One of the main factors affecting the absorbing performance of polycrystalline iron fiber absorbing material is its microwave permeability and theoretical studies have shown that the main factor affecting the microwave permeability of polycrystalline iron fiber is the intrinsic permeability of the fiber. , Conductivity, diameter and aspect ratio, etc.
(1) The influence of composition on microwave permeability
Three kinds of fibers, nickel, carbonyl iron and cobalt fibers with different components were prepared respectively. The diameter of nickel fiber was 25m, the diameter of carbonyl iron and cobalt fiber was 1~3m, and the length-to-diameter ratio of the three fibers was 15-25. The fibers were uniformly dispersed in paraffin to prepare electromagnetic parameter test samples, and the microwave permeability of the samples was tested using the material electromagnetic parameter test system based on HP8510B vector network analyzer. The test shows that among the above three kinds of fibers, the carbonyl iron fiber has the highest microwave permeability. Carbonyl iron fiber is significantly larger than nickel fiber and cobalt fiber, and carbonyl iron fiber is significantly larger than drill fiber. Figure 213 shows the S-band magnetic permeability test results of carbonyl iron fiber and cobalt fiber when the volume duty ratio is 10%. In the entire frequency range of 2.6-3.95GHz, the sum of carbonyl iron fibers is greater than that of cobalt fibers.
(2) The influence of fiber diameter on microwave permeability
Choose the carbonyl iron material (stealth material) to prepare fine fibers with a diameter of 1 to 3 m and thick fibers with a diameter of 4 to 6 m. The length-to-diameter ratio of the two fibers is 15-25. The above-mentioned fine fibers and thick fibers were uniformly dispersed in liquid paraffin respectively to prepare S-band waveguide test samples. The volume duty ratio of the fibers in both samples was 10%. The above two samples were tested separately. In the entire frequency range of 2.6~3.95GHz, the sum of fine fibers was greater than that of thick fibers. It can be seen that reducing the fiber diameter is one of the effective ways to improve the microwave permeability of polycrystalline iron fibers. 1. The above conclusion is consistent with the theoretical conclusion, the main reason is that the thicker the fiber, the more significant the electromagnetic skin effect in the fiber.
(3) The influence of fiber length to diameter ratio on microwave permeability
The carbonyl iron materials were selected to prepare long fibers with an aspect ratio of 15-25 and short fibers with an aspect ratio of 5-15. The diameters of the two fibers were 4-6m. The microwave permeability of these two fibers is tested. When the volumetric duty cycle is 10%, the X-band test is in the entire 8.2~12.4GHz frequency range, and the sum of long fibers is "slightly larger than that of short fibers." . It can be seen that when the aspect ratio is not very large, the microwave permeability of the polycrystalline iron fiber increases with the increase in the aspect ratio. The main reason is that the larger the aspect ratio, the weaker the demagnetization effect of the fiber axis is improved. The fiber aspect ratio is beneficial to improve the magnetic permeability of the fiber, but the fiber is too long to bend and deform. The above test results show that although the fiber length-to-diameter ratio is significantly increased from 5-15 to 15-25, the increase in permeability is not significant. Therefore, the range of aspect ratio can be larger when preparing polycrystalline iron fiber.
Based on the previous research, a new polycrystalline iron fiber—9914 fiber was developed by selecting the best components, further reducing the fiber diameter and controlling the aspect ratio. The diameter of the fiber is about 0.5~2m, and the aspect ratio is 5~20. When the volume duty cycle is 30%, the microwave permeability test result of 9901 fiber is shown in Figure 2-16. Figure 2-16 shows that 9901# fiber has a higher microwave permeability, with a rate of 4.65, which is greater than 2.50 in the frequency range of 2-5GHz.