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Electromagnetic radiation that adversely affects device performance is generally termed EMI (ElectroMagnetic Interference).
Currently, the FCC regulates EMI emission between 30 MHz and 2 GHz, but does not specify immunity to external interference. The trend toward higher operating frequencies therefore is helping drive the need for more EMI shielding.
Metals (due to their inherent conductivity) traditionally have been the material of choice for EMI shielding.
Cost effective – suitable for higher volumes (needed to offset tooling investment) and reduces assembly costs. Good physical properties – Inherently corrosion resistant and durability as well as high strength to weight ratio. Over the past few years, EMI Shielding Compounds have arrived on the market by incorporating EMI shielding fiber technology (both Stainless Steel and Nickel Coated Graphite) into thermoplastic compounds. Fiber properties are summarized in Table 1 for the most common fiber fillers for EMI shielding compounds. A metal foil or conductive fabric applied to plastic is labor intensive and ideal only for low volume and simple geometry designs. Using a simple metallic inner shield to isolate EMI at the most basic level (Printed Circuit Board, or “On-Board” Shielding) may reduce the requirements for shielding enclosures.
Within Conductive Coatings, there are three significant coating technologies (vacuum metallization, electroless plating, and conductive paints). Multiple stage chemical process deposits a thin layer of copper (high conductivity and SE) and overplates it with nickel (corrosion inhibition and a good surface for painting). Contain particles of silver, copper, or nickel dispersed in an acrylic, vinyl, epoxy, or urethane binder. The advantages and disadvantages EMI Shielding Compounds and Conductive Coatings are summarized in Table 2. While it is rather easy to compare the advantages and disadvantages, it is difficult to compare the shielding capabilities as EMI Shielding Compounds shield primarily by a different mechanism (absorption) than Conductive Coatings (reflection). The coating industry (where electrical conductivity is a surface property) utilizes surface resistivity as a mechanism to denote shielding capability; however, for absorption shielding (where electrical conductivity is mostly within part walls), there is little correlation between surface resistivity and shielding capability. Laboratory evaluation of shielding material samples (via ASTM D4935) can provide a measurement of shielding effectiveness, but determining the actual shielding effectiveness of a product requires testing of the finished assembly. Drawing 981221-AA (see Exhibit A) was submitted to two painters, two electroless platers, and two vacuum metallizers. No masking (coat entire part) appears cheaper for electroless plating and vacuum metallization (labor more costly than material). This example was designed to offer Conductive Coatings the most favorable conditions possible. Exact cost comparisons are almost impossible to make as there are many variables and assumptions that apply.
Electromagnetic radiation that adversely affects device performance is generally termed EMI (electromagnetic interference). An electronic device exhibits EMC (electromagnetic compatibility) if it operates effectively in its designated environment without unacceptable interference to other devices.
Electromagnetic waves consist of both an E (electric) field and an H (magnetic) field oscillating at right angles to each other. The importance of wave impedance is shown by an EMI wave encountering an obstacle such as a metal shield. In general, the intensity of the interference caused by the signal diminishes with increasing distance from its source. Effective placement of shielding (barrier between a susceptible system and an external source of electromagnetic radiation) causes an abrupt discontinuity in the path of electromagnetic waves. Shielding performance is a function of the properties and configuration of the shielding material (conductivity, permeability and thickness), the frequency, and distance from the source to the shield. How well a shield reduces (attenuates) the energy of a radiated electromagnetic field is referred to as its shielding effectiveness (SE). EMI should be considered at the design phase of any system so that potential interference problems can be minimized.
Printed Circuit Boards (PCB) – Noise originates and ultimately may affect the board level (most basic) components.
Apertures – The amount of EMI leakage through an opening is a function of the maximum dimension of the opening.
Uses for EMI shielding abound in computers, medical devices, telecommunications, and other types of electronic equipment. FCC regulations classify devices by their intended market – Class A devices include products for industrial and business environments while Class B devices are primarily intended for use in homes. Compliance testing requires sophisticated equipment and must be performed by accredited labs. Neil Hardwick is a Marketing Manager for Conductive Products at custom thermoplastics compounder RTP Company. Headquartered in Winona, Minnesota, RTP Company operates 10 additional full-service manufacturing facilities located throughout North America, Europe, and Asia. EMC Technologies are once again running EMC and Electrical Safety courses, presented by world famous EMC and electronic design engineer, Mr Keith Armstrong. MAST Technologies’ suite of conductive caulk and ink materials can meet a variety of demanding electrical and environmental specifications.
