the shield impedance, the same shield can produce different reflection loss values depending on the source and the separation distance.
Near-Field Reflection-Loss Equations
For the rod-like or straight antenna case, the near-field reflection loss can be expressed as:
RdB = 321.8 - (20 × log r) - (30 × log f) - [10 × log(μ / σ)]
For the small-coil case, the near-field reflection loss can be expressed as:
RdB = 14.6 + (20 × log r) + (10 × log f) + [10 × log(μ / σ)]
In these expressions, r is the distance between the wave source and the shield, f is frequency, μ is permeability, and σ is conductivity. The logarithms are base-10 logarithms, consistent with the decibel notation. The signs in the equations reflect the near-field trends described above. In the electric near field produced by a rod-like or straight antenna, reflection loss decreases as distance and frequency increase. In the magnetic near field produced by a small coil, reflection loss increases with distance and frequency. These equations describe the reflection term only. The total shielding effectiveness must still include absorption loss and, where applicable, the correction factor for multiple reflections.
Correction Factor for Thin Shields
The final term in the SE expression is correction factor B. It is calculated as:
B = 20 log[1 - exp(-2t / σ)]
This equation applies only to near magnetic-field environments and to cases where absorption loss is less than 10dB. Because the absorption efficiency of the shield is not high, re-reflection inside the shield increases the energy that passes through the opposite face of the shield layer. The correction factor is therefore negative, indicating a reduction in shielding efficiency. In practical terms, a thin shield with low absorption can allow multiple internal reflections to build up, so the simple sum of A and R overstates the actual attenuation unless B is included. The correction factor adjusts the result for this internal re-reflection effect.
The correction term is most significant when the shield is thin and absorption is low. Under those conditions, energy reflected from one face can travel back through the shield and contribute to the field on the protected side. When absorption is high, the reflected energy is attenuated before it can re-emerge, and the correction becomes less important. The condition that absorption loss be less than 10dB therefore defines the range in which this correction must be applied with care.
Taken together, the three terms show that metal shielding effectiveness is a system-level result. Absorption depends on material, frequency, and thickness. Reflection depends on the impedance mismatch between the field and the shield, which in turn depends on source type and distance. The correction factor accounts for multiple reflections inside a thin shield when absorption is limited. Evaluating all three terms gives a more realistic estimate of how a metal shield will perform in a near-field environment.
EMI Suppression Strategies
Only high-permeability materials such as metal and iron can achieve high shielding effectiveness at very low frequencies. The permeability of these materials falls as frequency rises. A strong initial magnetic field also lowers permeability, and mechanically forming the shield into the required shape reduces it further. Taken together, selecting a high-permeability material for shielding is a genuinely complex problem, and in most cases it means turning to EMI shielding material suppliers and specialist consultants for a workable solution.
At high-frequency electric fields, a thin metal layer used as the enclosure or as an internal liner delivers good shielding, but only on the condition that the shielding is continuous and completely covers the sensitive circuitry, with no gaps or seams, so that the structure behaves as a Faraday cage. In practice, a shield with no seams and no openings cannot be built. The shield must be split into several parts, which means seams have to be joined, and holes are normally cut so that mounting hardware, plug-in cards, and wiring to assemblies can pass through.
The real difficulty in shield design is that the manufacturing process inevitably produces apertures, and the equipment itself needs to use them. Fabrication, panel wiring, ventilation openings, external monitoring windows, and panel-mounted components all require holes in the shield, and each of them significantly degrades shielding performance. Slots and seams cannot be eliminated, but it is well worth considering slot length carefully in the shielding design, in relation to the wavelength corresponding to the circuit's operating frequency.
Aperture Length and Attenuation
The wavelength of an electromagnetic wave at any frequency is given by: wavelength (λ) = speed of light (C) / frequency (Hz). When the slot length reaches half a wavelength, that is, the cutoff frequency, the RF wave begins to attenuate at a rate of 20 dB per decade (1/10 of the cutoff frequency) or 6 dB per octave (1/2 of the cutoff frequency). Generally, the higher the RF emission frequency, the more severe the attenuation, because the wavelength is shorter. When the highest frequency is involved, any harmonics that may be present must be taken into account, although in practice only the first and second harmonics need to be considered.
