# Characterization of a Mechanical Antenna Based on Rotating Permanent Magnets
## 5 Discussion and Conclusions
From Section 4.4 and Equation (3) results for NdFeb magnets, we find the following:  
* In the case of a solenoid with dimensions similar to the ones of the CABM, we should apply a current of the order of 4 \(\times\) (236...298) A, as follows from Table 5. Obviously these are estimated values, but the order of magnitude is 1000 A;
* In the case of the CRRM, in order to equate the intensity of the magnetic field it generates, we should have a dimensionally comparable structure (coil with five turns and a radius of 22 mm) carrying a current of 1000 A (see Figure 17). From here, it follows that, for similar dimensions, the rotating magnet has a much higher efficiency than the coil/solenoid. Obviously, by increasing the number of turns, the performance of the circuit elements can be significantly improved. At the same time, it must be taken into account that at low frequencies, the value of the coil resistance is much higher than the value of the inductive reactance, so that only a small part of the generator's power is found in the produced magnetic field. In conclusion, these devices have come to the attention of the scientific community in the last decade, with applications mainly in non-destructive defectoscopy, but more importantly in underwater communications. In order for this latter application to become competitive, it is necessary to increase the emission power (reception of the magnetic field at greater distances) and increase the emission frequency. Increasing the emission power can be achieved by increasing the size of the permanent magnet. By increasing the emission frequency, a double advantage would be achieved: extending the reception distance when this is done with a solenoid (based on the law of magnetic induction) and improving the modulation characteristics of the carrier for information transmission--the main purpose of this application. Mechanical antennas based on rotating permanent magnets have, as shown in the bibliography, the advantage of relatively simple, compact constructions but may include limitations regarding the maximum speed of the drive motor, the size of the permanent magnet, centrifugal force, balancing problems, etc. However, an alternative method of development exists. As we showed in the article, for comparative dimensions, a coil/solenoid is much less efficient. Thus, to equalize the permanent magnet in dynamic mode, the current through the coil should be 1000 A, which obviously represents a non-technical solution, primarily due to the appearance of losses by the Joule-Lenz effect. On the other hand, a superconducting coil would eliminate this disadvantage, and, in addition, it would offer the possibility of operating at higher frequencies, unlike a rotating magnet. This comparison can be the subject of future research. A first qualitative evaluation for the performances of CRMM can be carried out in the laboratory via stationary magnetic field measurements for different sizes based on the conclusions of this article. Conceptualization, M.B., C.M., C.I.I. and N.T. ; methodology, M.B., C.M. and E.-A.P. ; software, C.D. and G.D.; validation, C.M. and M.B. ; resources, C.M. ; writing--original draft preparation, M.B. and C.M. ; project administration, E.-A.P. ; funding acquisition, C.M. All authors have read and agreed to the published version of the manuscript. This research was funded by the Romanian Ministry of Research, Innovation and Digitization, CCCDI-UEFISCDI, grant number PN23140301-42N/2023. Not applicable. Not applicable. Not applicable. Not applicable. Data Availability Statement: The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author. The authors declare no conflicts of interest. The authors declare no conflicts of interest.