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2700 Series Conductive Foam is an X, Y, Z axis conductive foam that consists of conductive open cell polyurethane foam, with a nickel over copper plated polyester fabric on either side. Ideal for applications requiring a conformable gasket with excellent conductivity at low compression force. Click here to download a PDF of Instructions for Installation of Shielding with Double Adhesive Transfer Tape. D-Connector gaskets are also available made from Metalized Fabric, Conductive Elastomers and Metal. Measurements of shielding attenuation were realised on the test setup prepared in the Institute of Telecommunications, Teleinformatics and Acoustics of Wroclaw University of Technology in accordance with the method of ASTM D4935-99.
Examinations performed have shown an influence of types of used substrates on a value of shielding attenuation of metallic layers. TFDa€™s unique sputtering process, IBS where deposition is performed at temperatures as low as 30 A°C a€“ 60 A°C.
The LTITOa„? sputtering process is unusual as it minimizes the temperature buildup on the part.
Shielding effectiveness of composite material polymer-metal is not only determined by its surface resistivity.
Composite materials working in alternating electrical fields are characterised by a presence, beside conductivity, also polarisation phenomena, that is they get a certain electrical moment m. Generally the polarisation phenomenon is that an arising on a dielectric surface, inserted into electric field, induced electric charges, which are bonded charges pp. A basement of the impedance spectroscopy method (IS) is a measurement of a linear electrical answer of an examined material to an excitation with a relatively small voltage signal of the sinusoidal form u(t) = Um sin (a t + ^u), in a wide frequency range f (a = 2 n f). Using the Fourier transform to both sides of equation (6) we get an answer of dielectric in the frequency domain (A.K. In the IS method we are not limited only to frequency analysis of impedance or admittance of examined material (their amplitude and phase characteristics or dependence of real and imaginary parts of the complex transmittance upon frequency), but we can also use other quantities, such as the complex capacitance C , or the complex permittivity e. The capacitance and the relative permittivity in a complex form are the most often used form of the spectral transmittance in the IS method.


Below the examinations of an answer of dielectric composite materials made of nonwoven fabrics covered by thin plasmatic layers of titanium and titanium monoxide as a representative for composites described in this topic are shown. The Bode diagram analysis suggests a possibility to use the equivalent scheme consisted of a parallel connection RC and also a presence of the Maxwell-Wagner polarisation to describing the polarisation phenomena.
More pieces of information about dielectric properties may be given by a form analysis of the complex capacitance presented as a function of frequency and on the complex plane (the Cole-Cole diagram).
Diagram forms for Ti and 3TiO samples suggest a possibility of a presence of relaxation processes in frequencies above the measuring range. The Cole-Cole diagram of the complex capacitance of examined composite structures is presented on figure 19.
The capability of composite materials to shield electromagnetic fields is coherently associated with their dielectric properties in a wide frequency band.
It should be noted that the performed studies and collected experience in the field of modern technologies of shielding have already solved a lot of actual problems but there is still a challenge for further work to improve the efficiency of shielding and to develop new designs of electromagnetic shields. As a reference point, computer processors operate in excess of 250 MHz and some newer portable phones operate at 900 MHz.
Shielding electronic products successfully from EMI is a complex problem with three essential ingredients: a source of interference, a receptor of interference, and a path connecting the source to the receptor.
While effective in terms of shielding, metals can be heavy and bulky solutions to the design challenge of EMI. As the plastic resin is insulative, these conductive fibers (with a high aspect ratio) create a conductive network within the resin. Without higher volumes (justify tooling investment) or cost minimization objectives, these applications would not be appropriate for EMI Shielding Compounds. For the purposes of this article, these three coating technologies will not be compared versus each other.
Conductive paints are the most common method of applying a conductive surface coating to plastics, but vacuum metallization is gaining ground due to its high quality control. In EMI Shielding Compounds, there is good correlation between volume resistivity (100 – 10-3 ohm-cm thought to provide effective shielding) and shielding effectiveness. While this step eliminates non-conductive parts, it does not identify other quality problems (scratched surfaces or poor coating adhesion and coating thickness variations).
The “revised” plastic part would need to incorporate EMI shielding, which might require a conductive coating. Typical 3% coating scrap rate not included (supply 103 parts to coater to make 100 “good” parts). Yet, even under the most favorable conditions for Conductive Coatings, Figures 1 and 2 highlights that EMI Shielding Compounds are less costly than Coatings under both low and high volume applications. 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. If the impedance of the wave differs greatly from the natural impedance of the shield, much of the energy is reflected and the rest is transmitted across the surface boundary where absorption in the shield further attenuates it.
Shielding can be applied to different areas of the electronic system from equipment enclosures to individual devices (such as circuit boards).
