# Optimal Design of a New Rotating Magnetic Beacon Structure Based on Halbach Array
## 1 Introduction  
Low-frequency magnetic field signals [1; 2; 3; 4; 5] have excellent properties such as high penetration, strong robustness, and easy extraction, and are suitable for positioning applications with high accuracy requirements in complex scenes. In the past, low-frequency magnetic field signals have been generated by energized solenoids [6; 7], but, with this method, the energy loss is large and the magnetic field strength is limited. With the progress of material technology [8; 9; 10; 11], permanent magnets made of strongly magnetic materials can now generate low-frequency magnetic field signals with longer propagation distances after rotation. In order to make better use of the advantages of low-frequency magnetic signals, experts and scholars worldwide have carried out research on this topic. In order to solve the problem of building walls blocking GPS signals in indoor navigation, the University of Michigan [12] proposed a method relying on multi-magnetic beacon area positioning based on electronic equipment. Within larger buildings, the positioning accuracy is higher, but, in practice, the complex electromagnetic environment will increase the computing load of electronic equipment, resulting in large errors. Starting from the principle of magnetic gradient tensor, [PERSON] et al. [13] analyzed the advantages of magnetic gradient tensor in magnetic source representation and proposed the idea of applying magnetic gradient tensor to localization. By deploying multiple tensor gradiometers, [PERSON] [14] designed a portable ranging and positioning robot based on artificial magnetic signal (MagSTAR), which could detect and calibrate magnetic targets. However, the site selected in the experiment was open, so the positioning performance of this machine in a complex electromagnetic environment could not be well proved. With the help of the magnetic gradient tensor algorithm, [PERSON] [15] of the China University of Geosciences proposed a real-time positioning method for horizontal directional drilling based on magnetic beacon positioning, which has important engineering application value. However, this method requires high-precision measurement of the ambient magnetic field in advance, and it is relatively complex. Weapon engineering student [PERSON] [16]applied magnetic beacon positioning to their ship, and considered a rotating propeller as a rotating magnetic dipole. The magnetic target location was calculated with the aid of magnetic gradient tensor inversion. However, in the process of ship motion, the next measurement point could only be determined by the preset value; with the increase in distance, the localization algorithm produces larger errors. Starting from the magnetic source, [PERSON] [17] designed and optimized the structure of a magnetic beacon, providing an effective solution for the limited transmission distance of the magnetic signal and the difficulty of signal extraction. However, for now, the above location methods require a high precision magnetic signal amplitude value, so the increase of magnetic positioning accuracy is mainly restricted to signal measurement. Furthermore, at the time of the measurement of a magnetic signal amplitude magnetometer, the cluttered electromagnetic environment, strong magnetic anomalous field and rapid attenuation of magnetic signal with increasing increase need to be solved. In radio navigation technology, the orientation information of the target is often combined with the position positioning, which has obvious positioning advantages. Therefore, in order to solve the problem that the amplitude positioning accuracy is not high enough, the radio navigation technology can be referred to, and the phase angle measurement method can be used to measure the target's orientation information. The literature [18] on low-frequency magnetic field signals verifies that the phase information of signals can correspond well with the orientation information of targets.