Test and Simulation of Electromagnetic Protection Performance of Radiation Protection Maternity Wear
〠Abstract 】 Based on the analysis of anti-radiation maternity clothes, the electromagnetic protection performance of two anti-radiation maternity vests was measured by experiments , and the test simulation model was established by using three-dimensional electromagnetic simulation software Ansofl HFSS according to the experimental conditions to obtain the shielding effectiveness of the clothing. The simulation model was used to analyze the effects of body shape changes on the electromagnetic protection performance of pregnant women during different pregnancy periods. The research results show that the simulation results of the electromagnetic shielding effectiveness test model of garments are consistent with the actual measurement results. The model can be used for the research of electromagnetic radiation protection functions. Studies have also shown that the rapid changes in the body shape of pregnant women will directly lead to an increase in the opening of the hem of the radiation-proof pregnant women. As the opening of the hem increases, the electromagnetic protection performance of the garments shows a downward trend. When the hem of the protective suit is increased to a certain extent, the shielding effectiveness of the clothing for electromagnetic waves of different frequencies is very low, and it has been unable to protect the electromagnetic radiation.
[ Keywords ] radiation protection; maternity clothes; shielding effectiveness; simulation
[ Chinese Library Classification Number ] : TS 941 . 2 document identification code: A Â Â Article ID: 0253-9721(2011)l0-0108-05
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Nowadays, the invisible killing of electromagnetic radiation has already filled people's entire living and working environment, which has caused certain harm to human health, especially pregnant women and fetuses are more vulnerable. In the first trimester, strong electromagnetic radiation will directly lead to abortion in pregnant women; in the second trimester, electromagnetic radiation may damage the central nervous system of the fetus, causing mental insufficiency and even causing dementia; in the third trimester, electromagnetic radiation may cause fetal immune function to be low. After birth, the body is weak and the resistance is poor [1-3] . However, as pregnant women who cannot escape from the electromagnetic radiation environment, they have to take some measures to protect electromagnetic radiation. At this time, radiation-proof maternity clothes are the first choice for pregnant women.
Anti-radiation maternity clothes as a functional clothing, not only must have the basic performance of maternity clothes, such as wearing comfortable, breathable, etc., but also have electromagnetic protection. There are already many anti-radiation maternity clothes on the market, but what is their protection against electromagnetic radiation is not known. Moreover, with the increase of pregnancy, the body shape of pregnant women changes significantly, which will cause the radiation protection of pregnant women to change the hem opening, which will further affect their electromagnetic protection performance [4] . Therefore, the electromagnetic protection of radiation-proof pregnant women's vests is carried out through experiments. The performance was analyzed in detail, and the electromagnetic protection performance test simulation model was established according to the experimental conditions. On the basis of verifying the reliability of the simulation model, the model was used to analyze the influence of body shape changes on the electromagnetic protection performance of the clothing during pregnancy.
1 Â Â Electromagnetic protection performance test
The test object is 2 pieces of anti-radiation maternity vest, the style is basically the same, as shown in Figure 1 . The fabric used in the vest is different, and the performance parameters of the fabric are shown in Table 1 .
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Figure 1 shows the style of the sample |
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Table 1 performance parameters of the fabric
 Sample number | Fabric composition | Yarn structure | Fabric organization | Conductivity / (s · m -1 ) | Fabric thickness Degree / mm |
1 | Silver fiber 50 %, polyester 50 % | Core | Twill | 7 003 | 0.34 |
2 | Stainless 锕 fiber 30 % , cotton 60 %, polyester 10 % | Blended | plain weave | 304 | 0.56 |
At present, the radiation protection maternity clothes on the market are marked with the shielding effectiveness test data of the fabrics used. However, the radiation protection maternity clothes are made according to the human body design and are three-dimensional. The test data of the fabric cannot be used to express the electromagnetics of the clothing. Protective performance, the test of electromagnetic protection performance of clothing is also different from the test of radiation protection fabric [5-6] . In testing the shielding effectiveness of clothing, it is necessary to simulate a human body - clothing - environment system according to the electromagnetic radiation environment in which the human body is located . Only the experimental data obtained in such a system is authentic and reliable [7] .
