Due to historical reasons, the development of military TEMPEST technology is the first, and the development of civil EMC technology is later. The research of military electromagnetic wave absorbing materials has always been ahead of the research of civil electromagnetic wave absorbing materials, and the same is true for the research of electromagnetic wave absorbers. On the whole, due to the requirements of technological development, higher requirements are put forward for the performance of electromagnetic wave absorbing materials and the design of electromagnetic wave absorbers, and a single material and structure can no longer meet the requirements.
For military electromagnetic wave absorbing materials, the development from single frequency band, narrow frequency band materials to multiple frequency bands and broad frequency bands. Ultra-fine structures and composite structures have become important development directions, and new electromagnetic wave absorbing materials and electromagnetic wave absorbing structures have become research hotspots.
Electromagnetic wave absorbers can not only be used as absorbing materials for electromagnetic wave shielding darkrooms, but also can be used for electromagnetic wave absorption and electromagnetic field design in various electronic devices. Electromagnetic wave absorber is an indispensable absorbing material for electromagnetic wave shielding anechoic chambers. There are pyramidal composite sponge absorbers impregnated with absorbing powder. Its size is related to the absorbing frequency. The shape is designed to match the impedance of electromagnetic waves. It can meet the electromagnetic wave absorption rate of 30MHz-40GHz and 10-20dB; the plate-shaped, grid-shaped and double-layer ferrite absorbing materials can meet the electromagnetic wave absorption rate of 30MHz-2GHz and 10dB. The electromagnetic wave absorber used in the electromagnetic wave shielding darkroom is adapted to the size of the darkroom, and the thickness is continuously reduced in order to effectively use the space.
Electromagnetic wave absorbers for electromagnetic wave shielding darkrooms cannot be used in civil electronic information products due to their volume and weight limitations. Electromagnetic wave absorbers with a thickness of millimeters have been used in military applications, but their development in civilian use is relatively slow due to various reasons. However, Japan and Western European countries have already exhibited electromagnetic wave absorbers with a thickness of millimeters. Products are rare.
In addition, in the actual electromagnetic leakage protection technology, different methods must be taken into account for the specific circuit conditions. Since the electromagnetic interference of electronic and electrical equipment is conducted in two ways: conduction and radiation, there are also two types of responses to EMC technology. (1) Conduction: Harmonics and clutter different from the frequency of the power supply are transmitted to the power grid through wires, and thus affect other equipment and cause information leakage. The conducted electromagnetic waves are generally low in frequency and can be suppressed by the design of the filter. (2) Radiation, the high-frequency electromagnetic oscillation inside the equipment radiates outward in the form of waves, directly affecting other equipment. In order to reduce the electromagnetic radiation of the equipment, the following methods are generally used to suppress:
(1) Low-radiation circuit design, (2) Equipment shielding, including case shielding, wiring holes and seam shielding, (3) Isolation technology, including equipment working environment shielding (for example, the Pentagon in the United States installed electromagnetic wave shielding materials) , (4) Shielding of power lines and signal lines, (5) Filtering of power lines and signal lines, (6) Methods of electromagnetic wave absorbing materials.
Due to the limitation of circuit design technology and cost, many products need to use shielding and wave absorption methods when they fail to meet EMC standards. The purpose of shielding and wave absorption is to confine electromagnetic waves in a certain area, the difference is that shielding mainly uses the reflection of conductive materials on electromagnetic waves to limit the propagation of electromagnetic waves. Generally, the entire radiation source needs to be shielded, otherwise, the phenomenon of weakening in one direction and increasing in other directions will occur.
Wave absorption is the use of materials to absorb electromagnetic waves, so that the electromagnetic field energy of electromagnetic waves can be converted into other forms of energy (usually converted into heat energy). Electromagnetic wave absorbing materials do not require high electrical conductivity, and are relatively easy to apply in equipment, and the technical requirements for use are lower. Research on EMC materials is currently mainly focused on shielding materials, and relatively little research on electromagnetic wave absorbing materials and absorbers. In fact, electromagnetic wave absorbing materials and absorbers play an irreplaceable role in EMC technology, such as shielding materials, and are currently becoming a hot spot in the development of EMC disciplines.
However, practical electromagnetic wave absorbing materials not only have specific requirements for the performance of the material, but also have specific requirements for the material in the use environment, such as use temperature and use size. These are the problems that must be solved for the practical use of electromagnetic wave absorbing materials. , Is also the research goal of a future stage.