At high frequencies, most of the wave energy is reflected from a shield’s surface, while a smaller portion is absorbed. If a system is properly grounded, all conductive elements are theoretically at zero potential. The separate parts of the enclosure must be electrically bonded together and grounded for the shielding to work. The decibel value is the ratio of two measurements of electromagnetic field strength taken before and after shielding is in place.
Establishing a system’s shielding requirements involves determining the radiated frequencies and the government specifications the unit must meet. A number of shielding products (not related to EMI Shielding Compounds) can reduce EMI cable problems.
FCC emission standards are more stringent for the mass-market Class B equipment than the Class A equipment.
The FCC in the United States and European Community (EC) set standards for EMI emission levels that electronic devices must meet before being sold in those countries. Many companies set their own specifications for immunity to EMI over a range of frequencies. EMI from one circuit can interfere with the function of another in the same system or subsystem (cross-talk).
The company has 11 manufacturing plants on three continents, plus sales representatives throughout the Americas, Europe, and Asia.
Each facility has complete make-to-order manufacturing, color lab, product development, and technical service on-site.
MAST utilizes electrically conductive fillers to achieve specific surface or volume conductivities in a variety of different binder types and viscosities. There are other physical phenomena occurring both in each composite layer and on interphases between them that play very important roles. An answer to a sinusoidal voltage signal is a sinusoidal form of current i(t) = Im sin (a t + with the same angle speed a.
These quantities are bonded with the complex admittance by frequency and geometrical parameters of sample. Their frequency analysis shows multiple phenomena, which take place simultaneously in an examined material. For these examinations the measurement system from the High Voltage Group of Wroclaw University of Technology was used.
The frequency spectrum of the modulus of impedance does not indicate significant differences between examined samples. It is possible to find analogies to examinations outcomes of some laminar structures (Nitsch, 1999).
It is confirmed on diagrams of the imaginary component of the complex capacitance presented on figure 18. We can observe a clear separation between dielectric properties of composites, in which the outer layer is formed by titanium (Ti), and of composites with the outer layer formed by a titanium monoxide (TiO). The method of impedance spectroscopy allows one to connect the measured frequency characteristics with the physical structure of tested material and the alternations in the structure. They can also be used in the shielding of power engineering systems, where a compatibility with environment in a wide sense of this meaning is the main problem (i.e. Additional EMI background information is provided in an EMI Primer at the end of this article. In recent years, there has been a tremendous surge in plastic resins (with conductive coatings or fibers) replacing metals due to the manufacturing flexibility, durability and weight reduction of plastic components. A Business Communications Company industry report estimated that the plastics shielding sector will account for 37% ($156 million) of the total United States EMI shielding market ($422 million). Performance of conductive fiber filled compounds is maximized by utilizing special long fiber manufacturing techniques and cube (dry) blending metal fiber bundles in order to minimize conductive fiber damage.
Rather, this article will help the reader become familiar with the competitive processes, advantages and disadvantages, and opportunities for EMI Shielding Compounds. Some coaters quoted both part P1 and P2, while others admitted that one or the other was not compatible with their process. A device operating at high voltage, with only a small amount of current flow, generates waves with high impedance. Ineffective grounding may actually increase EMI emission levels, with the ground itself becoming a major radiating source. A slot can act as an antenna if the length exceeds one half of a wavelength (problem becomes greater at higher frequencies).


Without attention to the design and shielding of these features, the assembly will behave like a leaky bucket. Each switching event results in a short duration electrical pulse, which has a characteristic frequency inversely proportional to its time length. This is not yet a FCC requirement, however EC regulations do include immunity requirements.
This problem frequently occurs in equipment with high-density packaging of PCBs and is the most common source of system EMI susceptibility.
RTP Company’s engineers develop customized thermoplastic compounds in over 60 different engineering resin systems for applications requiring color, conductive, elastomeric, flame retardant, high temperature, structural, and wear resistant properties.
MAST Technologies has standard off the shelf products but specializes in customizing these materials for targeted applications, levels of resistivity, and environmental attributes.
Please note that on orders of 10 sheets or more, MAST prefers to take the orders offline and will respond to you with a written quotation.
RoHS compliant 2700 Series Conductive Foam is available with or without pressure-sensitive conductive adhesive on one side. 11, increasing of shielding attenuation Ti layers of 10 dB for substrates of smooth surface (CORNIG glass) in comparison to the substrate of extended specific surface (nonwoven fabric PP) is observed. The coefficient of shielding efficiency SE versus frequency f, for different powers released on the Zn96%Bi4% target in case of unipolar DC-M supply. The coefficient of shielding efficiency SE versus frequency f, for different powers released on the Zn96%Bi4%target in case of bipolar DC-M supply. The coefficient of shielding efficiency SE versus frequency f, for different powers released on the Zn96%Bi4%target in case of unipolar DC-M supply.
