rus
Issue #3/2023
D. Grishin, I. Gusev
Construction Materials to Ensure the Electromagnetic Compatibility of Radio Equipment
Construction Materials to Ensure the Electromagnetic Compatibility of Radio Equipment
DOI: 10.22184/1993-7296.FRos.2023.17.3.210.217
Electromagnetic shielding is a widely used method for ensuring the electromagnetic compatibility (EMC) of radio equipment. The screening efficiency and operational reliability of the equipment are largely determined by the shield design, as well as the specifications and properties of the materials used for its manufacture. The article discusses the main construction materials used for electromagnetic shielding, such as the gaskets, contact springs, fabrics, heat shrink tubes, and RF absorbers with an adhesive layer. The method for confirming the specifications of shielding materials in the EMC laboratory of TESTPRIBOR JSC is described.
Electromagnetic shielding is a widely used method for ensuring the electromagnetic compatibility (EMC) of radio equipment. The screening efficiency and operational reliability of the equipment are largely determined by the shield design, as well as the specifications and properties of the materials used for its manufacture. The article discusses the main construction materials used for electromagnetic shielding, such as the gaskets, contact springs, fabrics, heat shrink tubes, and RF absorbers with an adhesive layer. The method for confirming the specifications of shielding materials in the EMC laboratory of TESTPRIBOR JSC is described.
Теги: electromagnetic compatibility electromagnetic wave absorbers поглотители электромагнитных волн электромагнитная совместимость электромагнитное экранирование
Construction Materials to Ensure the Electromagnetic Compatibility
of Radio Equipment
D. Grishin, I. Gusev,
TESTPRIBOR JSC, Moscow, Russia
Electromagnetic shielding is a widely used method for ensuring the electromagnetic compatibility (EMC) of radio equipment. The screening efficiency and operational reliability of the equipment are largely determined by the shield design, as well as the specifications and properties of the materials used for its manufacture. The article discusses the main construction materials used for electromagnetic shielding, such as the gaskets, contact springs, fabrics, heat shrink tubes, and RF absorbers with an adhesive layer. The method for confirming the specifications of shielding materials in the EMC laboratory of TESTPRIBOR JSC is described.
Keywords: electromagnetic compatibility, electromagnetic wave absorbers
The article received on: 07.04.2023
The article accepted on: 25.04.2023
Introduction
In the modern world, electronics and computer technology hold a specific place in many areas of human activities. However, the shared use of various electronic devices may result in unwanted electromagnetic interactions that may adversely affect the operation of such devices. One of the ways to solve such problems is to ensure electromagnetic compatibility [1].
Electromagnetic compatibility (EMC) is determined as the ability of an electronic system to function in the midst of other systems without any major impact on them. This means that the equipment intended for use in various electronic systems must comply with the certain EMC standards in order to be operated safely and reliably under various operating conditions.
For example, the up-to-date medical devices used for the patient diagnostics and treatment include many components and electrical appliances. The interaction of all these components can cause unwanted electromagnetic waves that leads to the device malfunctions, and even its destruction [2].
As the number of devices working in the electromagnetic spectrum is expanded, the scientists and engineers are finding new solutions to the EMC problem. The main method for ensuring electromagnetic compatibility in terms of electromagnetic field immunity, as well as compliance with the requirements for the radiated disturbance level, is electromagnetic shielding. Installation of the shield on the noise-emitting elements ensures the separation of signals required for the operation of electronic equipment, increases the receivers’ selectivity, interference immunity of the sensitive equipment, signal purity of the generators, and the device accuracy. The adequate choice of shielding method, shield material and design is very important at the initial design stage, since it will determine the possible successful passing the EMC tests and reliable operation of the developed equipment.
Currently, the industry produces a wide variety of EMC materials. These are the structural materials designed to improve shielding, electromagnetic wave adsorbers, as well as the electronic components: throttles, special filters and semiconductor devices.
In this article, we will take a closer look at the construction materials including the gaskets, contact springs, fabrics, compounds, ferrite products, as well as their combinations.
Construction materials
The contact springs (Fig. 1) are made of various alloys (beryllium copper, steel, monel, tinned copper) and are used to provide contact between two conductive surfaces. The springs are distinguished by a large number of compression cycles: more than 20 thousand without deterioration in the main specifications. The clamping pressure is approximately 800 g/cm. The shielding efficiency is highest in the frequency range from 100 MHz to 1 GHz and is decreased with the increasing frequency. By virtue of its design, the springs allow to obtain the running contact. The multipurpose mounting methods allow to have a running or pressure contact in any direction. One of several methods can be used for fastening: riveting, fastening to the grooves, fastening with an adhesive layer, fastening with a clip method, mounting with a glued rail, welding, or soldering. Such springs are used to obtain the blade contacts applied in the doors of acoustic chambers.
