# Characterization of a Mechanical Antenna Based on Rotating Permanent Magnets
## 3 Materials, Methodology and Experimental Setup  
### Materials and Structure  
In general, subjects in the field of physics should contain, in addition to purpose and applications, the trinomial characteristic of exact sciences: phenomenon, equations, and experiment. If the mathematical algorithm cannot be solved analytically, simulations/modellings are used, which must be validated experimentally. Consequently, the article tries to order and define all of these, highlighting the advantages and disadvantages in relation to other types of systems emitting in LF/VLF.  
Next, the stages corresponding to the subsections in Section 4 are successively analyzed from a methodologic point of view.  
The primary constituents of NdFeB magnets include neodymium (Nd), iron (Fe), and boron (B), with the general formula represented as (Nd\({}_{2}\)Fe\({}_{14}\)B). The microstructure is critical, as it determines the overall magnetic performance. To enhance the thermal stability and coercivity of NdFeB magnets, various alloying elements are introduced. Dysprosium (Dy) is commonly added to improve energy stability at elevated temperatures, addressing one of the vulnerabilities of NdFeB magnets--loss of magnetization at high temperatures [19]. Other elements, such as praseodymium (Pr) and terbium (Tb), are also explored for their beneficial effects on magnetic properties.  
Recent research has demonstrated that microstructural optimization significantly influences the performance of NdFeB magnets. Fine-tuning grain size and controlling the distribution of magnetic phases can lead to improvements in coercivity and remanence. Techniques such as rapid solidification and controlled annealing are employed to achieve desired microstructures [20]. Magnetic properties such as remanence (\(B_{\mathrm{r}}\)), coercivity (\(H_{c}\)), and the maximum energy product (\(BH\))\({}_{\mathrm{max}}\) are crucial for characterizing NdFeB magnets.  
A remanence of 1.1-1.2 T is indicative of an exceptionally strong magnet. This level of remanence is vital for applications that require stable magnetization under operational stress. Coercivity, on the other hand, reflects the ability of the magnet to withstand demagnetizing forces. High coercivity is necessary for applications involving dynamic conditions. The maximum energy product (\(BH\))\({}_{\mathrm{max}}\) is a critical measure of the magnet's usefulness in applications. Advances in alloy compositions and processing techniques have led to significant increases in (\(BH\))\({}_{\mathrm{max}}\) values in NdFeB magnets over the years [21, 22].  
For this purpose, NdFeB was chosen as a material with magnetic properties in two configurations: cylindrical radial ring magnet (CRRM) and cylindrical axial bar magnet (CABM), as shown in Figure 1a. The working frequencies in the experiments varied between 30 Hz and 100 Hz. To carry out the experiments, the two configurations of magnets were inserted into a holder whose shaft, mounted on bearings, allows coupling to an electric drive motor (Figure 1b).  
Figure 1: (**a**) Permanent magnet configurations considered; (**b**) permanent magnet holder.