# Design and Experiment of Magnetic Antenna Vibration and Noise Reduction System
## 4 Test Verification and Analysis
### Function Comparison Test  
After the dynamic simulation test, we have a clear understanding of the performance of the vibration damping system. Now, through the functional test of receiving electromagnetic wave signals, the suppression effect of the damping device on the induction noise of magnetic antenna motion can be verified. The experiment is carried out on a dedicatedly designed vibration excitation apparatus to avoid electromagnetic noise, so as to verify whether the electromagnetic noise induced by the magnetic antenna can be significantly reduced via the proposed vibration isolation design. The vibration base platform is made up of concrete. A temporarily designed pneumatic vibration exciter with a remote air pump is adopted to avoid electromagnetic noise. As mentioned before, the clearance between the annular polyoxymethylene structures and the tubular fiberglass shell is filled with glue so as to suppress resonant vibration of the vibration isolation system near 100 Hz. The specific steps are as follows:  
1. Install a single magnetic antenna and a magnetic antenna with a vibration damping system on two base surfaces with good vibration consistency, and compare the ambient electromagnetic noise received by the two antennas without vibration;
2. The acceleration sensors are respectively arranged on the shell of the magnetic antenna damping system and antenna, then use the vibration shaker to apply the same size of excitation to the two base mesa, respectively. Analyze and process acceleration sensor feedback data, and calculate the attenuation rate of vibration from the housing to the antenna;
3. Compare the ambient electromagnetic noise received by the two magnetic antennas with and without vibration reduction to verify whether the vibration reduction system meets the requirements. The test layout is shown in Figure 11.  
The shell-antenna vibration transmission curve is shown in Figure 12. The experimental result coincides roughly with that of Figure 10, because they both show overall trends of vibration attenuation of 40 dB within the frequency domain above 60 Hz. There are slight differences in the low frequency domain and some high frequency domains. Resonant vibration of the vibration isolation system near 100 Hz has been suppressed in comparison with Figure 10, which is mainly the result of the structural improvement by filling up the clearance between the annular polyoxymethylene structures and the tubular fiberglass shell. Another reason might be the difference of the vibration characteristics between the temporarily designed pneumatic vibration exciter and the standard electric shaking table. Since the key point of this experiment was to verify whether the electromagnetic noise induced by the magnetic antenna can be significantly reduced, the authors think that the vibration transmissibility test error is temporarily acceptable before a more precise vibration exciter without electromagnetic noise is developed. Function comparison test results are shown in Figure 13.  
Figure 10: Vibration transmissibility curve of the magnetic antenna damping system. According to the above comparison test results, when there is no excitation, the electromagnetic noise induced by the magnetic antenna with and without vibration damping is below 200 fT, which proves that the antenna has a good reception effect in a quiet environment. When the vibration excitation is applied, the electromagnetic noise of the magnetic antenna without vibration damping increases obviously and exceeds 200 fT, which will affect the normal reception. However, the electromagnetic noise of the magnetic antenna with vibration damping basically maintains the same as that of the magnetic antenna without vibration excitation, which does not rise significantly and remains below 200 fT. The vibration transmission rate of the vibration damping system is basically about 0.01 (\(-\)40 dB) at the concerned frequency of 60 Hz, which meets the needs of vibration damping.