The wire mesh gaskets are a mesh made of steel wire twisted into a tube or wrapped around the soft foam rubber (Fig. 2). They are mainly used in the assembly of high-load structures (acoustic chambers). An attachment bolt is placed between the gasket harnesses, thus making a continuous contact around the connection. The number of compression cycles is from 6 to 12 per year. Moreover, the braided wire tape is also available (Fig. 3) that allows the cable assemblies to be shielded by wrapping around the cable. It can be fixed with a heat shrink tube or in any other convenient way.
Today, the shielding gaskets made of conductive rubber and elastomers (Fig. 4) are becoming widespread. They are popular due to the ability to provide both tightness and electrical contact. They are highly flexible that allows them to be placed in the grooves with compound shape, as, for example, in the UHF housings. In addition, they are convenient for flow line production, as they can be made of the compound using an automatic line.
The spiral tubes (Fig. 5) are similar in functionality to the contact springs, but their installation method is different: they are installed in a groove and pressed against the top by a cover. The electrical contact is provided by the steel elasticity.
The most popular and easy to use method provides for the fabric conductive gaskets with an elastic filler and an adhesive layer (Fig. 6). They are made of a foam polymer covered with a conductive fabric. Such gaskets are available in various shapes and sizes. Due to the available conductive adhesive layer, they can be used on the unprepared housings in the absence of grooves. The number of compressions exceeds 500 thousand times. The fabric conductive gaskets have permanent residual deformation when the force and compression ratio are exceeded.
The shielding foil is used to shield the magnetic and electrical components of the electromagnetic field, depending on the foil material (Fig. 7). This foil is provided in the coils with a coated adhesive layer. It is very convenient to shield the cables and eliminate the gaps in the shields. The shielding ratio reaches 10.
To shield the transparent structures, a shielding film with an adhesive layer is applied. Its shielding ratio is from 20 to 30 dB. Moreover, to solve these problems, the ready-made shielded glasses are used, obtained by sintering two glasses and a wire mesh between them (Fig. 8). For attachment to an external screen, a skirt is left along the edges of this structure with the width of 10–50 mm for fixing to a conductive surface. When using such structures, it is necessary to remember that the higher the shielding ratio, the lower the light transmission ratio.
If it is necessary to shield the cable assembly while providing it with the mechanical protection, it is convenient to use the shielding heat shrink tubes (Fig. 9). A conductive layer or mesh is deposited inside such a tube. During the shrinking process, the tube tightly fits the cable, providing the necessary strength and shielding up to 60 dB at a frequency of 10 GHz. It must be remembered that in order to ensure the declared shielding ratio, during the connector termination, it is necessary to ensure electrical contact along the entire strain relief and its conductive body.
A special place among the shielding materials is held by the high-frequency radiation absorbers with an adhesive layer (Fig. 10). They are used to provide EMC inside the small enclosures. As it is known, in an enclosed casing, consisting of conductive materials, the electromagnetic waves are reflected from a conductive surface. Multiple re-reflections in a small confined space lead to the generation of standing waves, a change in the complex impedance of the space above the strip, and, in many cases, to the failure of the circuit that worked with the lid open. To solve this problem, the absorbers with an adhesive layer are applied. It is convenient to stick them on the housing cover, providing an absorption up to 10 dB.
Fig. 11 shows the gain dependence on frequency for an amplifier with automatic gain control. The diagram shows the gain ratio spikes due to the spatial resonances prior to the absorber application. After the absorber is glued, the specification becomes smooth, and the amplifier with AGC is suitable for use. The absorbers represent the frequency-dependent materials that should be considered when selecting them.
Given the rate of appearance of new materials in the industry, it is impossible to be familiar with the properties of all of them in advance, due to which the EMC laboratory of TESTPRIBOR JSC has developed a method for confirming some specifications of shielding materials. The method is based on the MIL-STD‑285 standard [3]. Confirmation of the shielding ratio of sheet materials is performed as follows. Prior to the measurements, the measuring system is calibrated. The receiving and measuring antennas with the well-known specifications are installed coaxially opposite each other in an acoustic chamber (Fig. 12).
The coupling ratio between the antennas is measured in the studied frequency range. Then the transmitting antenna and signal generator are installed in the chamber, and the receiving antenna is place outside the chamber (Fig. 13).
The studied samples of materials are sequentially installed in the access hole of the chamber, and the measurements are taken. The obtained values are compared with the coupling ratio of antennas without a shield between them, and the shielding ratio is calculated. This method is also suitable for assessing the operating efficiency of conductive gaskets. The gaskets are placed between the chamber and a steel plate with a well-known shielding ratio, since reduction in the shielding ratio can help to fairly accurately assess the operating efficiency of a particular gasket.
