Accurate position detection in wireless power transfer using magnetoresistive sensors for implant applications

Recently, the utilization of magnetic resonant coupling (MRC) mechanism for wireless power transfer (WPT) has been actively investigated. Among numerous applications of WPT technology, the ener-gization of implanted biomedical devices wirelessly and uninterruptedly from external supply is important because it can eliminate possible device replacement due to battery depletion. Given the implanted receiver is invisible from the external transmitter, the coil misalignment occurs easily which results in low transfer efficiency and high magnetic field leakage, and consequently endangers the human health [1]. Thus, the development of accurate position detection of the implanted receiver from the external transmitter is highly desirable. Presently, most studies ofthe position detection in WPT are focused on the application of electric vehicles. Although the corresponding technologies such as coil sets [2] or auxiliary multi-coils [3] have achieved fruitful outcome, they are too bulky and complicated to be used in implant applications. Due to the advantages of high stability, small size, low power consumption and high precision, the magnetoresistive (MR) sensor has been widely used in many industrial applications [4]. Generally, they are arranged in an array style to measure the magnetic field vector [5] or a moving magnetic object [6]. To the best of authors' knowledge, the application of MR sensors in WPT is absent in literature. In this paper, a new position detection approach in WPT is proposed and implemented, which is particularly suitable for implant applications. The key is to use a MR sensor array to directly measure the variation of magnetic field so as to precisely detect the relative position of the implanted receiver from the external transmitter. Therefore, the advantages of efficient and compact WPT for implant applications can be achieved.