A Coil-Embedded Beacon Pole for 3-D Localization of Surrounding Magnetic Flux Sensors

Abstract

In this study, we propose a novel 3-D localization method using a coil-embedded beacon pole and magnetoresistive-device-based magnetic flux sensors (MR sensors) aimed at underwater applications. The beacon pole is constructed by stacking multiple cylindrical modules, each containing three elliptic coils embedded in grooves on its side surface with mutually orthogonal plane normals. The coils are oriented at 54.74°. with respect to the cylinder axis and separated by 120°. in azimuth. By detecting the magnetic fields generated by the coils embedded in the pole, the magnetic sensors can determine their positions in axial, radial, and circumferential directions relative to the pole. Low-frequency (30.180 Hz) fields, which are advantageous for applications in water, are generated by the pole and can be detected by the MR sensors with a high signal-to-noise ratio. Numerical simulations indicated that, although the coils were discretely arranged at 120°. intervals in azimuth, the localization performance remained effectively axisymmetric. Uniform precision was achieved in all directions, and a localization uncertainty of approximately less than 2 mm was obtained within a 1 m-diameter region around the beacon pole. However, in practical experiments using a small-scale prototype of the beacon pole, the uncertainty was limited to better than 11 mm within a 0.6 m-diameter region, reflecting real-world measurement constraints. Real-time positioning of the magnetic sensor was successfully demonstrated, achieving position updates at approximately 20 Hz.