Therefore, according to GB / T 23463-2009 "protective clothing microwave radiation protective clothing" test clothing shielding effectiveness (SE) of electromagnetic waves , the experimental specific settings shown in Figure 2 . The radiation pregnant women wearing a suit manikin placed in a shielded room, emitted by the human body model is placed in the front of the transmitting antenna electromagnetic waves of different frequencies, the electric field inside the human body model using the probe positioned to receive signals, respectively not worn The electric field strength E 2 (V / m) of the electromagnetic wave and the electric field strength E 1 (V / m) of the electromagnetic wave when the sample is worn are calculated according to the formula shielding effectiveness = 20 lg ( E 2 / E 1 ) .
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Figure 2 clothing shielding effectiveness test room |
During the test, the positions of the transmitting antennas are different, and the obtained electromagnetic waves are polarized in different ways, and vertically polarized waves and horizontally polarized waves can be obtained respectively. By testing the shielding effectiveness of two samples at different frequency points, the shielding effectiveness against vertical polarized waves and levels as shown in Table 2 can be obtained .
Table 2 Â Shielding effectiveness of sample on vertical and horizontal polarized waves
Frequency / MHz | Shielding effectiveness / dB | |||
Vertically polarized wave | Horizontally polarized wave | |||
Sample 1 | Sample 2 | Sample 1 | Sample 2 | |
300 | 2.17 | 2.12 | 9.41 | 8.46 |
600 | 5.63 | 5.04 | 6.83 | 6.40 |
915 | 6.96 | 6.70 | 5.76 | 6.27 |
1800 | 4.70 | 4.13 | 10.12 | 10.39 |
2450 | 3.80 | 3.62 | 10.95 | 9.32 |
3000 | 2.42 | 2.10 | 9.80 | 8.90 |
Under the electromagnetic wave irradiation of different frequencies, the electromagnetic protection performance of the two sample clothes on the horizontally polarized wave is better than that of the vertical. Regardless of whether it is a vertically polarized wave or a horizontally polarized wave, the shielding effectiveness value of the sample 1 is higher than that of the sample 2 because the conductivity of the sample 1 using the silver fiber fabric is higher than that of the sample using the stainless steel fiber fabric 2 Be high. However, their difference is not very large, which is determined by the structural factors of the garment itself. The selected two samples have larger openings at the upper and lower sides , which will cause considerable electromagnetic leakage. The measured experimental data can be used for verification of the next simulation model.
2 Â Â Simulation of electromagnetic protection performance of radiation-proof maternity clothing
2 . 1 Â Â Establishment of simulation model
In order to obtain the shielding effectiveness value of the clothing under different frequency electromagnetic waves by simulation means, it is necessary to establish a clothing shielding effectiveness test simulation model in the simulation software HFSS-9 7 , as shown in Fig. 3 . It mainly includes three-dimensional clothing models, antenna models ( transmitting antennas and receiving antennas ), and boundary and solution settings.
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Figure 3 clothing shielding effectiveness test simulation model |
2 . 1 . 1Three -dimensional clothing model establishment
To minimize the error between the simulation and actual, three-dimensional model size clothing created in HFSS to experiment radiation clothing for pregnant women to wear the actual situation on the mannequin as a reference, in order to establish a model-based three-dimensional human body Clothing model. Wherein the height of the three-dimensional model of the garment is 68 cm, clothing cuffs on both sides approximately elliptical, the major axis and a minor axis dimensions are 20, 1 8 cm, chest and back is a rectangular opening, respectively, the size of 18 cm × 16 cm , 18 cm × 10 cm , the garment hem is approximately elliptical, and the major and minor axes are 36 and 30 cm , respectively .
2 . 1 . 2 Â Â Antenna model establishment
In the clothing shielding effectiveness test, the Yagi antenna and the horn antenna are used as the transmitting antennas at low frequency and high frequency respectively. When building a simulation model in HFSS , a half-wave dipole antenna is used as the transmitting antenna in consideration of factors such as complexity and memory consumption of the model. The clothing shielding effectiveness test is carried out in the far field. Therefore, only the far-field data of the half-wave dipole is introduced as the source of the simulation, and the two cases of vertical polarization and horizontal polarization are discussed separately.
In the experiment, a three-coordinate electric field probe was used as the receiving antenna. Therefore, in the simulation, when the frequency of the radiation source is 300 or 600 MHz , three perpendicular to each other are used, and the length is 55 . A 6 mm monopole analog receive antenna; the source of the radiation source at 915 , 1 800 , 2 450 , 3 000 MHz , with a 100 mm length monopole to simulate the receive antenna. Referring to the actual experimental arrangement, the receiving antennas are placed inside the model.