If we take into consideration the surface charge density for a capacitor not filled with dielectric po, then the total charge density for a capacitor with dielectric is a sum of the bounded charge pp and the free charge po.
This current is a sum of conductive current and polarisation (displacement) current (Walter S.
Its main elements are the precise impedance analyser Agilent 4294A and the measuring cell Agilent 16451B consisting of the three-electrode measuring capacitor. It varies for all examined samples in the same way, and additionally for samples 3TiO and Ti overlaps in almost entire spectrum of frequencies. Each of the examined samples distinguishes then with a specific relaxation process of different time-constants.
Even though plastics are inherently transparent to electromagnetic radiation, advances in conductive coatings, conductive fibers and compounding techniques have allowed design engineers to take advantage of the merits of plastics while enhancing EMI shielding effectiveness. The European market is substantially larger (due to more stringent agency standards) and the Asian market is even bigger due to the sheer volume of electronic systems assembled in that region. Conductive EMI gaskets inserted between mating surfaces preserve current continuity of the enclosure, thereby minimizing leakage. The FCC regulations define specific field strength limits between 30 MHz and 2000 MHz (2 GHz). The manufacturing method can easily be repeated and scaled up, but the most exciting development is the transistor itself.
The test settup consists of network analyser – model HP 8711A of Hewlett-Packard firm and measuring adapter, which is a section of an air concentric line of characteristic impedance 50 Ohm. This observation points to a possibility of obtaining higher values of SE for nonwoven fabrics.
15 , over twofold increase in SE value, for the same values of surface resitivity, was observed. Inserting of dielectric into electric field (flat capacitor configuration) causes increasing of the capacitance from value C0 to value C.
Table 1 includes the description of samples made of alternately covered titanium and titanium monoxide layers on nonwoven fabric. Furthermore we can observe a presence of the second semicircle for each of examined composites, what clearly suggests the presence of another relaxation process at higher frequencies.
In the diagram form of the imaginary component of the complex capacitance as a function of frequency, we do not observe a relaxation pick.
The possibilities to design desired electric properties of composite materials are also used to improve the shielding properties of the materials. In the light of the latest experiences it seems that the future in the area of EM field shielding is connected with the application of modern technologies to fabricate thin-film composite coatings, including nano-composites.
Conversely, if a device contains a large current flow compared to its voltage, it generates a low impedance, H field.
Low impedance waves (H field dominant) are mostly absorbed in a metal shield because they are more closely matched to the metal’s inherent impedance. It is faster than any other silicon-based flexible transistor, and it is capable of wirelessly transferring data or power. A MAST representative will contact you with further ordering instructions for quantities of 10 or more.
The ratio of the capacitor capacitance increasing to its capacitance C0 is defined as the electric susceptibility of the dielectric x, but the proportion of the capacitor capacitance with a dielectric to its capacitance without a dielectric, as the electrical permeability e. At the same time, the diagram form of this characteristic suggests the presence of a relaxation pick at frequencies higher than the measuring range.
The materials are capable to fulfil all conditions of effective shielding from EM fields and to eliminate all undesired occurrences associated with operation of the shielded systems. For maximum H-field absorption, shields need to have high magnetic permeability (ability of material to serve as path for magnetic energy). The […] In Compliance NewsA New Model for Designing MIMO Antennas in Minutes April 22, 2016A new model could cut the amount of time it takes to design antennas for small devices down to minutes, rather than days. Higher uniformity and continuity of Zn layers causes increase in the reflecting effect of electromagnetic wave from this surface. The results of our investigations, presented above, point out the possibility of industrial fabrication of the composite shielding materials with the coefficient of shielding efficiency exceeding 50 dB. Shielding attenuation is calculated as a difference between transmittances or between attenuation of a standard and an examined sample. In this case we can observe the strong dependence of dielectric composite properties upon a number of formed Ti-TiO layers. Good mechanical properties and high resistance to environmental effects are additional advantages of such materials. Increasing bismuth concentration from 4 to 10 % of atomic, causes increase in SE by approximately 20 dB (Fig. Frequency diagram forms of the imaginary component of the complex capacitance shows, in the examined measuring frequency range, the presence of a relaxation pick and a possibility of a presence of the second relaxation phenomenon at higher frequencies. The value and frequency of a relaxation pick presence are strictly depended on a number of Ti-TiO layers forming a composite. Increasing a number of layers results in reducing of a relaxation pick value and in displacement in the lower frequencies direction. Observed changes of SE value as a function of power released on the target, are caused by increase in Zn layer thickness. It is confirmed by Cole-Cole diagrams of the complex capacitance, in which there is a clear presence of a displacement of the semicircle centre to the right for 1TiO sample.



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