This method has been used to verify several material samples, and the results have confirmed the declared values.
Due to introduction of new construction materials on the market, it is becoming easier for the designers to meet the necessary EMC requirements. However, it is now more difficult to understand the variety of offered products. TESTPRIBOR JSC has its own testing laboratory capable of confirming the quality of the supplied materials that allows to offer the comprehensive solutions to EMC problems.
AUTHORS
Grishin D., test engineer, EMC Laboratory, TESTPRIBOR JSC, Moscow, Russia.
Gusev I., test engineer, EMC Laboratory, TESTPRIBOR JSC, Moscow, Russia.
of Radio Equipment
D. Grishin, I. Gusev,
TESTPRIBOR JSC, Moscow, Russia
Electromagnetic shielding is a widely used method for ensuring the electromagnetic compatibility (EMC) of radio equipment. The screening efficiency and operational reliability of the equipment are largely determined by the shield design, as well as the specifications and properties of the materials used for its manufacture. The article discusses the main construction materials used for electromagnetic shielding, such as the gaskets, contact springs, fabrics, heat shrink tubes, and RF absorbers with an adhesive layer. The method for confirming the specifications of shielding materials in the EMC laboratory of TESTPRIBOR JSC is described.
Keywords: electromagnetic compatibility, electromagnetic wave absorbers
The article received on: 07.04.2023
The article accepted on: 25.04.2023
Introduction
In the modern world, electronics and computer technology hold a specific place in many areas of human activities. However, the shared use of various electronic devices may result in unwanted electromagnetic interactions that may adversely affect the operation of such devices. One of the ways to solve such problems is to ensure electromagnetic compatibility [1].
Electromagnetic compatibility (EMC) is determined as the ability of an electronic system to function in the midst of other systems without any major impact on them. This means that the equipment intended for use in various electronic systems must comply with the certain EMC standards in order to be operated safely and reliably under various operating conditions.
For example, the up-to-date medical devices used for the patient diagnostics and treatment include many components and electrical appliances. The interaction of all these components can cause unwanted electromagnetic waves that leads to the device malfunctions, and even its destruction [2].
As the number of devices working in the electromagnetic spectrum is expanded, the scientists and engineers are finding new solutions to the EMC problem. The main method for ensuring electromagnetic compatibility in terms of electromagnetic field immunity, as well as compliance with the requirements for the radiated disturbance level, is electromagnetic shielding. Installation of the shield on the noise-emitting elements ensures the separation of signals required for the operation of electronic equipment, increases the receivers’ selectivity, interference immunity of the sensitive equipment, signal purity of the generators, and the device accuracy. The adequate choice of shielding method, shield material and design is very important at the initial design stage, since it will determine the possible successful passing the EMC tests and reliable operation of the developed equipment.
Currently, the industry produces a wide variety of EMC materials. These are the structural materials designed to improve shielding, electromagnetic wave adsorbers, as well as the electronic components: throttles, special filters and semiconductor devices.
In this article, we will take a closer look at the construction materials including the gaskets, contact springs, fabrics, compounds, ferrite products, as well as their combinations.
Construction materials
The contact springs (Fig. 1) are made of various alloys (beryllium copper, steel, monel, tinned copper) and are used to provide contact between two conductive surfaces. The springs are distinguished by a large number of compression cycles: more than 20 thousand without deterioration in the main specifications. The clamping pressure is approximately 800 g/cm. The shielding efficiency is highest in the frequency range from 100 MHz to 1 GHz and is decreased with the increasing frequency. By virtue of its design, the springs allow to obtain the running contact. The multipurpose mounting methods allow to have a running or pressure contact in any direction. One of several methods can be used for fastening: riveting, fastening to the grooves, fastening with an adhesive layer, fastening with a clip method, mounting with a glued rail, welding, or soldering. Such springs are used to obtain the blade contacts applied in the doors of acoustic chambers.
The wire mesh gaskets are a mesh made of steel wire twisted into a tube or wrapped around the soft foam rubber (Fig. 2). They are mainly used in the assembly of high-load structures (acoustic chambers). An attachment bolt is placed between the gasket harnesses, thus making a continuous contact around the connection. The number of compression cycles is from 6 to 12 per year. Moreover, the braided wire tape is also available (Fig. 3) that allows the cable assemblies to be shielded by wrapping around the cable. It can be fixed with a heat shrink tube or in any other convenient way.
