# A Novel Dual-Permanent-Magnet Mechanical Antenna for Pipeline Robot Localization and Communication
## 4 Conclusions and Discussion  
For pipeline robot positioning, compared with the wheel odometer, ray, and acoustic wave methods, the proposed method utilizes ultra-low-frequency electromagnetic waves with low attenuation, long transmission distance, and strong penetrability generated by the new small mechanical antenna made of permanent magnets. In this method, the amplitude modulation of the magnetic flux density is realized by changing the angle of the magnetic moments between the two permanent magnets. The effects of the mechanical antenna size on the magnetic field signal were studied using analytical theory and finite-element simulations. When \(r/\max(Dh)\geq 4\), the influence of the magnets' outer dimensions can be ignored. The experimental results showed that using the developed antenna, the quality of magnetic signal was satisfactory for communication at 10 m in the air and 3 m from a 20\(\#\) steel pipeline, which preliminarily verified the feasibility of the antenna for localizing and communicating with pipeline robots. The main factors affecting the communication quality of the proposed antenna can be summarized as follows:  
1. The magnetization \(M_{0}\) and volume \(V\) of the permanent magnet. According to (3) and (4), the amplitude of the magnetic flux density increases linearly with \(M_{0}\) and \(V\). Thus, \(M_{0}\) and \(V\) affect only the strength of the magnetic field and do not affect the modulation performance. Increasing \(M_{0}\) and \(V\) can improve the signal propagation distance. However, if \(V\) is substantially large, the overall volume and rotational inertia of the antenna will increase. Therefore, for a fixed propagation distance, a permanent magnetic material with a larger \(M_{0}\) can be selected without increasing the antenna volume. 2. The spacing \(d\) between the permanent magnets affects the near-field distribution and modulation performance of the antenna. When \(r>>\max(Dh)\), the effect of \(d\) is negligible. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Condition** & \(\alpha\) (\({}^{\circ}\)) & **Distance (m)** & \(B_{x}\) (nT) & \(B_{y}\) (nT) & \(B_{z}\) (nT) \\ \hline Without pipeline & 0 & 3 & 40.57 & 38.35 & 4.43 \\ With pipeline & 0 & 3 & 6.59 & 5.40 & 0.67 \\ Without pipeline & 120 & 3 & 19.17 & 18.16 & 2.83 \\ With pipeline & 120 & 3 & 2.88 & 2.51 & 0.46 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Measured results. Figure 10: The mechanical antenna placed in an actual 20\(\#\) steel pipeline. 3. The rotational speeds \(\omega\) of the carrier motor and \(\omega_{1}\) of the modulation motor. Due to the limits of power consumption and long communication distance in conductive media such as underground or underwater, \(\omega\) cannot be too large. However, the symbol transmission rate \(v\) (bit/s) depends on both \(\omega\) and \(\omega_{1}\). Assume the time required for the change of \(\alpha\): \(\alpha=0\rightarrow\alpha_{1}\) or \(\alpha=\alpha_{1}\to 0\) is \(t_{1}\), which is the switch time of the modulation motor from start to stop, and, to improve the demodulation accuracy at the receiver, the conditions \(v<<1/t_{1}\) and \(v\leq\omega/\pi\) should be satisfied. The new dual-permanent-magnet mechanical antenna has many application prospects in the field of communication through conductive media and finite space, such as in pipelines, underwater, undersea, and underground. However, there is still much work to be done before it can be applied. For the positioning of and communication with pipeline robots, its size needs to be further reduced, which can be implemented by using permanent magnets of higher magnetic energy density and optimizing the antenna structure. In addition, the current amount of data for validation is not very large.