# Characterization of a Mechanical Antenna Based on Rotating Permanent Magnets
## 5 Discussion and Conclusions
This assertion, together with the demonstration of the \(1/r^{3}\) dependence, immediately leads to the idea that in order to evaluate the intensity of the harmonic magnetic field radiated at a certain distance, we do not have to rotate the magnet: it is enough to measure the intensity of the static field in the laboratory at short distances. Thus, many articles declare the \(1/r^{3}\) dependence for the harmonic field emitted by the rotating magnet, which is somewhat assumed to be true due to the analytical relations (mainly the similarity with the magnetic field of the elementary magnetic dipole, respectively the loop antenna in the near-field zone)--Equations (4) and (5). Figure 16 experimentally demonstrates this dependence through measurements performed in a suburban environment with low magnetic noise over the range 1-25 m. If, in Table 4, we consider the ratio mV/uT as being constant (258-269) down to the last row (25 m), where the lower sensitivity of the Narda sensor no longer allowed the measurement in uT units, it follows that the magnetic field measured in mV units corresponds to a magnetic field of approximately 20 pT at a frequency of 70 Hz. Because the sensor used in the measurements (the made-in-house coil with 38,000 turns) gives a signal that is proportional to frequency according to the magnetic induction law, it follows that for a higher frequency, for instance, 350 Hz, we can measure a magnetic field of approximately 4 pT. This value can be considered the sensitivity limit of the experimental setup used in the measurements (the made-in-house coil with 38,000 turns and Rohde&Schwarz microvoltmeter). The harmonic analysis of the harmonic field generated by the two magnet configurations at a frequency of 70 Hz was performed by using the assembly presented in Figure 8 with two different pieces of equipment simultaneously within the replicate testing concept. For both magnet types, harmonics of second, third, and fourth order as well as interharmonics were detected. The highest harmonic in the case of the CRRM is the second harmonic, while in the case of the CABM, the third one is the highest. The CRRM proved to have a better performance in this test too, the second harmonic being approximately 282 times smaller than the level of the fundamental frequency, while for the CABM, the third harmonic is only 39 times smaller. The analysis of the analytical relationships and the measurement results lead to two very important conclusions that were not sufficiently explained in the studied bibliography. The first conclusion is based on the following two assertions demonstrated in the article:  
* The identity between the magnetic field intensities in static and harmonic regimes for the studied configurations;
* Both analytical and experimental demonstration of the \(1/r^{3}\)-distance dependence of the intensity of the emitted magnetic field. From here, it follows that in order to evaluate the performance of a rotating magnet system (CRRM and CABM), a few measurements at different distances (cm, m) in static mode are sufficient. By applying the above assertions, we can evaluate the emitted magnetic field intensity at any distance for the given configurations. Moreover, we can also evaluate the emitted signal reception sensitivity with the devices mentioned in this article as having the minimum estimated values of 20 pT and 4 pT at 70 Hz and 350 Hz, respectively. The second conclusion refers to the comparative analysis of the \"efficiency\" of the magnetic field generated by a rotating permanent magnet relative to the magnetic field generated by coils/solenoids.