Today, the shielding gaskets made of conductive rubber and elastomers (Fig. 4) are becoming widespread. They are popular due to the ability to provide both tightness and electrical contact. They are highly flexible that allows them to be placed in the grooves with compound shape, as, for example, in the UHF housings. In addition, they are convenient for flow line production, as they can be made of the compound using an automatic line.
The spiral tubes (Fig. 5) are similar in functionality to the contact springs, but their installation method is different: they are installed in a groove and pressed against the top by a cover. The electrical contact is provided by the steel elasticity.
The most popular and easy to use method provides for the fabric conductive gaskets with an elastic filler and an adhesive layer (Fig. 6). They are made of a foam polymer covered with a conductive fabric. Such gaskets are available in various shapes and sizes. Due to the available conductive adhesive layer, they can be used on the unprepared housings in the absence of grooves. The number of compressions exceeds 500 thousand times. The fabric conductive gaskets have permanent residual deformation when the force and compression ratio are exceeded.
The shielding foil is used to shield the magnetic and electrical components of the electromagnetic field, depending on the foil material (Fig. 7). This foil is provided in the coils with a coated adhesive layer. It is very convenient to shield the cables and eliminate the gaps in the shields. The shielding ratio reaches 10.
To shield the transparent structures, a shielding film with an adhesive layer is applied. Its shielding ratio is from 20 to 30 dB. Moreover, to solve these problems, the ready-made shielded glasses are used, obtained by sintering two glasses and a wire mesh between them (Fig. 8). For attachment to an external screen, a skirt is left along the edges of this structure with the width of 10–50 mm for fixing to a conductive surface. When using such structures, it is necessary to remember that the higher the shielding ratio, the lower the light transmission ratio.
If it is necessary to shield the cable assembly while providing it with the mechanical protection, it is convenient to use the shielding heat shrink tubes (Fig. 9). A conductive layer or mesh is deposited inside such a tube. During the shrinking process, the tube tightly fits the cable, providing the necessary strength and shielding up to 60 dB at a frequency of 10 GHz. It must be remembered that in order to ensure the declared shielding ratio, during the connector termination, it is necessary to ensure electrical contact along the entire strain relief and its conductive body.
A special place among the shielding materials is held by the high-frequency radiation absorbers with an adhesive layer (Fig. 10). They are used to provide EMC inside the small enclosures. As it is known, in an enclosed casing, consisting of conductive materials, the electromagnetic waves are reflected from a conductive surface. Multiple re-reflections in a small confined space lead to the generation of standing waves, a change in the complex impedance of the space above the strip, and, in many cases, to the failure of the circuit that worked with the lid open. To solve this problem, the absorbers with an adhesive layer are applied. It is convenient to stick them on the housing cover, providing an absorption up to 10 dB.
Fig. 11 shows the gain dependence on frequency for an amplifier with automatic gain control. The diagram shows the gain ratio spikes due to the spatial resonances prior to the absorber application. After the absorber is glued, the specification becomes smooth, and the amplifier with AGC is suitable for use. The absorbers represent the frequency-dependent materials that should be considered when selecting them.
Given the rate of appearance of new materials in the industry, it is impossible to be familiar with the properties of all of them in advance, due to which the EMC laboratory of TESTPRIBOR JSC has developed a method for confirming some specifications of shielding materials. The method is based on the MIL-STD‑285 standard [3]. Confirmation of the shielding ratio of sheet materials is performed as follows. Prior to the measurements, the measuring system is calibrated. The receiving and measuring antennas with the well-known specifications are installed coaxially opposite each other in an acoustic chamber (Fig. 12).
The coupling ratio between the antennas is measured in the studied frequency range. Then the transmitting antenna and signal generator are installed in the chamber, and the receiving antenna is place outside the chamber (Fig. 13).
The studied samples of materials are sequentially installed in the access hole of the chamber, and the measurements are taken. The obtained values are compared with the coupling ratio of antennas without a shield between them, and the shielding ratio is calculated. This method is also suitable for assessing the operating efficiency of conductive gaskets. The gaskets are placed between the chamber and a steel plate with a well-known shielding ratio, since reduction in the shielding ratio can help to fairly accurately assess the operating efficiency of a particular gasket.
This method has been used to verify several material samples, and the results have confirmed the declared values.
Due to introduction of new construction materials on the market, it is becoming easier for the designers to meet the necessary EMC requirements. However, it is now more difficult to understand the variety of offered products. TESTPRIBOR JSC has its own testing laboratory capable of confirming the quality of the supplied materials that allows to offer the comprehensive solutions to EMC problems.
AUTHORS
Grishin D., test engineer, EMC Laboratory, TESTPRIBOR JSC, Moscow, Russia.
Gusev I., test engineer, EMC Laboratory, TESTPRIBOR JSC, Moscow, Russia.
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