The aim of this work is to analyze Goal Line Technologies with focus on the electromagnetic field based approach GoalRef™. This paper will give an overview of the requirements that must be fulfilled by to get approved by FIFA. The existing solution approaches will be described and possible environmental influences like occlusion or deformation of the ball that can affect the system's performance will be discussed. Afterwards, GoalRef™ will be presented in detail.Finally measurement results for one test scenario in the lab will be presented to validate the system approach and to determine the potential accuracy range of the system.
Purpose
This paper aims to provide a flexible model for a system of inductively coupled loops in a quasi-static magnetic field. The outlined model is used for theoretical analyses on the magnetic field-based football goal detection system called as GoalRef, where a primary loop generates a magnetic field around the goal. The passive loops are integrated in the football, and a goal is deduced from induced voltages in loop antennas mounted on the goal frame.
Design/methodology/approach
Based on the law of Biot–Savart, the magnetic vector potential of a primary current loop is calculated. The induced voltages in secondary loops are derived by Faraday’s Law. Expressions to calculate induced voltages in elliptically shaped loops and their magnetic field are also presented.
Findings
The induced voltages in secondary loops close to the primary loop are derived by either numerically integrating the primary magnetic flux density over the area of the secondary loop or by integrating the primary magnetic vector potential over the boundary of that loop. Both approaches are examined and compared with respect to accuracy and calculation time. It is shown that using the magnetic vector potential instead of the magnetic flux density can decrease the processing time by a factor of around 100.
Research limitations/implications
Environmental influences like conductive or permeable obstacles are not considered in the model.
Practical implications
The model can be used to investigate the theoretical behavior of inductively coupled systems.
Originality/value
The proposed model provides a flexible, fast and accurate tool for calculations of inductively coupled systems, where the loops can have arbitrary shape, position and orientation.
This article provides both a theoretical analysis and a numerical method for the inverse source problem of locating multiple passive 3-D coils based on measurements of their superposed magnetic fields. In our context, a 3-D coil consists of three concentric circular coils being mutually perpendicular, and the term "passive" means that these coils are not connected to an active power source. Instead, their current is induced externally by a low-frequency alternating magnetic field which is generated by a closed exciter wire. The underlying inductively coupled system is modeled with regard to the 3-D coils as magnetic dipoles and their localization is formulated as an inverse problem. Since its ill posedness mainly arises from strong sensitivity to observational noise, an approximate upper bound for the localization error is derived mathematically by linearization. The Levenberg-Marquardt algorithm is applied as a method for localization and modified for better performance as well as the ability to estimate the number of 3-D coils in the localization area. Our method is tested with simulated and real data in order to confirm its capability of locating up to three passive 3-D coils within the front of a wooden shelf surrounded by the exciter wire and eight rectangular loop antennas.
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