2 . 1 . 3 Â Boundary and solution settings
When using the finite element method to solve the microwave radiation problem, it is necessary to use the absorbing boundary condition to make a limited truncation of the problem area, so that the finite element method can be used to calculate more accurately. In HFSS , the radiation boundary is an absorption boundary at the infinity of the simulated wave radiation to the space. The test of the shielding effectiveness of the garment is carried out in a semi-microwave darkroom. Therefore, in the simulation, the lower surface of the boundary air box is set as the ideal conductor boundary to simulate the ground effect; the other surfaces are set as the radiation boundary and serve as the absorbing material. effect.
In addition, subject to conditions such as computer memory resources, the size of the boundary air box should not be too large, and generally greater than one quarter of the wavelength of the electromagnetic wave in the main radiation direction. When performing different frequency simulations, you need to adjust the size of the radiation boundary at any time. Finally, the required model is established, and the electromagnetic parameter value and thickness value of the sample are substituted into the model. After the verification is correct, the excitation electromagnetic wave is introduced and the solution is started.
2 . 2 Â Â Verification of simulation model
By substituting the electrical conductivity, magnetic permeability ( permeability of the measured material ) and thickness value of the measured fabric into the established simulation model, the shielding effectiveness value of the garment can be simulated and compared with the actual measured value. The clothing shielding effectiveness values ( see Table 2) were compared to obtain the XY scatter plots of the measured values ​​and simulated values ​​of the shielding performance of the two sample garments in the vertical and horizontal polarization modes as shown in Fig. 4 .
It can be seen from Fig. 4 that the measured and simulated values ​​of the shielding effectiveness of the two samples are distributed around the line Y=X , indicating that the difference between the simulated and measured values ​​is relatively small. Moreover, in the vertical polarization mode, the simulation of the shielding effectiveness of the two samples is closer to the measured value, and it is close to the line of Y=X . The error between the simulation and the measured value is small, which can explain the model well. Reliability. In the horizontal polarization mode, the simulation results of the shielding performance of the two samples are slightly different from the measured values, and are evenly distributed around the line Y=X , with a maximum error of 2 . 74 dB . In addition, it can be seen that the electromagnetic protection performance of the two samples on the horizontally polarized wave is better than that on the vertical, which is consistent with the measured results.
The measured values ​​and simulated values ​​of the shielding effectiveness of the sample were tested by EXCEL , and the t values ​​of 0 were obtained under vertical and horizontal polarization, respectively . 729 , 0 . 697 , both less than t 0.01 (11) , the probability P values ​​are greater than 0.01 , indicating that there is no significant difference between the measured and simulated values. Moreover, the correlation coefficient between the measured and simulated values ​​of the sample shielding effectiveness is 0 in the vertical and horizontal polarization modes . 800 , 0 . 747 , relationship
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Figure 4 X - Y scatter plot of sE simulation and measured values |
The closer the absolute value of the number is to 1 , the closer the correlation is. Therefore, the simulation results obtained by the simulation model can well reflect the shielding effectiveness of the clothing on the electromagnetic wave, that is, the electromagnetic protection performance of the garment, thus demonstrating the reliability of the model. .
2 . 3 Â Application of simulation model
By using the established simulation model and changing the size of the three-dimensional clothing model, it is possible to simulate the shielding effectiveness of garments of different sizes, thereby obtaining the shielding effectiveness of the clothing after the size of the opening of the garment hem is changed due to the change of the body shape of the pregnant woman.
In order to analyze the influence of body shape changes on the electromagnetic protection performance of the clothing, the whole pregnancy period is divided into three stages: in the early pregnancy, the pregnant woman's body does not change much, the clothing hem is approximately elliptical, and the long axis and the short axis are 36 and 30 cm respectively . In the second trimester, the shape of the pregnant woman changes drastically, the chest and abdomen are prominent, and the abdomen is raised. At this time, the hem of the garment is approximately circular, and the diameter is 40 cm . In the late pregnancy, as in the second trimester, the hem of the garment is round. It has a diameter of 43 cm . After changing the established three-dimensional clothing model according to the requirements, the rest of the settings are unchanged, the excitation electromagnetic wave is introduced, and the solution is started, and the influence of the body shape change on the electromagnetic protection performance of the clothing under the vertical and horizontal polarization modes can be respectively obtained, as shown in the figure. 5 is shown.