Once the frequency and intensity of the RF radiation inside the shield are known, the maximum permissible gap and slot dimensions can be calculated. Consider a case where 1 GHz radiation, with a wavelength of 300 mm, must be attenuated by 26 dB. A 150 mm slot will begin to produce attenuation, so any gap smaller than 150 mm will attenuate the 1 GHz radiation. At 1 GHz, therefore, 20 dB of attenuation requires gaps smaller than 15 mm (1/10 of 150 mm); 26 dB of attenuation requires gaps smaller than 7.5 mm (more than 1/2 of 15 mm); and 32 dB of attenuation requires gaps smaller than 3.75 mm (more than 1/2 of 7.5 mm).
Suitable conductive gaskets can hold the gap dimensions within the specified limits, so that the calculated attenuation is actually realized in the assembled product.
Shielding Design Challenges
Because a seam reduces the conductivity of the shield, it also reduces shielding effectiveness. It is important to note that below the cutoff frequency, attenuation depends only on the length-to-diameter ratio of the aperture; a length-to-diameter ratio of 3, for example, yields 100 dB of attenuation. Where perforations are unavoidable, the waveguide behavior of small holes in a thick shield can be exploited. Another way to obtain a high length-to-diameter ratio is to add a small metal shield, such as a correctly sized gasket.
These principles, together with their extension to the case of many apertures, form the basis of multi-aperture shield design.
Multi-Aperture Thin Shields
Thin shields with many perforations are everywhere, ventilation holes in thin sheet metal being a typical example. When the spacing between the holes is small, the design has to be considered very carefully. For this situation, shielding effectiveness is calculated as:
SE = [20 log (fc / σ)] - 10 log n
Note that this formula applies only when the spacing between holes is smaller than the hole diameter. It can also be used to calculate the shielding effectiveness of metal mesh.
Seams and Joints
Welding, brazing, or soldering are the common methods for permanently fixing thin sheets to one another. The metal surfaces at the joint must be cleaned thoroughly so that the joint can be completely filled with conductive metal. Screws or rivets are not recommended for this purpose, because the low-resistance contact between fasteners is difficult to maintain over the long term.
The purpose of the conductive gasket is to reduce the slots, holes, or gaps at seams and joints so that RF radiation cannot escape. An EMI gasket is a conductive medium that fills the gaps inside a shield and provides a continuous low-impedance junction. In most cases, an EMI gasket provides a flexible connection between two conductors, so that current flowing on one conductor is transferred to the other.
Gasket selection can be guided by the following performance parameters: (1) shielding effectiveness over the specific frequency range; (2) mounting method and sealing strength; (3) compatibility with the enclosure current, together with resistance to corrosion from the external environment; (4) operating temperature range; (5) cost.
Most commercial gaskets provide sufficient shielding performance for equipment to meet EMC standards. The key point is to design the gasket correctly within the shield.
Gasket Systems
One important factor to consider is compression, because compression produces higher conductivity between the gasket and the mating surface. If conduction between the gasket and the mating surface is poor, shielding effectiveness drops. Furthermore, if a piece is missing at the joint, a narrow slit appears and acts as a slot antenna, with a radiation wavelength roughly four times smaller than the slot length.
Ensuring conduction starts with keeping the mating surface smooth and clean and properly treated so that it has good conductivity; these surfaces must be masked before the parts are joined. It is equally important that the gasket material adheres well and continuously to that surface. The compressibility of the conductive gasket compensates for any irregularity of the mating surface.
Every gasket has a minimum effective contact resistance. Designers can increase the compression force on the gasket to reduce the contact resistance of multiple gaskets, but this raises the sealing strength and makes the shield bow more. Most gaskets perform best when compressed to between 30% and 70% of their original thickness. Within the recommended minimum contact area, therefore, the pressure between two opposing contact points should be sufficient to guarantee good conductivity between the gasket and the mating surface.
