Microwave absorbing material
1. The setting for the study of microwave absorbing materials. In recent years, the rapid development and spread of various electronic equipment has brought huge convenience to people. At the same time, the electromagnetic radiation and electromagnetic interference that occur during the operation of electronic and electrical equipment have severely affected human production. And days. The damage of electromagnetic waves is mainly manifested in the following aspects: Electromagnetic radiation can damage human health through thermal, non-thermal and population effects; electromagnetic waves may interfere with electronic equipment, instrumentation, communication signals, etc., and even threaten military security and cause huge losses; Severe electromagnetic pollution can also affect plants, preventing plants from growing normally, genetic mutations and even death. Therefore, electromagnetic pollution is considered to be a new pollution source that is more damaging and difficult to protect after water, air and noise pollution. People have gradually realized the damage of electromagnetic waves. Now, there are two main aspects to effective restraint and reduction of electromagnetic radiation. On the one hand, it is to optimize the electronic circuit planning, and on the other hand, it is to use electromagnetic protection materials to protect against radiation. In the case that the equipment circuit has been confirmed, external protection methods are particularly important. Electromagnetic absorbing protection materials can effectively absorb and attenuate or even block the transmission of electromagnetic waves, reduce electromagnetic pollution, and ensure the normal operation of electronic equipment. The development of new broadband, light and thin, strong absorption, green absorbing materials has great application value. The electromagnetic waves in daily life are mainly microwaves with a frequency of 300KHz-300GHz, and the test scale of the absorption data is mainly 2-18GHz. 2. Definition of absorbing data The absorbing data refers to a kind of functional data that can transform the electromagnetic wave energy into heat or other forms of energy through the medium loss of the electromagnetic wave projected on its surface. This leads to two basic conditions for absorbing data: 1) The incident electromagnetic wave should enter the data at the maximum limit, instead of being reflected on the outside, that is, the impedance matching between the data and the space should be satisfied; The electromagnetic wave energy is almost completely attenuated, which is the attenuation characteristic. Figure 1 shows the path diagram of electromagnetic waves passing through the absorption data. As shown in the figure, when the incident wave reaches the surface of the data, a part of it will be reflected away, and only this part of the electromagnetic wave entering the data can be attenuated. Therefore, good absorbing materials simply do not reflect electromagnetic waves, but absorb them inside and attenuate them all. In order to "close the door and hit the dog" against electromagnetic waves, the data must be well satisfied with the above two basic conditions. These two basic conditions have become the guidelines for scientists to plan absorbing data. Figure 1 The transmission path diagram of electromagnetic waves in lossy media. So how should we comment on the absorbing function of the data? 3. Comments on the absorbing function There are two basic requirements for the absorbing data: 1. Strong electromagnetic wave absorbing ability; 2 . Wide coverage frequency scale. Firstly, explain the electromagnetic wave absorption capacity: now scholars have selected the most important targets for evaluating the electromagnetic wave absorption capacity. There are mainly two: 1) Reflection Loss (RL) of electromagnetic waves, the unit is dB, which indicates the loss of data to fixed frequency electromagnetic waves Ability, 2) The frequency width of RL<-10dB, also called useful absorption width, represents the frequency scale that can absorb 90% of energy electromagnetic waves, in GHz. Figure 2 is a typical function curve of absorbing data, where the ordinate is RL, and the abscissa is frequency. The curve represents the change of the reflection loss with frequency at a certain fixed thickness. Generally speaking, the lower the curve (that is, the smaller the ordinate), the wider the useful absorption width, and the better the wave-absorbing function of the data. Intuitively, the larger the area enclosed by the curve and the -10 dB line (the dark part in the figure), the better the absorbing function. In addition, sometimes there are also requirements for the frequency scale of the useful absorption bandwidth. The absorption peaks of general absorbing materials appear in the high-frequency region, that is, the useful absorption bandwidth is in the high-frequency region. Figure 2 Electromagnetic wave absorption function curve 4. Differences between absorbing materials and electromagnetic shielding materials There is also a sister to electromagnetic shielding materials-electromagnetic shielding materials. What is the difference between the two? Simply put, the absorbing material is to absorb all electromagnetic waves to reduce reflection and transmission, while the magnetic shielding material is to prevent electromagnetic waves from entering the equipment to be maintained, and reflect all the electromagnetic waves. The electromagnetic waves just happen. Transfer and did not disappear. So both are to prevent electromagnetic waves from passing through the equipment to be maintained, but one is absorption and the other is reflection. The review method of magnetic shielding data is different from that of absorbing data. The primary goal is shielding effectiveness (SE).
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