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Figure 5 Effect of maternal body shape on shielding effectiveness |
It can be seen from Fig. 5 that, in the vertical or horizontal polarization mode, the body shape of the pregnant woman changes significantly from the early pregnancy to the third trimester, which directly leads to an increase in the opening of the hem of the radiation-proof pregnant woman. As the opening of the hem increases, the shielding effectiveness of the garment decreases. Moreover, in the third trimester, when the anti-radiation maternity dress hem opening is increased to a certain extent, the shielding effectiveness of the clothing for different frequency electromagnetic waves is very small, and it has been unable to protect the electromagnetic radiation.
Because the maternity clothes itself is relatively large, the shielding effectiveness value is not very high, and the radiation protection effect of the radiation protection maternity clothes on different frequencies is limited. With the increase of pregnancy, the chest and abdomen of pregnant women increase sharply, especially in the abdomen, and it is huge and heavy in the third trimester, which will cause the pregnant woman to wear a larger hem opening. Low, all below 5 dB , almost lost the protection of pregnant women, therefore, for the characteristics of electromagnetic wave penetration, reflection and diffraction, the most ideal radiation protection maternity clothing should be a fully enclosed structural design. However, contrary to expectations, in the design and production of anti-radiation maternity clothes, it is necessary to consider its electromagnetic protection performance, but also to meet the comfort and convenience of pregnant women, anti-radiation maternity clothes can not be completely closed shielding, so only It can minimize the number and area of ​​the garment opening, reduce the stitching of the indirect seam of the garment piece, improve the tightness of the stitching, and achieve the best effect of electromagnetic protection.
Specifically, the structural design of the radiation protection apron on the market is difficult to meet the electromagnetic protection requirements unless the electromagnetic radiation around the pregnant woman is weak, such as no contact or little contact with some electrical appliances. If the pregnant woman works long hours or lives in a strong electromagnetic radiation environment, even if it is a vest style, although the electromagnetic protection performance is enhanced compared to the apron, the length and sleeves should be appropriately lengthened, and the sleeve length should be at least to the elbow joint, and The neckline, cuffs and hem should also be tightened as much as possible to form an O -shape ( such as the design of the closing structure of the sportswear ) , so as to be suitable for the change of the body shape of the pregnant woman without destroying the overall electromagnetic protection performance of the radiation-proof maternity clothes. In addition, in order to improve the electromagnetic protection performance of maternity clothes, it is also possible to consider increasing the thickness of the fabric, or adopting the structural design of the multi-layered fabric to resist the strong penetration of electromagnetic waves. Of course, the performance of different fabrics should also be considered. Compatibility to ensure the comfort of pregnant women.
3 Â Â in conclusion
Through the combination of experiment and simulation, this paper analyzes the electromagnetic protection performance of radiation-proof maternity clothes in detail, and draws the following conclusions.
(1) The selected 2 anti-radiation maternity vests are common anti-radiation maternity suits on the market, and their electromagnetic shielding effectiveness has been tested. The electromagnetic shielding effectiveness of the two samples is not very high, mainly because the upper and lower openings of the sample are large, which will cause considerable electromagnetic leakage. Moreover, under the electromagnetic wave irradiation of different frequencies, the electromagnetic shielding effectiveness of the two sample clothes on the horizontally polarized wave is better than that of the vertical.
(2) The simulation results of the electromagnetic shielding effectiveness test model of the garment are consistent with the measured results, indicating that the simulation results can reflect the shielding effectiveness of the clothing on the electromagnetic wave, that is, the electromagnetic protection performance of the garment, thus demonstrating the reliability of the model. Therefore, the simulation model can be used for research on electromagnetic radiation protection functions.
(3) Through the simulation model, the electromagnetic shielding effectiveness of the garment after the size of the opening of the garment hem is changed due to the change of the body shape of the pregnant woman. As the opening of the hem increases, the electromagnetic shielding effectiveness of the garment decreases. Moreover, by the third trimester, when the hem opening of the protective suit is increased to a certain extent, the shielding effectiveness of the clothing for electromagnetic waves of different frequencies is very small, and it has been protected from electromagnetic radiation to protect the pregnant woman and the fetus. Therefore, in designing anti-radiation maternity clothes, in order not to damage the electromagnetic protection performance of the clothing, it should be considered to appropriately lengthen the length and sleeve length, and tighten the neckline, cuffs and hem as much as possible; also consider increasing the thickness of the fabric, or adopting more The structural design of the layered fabrics is designed to enhance the electromagnetic protection of the radiation-proof maternity suit.
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