On the other hand, the pressure on the gasket should not be so high that the gasket is abnormally compressed, because this causes the gasket contact to fail and may produce electromagnetic leakage. The requirement to keep the gasket separate from the mating surface is important for holding compression within the manufacturer's recommended range. Such a design must ensure that the mating surface is stiff enough to prevent large deflection between fasteners. In some cases, additional fasteners may be needed to keep the enclosure structure from bending.
Compressibility is also an important characteristic at rotating joints, such as doors or plug-in boards. If the gasket compresses easily, shielding performance degrades with every movement of the door, and the gasket then needs a higher compression force to reach the same shielding performance as a new gasket. In most cases this is not achievable, so a long-term EMI solution is required.
If the shield or the mating surface is made of plastic coated with a conductive layer, adding an EMI gasket does not create much difficulty, but the designer must consider that many gaskets wear against the conductive surface, and plated surfaces of metal gaskets tend to wear more readily. Over time this wear reduces shielding effectiveness at the gasket joint and creates problems for later manufacturers.
If the shield or the mating surface is metallic, a gasket can be added to enclose the mating surface before the finishing material is sprayed on, using only conductive film and tape. If tape is used on both sides of the mating surface, the EMI gasket can be secured with mechanical fasteners, for example a "C-type" gasket with plastic rivets or pressure-sensitive adhesive (PSA). The gasket is mounted on one side of the mating surface to complete the EMI shielding.
Gaskets and Accessories
A very wide range of shielding and gasket products is available today, including beryllium-copper finger stock, metal mesh (with or without an elastomer core), metal mesh and oriented wire embedded in rubber, conductive rubber, and polyurethane foam gaskets with metal plating. Most shielding material manufacturers can provide estimated SE values for the various gaskets they offer, but it should be remembered that SE is a relative figure, and it depends on the apertures, the gasket dimensions, the gasket compression ratio, and the material composition.
Gaskets are available in many shapes for specific applications, including situations involving wear, sliding, and hinged joints. Many gaskets are supplied with adhesive, or with a fixing feature built into the gasket itself, such as a press-in fit, a pin-in mount, or barbs.
Among the various gasket types, coated foam gaskets are among the newest products and among the most widely used on the market. They can be made in many shapes with a thickness greater than 0.5mm, and the thickness can also be reduced to satisfy UL flammability and environmental sealing standards. Another new type is the combined environmental/EMI gasket, which removes the need for a separate sealing material and therefore lowers shield cost and complexity. The outer jacket of these gaskets is UV stable and resists moisture, wind, and cleaning solvents, while the inner coating is metallized and highly conductive. A further recent innovation is a plastic clip fitted to the EMI gasket; compared with conventional compression-type metal gaskets, it is lighter, takes less time to assemble, and costs less, which makes it more attractive to the market.
Conclusion
Equipment generally requires shielding because the structure itself contains slots and gaps. The shielding that is needed can be determined from a few basic principles, but theory and reality are not the same thing. For example, when calculating the size and spacing of gaskets at a given frequency, the signal strength must also be taken into account, as in the case where several processors are used within a single piece of equipment. Surface treatment and gasket design are the key factors in maintaining long-term shielding and achieving EMC performance.
Related Reading:
EMC Engineer Skills and Common Components: Chokes, Ferrite Beads, Filter Capacitors
EMC Design Principles and EMI/EMC Questions for PCB Engineers
PCB EMC Design Q&A: Differential Pairs, Grounding and Filtering
FCC and EMC Compliance Requirements Explained for PCB Design
Ferrite Beads vs. Inductors for High-Frequency Filtering on PCBs
Class-D Amplifier PCB Routing: EMC, Power, and ESD Essentials
EMC Fundamentals: Disturbance and Interference Control Terms
EMC Measurement, Equipment Classification, and Transceiver Terms
Power Control, Supply Impedance, and Flicker Terminology Explained
Internal EMC Design and PCB Layout Techniques for Electronic Products
